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Fix sys.excepthook #5830

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Merged
merged 1 commit into from
Jun 24, 2025
Merged

Fix sys.excepthook #5830

merged 1 commit into from
Jun 24, 2025

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@youknowone youknowone commented Jun 24, 2025

Summary by CodeRabbit

  • Bug Fixes
    • Improved error handling in exception reporting to provide clear messages when exception normalization fails.
  • Tests
    • Removed expected failure marks from several exception-related tests, indicating they now pass successfully.

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coderabbitai bot commented Jun 24, 2025

Walkthrough

The changes update exception handling behavior in both the compiler and runtime. The compiler now clears exception variables after a handler completes, matching CPython semantics. The runtime’s excepthook function is improved to print an error message to stderr if exception normalization fails. Several tests have their @unittest.expectedFailure decorators removed, indicating they are now expected to pass.

Changes

File(s) Change Summary
Lib/test/test_sys.py Removed @unittest.expectedFailure decorator from test_excepthook in ExceptHookTest.
Lib/test/test_exceptions.py Removed @unittest.expectedFailure decorators from three exception cleanup test methods.
compiler/codegen/src/compile.rs Enhanced compile_try_statement to clear and delete exception variables after handler completion.
vm/src/stdlib/sys.rs Modified excepthook to print an error to stderr if exception normalization fails, mimicking CPython.

Sequence Diagram(s)

sequenceDiagram
    participant User
    participant sys.excepthook
    participant VM

    User->>sys.excepthook: Call with exception info
    sys.excepthook->>VM: normalize_exception()
    alt Normalization succeeds
        sys.excepthook->>VM: Write exception to stderr
    else Normalization fails
        sys.excepthook->>VM: Write TypeError message to stderr (with type info)
    end
Loading
sequenceDiagram
    participant Compiler
    participant HandlerBody

    Compiler->>HandlerBody: Compile exception handler body
    HandlerBody-->>Compiler: Handler completes
    Compiler->>Compiler: Emit PopException
    alt Exception variable bound
        Compiler->>Compiler: Set variable to None
        Compiler->>Compiler: Delete variable
    end
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Poem

In the warren where exceptions hop,
Now they’re cleared when handlers stop.
If normalization stubs its toe,
A message prints, so you will know.
Tests now run with hopeful cheer,
For bugs and rabbits both appear! 🐇


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Actionable comments posted: 0

🧹 Nitpick comments (1)
vm/src/stdlib/sys.rs (1)

367-383: LGTM! Exception normalization error handling aligns with CPython behavior.

The change correctly implements graceful handling of exception normalization failures by printing an error message to stderr instead of propagating the exception, which matches CPython's behavior. The error message format and stderr output approach are appropriate.

Minor suggestions for improvement:

  • Consider using a more descriptive variable name than exc in the success case for consistency
  • The TODO comment on line 374 could be addressed to improve the error message accuracy

Apply this diff to improve variable naming consistency:

-        match vm.normalize_exception(exc_type.clone(), exc_val.clone(), exc_tb) {
-            Ok(exc) => vm.write_exception(&mut crate::py_io::PyWriter(stderr, vm), &exc),
+        match vm.normalize_exception(exc_type.clone(), exc_val.clone(), exc_tb) {
+            Ok(normalized_exc) => vm.write_exception(&mut crate::py_io::PyWriter(stderr, vm), &normalized_exc),
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  • compiler/codegen/src/compile.rs (1 hunks)
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📓 Path-based instructions (1)
`**/*.rs`: Follow the default rustfmt code style; use 'cargo fmt' to format Rust code. Always run clippy to lint Rust code ('cargo clippy') before completing tasks, and fix any war...

**/*.rs: Follow the default rustfmt code style; use 'cargo fmt' to format Rust code.
Always run clippy to lint Rust code ('cargo clippy') before completing tasks, and fix any warnings or lints introduced by your changes.

  • vm/src/stdlib/sys.rs
  • compiler/codegen/src/compile.rs
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  • GitHub Check: Run snippets and cpython tests on wasm-wasi
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🔇 Additional comments (1)
compiler/codegen/src/compile.rs (1)

1320-1327: LGTM! Excellent implementation of CPython-compatible exception variable cleanup.

This change correctly implements the CPython behavior of clearing exception variables after an except handler completes. The approach is well-structured:

  1. Proper sequencing: First sets the variable to None, then deletes it, matching CPython's exact behavior
  2. Conditional execution: Only performs cleanup when an exception variable was actually bound
  3. Correct placement: Happens after PopException but before finally block handling
  4. Error handling: Properly propagates errors from both store_name and compile_name operations

This addresses the exception variable lifecycle semantics that are important for consistent Python behavior and helps fix issues related to sys.excepthook handling.

@youknowone youknowone merged commit 9c2a469 into RustPython:main Jun 24, 2025
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@youknowone youknowone deleted the sys-excepthook branch June 24, 2025 07:58
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