lalrpop binary / feature dual support

parser/Cargo.toml

@@ -11,6 +11,8 @@ edition = "2021"
 [build-dependencies]
 tiny-keccak = { version = "2", features = ["sha3"] }
 phf_codegen = "0.10"
+lalrpop = { version = "0.19.8", optional = true }
+anyhow = "1.0.45"
 
 [dependencies]
 rustpython-ast = { path = "../ast" }

parser/build.rs

@@ -1,21 +1,19 @@
 use std::fmt::Write as _;
 use std::fs::File;
-use std::io::{self, BufRead, BufReader, BufWriter, Write};
+use std::io::{BufRead, BufReader, BufWriter, Write};
 use std::path::PathBuf;
-use std::process::{Command, ExitCode};
 use tiny_keccak::{Hasher, Sha3};
 
-fn main() -> ExitCode {
+fn main() -> anyhow::Result<()> {
     const SOURCE: &str = "python.lalrpop";
     const TARGET: &str = "python.rs";
 
     println!("cargo:rerun-if-changed={SOURCE}");
 
-    if let Err(exit_code) = try_lalrpop(SOURCE, TARGET) {
-        return exit_code;
-    }
+    try_lalrpop(SOURCE, TARGET)?;
     gen_phf();
-    ExitCode::SUCCESS
+
+    Ok(())
 }
 
 fn requires_lalrpop(source: &str, target: &str) -> bool {
@@ -67,28 +65,44 @@ fn requires_lalrpop(source: &str, target: &str) -> bool {
     !eq
 }
 
-fn try_lalrpop(source: &str, target: &str) -> Result<(), ExitCode> {
+fn try_lalrpop(source: &str, target: &str) -> anyhow::Result<()> {
     if !requires_lalrpop(source, target) {
         return Ok(());
     }
-    match Command::new("lalrpop").arg(source).status() {
+
+    #[cfg(feature = "lalrpop")]
+    lalrpop_dependency();
+    #[cfg(not(feature = "lalrpop"))]
+    lalrpop_command(source)?;
+
+    Ok(())
+}
+
+#[cfg(not(feature = "lalrpop"))]
+fn lalrpop_command(source: &str) -> anyhow::Result<()> {
+    match std::process::Command::new("lalrpop").arg(source).status() {
         Ok(stat) if stat.success() => Ok(()),
         Ok(stat) => {
             eprintln!("failed to execute lalrpop; exited with {stat}");
             let exit_code = stat.code().map(|v| (v % 256) as u8).unwrap_or(1);
-            Err(ExitCode::from(exit_code))
+            Err(anyhow::anyhow!("lalrpop error status: {}", exit_code))
         }
-        Err(e) if e.kind() == io::ErrorKind::NotFound => {
-            eprintln!(
-                "the lalrpop executable is not installed and parser/{source} has been changed"
-            );
-            eprintln!("please install lalrpop with `cargo install lalrpop`");
-            Err(ExitCode::FAILURE)
+        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
+            eprintln!("please install lalrpop with `cargo install lalrpop` or\n`cargo build --manifest-path=parser/Cargo.toml --features=lalrpop`");
+            Err(anyhow::anyhow!(
+                "the lalrpop executable is not installed and parser/{} has been changed",
+                source
+            ))
         }
-        Err(e) => panic!("io error {e:#}"),
+        Err(e) => Err(anyhow::Error::new(e)),
     }
 }
 
+#[cfg(feature = "lalrpop")]
+fn lalrpop_dependency() {
+    lalrpop::process_root().unwrap()
+}
+
 fn sha_equal(expected_sha3_str: &str, actual_sha3: &[u8; 32]) -> bool {
     if expected_sha3_str.len() != 64 {
         panic!("lalrpop version? hash bug is fixed in 0.19.8");