FromArgs with error_msg by youknowone · Pull Request #6804 · RustPython/RustPython

youknowone

📝 Walkthrough

Walkthrough

This PR introduces an error_msg attribute feature to the argument derive macro system, allowing custom error messages for argument validation. The derive implementation is enhanced to parse and handle error_msg in attribute declarations, and several builtins are updated to provide more specific error messages for their optional arguments.

Changes

Cohort / File(s)	Summary
Derive Macro Error Message Support `crates/derive-impl/src/from_args.rs`	Adds `error_msg` field to `ArgAttribute` struct and implements parsing logic to extract custom error messages from `pyarg(error_msg = "...")` annotations. Generates code to map conversion errors to type errors with the provided message, with guards against duplicate definitions.
Builtin Function Argument Validation `crates/vm/src/builtins/function.rs`	Annotates optional fields in `PyFunctionNewArgs` with `error_msg` attributes specifying type constraints for `name`, `argdefs`, `closure`, and `kwdefaults` arguments.
Builtin Interpolation Argument Handling `crates/vm/src/builtins/interpolation.rs`	Refines `conversion` argument from `OptionalArg<PyObjectRef>` to `Option<PyStrRef>` with explicit `error_msg` attribute and simplified string validation logic. Moves validation to early checks instead of runtime pattern matching.
Builtin Super Type Argument `crates/vm/src/builtins/super.rs`	Narrows `py_type` argument in `InitArgs` from `OptionalArg<PyObjectRef>` to `OptionalArg<PyTypeRef>` and adds `error_msg` attribute. Removes runtime downcast logic in favor of compile-time argument type constraint.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

Pyfunction builtins and constructor #5823: Introduced PyFunctionNewArgs struct; this PR augments it with error message annotations on the same fields.
fix fcntl, sslsocket traverse, super , excepthook #6623: Previously modified InitArgs::py_type in super.rs by widening it to OptionalArg<PyObjectRef>; this PR narrows it back to OptionalArg<PyTypeRef> with stricter validation.

Suggested reviewers

ShaharNaveh
arihant2math

Poem

🐰 A macro whispers soft and clear,
"Show the user what they fear!"
No more vague errors in the night,
Just helpful messages, shining bright. ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'FromArgs with error_msg' accurately reflects the main change: adding an error_msg capability to the FromArgs derive macro and its argument parsing system.

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✨ Finishing touches

📝 Generate docstrings

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