fix(compiler): keep parentheses that JavaScript requires (arrow bodies, unary ** bases)

[Brooooooklyn]

Summary

Fixes #510 — the emitter dropped source parentheses, so an arrow body whose leftmost token is { printed invalid JS:

@Input({transform: (v: any) => ({value: v}).value}) a: any;
// was: (v) => {value:v}.value   (invalid / wrong meaning)
// now: (v) => ({value:v}).value

Upstream ngtsc never hits this: it emits source expressions verbatim through WrappedNodeExpr. Our converter rebuilds the AST (Expression::ParenthesizedExpression → OutputExpression::Parenthesized), and the emitter dropped the parens unconditionally. That also masked other required parens — (-1) ** 2, (1).toString(), (obj?.m)(), (() => f)() all lost theirs.

Changes

src/output/emitter.rs:

• Parenthesized now keeps its parens — they're source parens ngtsc would emit verbatim, or required parens the strip phase kept. Skipped only when the inner expression already self-parenthesizes (BinaryOperator, Conditional, Comma, UnaryOperator with parens), so ((a + b)) sources don't emit double parens.
• New emits_leading_brace helper walks the leftmost emitted token through ReadProp/ReadKey receivers, InvokeFunction callees and TaggedTemplateLiteral tags; the ArrowFunction body check uses it, replacing the LiteralMap/raw-source whole-body check. () => ({...}) still emits exactly once.

src/pipeline/phases/strip_nonrequired_parentheses.rs:

• The strip phase now handles IrExpression::Parenthesized — our pipe-aware ingest produces IR-level parens (e.g. (a | async) || b) that were invisible to it before; the emitter's drop-parens behavior masked that. Non-required IR parens are stripped like upstream's single-tree pass.
• check_ir_expression_for_required_parens marks Parenthesized operands of IR Binary (**, ??, &&/||) as required, mirroring upstream checkExponentiationParens/checkNullishCoalescingParens/checkAndOrParens.
• The **-base check covers !/typeof/void unary bases too, and classifiers look through nested Parenthesized (((-1)) ** 2 keeps the required wrapper). Upstream needs only UnaryOperatorExpr because its emit goes through the TypeScript printer, which re-adds parens — we emit raw JS.

Tests

New tests/arrow_paren_emit_test.rs (9 tests): both issue repros in @Input transform and useFactory metadata (full + partial mode), () => ({...}) (issue #43), call/member chains on parenthesized objects, verbatim source parens, (-1) ** 2 / (1).toString() / (o?.m)() in metadata, and template-pipeline coverage for all four unary ** bases, nested parens, paren stripping, and ??/&&/?: mixes.

Verification

• cargo test --all-features: 3077 pass — including the pipe_in_binary_with_safe_property_read snapshot, which now round-trips through the corrected strip phase
• cargo check + --all-features, cargo fmt --check: clean
• cargo run -p oxc_angular_conformance: 1264/1264

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-07T09:00:24.416093Z	0bb0d97	PR opened

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