From 908f758cbedcb0bddb3f5b32c99aa4855da668eb Mon Sep 17 00:00:00 2001
From: Aviv Palivoda <palaviv@gmail.com>
Date: Fri, 12 Apr 2019 15:50:17 +0300
Subject: [PATCH] Print cause on exception

---
 vm/src/exceptions.rs | 15 +++++++++++++--
 vm/src/frame.rs      |  1 +
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/vm/src/exceptions.rs b/vm/src/exceptions.rs
index d81764e25..abd670a14 100644
--- a/vm/src/exceptions.rs
+++ b/vm/src/exceptions.rs
@@ -2,7 +2,7 @@ use crate::function::PyFuncArgs;
 use crate::obj::objsequence;
 use crate::obj::objtype;
 use crate::obj::objtype::PyClassRef;
-use crate::pyobject::{create_type, PyContext, PyObjectRef, PyResult, TypeProtocol};
+use crate::pyobject::{create_type, IdProtocol, PyContext, PyObjectRef, PyResult, TypeProtocol};
 use crate::vm::VirtualMachine;
 
 fn exception_init(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
@@ -18,8 +18,19 @@ fn exception_init(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
     Ok(vm.get_none())
 }
 
-// Print exception including traceback:
+// print excption chain
 pub fn print_exception(vm: &VirtualMachine, exc: &PyObjectRef) {
+    if let Ok(cause) = vm.get_attribute(exc.clone(), "__cause__") {
+        if !vm.get_none().is(&cause) {
+            print_exception(vm, &cause);
+            println!("\nThe above exception was the direct cause of the following exception:\n");
+        }
+    }
+    print_exception_inner(vm, exc)
+}
+
+// Print exception including traceback:
+pub fn print_exception_inner(vm: &VirtualMachine, exc: &PyObjectRef) {
     if let Ok(tb) = vm.get_attribute(exc.clone(), "__traceback__") {
         println!("Traceback (most recent call last):");
         if objtype::isinstance(&tb, &vm.ctx.list_type()) {
diff --git a/vm/src/frame.rs b/vm/src/frame.rs
index a3dfd6032..a1da85d3a 100644
--- a/vm/src/frame.rs
+++ b/vm/src/frame.rs
@@ -686,6 +686,7 @@ impl Frame {
                     0 | 3 => panic!("Not implemented!"),
                     _ => panic!("Invalid parameter for RAISE_VARARGS, must be between 0 to 3"),
                 };
+                info!("Exception raised: {:?} with cause: {:?}", exception, cause);
                 vm.set_attr(&exception, vm.new_str("__cause__".to_string()), cause)?;
                 Err(exception)
             }