Add more error functions to the c-api

[bschoenmaeckers]

Summary by CodeRabbit

• New Features
  • Expanded C API support for Python exception lifecycle control, including traceback handling plus clear/match and fetch/restore and exc-info/pending exception helpers.
  • Added helpers to convert OS errors into Python exceptions, including errno-based and Windows-specific variants with optional filename support.
  • Added C-ABI functions for creating Unicode decode/encode/translate error objects and getting/setting their attributes.
• Bug Fixes
  • Improved native/FFI error propagation for functions that otherwise have no return value.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between bebdf8e and 6d1ac15.

📒 Files selected for processing (18)

• crates/capi/src/pyerrors/windows.rs
• crates/codegen/src/compile.rs
• crates/codegen/src/symboltable.rs
• crates/derive-impl/src/util.rs
• crates/vm/src/builtins/builtin_func.rs
• crates/vm/src/builtins/descriptor.rs
• crates/vm/src/builtins/memory.rs
• crates/vm/src/builtins/super.rs
• crates/vm/src/builtins/type.rs
• crates/vm/src/frame.rs
• crates/vm/src/object/core.rs
• crates/vm/src/object/payload.rs
• crates/vm/src/stdlib/_ast/argument.rs
• crates/vm/src/stdlib/_ctypes/function.rs
• crates/vm/src/stdlib/_io.rs
• crates/vm/src/stdlib/_sysconfigdata.rs
• crates/vm/src/vm/vm_ops.rs
• src/lib.rs

💤 Files with no reviewable changes (1)

• crates/vm/src/stdlib/_ast/argument.rs

✅ Files skipped from review due to trivial changes (13)

• crates/vm/src/builtins/memory.rs
• crates/vm/src/builtins/super.rs
• crates/vm/src/vm/vm_ops.rs
• crates/vm/src/stdlib/_ctypes/function.rs
• crates/vm/src/stdlib/_io.rs
• crates/vm/src/stdlib/_sysconfigdata.rs
• crates/derive-impl/src/util.rs
• src/lib.rs
• crates/vm/src/builtins/builtin_func.rs
• crates/vm/src/frame.rs
• crates/vm/src/builtins/type.rs
• crates/vm/src/object/core.rs
• crates/codegen/src/symboltable.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• crates/capi/src/pyerrors/windows.rs

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📝 Walkthrough

Walkthrough

The C-API exception layer adds VM-backed exception state operations, errno and Windows error conversion helpers, Unicode error accessors, pointer-returning FFI error handling, and unrelated Rust syntax and formatting simplifications.

Changes

Exception and error C-API

Layer / File(s)	Summary
Exception state and FFI error plumbing crates/capi/src/pyerrors.rs, crates/capi/src/util.rs	Adds traceback, pending-exception, interrupt, fatal-error, exception-triple, handled-exception, exc_info, and exception-args APIs, plus public helper re-exports and pointer-returning error conversion.
Errno exception construction crates/capi/src/pyerrors/errno.rs	Adds errno-based exception constructors supporting C-string and Python filename arguments, EINTR signal checks, and exception-instance validation.
Unicode error accessors crates/capi/src/pyerrors/unicode.rs	Adds Unicode decode-error construction and attribute getters/setters for decode, encode, and translate errors, including bounds and UTF-8 validation.
Windows error construction crates/capi/src/pyerrors/windows.rs	Adds Windows error conversion helpers for targeted exception types and OSError, with optional filename arguments and last-error lookup.

Rust cleanup

Layer / File(s)	Summary
Compiler and symbol-table pattern cleanup crates/codegen/src/compile.rs, crates/codegen/src/symboltable.rs	Simplifies AST destructuring while preserving symbol lookup, scanning, scope, and validation behavior.
Runtime formatting and propagation cleanup crates/derive-impl/src/util.rs, crates/vm/**, src/lib.rs	Removes redundant formatting borrows, simplifies AST argument destructuring, and replaces one explicit error match with ? without described behavior changes.

Estimated code review effort: 4 (Complex) | ~75 minutes

Sequence Diagram(s)

sequenceDiagram
  participant C_API
  participant VM
  participant OS_Error
  participant Exception_Type
  C_API->>VM: invoke exception or OS-error helper
  VM->>OS_Error: read errno or Windows last-error data
  OS_Error-->>VM: error code and message
  VM->>Exception_Type: construct exception with optional filenames
  Exception_Type-->>C_API: return exception object

Loading

Possibly related PRs

• RustPython/RustPython#7787: Earlier C-API exception and error support in pyerrors.
• RustPython/RustPython#8000: Adds adjacent exception-state APIs, including traceback handling.

Suggested reviewers: youknowone, ShaharNaveh

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding additional error-related C-API functions.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

crates/capi/src/pyerrors/errno.rs (1)

18-56: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Reduce duplication by delegating to the object-based helper.

PyErr_SetFromErrnoWithFilename re-implements the errno read, EINTR handling, message construction, downcast, and call logic that already exists in PyErr_SetFromErrnoWithFilenameObjects. As in CPython, this can decode the filename and then delegate to PyErr_SetFromErrnoWithFilenameObject, keeping the errno/message logic in one place.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@crates/capi/src/pyerrors/errno.rs` around lines 18 - 56, Refactor
PyErr_SetFromErrnoWithFilename to only decode the optional C filename, convert
it to a Python object, and delegate to PyErr_SetFromErrnoWithFilenameObject.
Remove its duplicated errno retrieval, EINTR handling, message construction,
exception downcast, and call logic so the object-based helper remains the single
implementation.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@crates/capi/src/pyerrors/windows.rs`:
- Around line 69-84: In the Windows error conversion branch, avoid leaking the
decoded filename created by decode_fsdefault_and_size. Update the
Some(Ok(filename)) handling to keep the PyObjectRef alive locally and pass its
borrowed raw pointer to set_windows_error, rather than calling into_raw();
preserve the existing error and None handling.

---

Nitpick comments:
In `@crates/capi/src/pyerrors/errno.rs`:
- Around line 18-56: Refactor PyErr_SetFromErrnoWithFilename to only decode the
optional C filename, convert it to a Python object, and delegate to
PyErr_SetFromErrnoWithFilenameObject. Remove its duplicated errno retrieval,
EINTR handling, message construction, exception downcast, and call logic so the
object-based helper remains the single implementation.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: 05c2152b-5010-4ab6-a5ca-c0afe9842760

📥 Commits

Reviewing files that changed from the base of the PR and between 9c064c1 and bebdf8e.

📒 Files selected for processing (5)

• crates/capi/src/pyerrors.rs
• crates/capi/src/pyerrors/errno.rs
• crates/capi/src/pyerrors/unicode.rs
• crates/capi/src/pyerrors/windows.rs
• crates/capi/src/util.rs