feat: add async exercises

test idempotence of `trim_me` in `strings3.rs`

.cargo/config.toml

@@ -0,0 +1,2 @@
+[alias]
+dev = ["run", "--", "dev"]

.github/workflows/rust.yml

@@ -22,22 +22,22 @@ jobs:
       - uses: DavidAnson/markdownlint-cli2-action@v16
         with:
           globs: "exercises/**/*.md"
-      - name: Run cargo fmt
-        run: cargo fmt --all -- --check
+      - name: rustfmt
+        run: cargo fmt --all --check
   test:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, windows-latest, macOS-latest]
+        os: [ubuntu-latest, windows-latest, macos-latest]
     steps:
       - uses: actions/checkout@v4
       - uses: swatinem/rust-cache@v2
-      - name: Run cargo test
-        run: cargo test
+      - name: cargo test
+        run: cargo test --workspace
   dev-check:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
       - uses: swatinem/rust-cache@v2
-      - name: Run rustlings dev check
+      - name: rustlings dev check
         run: cargo run -- dev check --require-solutions

.typos.toml

@@ -1,7 +1,7 @@
+[default.extend-words]
+"earch" = "earch" # Because of <s>earch in the list footer
+
 [files]
 extend-exclude = [
   "CHANGELOG.md",
 ]
-
-[default.extend-words]
-"ratatui" = "ratatui"

CHANGELOG.md

@@ -1,3 +1,100 @@
+## Unreleased
+
+### Changed
+
+- Upgrade to Rust edition 2024
+- Raise the minimum supported Rust version to `1.87`
+
+<a name="6.4.0"></a>
+
+## 6.4.0 (2024-11-11)
+
+### Added
+
+- The list of exercises is now searchable by pressing `s` or `/` 🔍️ (thanks to [@frroossst](https://github.com/frroossst))
+- New option `c` in the prompt to manually check all exercises ✅ (thanks to [@Nahor](https://github.com/Nahor))
+- New command `check-all` to manually check all exercises ✅ (thanks to [@Nahor](https://github.com/Nahor))
+- Addictive animation for showing the progress of checking all exercises. A nice showcase of parallelism in Rust ✨
+- New option `x` in the prompt to reset the file of the current exercise 🔄
+- Allow `dead_code` for all exercises and solutions ⚰️ (thanks to [@huss4in](https://github.com/huss4in))
+- Pause input while running an exercise to avoid unexpected prompt interactions ⏸️
+- Limit the maximum number of exercises to 999. Any third-party exercises willing to reach that limit? 🔝
+
+### Changed
+
+- `enums3`: Remove redundant enum definition task (thanks to [@senekor](https://github.com/senekor))
+- `if2`: Make the exercise less confusing by avoiding "fizz", "fuzz", "foo", "bar" and "baz" (thanks to [@senekor](https://github.com/senekor))
+- `hashmap3`: Use the method `Entry::or_default`.
+- Update the state of all exercises when checking all of them (thanks to [@Nahor](https://github.com/Nahor))
+- The main prompt doesn't need a confirmation with ENTER on Unix-like systems anymore.
+- No more jumping back to a previous exercise when its file is changed. Use the list to jump between exercises.
+- Dump the solution file after an exercise is done even if the solution's directory doesn't exist.
+- Rework the footer in the list.
+- Optimize the file watcher.
+
+### Fixed
+
+- Fix bad contrast in the list on terminals with a light theme.
+
+<a name="6.3.0"></a>
+
+## 6.3.0 (2024-08-29)
+
+### Added
+
+- Add the following exercise lints:
+  - `forbid(unsafe_code)`: You shouldn't write unsafe code in Rustlings.
+  - `forbid(unstable_features)`: You don't need unstable features in Rustlings and shouldn't rely on them while learning Rust.
+  - `forbid(todo)`: You forgot a `todo!()`.
+  - `forbid(empty_loop)`: This can only happen by mistake in Rustlings.
+  - `deny(infinite_loop)`: No infinite loops are needed in Rustlings.
+  - `deny(mem_forget)`: You shouldn't leak memory while still learning Rust.
+- Show a link to every exercise file in the list.
+- Add scroll padding in the list.
+- Break the help footer of the list into two lines when the terminal width isn't big enough.
+- Enable scrolling with the mouse in the list.
+- `dev check`: Show the progress of checks.
+- `dev check`: Check that the length of all exercise names is lower than 32.
+- `dev check`: Check if exercise contains no tests and isn't marked with `test = false`.
+
+### Changed
+
+- The compilation time when installing Rustlings is reduced.
+- Pressing `c` in the list for "continue on" now quits the list after setting the selected exercise as the current one.
+- Better highlighting of the solution file after an exercise is done.
+- Don't show the output of successful tests anymore. Instead, show the pretty output for tests.
+- Be explicit about `q` only quitting the list and not the whole program in the list.
+- Be explicit about `r` only resetting one exercise (the selected one) in the list.
+- Ignore the standard output of `git init`.
+- `threads3`: Remove the queue length and improve tests.
+- `errors4`: Use match instead of a comparison chain in the solution.
+- `functions3`: Only take `u8` to avoid using a too high number of iterations by mistake.
+- `dev check`: Always check with strict Clippy (warnings to errors) when checking the solutions.
+
+### Fixed
+
+- Fix the error on some systems about too many open files during the final check of all exercises.
+- Fix the list when the terminal height is too low.
+- Restore the terminal after an error in the list.
+
+<a name="6.2.0"></a>
+
+## 6.2.0 (2024-08-09)
+
+### Added
+
+- Show a message before checking and running an exercise. This gives the user instant feedback and avoids confusion if the checks take too long.
+- Show a helpful error message when trying to install Rustlings with a Rust version lower than the minimum one that Rustlings supports.
+- Add a `README.md` file to the `solutions/` directory.
+- Allow initializing Rustlings in a Cargo workspace.
+- `dev check`: Check that all solutions are formatted with `rustfmt`.
+
+### Changed
+
+- Remove the state file and the solutions directory from the generated `.gitignore` file.
+- Run the final check of all exercises in parallel.
+- Small exercise improvements.
+
 <a name="6.1.0"></a>
 
 ## 6.1.0 (2024-07-10)
@@ -54,7 +151,7 @@ You can read about the motivations of this change in [this issue](https://github
 
 ### List mode
 
-A list mode was added using [Ratatui](https://ratatui.rs).
+A new list mode was added!
 You can enter it by entering `l` in the watch mode.
 It offers the following features:
 
@@ -755,7 +852,7 @@ Then follow the link to the guide about [third-party exercises](THIRD_PARTY_EXER
 
 #### Bug Fixes
 
-- Update deps to version compatable with aarch64-pc-windows (#263) ([19a93428](https://github.com/rust-lang/rustlings/commit/19a93428b3c73d994292671f829bdc8e5b7b3401))
+- Update deps to version compatible with aarch64-pc-windows (#263) ([19a93428](https://github.com/rust-lang/rustlings/commit/19a93428b3c73d994292671f829bdc8e5b7b3401))
 - **docs:**
   - Added a necessary step to Windows installation process (#242) ([3906efcd](https://github.com/rust-lang/rustlings/commit/3906efcd52a004047b460ed548037093de3f523f))
   - Fixed mangled sentence from book; edited for clarity (#266) ([ade52ff](https://github.com/rust-lang/rustlings/commit/ade52ffb739987287ddd5705944c8777705faed9))

Cargo.toml

@@ -1,27 +1,26 @@
 [workspace]
 resolver = "2"
 exclude = [
-  "tests/fixture/failure",
-  "tests/fixture/state",
-  "tests/fixture/success",
+  "tests/test_exercises",
   "dev",
 ]
 
 [workspace.package]
-version = "6.1.0"
+version = "6.4.0"
 authors = [
-  "Liv <mokou@fastmail.com>",
-  "Mo Bitar <mo8it@proton.me>",
+  "Mo Bitar <mo8it@proton.me>", # https://github.com/mo8it
+  "Liv <mokou@fastmail.com>", # https://github.com/shadows-withal
   # Alumni
-  "Carol (Nichols || Goulding) <carol.nichols@gmail.com>",
+  "Carol (Nichols || Goulding) <carol.nichols@gmail.com>", # https://github.com/carols10cents
 ]
 repository = "https://github.com/rust-lang/rustlings"
 license = "MIT"
-edition = "2021"
+edition = "2024" # On Update: Update the edition of `rustfmt` in `dev check` and `CARGO_TOML` in `dev new`.
+rust-version = "1.87"
 
 [workspace.dependencies]
-serde = { version = "1.0.204", features = ["derive"] }
-toml_edit = { version = "0.22.15", default-features = false, features = ["parse", "serde"] }
+serde = { version = "1.0", features = ["derive"] }
+toml_edit = { version = "0.22", default-features = false, features = ["parse", "serde"] }
 
 [package]
 name = "rustlings"
@@ -31,6 +30,7 @@ authors.workspace = true
 repository.workspace = true
 license.workspace = true
 edition.workspace = true
+rust-version.workspace = true
 keywords = [
   "exercise",
   "learning",
@@ -46,21 +46,20 @@ include = [
 ]
 
 [dependencies]
-anyhow = "1.0.86"
-clap = { version = "4.5.9", features = ["derive"] }
-crossterm = "0.27.0"
-hashbrown = "0.14.5"
-notify-debouncer-mini = { version = "0.4.1", default-features = false }
-os_pipe = "1.2.0"
-ratatui = { version = "0.27.0", default-features = false, features = ["crossterm"] }
-rustlings-macros = { path = "rustlings-macros", version = "=6.1.0" }
-serde_json = "1.0.120"
+anyhow = "1.0"
+clap = { version = "4.5", features = ["derive"] }
+crossterm = { version = "0.29", default-features = false, features = ["windows", "events"] }
+notify = "8.0"
+rustlings-macros = { path = "rustlings-macros", version = "=6.4.0" }
+serde_json = "1.0"
 serde.workspace = true
 toml_edit.workspace = true
 
+[target.'cfg(not(windows))'.dependencies]
+rustix = { version = "1.0", default-features = false, features = ["std", "stdio", "termios"] }
+
 [dev-dependencies]
-assert_cmd = "2.0.14"
-predicates = "3.1.0"
+tempfile = "3.19"
 
 [profile.release]
 panic = "abort"
@@ -70,3 +69,20 @@ panic = "abort"
 
 [package.metadata.release]
 pre-release-hook = ["./release-hook.sh"]
+pre-release-commit-message = "Release 🎉"
+
+[workspace.lints.rust]
+unsafe_code = "forbid"
+unstable_features = "forbid"
+
+[workspace.lints.clippy]
+empty_loop = "forbid"
+disallowed-types = "deny"
+disallowed-methods = "deny"
+infinite_loop = "deny"
+mem_forget = "deny"
+dbg_macro = "warn"
+todo = "warn"
+
+[lints]
+workspace = true

README.md

@@ -17,16 +17,17 @@ It contains code examples and exercises similar to Rustlings, but online.
 
 ### Installing Rust
 
-Before installing Rustlings, you need to have _Rust installed_.
+Before installing Rustlings, you need to have the **latest version of Rust** installed.
 Visit [www.rust-lang.org/tools/install](https://www.rust-lang.org/tools/install) for further instructions on installing Rust.
 This will also install _Cargo_, Rust's package/project manager.
 
-> 🐧 If you're on Linux, make sure you've installed `gcc` (for a linker).
+> 🐧 If you are on Linux, make sure you have installed `gcc` (for a linker).
 >
-> Deb: `sudo apt install gcc`.
-> Dnf: `sudo dnf install gcc`.
+> Deb: `sudo apt install gcc`
+>
+> Dnf: `sudo dnf install gcc`
 
-> 🍎 If you're on MacOS, make sure you've installed Xcode and its developer tools by running `xcode-select --install`.
+> 🍎 If you are on MacOS, make sure you have installed Xcode and its developer tools by running `xcode-select --install`.
 
 ### Installing Rustlings
 
@@ -53,6 +54,21 @@ After installing Rustlings, run the following command to initialize the `rustlin
 rustlings init
 ```
 
+<details>
+<summary><strong>If the command <code>rustlings</code> can't be found…</strong> (<em>click to expand</em>)</summary>
+
+You are probably using Linux and installed Rust using your package manager.
+
+Cargo installs binaries to the directory `~/.cargo/bin`.
+Sadly, package managers often don't add `~/.cargo/bin` to your `PATH` environment variable.
+
+The solution is to …
+
+- either add `~/.cargo/bin` manually to `PATH`
+- or to uninstall Rust from the package manager and install it using the official way with `rustup`: https://www.rust-lang.org/tools/install
+
+</details>
+
 Now, go into the newly initialized directory and launch Rustlings for further instructions on getting started with the exercises:
 
 ```bash
@@ -73,8 +89,6 @@ While working with Rustlings, please use a modern terminal for the best user exp
 The default terminal on Linux and Mac should be sufficient.
 On Windows, we recommend the [Windows Terminal](https://aka.ms/terminal).
 
-If you use VS Code, the builtin terminal should also be fine.
-
 ## Doing exercises
 
 The exercises are sorted by topic and can be found in the subdirectory `exercises/<topic>`.
@@ -89,7 +103,7 @@ Ask for hints by entering `h` in the _watch mode_ 💡
 
 ### Watch Mode
 
-After [initialization](#initialization), Rustlings can be launched by simply running the command `rustlings`.
+After the [initialization](#initialization), Rustlings can be launched by simply running the command `rustlings`.
 
 This will start the _watch mode_ which walks you through the exercises in a predefined order (what we think is best for newcomers).
 It will rerun the current exercise automatically every time you change the exercise's file in the `exercises/` directory.
@@ -111,21 +125,31 @@ The list allows you to…
 
 - See the status of all exercises (done or pending)
 - `c`: Continue at another exercise (temporarily skip some exercises or go back to a previous one)
-- `r`: Reset status and file of an exercise (you need to _reload/reopen_ its file in your editor afterwards)
+- `r`: Reset status and file of the selected exercise (you need to _reload/reopen_ its file in your editor afterwards)
 
 See the footer of the list for all possible keys.
 
+## Questions?
+
+If you need any help while doing the exercises and the builtin-hints aren't helpful, feel free to ask in the [_Q&A_ category of the discussions](https://github.com/rust-lang/rustlings/discussions/categories/q-a?discussions_q=) if your question wasn't asked yet 💡
+
+## Third-Party Exercises
+
+Third-party exercises are a set of exercises maintained by the community.
+You can use the same `rustlings` program that you installed with `cargo install rustlings` to run them:
+
+- 🇯🇵 [Japanese Rustlings](https://github.com/sotanengel/rustlings-jp)：A Japanese translation of the Rustlings exercises.
+- 🇨🇳 [Simplified Chinese Rustlings](https://github.com/SandmeyerX/rustlings-zh-cn): A simplified Chinese translation of the Rustlings exercises.
+
+Do you want to create your own set of Rustlings exercises to focus on some specific topic?
+Or do you want to translate the original Rustlings exercises?
+Then follow the the guide about [third-party exercises](https://github.com/rust-lang/rustlings/blob/main/THIRD_PARTY_EXERCISES.md)!
+
 ## Continuing On
 
 Once you've completed Rustlings, put your new knowledge to good use!
 Continue practicing your Rust skills by building your own projects, contributing to Rustlings, or finding other open-source projects to contribute to.
 
-## Third-Party Exercises
-
-Do you want to create your own set of Rustlings exercises to focus on some specific topic?
-Or do you want to translate the original Rustlings exercises?
-Then follow the link to the guide about [third-party exercises](https://github.com/rust-lang/rustlings/blob/main/THIRD_PARTY_EXERCISES.md)!
-
 ## Uninstalling Rustlings
 
 If you want to remove Rustlings from your system, run the following command:
@@ -138,6 +162,4 @@ cargo uninstall rustlings
 
 See [CONTRIBUTING.md](https://github.com/rust-lang/rustlings/blob/main/CONTRIBUTING.md) 🔗
 
-## Contributors ✨
-
-Thanks to [all the wonderful contributors](https://github.com/rust-lang/rustlings/graphs/contributors) 🎉
+Thanks to [all the wonderful contributors](https://github.com/rust-lang/rustlings/graphs/contributors) ✨

build.rs

@@ -0,0 +1,5 @@
+fn main() {
+    // Fix building from source on Windows because it can't handle file links.
+    #[cfg(windows)]
+    let _ = std::fs::copy("dev/Cargo.toml", "dev-Cargo.toml");
+}

clippy.toml

@@ -0,0 +1,15 @@
+disallowed-types = [
+  # Inefficient. Use `.queue(…)` instead.
+  "crossterm::style::Stylize",
+  "crossterm::style::styled_content::StyledContent",
+]
+
+disallowed-methods = [
+  # Inefficient. Use `.queue(…)` instead.
+  "crossterm::style::style",
+  # Use `thread::Builder::spawn` instead and handle the error.
+  "std::thread::spawn",
+  "std::thread::Scope::spawn",
+  # Return `ExitCode` instead.
+  "std::process::exit",
+]

dev/Cargo.toml

@@ -1,4 +1,4 @@
-# Don't edit the `bin` list manually! It is updated by `cargo run -- dev update`. This comment line will be stripped in `rustlings init`.
+# Don't edit the `bin` list manually! It is updated by `cargo dev update`. This comment line will be stripped in `rustlings init`.
 bin = [
   { name = "intro1", path = "../exercises/00_intro/intro1.rs" },
   { name = "intro1_sol", path = "../solutions/00_intro/intro1.rs" },
@@ -164,34 +164,67 @@ bin = [
   { name = "threads2_sol", path = "../solutions/20_threads/threads2.rs" },
   { name = "threads3", path = "../exercises/20_threads/threads3.rs" },
   { name = "threads3_sol", path = "../solutions/20_threads/threads3.rs" },
-  { name = "macros1", path = "../exercises/21_macros/macros1.rs" },
-  { name = "macros1_sol", path = "../solutions/21_macros/macros1.rs" },
-  { name = "macros2", path = "../exercises/21_macros/macros2.rs" },
-  { name = "macros2_sol", path = "../solutions/21_macros/macros2.rs" },
-  { name = "macros3", path = "../exercises/21_macros/macros3.rs" },
-  { name = "macros3_sol", path = "../solutions/21_macros/macros3.rs" },
-  { name = "macros4", path = "../exercises/21_macros/macros4.rs" },
-  { name = "macros4_sol", path = "../solutions/21_macros/macros4.rs" },
-  { name = "clippy1", path = "../exercises/22_clippy/clippy1.rs" },
-  { name = "clippy1_sol", path = "../solutions/22_clippy/clippy1.rs" },
-  { name = "clippy2", path = "../exercises/22_clippy/clippy2.rs" },
-  { name = "clippy2_sol", path = "../solutions/22_clippy/clippy2.rs" },
-  { name = "clippy3", path = "../exercises/22_clippy/clippy3.rs" },
-  { name = "clippy3_sol", path = "../solutions/22_clippy/clippy3.rs" },
-  { name = "using_as", path = "../exercises/23_conversions/using_as.rs" },
-  { name = "using_as_sol", path = "../solutions/23_conversions/using_as.rs" },
-  { name = "from_into", path = "../exercises/23_conversions/from_into.rs" },
-  { name = "from_into_sol", path = "../solutions/23_conversions/from_into.rs" },
-  { name = "from_str", path = "../exercises/23_conversions/from_str.rs" },
-  { name = "from_str_sol", path = "../solutions/23_conversions/from_str.rs" },
-  { name = "try_from_into", path = "../exercises/23_conversions/try_from_into.rs" },
-  { name = "try_from_into_sol", path = "../solutions/23_conversions/try_from_into.rs" },
-  { name = "as_ref_mut", path = "../exercises/23_conversions/as_ref_mut.rs" },
-  { name = "as_ref_mut_sol", path = "../solutions/23_conversions/as_ref_mut.rs" },
+  { name = "async1", path = "../exercises/21_async/async1.rs" },
+  { name = "async1_sol", path = "../solutions/21_async/async1.rs" },
+  { name = "async2", path = "../exercises/21_async/async2.rs" },
+  { name = "async2_sol", path = "../solutions/21_async/async2.rs" },
+  { name = "macros1", path = "../exercises/22_macros/macros1.rs" },
+  { name = "macros1_sol", path = "../solutions/22_macros/macros1.rs" },
+  { name = "macros2", path = "../exercises/22_macros/macros2.rs" },
+  { name = "macros2_sol", path = "../solutions/22_macros/macros2.rs" },
+  { name = "macros3", path = "../exercises/22_macros/macros3.rs" },
+  { name = "macros3_sol", path = "../solutions/22_macros/macros3.rs" },
+  { name = "macros4", path = "../exercises/22_macros/macros4.rs" },
+  { name = "macros4_sol", path = "../solutions/22_macros/macros4.rs" },
+  { name = "clippy1", path = "../exercises/23_clippy/clippy1.rs" },
+  { name = "clippy1_sol", path = "../solutions/23_clippy/clippy1.rs" },
+  { name = "clippy2", path = "../exercises/23_clippy/clippy2.rs" },
+  { name = "clippy2_sol", path = "../solutions/23_clippy/clippy2.rs" },
+  { name = "clippy3", path = "../exercises/23_clippy/clippy3.rs" },
+  { name = "clippy3_sol", path = "../solutions/23_clippy/clippy3.rs" },
+  { name = "using_as", path = "../exercises/24_conversions/using_as.rs" },
+  { name = "using_as_sol", path = "../solutions/24_conversions/using_as.rs" },
+  { name = "from_into", path = "../exercises/24_conversions/from_into.rs" },
+  { name = "from_into_sol", path = "../solutions/24_conversions/from_into.rs" },
+  { name = "from_str", path = "../exercises/24_conversions/from_str.rs" },
+  { name = "from_str_sol", path = "../solutions/24_conversions/from_str.rs" },
+  { name = "try_from_into", path = "../exercises/24_conversions/try_from_into.rs" },
+  { name = "try_from_into_sol", path = "../solutions/24_conversions/try_from_into.rs" },
+  { name = "as_ref_mut", path = "../exercises/24_conversions/as_ref_mut.rs" },
+  { name = "as_ref_mut_sol", path = "../solutions/24_conversions/as_ref_mut.rs" },
 ]
 
 [package]
 name = "exercises"
-edition = "2021"
+edition = "2024"
 # Don't publish the exercises on crates.io!
 publish = false
+
+[dependencies]
+tokio = { version = "1.45.0", features = ["rt-multi-thread", "macros"] }
+
+[profile.release]
+panic = "abort"
+
+[profile.dev]
+panic = "abort"
+
+[lints.rust]
+# You shouldn't write unsafe code in Rustlings!
+unsafe_code = "forbid"
+# You don't need unstable features in Rustlings and shouldn't rely on them while learning Rust.
+unstable_features = "forbid"
+# Dead code warnings can't be avoided in some exercises and might distract while learning.
+dead_code = "allow"
+
+[lints.clippy]
+# You forgot a `todo!()`!
+todo = "forbid"
+# This can only happen by mistake in Rustlings.
+empty_loop = "forbid"
+# No infinite loops are needed in Rustlings.
+infinite_loop = "deny"
+# You shouldn't leak memory while still learning Rust!
+mem_forget = "deny"
+# Currently, there are no disallowed methods. This line avoids problems when developing Rustlings.
+disallowed_methods = "allow"

exercises/00_intro/intro1.rs

@@ -1,4 +1,4 @@
-// TODO: We sometimes encourage you to keep trying things on a given exercise,
+// TODO: We sometimes encourage you to keep trying things on a given exercise
 // even after you already figured it out. If you got everything working and feel
 // ready for the next exercise, enter `n` in the terminal.
 //
@@ -6,8 +6,7 @@
 // Try adding a new `println!` and check the updated output in the terminal.
 
 fn main() {
-    println!("Hello and");
-    println!(r#"       welcome to...                      "#);
+    println!(r#"       Welcome to...                      "#);
     println!(r#"                 _   _ _                  "#);
     println!(r#"  _ __ _   _ ___| |_| (_)_ __   __ _ ___  "#);
     println!(r#" | '__| | | / __| __| | | '_ \ / _` / __| "#);

exercises/01_variables/README.md

@@ -1,7 +1,7 @@
 # Variables
 
 In Rust, variables are immutable by default.
-When a variable is immutable, once a value is bound to a name, you can’t change that value.
+When a variable is immutable, once a value is bound to a name, you can't change that value.
 You can make them mutable by adding `mut` in front of the variable name.
 
 ## Further information

exercises/01_variables/variables1.rs

@@ -1,5 +1,5 @@
 fn main() {
-    // TODO: Add missing keyword.
+    // TODO: Add the missing keyword.
     x = 5;
 
     println!("x has the value {x}");

exercises/01_variables/variables5.rs

@@ -1,6 +1,6 @@
 fn main() {
     let number = "T-H-R-E-E"; // Don't change this line
-    println!("Spell a number: {}", number);
+    println!("Spell a number: {number}");
 
     // TODO: Fix the compiler error by changing the line below without renaming the variable.
     number = 3;

exercises/02_functions/functions3.rs

@@ -1,4 +1,4 @@
-fn call_me(num: u32) {
+fn call_me(num: u8) {
     for i in 0..num {
         println!("Ring! Call number {}", i + 1);
     }

exercises/03_if/if2.rs

@@ -1,7 +1,7 @@
 // TODO: Fix the compiler error on this function.
-fn foo_if_fizz(fizzish: &str) -> &str {
-    if fizzish == "fizz" {
-        "foo"
+fn picky_eater(food: &str) -> &str {
+    if food == "strawberry" {
+        "Yummy!"
     } else {
         1
     }
@@ -18,18 +18,20 @@ mod tests {
     use super::*;
 
     #[test]
-    fn foo_for_fizz() {
-        // This means that calling `foo_if_fizz` with the argument "fizz" should return "foo".
-        assert_eq!(foo_if_fizz("fizz"), "foo");
+    fn yummy_food() {
+        // This means that calling `picky_eater` with the argument "strawberry" should return "Yummy!".
+        assert_eq!(picky_eater("strawberry"), "Yummy!");
     }
 
     #[test]
-    fn bar_for_fuzz() {
-        assert_eq!(foo_if_fizz("fuzz"), "bar");
+    fn neutral_food() {
+        assert_eq!(picky_eater("potato"), "I guess I can eat that.");
     }
 
     #[test]
-    fn default_to_baz() {
-        assert_eq!(foo_if_fizz("literally anything"), "baz");
+    fn default_disliked_food() {
+        assert_eq!(picky_eater("broccoli"), "No thanks!");
+        assert_eq!(picky_eater("gummy bears"), "No thanks!");
+        assert_eq!(picky_eater("literally anything"), "No thanks!");
     }
 }

exercises/08_enums/README.md

@@ -1,10 +1,10 @@
 # Enums
 
 Rust allows you to define types called "enums" which enumerate possible values.
-Enums are a feature in many languages, but their capabilities differ in each language. Rust’s enums are most similar to algebraic data types in functional languages, such as F#, OCaml, and Haskell.
+Enums are a feature in many languages, but their capabilities differ in each language. Rust's enums are most similar to algebraic data types in functional languages, such as F#, OCaml, and Haskell.
 Useful in combination with enums is Rust's "pattern matching" facility, which makes it easy to run different code for different values of an enumeration.
 
 ## Further information
 
 - [Enums](https://doc.rust-lang.org/book/ch06-00-enums.html)
-- [Pattern syntax](https://doc.rust-lang.org/book/ch18-03-pattern-syntax.html)
+- [Pattern syntax](https://doc.rust-lang.org/book/ch19-03-pattern-syntax.html)

exercises/08_enums/enums2.rs

@@ -1,5 +1,3 @@
-#![allow(dead_code)]
-
 #[derive(Debug)]
 struct Point {
     x: u64,

exercises/08_enums/enums3.rs

@@ -4,7 +4,11 @@ struct Point {
 }
 
 enum Message {
-    // TODO: Implement the message variant types based on their usage below.
+    Resize { width: u64, height: u64 },
+    Move(Point),
+    Echo(String),
+    ChangeColor(u8, u8, u8),
+    Quit,
 }
 
 struct State {

exercises/09_strings/strings3.rs

@@ -23,6 +23,7 @@ mod tests {
         assert_eq!(trim_me("Hello!     "), "Hello!");
         assert_eq!(trim_me("  What's up!"), "What's up!");
         assert_eq!(trim_me("   Hola!  "), "Hola!");
+        assert_eq!(trim_me("Hi!"), "Hi!");
     }
 
     #[test]

exercises/10_modules/modules2.rs

@@ -1,7 +1,6 @@
 // You can bring module paths into scopes and provide new names for them with
 // the `use` and `as` keywords.
 
-#[allow(dead_code)]
 mod delicious_snacks {
     // TODO: Add the following two `use` statements after fixing them.
     // use self::fruits::PEAR as ???;

exercises/11_hashmaps/hashmaps2.rs

@@ -6,7 +6,7 @@
 // must add fruit to the basket so that there is at least one of each kind and
 // more than 11 in total - we have a lot of mouths to feed. You are not allowed
 // to insert any more of the fruits that are already in the basket (Apple,
-// Mango, and Lyche).
+// Mango, and Lychee).
 
 use std::collections::HashMap;
 

exercises/11_hashmaps/hashmaps3.rs

@@ -10,14 +10,14 @@ use std::collections::HashMap;
 
 // A structure to store the goal details of a team.
 #[derive(Default)]
-struct Team {
+struct TeamScores {
     goals_scored: u8,
     goals_conceded: u8,
 }
 
-fn build_scores_table(results: &str) -> HashMap<&str, Team> {
+fn build_scores_table(results: &str) -> HashMap<&str, TeamScores> {
     // The name of the team is the key and its associated struct is the value.
-    let mut scores = HashMap::new();
+    let mut scores = HashMap::<&str, TeamScores>::new();
 
     for line in results.lines() {
         let mut split_iterator = line.split(',');

exercises/12_options/options1.rs

@@ -1,8 +1,8 @@
-// This function returns how much icecream there is left in the fridge.
+// This function returns how much ice cream there is left in the fridge.
 // If it's before 22:00 (24-hour system), then 5 scoops are left. At 22:00,
-// someone eats it all, so no icecream is left (value 0). Return `None` if
+// someone eats it all, so no ice cream is left (value 0). Return `None` if
 // `hour_of_day` is higher than 23.
-fn maybe_icecream(hour_of_day: u16) -> Option<u16> {
+fn maybe_ice_cream(hour_of_day: u16) -> Option<u16> {
     // TODO: Complete the function body.
 }
 
@@ -18,19 +18,19 @@ mod tests {
     fn raw_value() {
         // TODO: Fix this test. How do you get the value contained in the
         // Option?
-        let icecreams = maybe_icecream(12);
+        let ice_creams = maybe_ice_cream(12);
 
-        assert_eq!(icecreams, 5); // Don't change this line.
+        assert_eq!(ice_creams, 5); // Don't change this line.
     }
 
     #[test]
-    fn check_icecream() {
-        assert_eq!(maybe_icecream(0), Some(5));
-        assert_eq!(maybe_icecream(9), Some(5));
-        assert_eq!(maybe_icecream(18), Some(5));
-        assert_eq!(maybe_icecream(22), Some(0));
-        assert_eq!(maybe_icecream(23), Some(0));
-        assert_eq!(maybe_icecream(24), None);
-        assert_eq!(maybe_icecream(25), None);
+    fn check_ice_cream() {
+        assert_eq!(maybe_ice_cream(0), Some(5));
+        assert_eq!(maybe_ice_cream(9), Some(5));
+        assert_eq!(maybe_ice_cream(18), Some(5));
+        assert_eq!(maybe_ice_cream(22), Some(0));
+        assert_eq!(maybe_ice_cream(23), Some(0));
+        assert_eq!(maybe_ice_cream(24), None);
+        assert_eq!(maybe_ice_cream(25), None);
     }
 }

exercises/12_options/options3.rs

@@ -9,7 +9,7 @@ fn main() {
 
     // TODO: Fix the compiler error by adding something to this match statement.
     match optional_point {
-        Some(p) => println!("Co-ordinates are {},{}", p.x, p.y),
+        Some(p) => println!("Coordinates are {},{}", p.x, p.y),
         _ => panic!("No match!"),
     }
 

exercises/13_error_handling/README.md

@@ -1,8 +1,8 @@
 # Error handling
 
-Most errors aren’t serious enough to require the program to stop entirely.
-Sometimes, when a function fails, it’s for a reason that you can easily interpret and respond to.
-For example, if you try to open a file and that operation fails because the file doesn’t exist, you might want to create the file instead of terminating the process.
+Most errors aren't serious enough to require the program to stop entirely.
+Sometimes, when a function fails, it's for a reason that you can easily interpret and respond to.
+For example, if you try to open a file and that operation fails because the file doesn't exist, you might want to create the file instead of terminating the process.
 
 ## Further information
 

exercises/13_error_handling/errors1.rs

@@ -6,7 +6,7 @@
 // of `Option<String>`.
 fn generate_nametag_text(name: String) -> Option<String> {
     if name.is_empty() {
-        // Empty names aren't allowed.
+        // Empty names aren't allowed
         None
     } else {
         Some(format!("Hi! My name is {name}"))

exercises/13_error_handling/errors4.rs

@@ -1,5 +1,3 @@
-#![allow(clippy::comparison_chain)]
-
 #[derive(PartialEq, Debug)]
 enum CreationError {
     Negative,

exercises/13_error_handling/errors5.rs

@@ -6,7 +6,7 @@
 //
 // In short, this particular use case for boxes is for when you want to own a
 // value and you care only that it is a type which implements a particular
-// trait. To do so, The `Box` is declared as of type `Box<dyn Trait>` where
+// trait. To do so, the `Box` is declared as of type `Box<dyn Trait>` where
 // `Trait` is the trait the compiler looks for on any value used in that
 // context. For this exercise, that context is the potential errors which
 // can be returned in a `Result`.

exercises/13_error_handling/errors6.rs

@@ -25,7 +25,7 @@ impl ParsePosNonzeroError {
     }
 
     // TODO: Add another error conversion function here.
-    // fn from_parseint(???) -> Self { ??? }
+    // fn from_parse_int(???) -> Self { ??? }
 }
 
 #[derive(PartialEq, Debug)]

exercises/15_traits/traits3.rs

@@ -1,5 +1,3 @@
-#![allow(dead_code)]
-
 trait Licensed {
     // TODO: Add a default implementation for `licensing_info` so that
     // implementors like the two structs below can share that default behavior

exercises/17_tests/tests3.rs

@@ -9,7 +9,7 @@ impl Rectangle {
         if width <= 0 || height <= 0 {
             // Returning a `Result` would be better here. But we want to learn
             // how to test functions that can panic.
-            panic!("Rectangle width and height can't be negative");
+            panic!("Rectangle width and height must be positive");
         }
 
         Rectangle { width, height }

exercises/19_smart_pointers/rc1.rs

@@ -8,7 +8,6 @@ use std::rc::Rc;
 #[derive(Debug)]
 struct Sun;
 
-#[allow(dead_code)]
 #[derive(Debug)]
 enum Planet {
     Mercury(Rc<Sun>),

exercises/20_threads/threads1.rs

@@ -1,5 +1,5 @@
-// This program spawns multiple threads that each run for at least 250ms, and
-// each thread returns how much time they took to complete. The program should
+// This program spawns multiple threads that each runs for at least 250ms, and
+// each thread returns how much time it took to complete. The program should
 // wait until all the spawned threads have finished and should collect their
 // return values into a vector.
 

exercises/20_threads/threads3.rs

@@ -1,7 +1,6 @@
 use std::{sync::mpsc, thread, time::Duration};
 
 struct Queue {
-    length: u32,
     first_half: Vec<u32>,
     second_half: Vec<u32>,
 }
@@ -9,7 +8,6 @@ struct Queue {
 impl Queue {
     fn new() -> Self {
         Self {
-            length: 10,
             first_half: vec![1, 2, 3, 4, 5],
             second_half: vec![6, 7, 8, 9, 10],
         }
@@ -48,17 +46,15 @@ mod tests {
     fn threads3() {
         let (tx, rx) = mpsc::channel();
         let queue = Queue::new();
-        let queue_length = queue.length;
 
         send_tx(queue, tx);
 
-        let mut total_received: u32 = 0;
-        for received in rx {
-            println!("Got: {received}");
-            total_received += 1;
+        let mut received = Vec::with_capacity(10);
+        for value in rx {
+            received.push(value);
         }
 
-        println!("Number of received values: {total_received}");
-        assert_eq!(total_received, queue_length);
+        received.sort();
+        assert_eq!(received, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
     }
 }

exercises/21_async/README.md

@@ -0,0 +1,10 @@
+# Async
+
+Rust includes built-in support for asynchronous programming. In other languages, this might be known as Promises or
+Coroutines. async programming uses async functions, which are powerful, but may require some getting used to,
+especially if you haven't used something similar in another language.
+
+The [relevant book chapter][1] is essential reading. The [tokio docs][2] are also very helpful!
+
+[1]: https://doc.rust-lang.org/book/ch17-00-async-await.html
+[2]: https://tokio.rs/tokio/tutorial

exercises/21_async/async1.rs

@@ -0,0 +1,44 @@
+// Our loyal worker works hard to create a new number.
+#[derive(Default)]
+struct Worker;
+
+struct NumberContainer {
+    number: i32,
+}
+
+impl Worker {
+    async fn work(&self) -> NumberContainer {
+        // Pretend this takes a while...
+        let new_number = 32;
+        NumberContainer { number: new_number }
+    }
+}
+
+impl NumberContainer {
+    async fn extract_number(&self) -> i32 {
+        // And this too...
+        self.number
+    }
+}
+
+// TODO: Fix the function signature!
+fn run_worker() -> i32 {
+    // TODO: Make our worker create a new number and return it.
+}
+
+fn main() {
+    // Feel free to experiment here. You may need to make some adjustments
+    // to this function, though.
+}
+
+mod tests {
+    use super::*;
+
+    // Don't worry about this attribute for now.
+    // If you want to know what this does, read the hint!
+    #[tokio::test]
+    async fn test_if_it_works() {
+        let number = run_worker().await;
+        assert_eq!(number, 32);
+    }
+}

exercises/21_async/async2.rs

@@ -0,0 +1,42 @@
+use tokio::task::JoinSet;
+
+// A MultiWorker can work with the power of 5 normal workers,
+// allowing us to create 5 new numbers at once!
+struct MultiWorker;
+
+impl MultiWorker {
+    async fn start_work(&self) -> JoinSet<i32> {
+        let mut set = JoinSet::new();
+
+        for i in 30..35 {
+            // TODO: `set.spawn` accepts an async function that will return the number
+            //       we want. Implement this function as a closure!
+            set.spawn(???);
+        }
+
+        set
+    }
+}
+
+async fn run_multi_worker() -> Vec<i32> {
+    let tasks = MultiWorker.start_work().await;
+
+    // TODO: We have a bunch of tasks, how do we run them to completion
+    //       to get at the i32s they create?
+}
+
+fn main() {
+    // Feel free to experiment here. You may need to make some adjustments
+    // to this function, though.
+}
+
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn test_if_it_works() {
+        let mut numbers = run_multi_worker().await;
+        numbers.sort(); // in case tasks run out-of-order
+        assert_eq!(numbers, vec![30, 31, 32, 33, 34]);
+    }
+}

exercises/22_macros/README.md

@@ -10,5 +10,6 @@ of exercises to Rustlings, but is all about learning to write Macros.
 
 ## Further information
 
-- [Macros](https://doc.rust-lang.org/book/ch19-06-macros.html)
+- [The Rust Book - Macros](https://doc.rust-lang.org/book/ch20-05-macros.html)
 - [The Little Book of Rust Macros](https://veykril.github.io/tlborm/)
+- [Rust by Example - macro_rules!](https://doc.rust-lang.org/rust-by-example/macros.html)

exercises/23_clippy/clippy3.rs

@@ -4,9 +4,11 @@
 #[rustfmt::skip]
 #[allow(unused_variables, unused_assignments)]
 fn main() {
-    let my_option: Option<()> = None;
+    let my_option: Option<&str> = None;
+    // Assume that you don't know the value of `my_option`.
+    // In the case of `Some`, we want to print its value.
     if my_option.is_none() {
-        println!("{:?}", my_option.unwrap());
+        println!("{}", my_option.unwrap());
     }
 
     let my_arr = &[

exercises/24_conversions/as_ref_mut.rs

@@ -2,10 +2,11 @@
 // about them at https://doc.rust-lang.org/std/convert/trait.AsRef.html and
 // https://doc.rust-lang.org/std/convert/trait.AsMut.html, respectively.
 
-// Obtain the number of bytes (not characters) in the given argument.
+// Obtain the number of bytes (not characters) in the given argument
+// (`.len()` returns the number of bytes in a string).
 // TODO: Add the `AsRef` trait appropriately as a trait bound.
 fn byte_counter<T>(arg: T) -> usize {
-    arg.as_ref().as_bytes().len()
+    arg.as_ref().len()
 }
 
 // Obtain the number of characters (not bytes) in the given argument.

exercises/24_conversions/from_str.rs

@@ -25,7 +25,7 @@ enum ParsePersonError {
     ParseInt(ParseIntError),
 }
 
-// TODO: Complete this `From` implementation to be able to parse a `Person`
+// TODO: Complete this `FromStr` implementation to be able to parse a `Person`
 // out of a string in the form of "Mark,20".
 // Note that you'll need to parse the age component into a `u8` with something
 // like `"4".parse::<u8>()`.

exercises/README.md

@@ -22,6 +22,7 @@
 | iterators              | §13.2-4             |
 | smart_pointers         | §15, §16.3          |
 | threads                | §16.1-3             |
+| async                  | §17                 |
 | macros                 | §19.5               |
 | clippy                 | §21.4               |
 | conversions            | n/a                 |

exercises/quizzes/quiz2.rs

@@ -26,7 +26,7 @@ enum Command {
 mod my_module {
     use super::Command;
 
-    // TODO: Complete the function.
+    // TODO: Complete the function as described above.
     // pub fn transformer(input: ???) -> ??? { ??? }
 }
 

oranda.json

@@ -1,4 +1,7 @@
 {
+  "build": {
+    "path_prefix": "rustlings"
+  },
   "project": {
     "homepage": "https://rustlings.cool",
     "repository": "https://github.com/rust-lang/rustlings"

release-hook.sh

@@ -3,7 +3,14 @@
 # Error out if any command fails
 set -e
 
-cargo run -- dev check
 typos
-cargo outdated -w --exit-code 1
+cargo upgrades
+
+# Similar to CI
+cargo clippy -- --deny warnings
+cargo fmt --all --check
 cargo test --workspace --all-targets
+cargo run -- dev check --require-solutions
+
+# MSRV
+cargo +1.85 run -- dev check --require-solutions

rustlings-macros/Cargo.toml

@@ -6,6 +6,7 @@ authors.workspace = true
 repository.workspace = true
 license.workspace = true
 edition.workspace = true
+rust-version.workspace = true
 include = [
   "/src/",
   "/info.toml",
@@ -15,6 +16,9 @@ include = [
 proc-macro = true
 
 [dependencies]
-quote = "1.0.36"
+quote = "1.0"
 serde.workspace = true
 toml_edit.workspace = true
+
+[lints]
+workspace = true

rustlings-macros/info.toml

@@ -1,6 +1,7 @@
 format_version = 1
 
-welcome_message = """Is this your first time? Don't worry, Rustlings is made for beginners!
+welcome_message = """
+Is this your first time? Don't worry, Rustlings is made for beginners!
 We are going to teach you a lot of things about Rust, but before we can
 get started, here are some notes about how Rustlings operates:
 
@@ -10,15 +11,16 @@ get started, here are some notes about how Rustlings operates:
    and fix them!
 2. Make sure to have your editor open in the `rustlings/` directory. Rustlings
    will show you the path of the current exercise under the progress bar. Open
-   the exercise file in your editor, fix errors and save the file. Rustlings will
-   automatically detect the file change and rerun the exercise. If all errors are
-   fixed, Rustlings will ask you to move on to the next exercise.
+   the exercise file in your editor, fix errors and save the file. Rustlings
+   will automatically detect the file change and rerun the exercise. If all
+   errors are fixed, Rustlings will ask you to move on to the next exercise.
 3. If you're stuck on an exercise, enter `h` to show a hint.
-4. If an exercise doesn't make sense to you, feel free to open an issue on GitHub!
-   (https://github.com/rust-lang/rustlings). We look at every issue, and sometimes,
-   other learners do too so you can help each other out!"""
+4. If an exercise doesn't make sense to you, feel free to open an issue on
+   GitHub! (https://github.com/rust-lang/rustlings). We look at every issue, and
+   sometimes, other learners do too so you can help each other out!"""
 
-final_message = """We hope you enjoyed learning about the various aspects of Rust!
+final_message = """
+We hope you enjoyed learning about the various aspects of Rust!
 If you noticed any issues, don't hesitate to report them on Github.
 You can also contribute your own exercises to help the greater community!
 
@@ -120,10 +122,10 @@ dir = "01_variables"
 test = false
 hint = """
 We know about variables and mutability, but there is another important type of
-variables available: constants.
+variable available: constants.
 
-Constants are always immutable. They are declared with the keyword `const` instead
-of `let`.
+Constants are always immutable. They are declared with the keyword `const`
+instead of `let`.
 
 The type of Constants must always be annotated.
 
@@ -253,7 +255,7 @@ require you to type in 100 items (but you certainly can if you want!).
 
 For example, you can do:
 ```
-let array = ["Are we there yet?"; 10];
+let array = ["Are we there yet?"; 100];
 ```
 
 Bonus: what are some other things you could have that would return `true`
@@ -319,7 +321,8 @@ hint = """
 In the first function, we create an empty vector and want to push new elements
 to it.
 
-In the second function, we map the values of the input and collect them into a vector.
+In the second function, we map the values of the input and collect them into
+a vector.
 
 After you've completed both functions, decide for yourself which approach you
 like better.
@@ -332,8 +335,8 @@ What do you think is the more commonly used pattern under Rust developers?"""
 name = "move_semantics1"
 dir = "06_move_semantics"
 hint = """
-So you've got the "cannot borrow `vec` as mutable, as it is not declared as mutable"
-error on the line where we push an element to the vector, right?
+So you've got the "cannot borrow `vec` as mutable, as it is not declared as
+mutable" error on the line where we push an element to the vector, right?
 
 The fix for this is going to be adding one keyword, and the addition is NOT on
 the line where we push to the vector (where the error is).
@@ -369,7 +372,8 @@ hint = """
 Carefully reason about the range in which each mutable reference is in
 scope. Does it help to update the value of `x` immediately after
 the mutable reference is taken?
-Read more about 'Mutable References' in the book's section 'References and Borrowing':
+Read more about 'Mutable References' in the book's section 'References and
+Borrowing':
 https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html#mutable-references."""
 
 [[exercises]]
@@ -498,14 +502,18 @@ some of them:
 https://doc.rust-lang.org/std/string/struct.String.html#method.trim
 
 For the `compose_me` method: You can either use the `format!` macro, or convert
-the string slice into an owned string, which you can then freely extend."""
+the string slice into an owned string, which you can then freely extend.
+
+For the `replace_me` method, you can check out the `replace` method:
+https://doc.rust-lang.org/std/string/struct.String.html#method.replace"""
 
 [[exercises]]
 name = "strings4"
 dir = "09_strings"
 test = false
 hint = """
-Replace `placeholder` with either `string` or `string_slice` in the `main` function.
+Replace `placeholder` with either `string` or `string_slice` in the `main`
+function.
 
 Example:
 `placeholder("blue");`
@@ -567,12 +575,8 @@ https://doc.rust-lang.org/book/ch08-03-hash-maps.html#only-inserting-a-value-if-
 name = "hashmaps3"
 dir = "11_hashmaps"
 hint = """
-Hint 1: Use the `entry()` and `or_insert()` (or `or_insert_with()`) methods of
-        `HashMap` to insert the default value of `Team` if a team doesn't
-        exist in the table yet.
-
-Learn more in The Book:
-https://doc.rust-lang.org/book/ch08-03-hash-maps.html#only-inserting-a-value-if-the-key-has-no-value
+Hint 1: Use the `entry()` and `or_default()` methods of `HashMap` to insert the
+        default value of `TeamScores` if a team doesn't exist in the table yet.
 
 Hint 2: If there is already an entry for a given key, the value returned by
         `entry()` can be updated based on the existing value.
@@ -760,7 +764,7 @@ Notice how the trait takes ownership of `self` and returns `Self`.
 
 Although the signature of `append_bar` in the trait takes `self` as argument,
 the implementation can take `mut self` instead. This is possible because the
-the value is owned anyway."""
+value is owned anyway."""
 
 [[exercises]]
 name = "traits3"
@@ -1075,11 +1079,51 @@ original sending end.
 Related section in The Book:
 https://doc.rust-lang.org/book/ch16-02-message-passing.html"""
 
+# ASYNC
+
+[[exercises]]
+name = "async1"
+dir = "21_async"
+test = true
+hint = """
+Async functions are not the same as normal functions -- they have to be marked with a
+special bit of syntax, `async fn`. These functions don't immediately return or even
+execute, you have to encourage them to do so by calling another special bit of syntax
+on them.
+
+Another thing - an async function can't be properly called in a normal function. Think of
+it as something contagious -- everything that it touches needs to be marked as such. Keeping
+that in mind, what adjustment do you need to make to the function signature?
+
+Aside:
+`#[tokio::test]` (and `#[tokio::main]`) are "magic" attributes that automatically
+set up what we call an async runtime. The Rust compiler intentionally doesn't supply
+a default implementation of this runtime. Tokio is by far the most popular
+community-developed runtime, and this macro does a lot of the heavy lifting to let
+us use it.
+"""
+
+[[exercises]]
+name = "async2"
+dir = "21_async"
+test = true
+hint = """
+Async functions can be used to run multiple things in parallel, or to more efficiently
+run things on multiple cores. Here, we use Tokio's tasks to schedule some work to run
+at the same time. We use a `JoinSet`, which is a list of tasks that lets us decide how
+to best execute them.
+
+One of the ways to execute tasks is `JoinSet::join_all`, which even gives us a neat
+Vec that we can immediately return! You can also do this sequentially, with an iterator.
+See if you can also find a way to do it that doesn't use `JoinSet`! You have access to
+most of Tokio's task-based functionality here.
+"""
+
 # MACROS
 
 [[exercises]]
 name = "macros1"
-dir = "21_macros"
+dir = "22_macros"
 test = false
 hint = """
 When you call a macro, you need to add something special compared to a regular
@@ -1087,7 +1131,7 @@ function call."""
 
 [[exercises]]
 name = "macros2"
-dir = "21_macros"
+dir = "22_macros"
 test = false
 hint = """
 Macros don't quite play by the same rules as the rest of Rust, in terms of
@@ -1098,7 +1142,7 @@ Unlike other things in Rust, the order of "where you define a macro" versus
 
 [[exercises]]
 name = "macros3"
-dir = "21_macros"
+dir = "22_macros"
 test = false
 hint = """
 In order to use a macro outside of its module, you need to do something
@@ -1106,7 +1150,7 @@ special to the module to lift the macro out into its parent."""
 
 [[exercises]]
 name = "macros4"
-dir = "21_macros"
+dir = "22_macros"
 test = false
 hint = """
 You only need to add a single character to make this compile.
@@ -1123,7 +1167,7 @@ https://veykril.github.io/tlborm/"""
 
 [[exercises]]
 name = "clippy1"
-dir = "22_clippy"
+dir = "23_clippy"
 test = false
 strict_clippy = true
 hint = """
@@ -1136,11 +1180,11 @@ constants, but clippy recognizes those imprecise mathematical constants as a
 source of potential error.
 
 See the suggestions of the Clippy warning in the compile output and use the
-appropriate replacement constant from `std::f32::consts`..."""
+appropriate replacement constant from `std::f32::consts`."""
 
 [[exercises]]
 name = "clippy2"
-dir = "22_clippy"
+dir = "23_clippy"
 test = false
 strict_clippy = true
 hint = """
@@ -1153,7 +1197,7 @@ https://doc.rust-lang.org/std/option/#iterating-over-option"""
 
 [[exercises]]
 name = "clippy3"
-dir = "22_clippy"
+dir = "23_clippy"
 test = false
 strict_clippy = true
 hint = "No hints this time!"
@@ -1162,20 +1206,20 @@ hint = "No hints this time!"
 
 [[exercises]]
 name = "using_as"
-dir = "23_conversions"
+dir = "24_conversions"
 hint = """
 Use the `as` operator to cast one of the operands in the last line of the
 `average` function into the expected return type."""
 
 [[exercises]]
 name = "from_into"
-dir = "23_conversions"
+dir = "24_conversions"
 hint = """
 Follow the steps provided right before the `From` implementation."""
 
 [[exercises]]
 name = "from_str"
-dir = "23_conversions"
+dir = "24_conversions"
 hint = """
 The implementation of `FromStr` should return an `Ok` with a `Person` object,
 or an `Err` with an error if the string is not valid.
@@ -1192,15 +1236,16 @@ https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/reen
 
 [[exercises]]
 name = "try_from_into"
-dir = "23_conversions"
+dir = "24_conversions"
 hint = """
 Is there an implementation of `TryFrom` in the standard library that can both do
 the required integer conversion and check the range of the input?
 
-Challenge: Can you make the `TryFrom` implementations generic over many integer types?"""
+Challenge: Can you make the `TryFrom` implementations generic over many integer
+types?"""
 
 [[exercises]]
 name = "as_ref_mut"
-dir = "23_conversions"
+dir = "24_conversions"
 hint = """
 Add `AsRef<str>` or `AsMut<u32>` as a trait bound to the functions."""

solutions/01_variables/variables5.rs

@@ -1,6 +1,6 @@
 fn main() {
     let number = "T-H-R-E-E";
-    println!("Spell a number: {}", number);
+    println!("Spell a number: {number}");
 
     // Using variable shadowing
     // https://doc.rust-lang.org/book/ch03-01-variables-and-mutability.html#shadowing

solutions/02_functions/functions3.rs

@@ -1,4 +1,4 @@
-fn call_me(num: u32) {
+fn call_me(num: u8) {
     for i in 0..num {
         println!("Ring! Call number {}", i + 1);
     }

solutions/03_if/if1.rs

@@ -1,9 +1,5 @@
 fn bigger(a: i32, b: i32) -> i32 {
-    if a > b {
-        a
-    } else {
-        b
-    }
+    if a > b { a } else { b }
 }
 
 fn main() {

solutions/03_if/if2.rs

@@ -1,10 +1,10 @@
-fn foo_if_fizz(fizzish: &str) -> &str {
-    if fizzish == "fizz" {
-        "foo"
-    } else if fizzish == "fuzz" {
-        "bar"
+fn picky_eater(food: &str) -> &str {
+    if food == "strawberry" {
+        "Yummy!"
+    } else if food == "potato" {
+        "I guess I can eat that."
     } else {
-        "baz"
+        "No thanks!"
     }
 }
 
@@ -17,17 +17,19 @@ mod tests {
     use super::*;
 
     #[test]
-    fn foo_for_fizz() {
-        assert_eq!(foo_if_fizz("fizz"), "foo");
+    fn yummy_food() {
+        assert_eq!(picky_eater("strawberry"), "Yummy!");
     }
 
     #[test]
-    fn bar_for_fuzz() {
-        assert_eq!(foo_if_fizz("fuzz"), "bar");
+    fn neutral_food() {
+        assert_eq!(picky_eater("potato"), "I guess I can eat that.");
     }
 
     #[test]
-    fn default_to_baz() {
-        assert_eq!(foo_if_fizz("literally anything"), "baz");
+    fn default_disliked_food() {
+        assert_eq!(picky_eater("broccoli"), "No thanks!");
+        assert_eq!(picky_eater("gummy bears"), "No thanks!");
+        assert_eq!(picky_eater("literally anything"), "No thanks!");
     }
 }

solutions/06_move_semantics/move_semantics4.rs

@@ -4,8 +4,6 @@ fn main() {
 
 #[cfg(test)]
 mod tests {
-    // TODO: Fix the compiler errors only by reordering the lines in the test.
-    // Don't add, change or remove any line.
     #[test]
     fn move_semantics4() {
         let mut x = Vec::new();

solutions/08_enums/enums2.rs

@@ -1,5 +1,3 @@
-#![allow(dead_code)]
-
 #[derive(Debug)]
 struct Point {
     x: u64,

solutions/08_enums/enums3.rs

@@ -46,8 +46,8 @@ impl State {
         match message {
             Message::Resize { width, height } => self.resize(width, height),
             Message::Move(point) => self.move_position(point),
-            Message::Echo(s) => self.echo(s),
-            Message::ChangeColor(r, g, b) => self.change_color(r, g, b),
+            Message::Echo(string) => self.echo(string),
+            Message::ChangeColor(red, green, blue) => self.change_color(red, green, blue),
             Message::Quit => self.quit(),
         }
     }

solutions/09_strings/strings3.rs

@@ -26,6 +26,7 @@ mod tests {
         assert_eq!(trim_me("Hello!     "), "Hello!");
         assert_eq!(trim_me("  What's up!"), "What's up!");
         assert_eq!(trim_me("   Hola!  "), "Hola!");
+        assert_eq!(trim_me("Hi!"), "Hi!");
     }
 
     #[test]

solutions/09_strings/strings4.rs

@@ -18,12 +18,11 @@ fn main() {
     // Here, both answers work.
     // `.into()` converts a type into an expected type.
     // If it is called where `String` is expected, it will convert `&str` to `String`.
-    // But if is called where `&str` is expected, then `&str` is kept `&str` since no
-    // conversion is needed.
     string("nice weather".into());
+    // But if it is called where `&str` is expected, then `&str` is kept `&str` since no conversion is needed.
+    // If you remove the `#[allow(…)]` line, then Clippy will tell you to remove `.into()` below since it is a useless conversion.
+    #[allow(clippy::useless_conversion)]
     string_slice("nice weather".into());
-    //                         ^^^^^^^ the compiler recommends removing the `.into()`
-    //                                 call because it is a useless conversion.
 
     string(format!("Interpolation {}", "Station"));
 

solutions/10_modules/modules2.rs

@@ -1,4 +1,3 @@
-#[allow(dead_code)]
 mod delicious_snacks {
     // Added `pub` and used the expected alias after `as`.
     pub use self::fruits::PEAR as fruit;

solutions/11_hashmaps/hashmaps2.rs

@@ -5,7 +5,8 @@
 // Apple (4), Mango (2) and Lychee (5) are already in the basket hash map. You
 // must add fruit to the basket so that there is at least one of each kind and
 // more than 11 in total - we have a lot of mouths to feed. You are not allowed
-// to insert any more of these fruits!
+// to insert any more of the fruits that are already in the basket (Apple,
+// Mango, and Lychee).
 
 use std::collections::HashMap;
 

solutions/11_hashmaps/hashmaps3.rs

@@ -10,14 +10,14 @@ use std::collections::HashMap;
 
 // A structure to store the goal details of a team.
 #[derive(Default)]
-struct Team {
+struct TeamScores {
     goals_scored: u8,
     goals_conceded: u8,
 }
 
-fn build_scores_table(results: &str) -> HashMap<&str, Team> {
+fn build_scores_table(results: &str) -> HashMap<&str, TeamScores> {
     // The name of the team is the key and its associated struct is the value.
-    let mut scores = HashMap::new();
+    let mut scores = HashMap::<&str, TeamScores>::new();
 
     for line in results.lines() {
         let mut split_iterator = line.split(',');
@@ -28,13 +28,13 @@ fn build_scores_table(results: &str) -> HashMap<&str, Team> {
         let team_2_score: u8 = split_iterator.next().unwrap().parse().unwrap();
 
         // Insert the default with zeros if a team doesn't exist yet.
-        let team_1 = scores.entry(team_1_name).or_insert_with(Team::default);
+        let team_1 = scores.entry(team_1_name).or_default();
         // Update the values.
         team_1.goals_scored += team_1_score;
         team_1.goals_conceded += team_2_score;
 
-        // Similarely for the second team.
-        let team_2 = scores.entry(team_2_name).or_insert_with(Team::default);
+        // Similarly for the second team.
+        let team_2 = scores.entry(team_2_name).or_default();
         team_2.goals_scored += team_2_score;
         team_2.goals_conceded += team_1_score;
     }
@@ -60,9 +60,11 @@ England,Spain,1,0";
     fn build_scores() {
         let scores = build_scores_table(RESULTS);
 
-        assert!(["England", "France", "Germany", "Italy", "Poland", "Spain"]
-            .into_iter()
-            .all(|team_name| scores.contains_key(team_name)));
+        assert!(
+            ["England", "France", "Germany", "Italy", "Poland", "Spain"]
+                .into_iter()
+                .all(|team_name| scores.contains_key(team_name))
+        );
     }
 
     #[test]

solutions/12_options/options3.rs

@@ -10,7 +10,7 @@ fn main() {
     // Solution 1: Matching over the `Option` (not `&Option`) but without moving
     // out of the `Some` variant.
     match optional_point {
-        Some(ref p) => println!("Co-ordinates are {},{}", p.x, p.y),
+        Some(ref p) => println!("Coordinates are {},{}", p.x, p.y),
         //   ^^^ added
         _ => panic!("No match!"),
     }
@@ -18,7 +18,8 @@ fn main() {
     // Solution 2: Matching over a reference (`&Option`) by added `&` before
     // `optional_point`.
     match &optional_point {
-        Some(p) => println!("Co-ordinates are {},{}", p.x, p.y),
+        //^ added
+        Some(p) => println!("Coordinates are {},{}", p.x, p.y),
         _ => panic!("No match!"),
     }
 

solutions/13_error_handling/errors2.rs

@@ -16,7 +16,7 @@
 
 use std::num::ParseIntError;
 
-#[allow(unused_variables)]
+#[allow(unused_variables, clippy::question_mark)]
 fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
     let processing_fee = 1;
     let cost_per_item = 5;

solutions/13_error_handling/errors4.rs

@@ -1,4 +1,4 @@
-#![allow(clippy::comparison_chain)]
+use std::cmp::Ordering;
 
 #[derive(PartialEq, Debug)]
 enum CreationError {
@@ -11,12 +11,10 @@ struct PositiveNonzeroInteger(u64);
 
 impl PositiveNonzeroInteger {
     fn new(value: i64) -> Result<Self, CreationError> {
-        if value == 0 {
-            Err(CreationError::Zero)
-        } else if value < 0 {
-            Err(CreationError::Negative)
-        } else {
-            Ok(Self(value as u64))
+        match value.cmp(&0) {
+            Ordering::Less => Err(CreationError::Negative),
+            Ordering::Equal => Err(CreationError::Zero),
+            Ordering::Greater => Ok(Self(value as u64)),
         }
     }
 }

solutions/13_error_handling/errors6.rs

@@ -24,11 +24,26 @@ impl ParsePosNonzeroError {
         Self::Creation(err)
     }
 
-    fn from_parseint(err: ParseIntError) -> Self {
+    fn from_parse_int(err: ParseIntError) -> Self {
         Self::ParseInt(err)
     }
 }
 
+// As an alternative solution, implementing the `From` trait allows for the
+// automatic conversion from a `ParseIntError` into a `ParsePosNonzeroError`
+// using the `?` operator, without the need to call `map_err`.
+//
+// ```
+// let x: i64 = s.parse()?;
+// ```
+//
+// Traits like `From` will be dealt with in later exercises.
+impl From<ParseIntError> for ParsePosNonzeroError {
+    fn from(err: ParseIntError) -> Self {
+        ParsePosNonzeroError::ParseInt(err)
+    }
+}
+
 #[derive(PartialEq, Debug)]
 struct PositiveNonzeroInteger(u64);
 
@@ -44,7 +59,7 @@ impl PositiveNonzeroInteger {
     fn parse(s: &str) -> Result<Self, ParsePosNonzeroError> {
         // Return an appropriate error instead of panicking when `parse()`
         // returns an error.
-        let x: i64 = s.parse().map_err(ParsePosNonzeroError::from_parseint)?;
+        let x: i64 = s.parse().map_err(ParsePosNonzeroError::from_parse_int)?;
         //                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
         Self::new(x).map_err(ParsePosNonzeroError::from_creation)
     }

solutions/15_traits/traits3.rs

@@ -1,5 +1,3 @@
-#![allow(dead_code)]
-
 trait Licensed {
     fn licensing_info(&self) -> String {
         "Default license".to_string()

solutions/16_lifetimes/lifetimes1.rs

@@ -5,11 +5,7 @@
 
 fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
     //    ^^^^     ^^          ^^          ^^
-    if x.len() > y.len() {
-        x
-    } else {
-        y
-    }
+    if x.len() > y.len() { x } else { y }
 }
 
 fn main() {

solutions/16_lifetimes/lifetimes2.rs

@@ -1,9 +1,5 @@
 fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
-    if x.len() > y.len() {
-        x
-    } else {
-        y
-    }
+    if x.len() > y.len() { x } else { y }
 }
 
 fn main() {

solutions/17_tests/tests3.rs

@@ -9,7 +9,7 @@ impl Rectangle {
         if width <= 0 || height <= 0 {
             // Returning a `Result` would be better here. But we want to learn
             // how to test functions that can panic.
-            panic!("Rectangle width and height can't be negative");
+            panic!("Rectangle width and height must be positive");
         }
 
         Rectangle { width, height }

solutions/18_iterators/iterators4.rs

@@ -25,6 +25,7 @@ fn factorial_fold(num: u64) -> u64 {
     //              -> 1 * 2 is calculated, then the result 2 is multiplied by
     //                 the second element 3 so the result 6 is returned.
     // And so on…
+    #[allow(clippy::unnecessary_fold)]
     (2..=num).fold(1, |acc, x| acc * x)
 }
 

solutions/19_smart_pointers/rc1.rs

@@ -8,7 +8,6 @@ use std::rc::Rc;
 #[derive(Debug)]
 struct Sun;
 
-#[allow(dead_code)]
 #[derive(Debug)]
 enum Planet {
     Mercury(Rc<Sun>),
@@ -64,12 +63,10 @@ mod tests {
         println!("reference count = {}", Rc::strong_count(&sun)); // 7 references
         saturn.details();
 
-        // TODO
         let uranus = Planet::Uranus(Rc::clone(&sun));
         println!("reference count = {}", Rc::strong_count(&sun)); // 8 references
         uranus.details();
 
-        // TODO
         let neptune = Planet::Neptune(Rc::clone(&sun));
         println!("reference count = {}", Rc::strong_count(&sun)); // 9 references
         neptune.details();

solutions/20_threads/threads1.rs

@@ -1,5 +1,5 @@
-// This program spawns multiple threads that each run for at least 250ms, and
-// each thread returns how much time they took to complete. The program should
+// This program spawns multiple threads that each runs for at least 250ms, and
+// each thread returns how much time it took to complete. The program should
 // wait until all the spawned threads have finished and should collect their
 // return values into a vector.
 

solutions/20_threads/threads3.rs

@@ -1,7 +1,6 @@
 use std::{sync::mpsc, thread, time::Duration};
 
 struct Queue {
-    length: u32,
     first_half: Vec<u32>,
     second_half: Vec<u32>,
 }
@@ -9,7 +8,6 @@ struct Queue {
 impl Queue {
     fn new() -> Self {
         Self {
-            length: 10,
             first_half: vec![1, 2, 3, 4, 5],
             second_half: vec![6, 7, 8, 9, 10],
         }
@@ -50,17 +48,15 @@ mod tests {
     fn threads3() {
         let (tx, rx) = mpsc::channel();
         let queue = Queue::new();
-        let queue_length = queue.length;
 
         send_tx(queue, tx);
 
-        let mut total_received: u32 = 0;
-        for received in rx {
-            println!("Got: {received}");
-            total_received += 1;
+        let mut received = Vec::with_capacity(10);
+        for value in rx {
+            received.push(value);
         }
 
-        println!("Number of received values: {total_received}");
-        assert_eq!(total_received, queue_length);
+        received.sort();
+        assert_eq!(received, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
     }
 }

solutions/21_async/async1.rs

@@ -0,0 +1,45 @@
+// Our loyal worker works hard to create a new number.
+#[derive(Default)]
+struct Worker;
+
+struct NumberContainer {
+    number: i32,
+}
+
+impl Worker {
+    async fn work(&self) -> NumberContainer {
+        // Pretend this takes a while...
+        let new_number = 32;
+        NumberContainer { number: new_number }
+    }
+}
+
+impl NumberContainer {
+    async fn extract_number(&self) -> i32 {
+        // And this too...
+        self.number
+    }
+}
+
+async fn run_worker() -> i32 {
+    // TODO: Make our worker create a new number and return it.
+    Worker.work().await.extract_number().await
+}
+
+fn main() {
+    // Feel free to experiment here. You may need to make some adjustments
+    // to this function, though.
+}
+
+mod tests {
+    use super::*;
+
+    // Don't worry about this attribute for now.
+    // If you want to know what this does, read the hint!
+    #[tokio::test]
+    // TODO: Fix the test function signature
+    fn test_if_it_works() {
+        let number = run_worker().await;
+        assert_eq!(number, 32);
+    }
+}

solutions/21_async/async2.rs

@@ -0,0 +1,43 @@
+use tokio::task::JoinSet;
+
+// A MultiWorker can work with the power of 5 normal workers,
+// allowing us to create 5 new numbers at once!
+struct MultiWorker;
+
+impl MultiWorker {
+    async fn start_work(&self) -> JoinSet<i32> {
+        let mut set = JoinSet::new();
+
+        for i in 30..35 {
+            // TODO: `set.spawn` accepts an async function that will return the number
+            //       we want. Implement this function as a closure!
+            set.spawn(async move { i });
+        }
+
+        set
+    }
+}
+
+async fn run_multi_worker() -> Vec<i32> {
+    let tasks = MultiWorker.start_work().await;
+
+    // TODO: We have a bunch of tasks, how do we run them to completion
+    //       to get at the i32s they create?
+    tasks.join_all().await
+}
+
+fn main() {
+    // Feel free to experiment here. You may need to make some adjustments
+    // to this function, though.
+}
+
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn test_if_it_works() {
+        let mut numbers = run_multi_worker().await;
+        numbers.sort(); // in case tasks run out-of-order
+        assert_eq!(numbers, vec![30, 31, 32, 33, 34]);
+    }
+}

solutions/23_clippy/clippy3.rs

@@ -3,11 +3,11 @@ use std::mem;
 #[rustfmt::skip]
 #[allow(unused_variables, unused_assignments)]
 fn main() {
-    let my_option: Option<()> = None;
+    let my_option: Option<&str> = None;
     // `unwrap` of an `Option` after checking if it is `None` will panic.
     // Use `if-let` instead.
     if let Some(value) = my_option {
-        println!("{value:?}");
+        println!("{value}");
     }
 
     // A comma was missing.
@@ -15,7 +15,7 @@ fn main() {
         -1, -2, -3,
         -4, -5, -6,
     ];
-    println!("My array! Here it is: {:?}", my_arr);
+    println!("My array! Here it is: {my_arr:?}");
 
     let mut my_empty_vec = vec![1, 2, 3, 4, 5];
     // `resize` mutates a vector instead of returning a new one.
@@ -27,5 +27,5 @@ fn main() {
     let mut value_b = 66;
     // Use `mem::swap` to correctly swap two values.
     mem::swap(&mut value_a, &mut value_b);
-    println!("value a: {}; value b: {}", value_a, value_b);
+    println!("value a: {value_a}; value b: {value_b}");
 }

solutions/24_conversions/as_ref_mut.rs

@@ -2,9 +2,10 @@
 // about them at https://doc.rust-lang.org/std/convert/trait.AsRef.html and
 // https://doc.rust-lang.org/std/convert/trait.AsMut.html, respectively.
 
-// Obtain the number of bytes (not characters) in the given argument.
+// Obtain the number of bytes (not characters) in the given argument
+// (`.len()` returns the number of bytes in a string).
 fn byte_counter<T: AsRef<str>>(arg: T) -> usize {
-    arg.as_ref().as_bytes().len()
+    arg.as_ref().len()
 }
 
 // Obtain the number of characters (not bytes) in the given argument.

solutions/README.md

@@ -0,0 +1,6 @@
+# Official Rustlings solutions
+
+Before you finish an exercise, its solution file will only contain an empty `main` function.
+The content of this file will be automatically replaced by the actual solution once you finish the exercise.
+
+Note that these solutions are often only _one possibility_ to solve an exercise.

solutions/quizzes/quiz2.rs

@@ -62,8 +62,8 @@ mod tests {
     // Import `transformer`.
     use super::my_module::transformer;
 
-    use super::my_module::transformer_iter;
     use super::Command;
+    use super::my_module::transformer_iter;
 
     #[test]
     fn it_works() {

src/app_state.rs

@@ -1,32 +1,39 @@
-use anyhow::{bail, Context, Result};
-use crossterm::style::Stylize;
-use serde::Deserialize;
+use anyhow::{Context, Error, Result, bail};
+use crossterm::{QueueableCommand, cursor, terminal};
 use std::{
-    fs::{self, File},
-    io::{Read, StdoutLock, Write},
-    path::{Path, PathBuf},
+    collections::HashSet,
+    env,
+    fs::{File, OpenOptions},
+    io::{Read, Seek, StdoutLock, Write},
+    path::{MAIN_SEPARATOR_STR, Path},
     process::{Command, Stdio},
+    sync::{
+        atomic::{AtomicUsize, Ordering::Relaxed},
+        mpsc,
+    },
+    thread,
 };
 
 use crate::{
     clear_terminal,
+    cmd::CmdRunner,
     embedded::EMBEDDED_FILES,
-    exercise::{Exercise, RunnableExercise, OUTPUT_CAPACITY},
+    exercise::{Exercise, RunnableExercise},
     info_file::ExerciseInfo,
-    DEBUG_PROFILE,
+    term::{self, CheckProgressVisualizer},
 };
 
 const STATE_FILE_NAME: &str = ".rustlings-state.txt";
-const BAD_INDEX_ERR: &str = "The current exercise index is higher than the number of exercises";
+const DEFAULT_CHECK_PARALLELISM: usize = 8;
 
 #[must_use]
 pub enum ExercisesProgress {
     // All exercises are done.
     AllDone,
-    // The current exercise failed and is still pending.
-    CurrentPending,
     // A new exercise is now pending.
     NewPending,
+    // The current exercise is still pending.
+    CurrentPending,
 }
 
 pub enum StateFileStatus {
@@ -34,29 +41,12 @@ pub enum StateFileStatus {
     NotRead,
 }
 
-// Parses parts of the output of `cargo metadata`.
-#[derive(Deserialize)]
-struct CargoMetadata {
-    target_directory: PathBuf,
-}
-
-pub fn parse_target_dir() -> Result<PathBuf> {
-    // Get the target directory from Cargo.
-    let metadata_output = Command::new("cargo")
-        .arg("metadata")
-        .arg("-q")
-        .arg("--format-version")
-        .arg("1")
-        .arg("--no-deps")
-        .stdin(Stdio::null())
-        .stderr(Stdio::inherit())
-        .output()
-        .context(CARGO_METADATA_ERR)?
-        .stdout;
-
-    serde_json::de::from_slice::<CargoMetadata>(&metadata_output)
-        .context("Failed to read the field `target_directory` from the `cargo metadata` output")
-        .map(|metadata| metadata.target_directory)
+#[derive(Clone, Copy)]
+pub enum CheckProgress {
+    None,
+    Checking,
+    Done,
+    Pending,
 }
 
 pub struct AppState {
@@ -65,67 +55,33 @@ pub struct AppState {
     // Caches the number of done exercises to avoid iterating over all exercises every time.
     n_done: u16,
     final_message: String,
+    state_file: File,
     // Preallocated buffer for reading and writing the state file.
     file_buf: Vec<u8>,
     official_exercises: bool,
-    // Cargo's target directory.
-    target_dir: PathBuf,
+    cmd_runner: CmdRunner,
+    // Running in VS Code.
+    vs_code: bool,
 }
 
 impl AppState {
-    // Update the app state from the state file.
-    fn update_from_file(&mut self) -> StateFileStatus {
-        self.file_buf.clear();
-        self.n_done = 0;
-
-        if File::open(STATE_FILE_NAME)
-            .and_then(|mut file| file.read_to_end(&mut self.file_buf))
-            .is_err()
-        {
-            return StateFileStatus::NotRead;
-        }
-
-        // See `Self::write` for more information about the file format.
-        let mut lines = self.file_buf.split(|c| *c == b'\n').skip(2);
-
-        let Some(current_exercise_name) = lines.next() else {
-            return StateFileStatus::NotRead;
-        };
-
-        if current_exercise_name.is_empty() || lines.next().is_none() {
-            return StateFileStatus::NotRead;
-        }
-
-        let mut done_exercises = hashbrown::HashSet::with_capacity(self.exercises.len());
-
-        for done_exerise_name in lines {
-            if done_exerise_name.is_empty() {
-                break;
-            }
-            done_exercises.insert(done_exerise_name);
-        }
-
-        for (ind, exercise) in self.exercises.iter_mut().enumerate() {
-            if done_exercises.contains(exercise.name.as_bytes()) {
-                exercise.done = true;
-                self.n_done += 1;
-            }
-
-            if exercise.name.as_bytes() == current_exercise_name {
-                self.current_exercise_ind = ind;
-            }
-        }
-
-        StateFileStatus::Read
-    }
-
     pub fn new(
         exercise_infos: Vec<ExerciseInfo>,
         final_message: String,
     ) -> Result<(Self, StateFileStatus)> {
-        let target_dir = parse_target_dir()?;
+        let cmd_runner = CmdRunner::build()?;
+        let mut state_file = OpenOptions::new()
+            .create(true)
+            .read(true)
+            .write(true)
+            .truncate(false)
+            .open(STATE_FILE_NAME)
+            .with_context(|| {
+                format!("Failed to open or create the state file {STATE_FILE_NAME}")
+            })?;
 
-        let exercises = exercise_infos
+        let dir_canonical_path = term::canonicalize("exercises");
+        let mut exercises = exercise_infos
             .into_iter()
             .map(|exercise_info| {
                 // Leaking to be able to borrow in the watch mode `Table`.
@@ -134,33 +90,99 @@ impl AppState {
                 let path = exercise_info.path().leak();
                 let name = exercise_info.name.leak();
                 let dir = exercise_info.dir.map(|dir| &*dir.leak());
+                let hint = exercise_info.hint.leak().trim_ascii();
 
-                let hint = exercise_info.hint.trim().to_owned();
+                let canonical_path = dir_canonical_path.as_deref().map(|dir_canonical_path| {
+                    let mut canonical_path;
+                    if let Some(dir) = dir {
+                        canonical_path = String::with_capacity(
+                            2 + dir_canonical_path.len() + dir.len() + name.len(),
+                        );
+                        canonical_path.push_str(dir_canonical_path);
+                        canonical_path.push_str(MAIN_SEPARATOR_STR);
+                        canonical_path.push_str(dir);
+                    } else {
+                        canonical_path =
+                            String::with_capacity(1 + dir_canonical_path.len() + name.len());
+                        canonical_path.push_str(dir_canonical_path);
+                    }
+
+                    canonical_path.push_str(MAIN_SEPARATOR_STR);
+                    canonical_path.push_str(name);
+                    canonical_path.push_str(".rs");
+                    canonical_path
+                });
 
                 Exercise {
                     dir,
                     name,
                     path,
+                    canonical_path,
                     test: exercise_info.test,
                     strict_clippy: exercise_info.strict_clippy,
                     hint,
-                    // Updated in `Self::update_from_file`.
+                    // Updated below.
                     done: false,
                 }
             })
             .collect::<Vec<_>>();
 
-        let mut slf = Self {
-            current_exercise_ind: 0,
-            exercises,
-            n_done: 0,
-            final_message,
-            file_buf: Vec::with_capacity(2048),
-            official_exercises: !Path::new("info.toml").exists(),
-            target_dir,
+        let mut current_exercise_ind = 0;
+        let mut n_done = 0;
+        let mut file_buf = Vec::with_capacity(2048);
+        let state_file_status = 'block: {
+            if state_file.read_to_end(&mut file_buf).is_err() {
+                break 'block StateFileStatus::NotRead;
+            }
+
+            // See `Self::write` for more information about the file format.
+            let mut lines = file_buf.split(|c| *c == b'\n').skip(2);
+
+            let Some(current_exercise_name) = lines.next() else {
+                break 'block StateFileStatus::NotRead;
+            };
+
+            if current_exercise_name.is_empty() || lines.next().is_none() {
+                break 'block StateFileStatus::NotRead;
+            }
+
+            let mut done_exercises = HashSet::with_capacity(exercises.len());
+
+            for done_exercise_name in lines {
+                if done_exercise_name.is_empty() {
+                    break;
+                }
+                done_exercises.insert(done_exercise_name);
+            }
+
+            for (ind, exercise) in exercises.iter_mut().enumerate() {
+                if done_exercises.contains(exercise.name.as_bytes()) {
+                    exercise.done = true;
+                    n_done += 1;
+                }
+
+                if exercise.name.as_bytes() == current_exercise_name {
+                    current_exercise_ind = ind;
+                }
+            }
+
+            StateFileStatus::Read
         };
 
-        let state_file_status = slf.update_from_file();
+        file_buf.clear();
+        file_buf.extend_from_slice(STATE_FILE_HEADER);
+
+        let slf = Self {
+            current_exercise_ind,
+            exercises,
+            n_done,
+            final_message,
+            state_file,
+            file_buf,
+            official_exercises: !Path::new("info.toml").exists(),
+            cmd_runner,
+            vs_code: env::var_os("TERM_PROGRAM").is_some_and(|v| v == "vscode"),
+        };
 
         Ok((slf, state_file_status))
     }
@@ -180,14 +202,24 @@ impl AppState {
         self.n_done
     }
 
+    #[inline]
+    pub fn n_pending(&self) -> u16 {
+        self.exercises.len() as u16 - self.n_done
+    }
+
     #[inline]
     pub fn current_exercise(&self) -> &Exercise {
         &self.exercises[self.current_exercise_ind]
     }
 
     #[inline]
-    pub fn target_dir(&self) -> &Path {
-        &self.target_dir
+    pub fn cmd_runner(&self) -> &CmdRunner {
+        &self.cmd_runner
+    }
+
+    #[inline]
+    pub fn vs_code(&self) -> bool {
+        self.vs_code
     }
 
     // Write the state file.
@@ -199,10 +231,8 @@ impl AppState {
     // - The fourth line is an empty line.
     // - All remaining lines are the names of done exercises.
     fn write(&mut self) -> Result<()> {
-        self.file_buf.clear();
+        self.file_buf.truncate(STATE_FILE_HEADER.len());
 
-        self.file_buf
-            .extend_from_slice(b"DON'T EDIT THIS FILE!\n\n");
         self.file_buf
             .extend_from_slice(self.current_exercise().name.as_bytes());
         self.file_buf.push(b'\n');
@@ -214,7 +244,14 @@ impl AppState {
             }
         }
 
-        fs::write(STATE_FILE_NAME, &self.file_buf)
+        self.state_file
+            .rewind()
+            .with_context(|| format!("Failed to rewind the state file {STATE_FILE_NAME}"))?;
+        self.state_file
+            .set_len(0)
+            .with_context(|| format!("Failed to truncate the state file {STATE_FILE_NAME}"))?;
+        self.state_file
+            .write_all(&self.file_buf)
             .with_context(|| format!("Failed to write the state file {STATE_FILE_NAME}"))?;
 
         Ok(())
@@ -246,15 +283,31 @@ impl AppState {
         self.write()
     }
 
-    pub fn set_pending(&mut self, exercise_ind: usize) -> Result<()> {
+    // Set the status of an exercise without saving. Returns `true` if the
+    // status actually changed (and thus needs saving later).
+    pub fn set_status(&mut self, exercise_ind: usize, done: bool) -> Result<bool> {
         let exercise = self
             .exercises
             .get_mut(exercise_ind)
             .context(BAD_INDEX_ERR)?;
 
-        if exercise.done {
-            exercise.done = false;
+        if exercise.done == done {
+            return Ok(false);
+        }
+
+        exercise.done = done;
+        if done {
+            self.n_done += 1;
+        } else {
             self.n_done -= 1;
+        }
+
+        Ok(true)
+    }
+
+    // Set the status of an exercise to "pending" and save.
+    pub fn set_pending(&mut self, exercise_ind: usize) -> Result<()> {
+        if self.set_status(exercise_ind, false)? {
             self.write()?;
         }
 
@@ -298,6 +351,7 @@ impl AppState {
         Ok(exercise.path)
     }
 
+    // Reset the exercise by index and return its name.
     pub fn reset_exercise_by_ind(&mut self, exercise_ind: usize) -> Result<&'static str> {
         if exercise_ind >= self.exercises.len() {
             bail!(BAD_INDEX_ERR);
@@ -307,36 +361,33 @@ impl AppState {
         let exercise = &self.exercises[exercise_ind];
         self.reset(exercise_ind, exercise.path)?;
 
-        Ok(exercise.path)
+        Ok(exercise.name)
     }
 
     // Return the index of the next pending exercise or `None` if all exercises are done.
     fn next_pending_exercise_ind(&self) -> Option<usize> {
-        if self.current_exercise_ind == self.exercises.len() - 1 {
-            // The last exercise is done.
-            // Search for exercises not done from the start.
-            return self.exercises[..self.current_exercise_ind]
-                .iter()
-                .position(|exercise| !exercise.done);
-        }
-
-        // The done exercise isn't the last one.
-        // Search for a pending exercise after the current one and then from the start.
-        match self.exercises[self.current_exercise_ind + 1..]
-            .iter()
-            .position(|exercise| !exercise.done)
-        {
-            Some(ind) => Some(self.current_exercise_ind + 1 + ind),
-            None => self.exercises[..self.current_exercise_ind]
-                .iter()
-                .position(|exercise| !exercise.done),
-        }
+        let next_ind = self.current_exercise_ind + 1;
+        self.exercises
+            // If the exercise done isn't the last, search for pending exercises after it.
+            .get(next_ind..)
+            .and_then(|later_exercises| {
+                later_exercises
+                    .iter()
+                    .position(|exercise| !exercise.done)
+                    .map(|ind| next_ind + ind)
+            })
+            // Search from the start.
+            .or_else(|| {
+                self.exercises[..self.current_exercise_ind]
+                    .iter()
+                    .position(|exercise| !exercise.done)
+            })
     }
 
-    /// Official exercises: Dump the solution file form the binary and return its path.
+    /// Official exercises: Dump the solution file from the binary and return its path.
     /// Third-party exercises: Check if a solution file exists and return its path in that case.
     pub fn current_solution_path(&self) -> Result<Option<String>> {
-        if DEBUG_PROFILE {
+        if cfg!(debug_assertions) {
             return Ok(None);
         }
 
@@ -347,24 +398,135 @@ impl AppState {
                 .write_solution_to_disk(self.current_exercise_ind, current_exercise.name)
                 .map(Some)
         } else {
-            let solution_path = if let Some(dir) = current_exercise.dir {
-                format!("solutions/{dir}/{}.rs", current_exercise.name)
-            } else {
-                format!("solutions/{}.rs", current_exercise.name)
-            };
+            let sol_path = current_exercise.sol_path();
 
-            if Path::new(&solution_path).exists() {
-                return Ok(Some(solution_path));
+            if Path::new(&sol_path).exists() {
+                return Ok(Some(sol_path));
             }
 
             Ok(None)
         }
     }
 
+    fn check_all_exercises_impl(&mut self, stdout: &mut StdoutLock) -> Result<Option<usize>> {
+        let term_width = terminal::size()
+            .context("Failed to get the terminal size")?
+            .0;
+        let mut progress_visualizer = CheckProgressVisualizer::build(stdout, term_width)?;
+
+        let next_exercise_ind = AtomicUsize::new(0);
+        let mut progresses = vec![CheckProgress::None; self.exercises.len()];
+
+        thread::scope(|s| {
+            let (exercise_progress_sender, exercise_progress_receiver) = mpsc::channel();
+            let n_threads = thread::available_parallelism()
+                .map_or(DEFAULT_CHECK_PARALLELISM, |count| count.get());
+
+            for _ in 0..n_threads {
+                let exercise_progress_sender = exercise_progress_sender.clone();
+                let next_exercise_ind = &next_exercise_ind;
+                let slf = &self;
+                thread::Builder::new()
+                    .spawn_scoped(s, move || {
+                        loop {
+                            let exercise_ind = next_exercise_ind.fetch_add(1, Relaxed);
+                            let Some(exercise) = slf.exercises.get(exercise_ind) else {
+                                // No more exercises.
+                                break;
+                            };
+
+                            if exercise_progress_sender
+                                .send((exercise_ind, CheckProgress::Checking))
+                                .is_err()
+                            {
+                                break;
+                            };
+
+                            let success = exercise.run_exercise(None, &slf.cmd_runner);
+                            let progress = match success {
+                                Ok(true) => CheckProgress::Done,
+                                Ok(false) => CheckProgress::Pending,
+                                Err(_) => CheckProgress::None,
+                            };
+
+                            if exercise_progress_sender
+                                .send((exercise_ind, progress))
+                                .is_err()
+                            {
+                                break;
+                            }
+                        }
+                    })
+                    .context("Failed to spawn a thread to check all exercises")?;
+            }
+
+            // Drop this sender to detect when the last thread is done.
+            drop(exercise_progress_sender);
+
+            while let Ok((exercise_ind, progress)) = exercise_progress_receiver.recv() {
+                progresses[exercise_ind] = progress;
+                progress_visualizer.update(&progresses)?;
+            }
+
+            Ok::<_, Error>(())
+        })?;
+
+        let mut first_pending_exercise_ind = None;
+        for exercise_ind in 0..progresses.len() {
+            match progresses[exercise_ind] {
+                CheckProgress::Done => {
+                    self.set_status(exercise_ind, true)?;
+                }
+                CheckProgress::Pending => {
+                    self.set_status(exercise_ind, false)?;
+                    if first_pending_exercise_ind.is_none() {
+                        first_pending_exercise_ind = Some(exercise_ind);
+                    }
+                }
+                CheckProgress::None | CheckProgress::Checking => {
+                    // If we got an error while checking all exercises in parallel,
+                    // it could be because we exceeded the limit of open file descriptors.
+                    // Therefore, try running exercises with errors sequentially.
+                    progresses[exercise_ind] = CheckProgress::Checking;
+                    progress_visualizer.update(&progresses)?;
+
+                    let exercise = &self.exercises[exercise_ind];
+                    let success = exercise.run_exercise(None, &self.cmd_runner)?;
+                    if success {
+                        progresses[exercise_ind] = CheckProgress::Done;
+                    } else {
+                        progresses[exercise_ind] = CheckProgress::Pending;
+                        if first_pending_exercise_ind.is_none() {
+                            first_pending_exercise_ind = Some(exercise_ind);
+                        }
+                    }
+                    self.set_status(exercise_ind, success)?;
+                    progress_visualizer.update(&progresses)?;
+                }
+            }
+        }
+
+        self.write()?;
+
+        Ok(first_pending_exercise_ind)
+    }
+
+    // Return the exercise index of the first pending exercise found.
+    pub fn check_all_exercises(&mut self, stdout: &mut StdoutLock) -> Result<Option<usize>> {
+        stdout.queue(cursor::Hide)?;
+        let res = self.check_all_exercises_impl(stdout);
+        stdout.queue(cursor::Show)?;
+
+        res
+    }
+
     /// Mark the current exercise as done and move on to the next pending exercise if one exists.
     /// If all exercises are marked as done, run all of them to make sure that they are actually
     /// done. If an exercise which is marked as done fails, mark it as pending and continue on it.
-    pub fn done_current_exercise(&mut self, writer: &mut StdoutLock) -> Result<ExercisesProgress> {
+    pub fn done_current_exercise<const CLEAR_BEFORE_FINAL_CHECK: bool>(
+        &mut self,
+        stdout: &mut StdoutLock,
+    ) -> Result<ExercisesProgress> {
         let exercise = &mut self.exercises[self.current_exercise_ind];
         if !exercise.done {
             exercise.done = true;
@@ -373,62 +535,42 @@ impl AppState {
 
         if let Some(ind) = self.next_pending_exercise_ind() {
             self.set_current_exercise_ind(ind)?;
+            return Ok(ExercisesProgress::NewPending);
+        }
+
+        if CLEAR_BEFORE_FINAL_CHECK {
+            clear_terminal(stdout)?;
+        } else {
+            stdout.write_all(b"\n")?;
+        }
+
+        if let Some(first_pending_exercise_ind) = self.check_all_exercises(stdout)? {
+            self.set_current_exercise_ind(first_pending_exercise_ind)?;
 
             return Ok(ExercisesProgress::NewPending);
         }
 
-        writer.write_all(RERUNNING_ALL_EXERCISES_MSG)?;
-
-        let mut output = Vec::with_capacity(OUTPUT_CAPACITY);
-        for (exercise_ind, exercise) in self.exercises().iter().enumerate() {
-            write!(writer, "Running {exercise} ... ")?;
-            writer.flush()?;
-
-            let success = exercise.run_exercise(&mut output, &self.target_dir)?;
-            if !success {
-                writeln!(writer, "{}\n", "FAILED".red())?;
-
-                self.current_exercise_ind = exercise_ind;
-
-                // No check if the exercise is done before setting it to pending
-                // because no pending exercise was found.
-                self.exercises[exercise_ind].done = false;
-                self.n_done -= 1;
-
-                self.write()?;
-
-                return Ok(ExercisesProgress::NewPending);
-            }
-
-            writeln!(writer, "{}", "ok".green())?;
-        }
-
-        // Write that the last exercise is done.
-        self.write()?;
-
-        clear_terminal(writer)?;
-        writer.write_all(FENISH_LINE.as_bytes())?;
-
-        let final_message = self.final_message.trim();
-        if !final_message.is_empty() {
-            writer.write_all(final_message.as_bytes())?;
-            writer.write_all(b"\n")?;
-        }
+        self.render_final_message(stdout)?;
 
         Ok(ExercisesProgress::AllDone)
     }
+
+    pub fn render_final_message(&self, stdout: &mut StdoutLock) -> Result<()> {
+        clear_terminal(stdout)?;
+        stdout.write_all(FENISH_LINE.as_bytes())?;
+
+        let final_message = self.final_message.trim_ascii();
+        if !final_message.is_empty() {
+            stdout.write_all(final_message.as_bytes())?;
+            stdout.write_all(b"\n")?;
+        }
+
+        Ok(())
+    }
 }
 
-const CARGO_METADATA_ERR: &str = "Failed to run the command `cargo metadata …`
-Did you already install Rust?
-Try running `cargo --version` to diagnose the problem.";
-
-const RERUNNING_ALL_EXERCISES_MSG: &[u8] = b"
-All exercises seem to be done.
-Recompiling and running all exercises to make sure that all of them are actually done.
-
-";
-
+const BAD_INDEX_ERR: &str = "The current exercise index is higher than the number of exercises";
+const STATE_FILE_HEADER: &[u8] = b"DON'T EDIT THIS FILE!\n\n";
 const FENISH_LINE: &str = "+----------------------------------------------------+
 |          You made it to the Fe-nish line!          |
 +--------------------------  ------------------------+
@@ -460,9 +602,10 @@ mod tests {
             dir: None,
             name: "0",
             path: "exercises/0.rs",
+            canonical_path: None,
             test: false,
             strict_clippy: false,
-            hint: String::new(),
+            hint: "",
             done: false,
         }
     }
@@ -474,9 +617,11 @@ mod tests {
             exercises: vec![dummy_exercise(), dummy_exercise(), dummy_exercise()],
             n_done: 0,
             final_message: String::new(),
+            state_file: tempfile::tempfile().unwrap(),
             file_buf: Vec::new(),
             official_exercises: true,
-            target_dir: PathBuf::new(),
+            cmd_runner: CmdRunner::build().unwrap(),
+            vs_code: false,
         };
 
         let mut assert = |done: [bool; 3], expected: [Option<usize>; 3]| {