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Fix new-expression emit parentheses after type erasure (#64981) - #65015
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Parenthesize new-expression operands whose leftmost expression is a call, including after as/satisfies/non-null erasure and through parentheses, so `new (f() as T).C()` emits as `new (f().C)()`. AI assistance disclosure: this change was authored with Cursor Agent.
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🟡 Changes recommended
Traversing retained parentheses causes emitConciseBody to double-wrap already-parenthesized object literals, breaking two unchanged arrow-function output baselines.
1 open issue
What changed in this PR
This PR addresses #64981 in the native TypeScript compiler by preserving constructor grouping when type erasure exposes a call expression.
Changes:
- Detects calls along the leftmost constructor-expression chain and adds parentheses during emit.
- Extends shared expression traversal to look through parentheses.
- Adds printer and type-erasure regression tests for property-access constructors.
| File | Description |
|---|---|
tsc/internal/transformers/tstransforms/typeeraser_test.go |
Adds constructor cases covering assertions, satisfies, and non-null expressions. |
tsc/internal/printer/printer.go |
Parenthesizes constructor expressions with leftmost calls. |
tsc/internal/printer/printer_test.go |
Tests printing a constructor accessed from a call result. |
tsc/internal/ast/precedence.go |
Extends leftmost-expression traversal through parentheses. |
Review effort: Balanced
| KindPropertyAccessExpression, | ||
| KindNonNullExpression, | ||
| KindPartiallyEmittedExpression, | ||
| KindParenthesizedExpression, |
Author
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Thanks — addressed in 9391b36.
ast.GetLeftmostExpressionno longer walksKindParenthesizedExpression(shared helper keeps its parentheses boundary soemitConciseBodydoes not double-wrap() => ({...})).- New-expression call detection is printer-local via
newExpressionOperandNeedsParens, which walks parentheses / property-element access / as / satisfies / non-null / partially-emitted only foremitNewExpression. NewExpression6still expectsnew ((f()).C)()because non-null does not elide the original parentheses the wayas/satisfiesdo.- Arrow object-literal baselines remain correct with this approach.
…s in GetLeftmostExpression Address Copilot review on microsoft#65015: do not teach GetLeftmostExpression to traverse ParenthesizedExpression (that double-wrapped arrow concise bodies like `() => ({...})`). Detect leftmost calls for `new` in a printer-local helper that may walk parentheses, preserving emitConciseBody behavior while still emitting `new (f().C)()` after type erasure. AI assistance disclosure: authored with Cursor Agent.
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Summary
Fixes #64981 —
new (f() as T).C()drops required parentheses on emit.new (getPlugins() as any).Linker()was emitted asnew getPlugins().Linker()(i.e.(new getPlugins()).Linker()), causing a runtime TypeError.Change:
emitNewExpression, parenthesize when the leftmost expression (stopping at calls) is aCallExpression.KindParenthesizedExpressioninGetLeftmostExpressionso parentheses / assertion wrappers are handled consistently with classic TS6 emit:new (getPlugins().Linker)().Test plan
TestParenthesizeNew4inprinter_test.goNewExpression3–NewExpression6coveringas/satisfies/ non-nullRelates to
This focused PR replaces the emit portion of the combined #65013 (which is being closed in favor of two single-issue PRs).
AI assistance disclosure
This change was authored with Cursor Agent (an LLM-based coding agent). A human operator directed the investigation at this specific open issue, reviewed the resulting patch, and is submitting it for review. Per CONTRIBUTING.md, AI tool use is disclosed here.