Update _ast_unparse and fix unparse, type_comments by youknowone · Pull Request #6961 · RustPython/RustPython

youknowone

📝 Walkthrough

Walkthrough

Convert internal panics/asserts into explicit syntax errors in codegen; guard truncated string-literal parsing; add t-string unparse support; restrict type subscripting to non-None __class_getitem__; add AST field-defaulting, default_value for type-parameter nodes, and always emit type_comment = None for certain nodes; implement PyCF_ONLY_AST short-circuit in compile().

Changes

Cohort / File(s)	Summary
Codegen / Pattern validation `crates/codegen/src/compile.rs`	Replace panics/asserts with explicit `self.error(...)` returns for forbidden-name checks, class-pattern (too many subpatterns), and `MatchOr` size ≤ 1; tighten error handling.
String parsing & t-string unparse `crates/codegen/src/string_parser.rs`, `crates/codegen/src/unparse.rs`	Guard `parse_string_literal` against truncated sources (return raw source when too short); add `unparse_tstring(&TStringValue)` and route `TString` rendering through it using fstring-body composition + UnicodeEscape.
VM protocol / subscripting error `crates/vm/src/protocol/object.rs`	Only call `__class_getitem__` on types when attribute exists and is not `None`; otherwise raise `TypeError: type '<Name>' is not subscriptable`.
AST init & defaulting `crates/vm/src/stdlib/ast/python.rs`, `crates/vm/src/stdlib/ast/pyast.rs`	Track provided fields during AST init, mark built-ins with `_field_types`, default missing built-in fields (lists → [], others → None), and add `default_value` to TypeVar/ParamSpec/TypeVarTuple field lists.
AST serialization / node emissions `crates/vm/src/stdlib/ast/expression.rs`, `crates/vm/src/stdlib/ast/parameter.rs`, `crates/vm/src/stdlib/ast/statement.rs`, `crates/vm/src/stdlib/ast/type_parameters.rs`, `crates/vm/src/stdlib/ast.rs`	Emit `args` as `empty_arguments_object` for lambdas with no params; always emit `type_comment = None` for several nodes; add round-trip `default_value` handling for type-parameter nodes; add `empty_arguments_object` and `mode_type_and_name` helpers.
Compile builtin: AST-only mode `crates/vm/src/stdlib/builtins.rs`, `crates/vm/src/stdlib/ast.rs`	Implement `PyCF_ONLY_AST` handling: parse flags, map `mode` → expected AST node class, validate mode, and short-circuit by returning AST node when it matches expected type.
Minor serialization cast change `crates/vm/src/stdlib/ast/other.rs`	Serialize `ConversionFlag` as `i8` instead of `u8`.
Docs / scripts `AGENTS.md`, `DEVELOPMENT.md`	Exclude additional crate `rustpython-venvlauncher` from workspace `cargo test` invocations.

Sequence Diagram(s)

sequenceDiagram
    participant Caller
    participant BuiltinsCompile as builtins::compile
    participant Parser
    participant ASTNode as ParsedAST
    Caller->>BuiltinsCompile: compile(source, filename, mode, flags)
    BuiltinsCompile->>BuiltinsCompile: extract PyCF_ONLY_AST from flags
    BuiltinsCompile->>Parser: parse(source) -> ParsedAST
    alt PyCF_ONLY_AST set
        BuiltinsCompile->>BuiltinsCompile: mode_type_and_name(mode) -> expected_type
        BuiltinsCompile->>ASTNode: inspect node type
        alt node.type == expected_type
            BuiltinsCompile-->>Caller: return AST node (short-circuit)
        else mismatch
            BuiltinsCompile-->>Caller: raise TypeError (expected vs actual)
        end
    else normal compile
        BuiltinsCompile->>BuiltinsCompile: continue compile pipeline
        BuiltinsCompile-->>Caller: return compiled result
    end

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~50 minutes

Possibly related PRs

Py 3.14 changes fix #6755: related changes to forbidden-name/error handling in crates/codegen/src/compile.rs.
Prohibit AI PR submit #6813: related VM stdlib/path initialization and stdlib_dir changes that touch the same VM areas.

Suggested labels

skip:ci

Suggested reviewers

ShaharNaveh

Poem

🐇 I nudged the panics into softer sighs,
I checked the quotes where tiny truncation lies,
T-strings now sparkle, defaults tucked in place,
Subscripted types now fail with kinder grace,
🥕 A hop, a nibble—code in tidy files.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 21.74% 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 refers to AST unparsing and type comments, which are core to multiple changes across the PR, particularly in unparse.rs, statement.rs, and parameter.rs files.

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✨ Finishing touches

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