ast: Populate _field_types with real type objects by youknowone · Pull Request #6981 · RustPython/RustPython · GitHub

Add FieldType enum and FIELD_TYPES static table mapping all AST node classes to their ASDL field types
Resolve markers to real Python type objects (GenericAlias, Union, plain types) at module init in populate_field_types()
Set class-level None defaults for optional fields
Replace hardcoded LIST_FIELDS and class-name checks in slot_init with _field_types-based lookup
Add expr_context default to Load(), fix ImportFrom.level default (now None instead of 0)
Fix class_getitem None check, compile() formatting

Summary by CodeRabbit

Refactor
- Improved internal handling of AST field type resolution and default value assignment to enhance maintainability and flexibility in the runtime environment.

- Add FieldType enum and FIELD_TYPES static table mapping all AST node classes to their ASDL field types - Resolve markers to real Python type objects (GenericAlias, Union, plain types) at module init in populate_field_types() - Set class-level None defaults for optional fields - Replace hardcoded LIST_FIELDS and class-name checks in slot_init with _field_types-based lookup - Add expr_context default to Load(), fix ImportFrom.level default (now None instead of 0) - Fix __class_getitem__ None check, compile() formatting - Remove 14 @expectedfailure decorators from test_ast

📝 Walkthrough

Walkthrough

This PR refactors the AST field initialization system by introducing a type-driven approach. It adds a FieldType enum, a FIELD_TYPES constant enumerating AST class fields, and a populate_field_types function to dynamically resolve and populate _field_types attributes on AST classes at module initialization, replacing prior hard-coded defaulting logic.

Changes

Cohort / File(s)	Summary
AST Type Metadata Infrastructure crates/vm/src/stdlib/ast/pyast.rs	Introduces FieldType enum to categorize field types (Node, Builtin, ListOf, Optional, etc.), adds FIELD_TYPES constant with per-class field metadata, and implements populate_field_types function that resolves builtin types, AST node references, and constructs generic aliases and unions for list and optional fields, then populates _field_types attributes at runtime.
Field Defaulting Logic crates/vm/src/stdlib/ast/python.rs	Replaces per-node hard-coded defaults with field-type-driven approach using _field_types metadata; now applies empty list defaults for list fields, None for optional fields, Load context for expression contexts, and skips defaults otherwise.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

#6011: Modifies AST node initialization logic in the same python.rs file; introduces custom Constructor for NodeAst which overlaps with the field defaulting mechanism refactored in this PR.

Poem

🐰 Hops with delight...

Field types now dance in metadata's glow,
No more hard-coded defaults we sow,
Types resolve at runtime, a structured way,
Lists, optionals, nodes—all here to stay!
The AST now speaks the language so true. 🌿✨

🚥 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 'ast: Populate _field_types with real type objects' accurately and concisely summarizes the main change: implementing the populate_field_types() function that resolves AST field type annotations to actual Python type objects at runtime.

✏️ Tip: You can configure your own custom pre-merge checks in the settings.

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📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

[x] lib: cpython/Lib/ast.py
[x] lib: cpython/Lib/_ast_unparse.py
[x] test: cpython/Lib/test/test_unparse.py (TODO: 6)
[x] test: cpython/Lib/test/test_type_comments.py (TODO: 15)

dependencies:

ast

dependent tests: (48 tests)

ast: test_ast test_builtin test_compile test_dis test_fstring test_future_stmt test_site test_ssl test_type_comments test_ucn test_unparse
- annotationlib: test_functools test_inspect test_reprlib test_typing
  - inspect: test_abc test_argparse test_asyncgen test_code test_collections test_coroutines test_decimal test_enum test_generators test_grammar test_ntpath test_operator test_patma test_posixpath test_signal test_traceback test_types test_unittest test_yield_from test_zipimport
- dbm.dumb: test_dbm_dumb
- inspect:
  - bdb: test_bdb
  - dataclasses: test__colorize test_genericalias test_pprint test_regrtest test_zoneinfo
  - importlib.metadata: test_importlib
  - rlcompleter: test_rlcompleter
  - trace: test_trace
  - xmlrpc.server: test_docxmlrpc test_xmlrpc
- pyclbr: test_pyclbr

Legend:

[+] path exists in CPython
[x] up-to-date, [ ] outdated

youknowone marked this pull request as ready for review February 3, 2026 12:56

Merge branch 'main' into ast

b45cea5

youknowone merged commit 8d07c45 into RustPython:main Feb 3, 2026
13 checks passed

youknowone deleted the ast branch February 3, 2026 13:05

coderabbitai Bot mentioned this pull request Aug 13, 2026

Fix 33 reproduced fuzzing and static-review defects #8514

Merged

ast: Populate _field_types with real type objects by youknowone · Pull Request #6981 · RustPython/RustPython · GitHub

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ast: Populate _field_types with real type objects - #6981

ast: Populate _field_types with real type objects#6981
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RustPython:mainfrom
youknowone:ast

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ast: Populate _field_types with real type objects by youknowone · Pull Request #6981 · RustPython/RustPython · GitHub

Uh oh!

ast: Populate _field_types with real type objects - #6981

ast: Populate _field_types with real type objects#6981youknowone merged 2 commits intoRustPython:mainRustPython/RustPython:mainfrom youknowone:astyouknowone/RustPython:astCopy head branch name to clipboard

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Summary by CodeRabbit

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Walkthrough

Changes

Estimated code review effort

Possibly related PRs

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📦 Library Dependencies

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ast: Populate _field_types with real type objects#6981
youknowone merged 2 commits into
RustPython:mainfrom
youknowone:ast

youknowone commented Feb 3, 2026 •
edited by coderabbitai Bot
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