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fix(codegen): give TSTypeAssertion unary precedence#23002

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fix/codegen-type-assertion-precedence
Jun 6, 2026
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fix(codegen): give TSTypeAssertion unary precedence#23002
graphite-app[bot] merged 1 commit into
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fix/codegen-type-assertion-precedence

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@Boshen

@Boshen Boshen commented Jun 6, 2026

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What

A TS angle-bracket assertion <T>x is a unary expression (ECMA/TS grammar: < Type > UnaryExpression), but TSTypeAssertion::precedence() returned Precedence::Lowest. The wrap condition precedence >= self.precedence() is therefore always true, so the assertion was parenthesized in every position.

It now reports Precedence::Prefix like other unary expressions, and joins the **-base special case (a unary expression can't be a ** base, so it must stay wrapped there).

Examples

Input Before After
y = <T>x y = (<T>x) y = <T>x
foo(<T>x) foo((<T>x)) foo(<T>x)
z = <T>x + 1 z = (<T>x) + 1 z = <T>x + 1
c = -<T>x c = -(<T>x) c = -<T>x

Positions that genuinely require parentheses still keep them, because they print the assertion at a higher precedence than Prefix:

Input Output
(<T>x).foo (<T>x).foo
(<T>x)() (<T>x)()
(<T>x) ** 2 (<T>x) ** 2

@github-actions github-actions Bot added A-ast Area - AST A-codegen Area - Code Generation labels Jun 6, 2026

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Comment thread crates/oxc_ast/src/precedence.rs
@codspeed-hq

codspeed-hq Bot commented Jun 6, 2026

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Merging this PR will not alter performance

✅ 57 untouched benchmarks
⏩ 9 skipped benchmarks1


Comparing fix/codegen-type-assertion-precedence (5399472) with main (d727b6b)

Open in CodSpeed

Footnotes

  1. 9 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports.

@Boshen

Boshen commented Jun 6, 2026

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Addressed the </<T> boundary issue (P1): in minify mode a < <T>x was emitting a<<T>x, which re-tokenizes as a shift-left. TSTypeAssertion now emits a hard space before its leading < when the previous byte is also <, so the output stays a< <T>x and round-trips to the correct AST. Added a minify regression test.

@Boshen Boshen added the 0-merge Merge with Graphite Merge Queue label Jun 6, 2026

Boshen commented Jun 6, 2026

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## What

A TS angle-bracket assertion `<T>x` is a unary expression (ECMA/TS grammar: `< Type > UnaryExpression`), but `TSTypeAssertion::precedence()` returned `Precedence::Lowest`. The wrap condition `precedence >= self.precedence()` is therefore always true, so the assertion was parenthesized in **every** position.

It now reports `Precedence::Prefix` like other unary expressions, and joins the `**`-base special case (a unary expression can't be a `**` base, so it must stay wrapped there).

## Examples

| Input | Before | After |
| --- | --- | --- |
| `y = <T>x` | `y = (<T>x)` | `y = <T>x` |
| `foo(<T>x)` | `foo((<T>x))` | `foo(<T>x)` |
| `z = <T>x + 1` | `z = (<T>x) + 1` | `z = <T>x + 1` |
| `c = -<T>x` | `c = -(<T>x)` | `c = -<T>x` |

Positions that genuinely require parentheses still keep them, because they print the assertion at a higher precedence than `Prefix`:

| Input | Output |
| --- | --- |
| `(<T>x).foo` | `(<T>x).foo` |
| `(<T>x)()` | `(<T>x)()` |
| `(<T>x) ** 2` | `(<T>x) ** 2` |
@graphite-app graphite-app Bot force-pushed the fix/codegen-type-assertion-precedence branch from 5399472 to 786d96f Compare June 6, 2026 07:44
@graphite-app graphite-app Bot merged commit 786d96f into main Jun 6, 2026
29 checks passed
@graphite-app graphite-app Bot removed the 0-merge Merge with Graphite Merge Queue label Jun 6, 2026
@graphite-app graphite-app Bot deleted the fix/codegen-type-assertion-precedence branch June 6, 2026 07:47
graphite-app Bot pushed a commit that referenced this pull request Jun 6, 2026
## What

The operand of an angle-bracket assertion `<T>x` is a `UnaryExpression` (TS grammar: `< Type > UnaryExpression`), but codegen printed it at `Precedence::Member`. That wrapped **every** unary operand in redundant parentheses.

It now prints the operand at `Precedence::Exponentiation` — exactly what `UnaryExpression::gen_expr` uses for its own argument — so a `UnaryExpression` operand stays bare while looser operands (binary, conditional, `**`) are still wrapped.

## Examples

| Input | Before | After |
| --- | --- | --- |
| `<T>-x` | `<T>(-x)` | `<T>-x` |
| `<T>typeof x` | `<T>(typeof x)` | `<T>typeof x` |
| `<T><U>x` | `<T>(<U>x)` | `<T><U>x` |
| `<T>x()` | `<T>(x())` | `<T>x()` |

Operands that genuinely require parentheses keep them:

| Input | Output |
| --- | --- |
| `<T>(b + c)` | `<T>(b + c)` |
| `<T>(d ** e)` | `<T>(d ** e)` |
| `<T>(h ? i : j)` | `<T>(h ? i : j)` |

Follow-up to #23002.
Boshen added a commit that referenced this pull request Jun 8, 2026
### 💥 BREAKING CHANGES

- ee4dc73 ast: [**BREAKING**] Add `#[non_exhaustive]` to AST nodes
(#23046) (overlookmotel)
- 4c35362 ast: [**BREAKING**] Add
`AstBuilder::template_element_escape_raw` and
`template_element_escape_raw_with_lone_surrogates` methods (#23047)
(overlookmotel)

### 🚀 Features

- b846ab2 react_compiler: Integrate the Rust port of the React Compiler
(#22942) (Boshen)
- 5b8dd68 parser: Report TS1255 for invalid class definite assertions
(#22917) (camc314)
- 85efabf semantic: Make building the class table optional, off by
default (#22862) (Boshen)

### 🐛 Bug Fixes

- 556acdc codegen: Parenthesize TS-cast assignment targets (#23112)
(Boshen)
- 37169ff codegen: Don't emit space between postfix `--` and `>` when
minifying (#23036) (Boshen)
- a4b1bf7 codegen: Drop redundant whitespace in minified TypeScript
output (#23038) (Boshen)
- cf53285 parser: Report reserved type-declaration names in the parser
(#23035) (Boshen)
- 4e44969 ast: Fix UB in `escape_template_element_raw` (#23052)
(overlookmotel)
- c543154 parser: Report comma operator in JSX expression in the parser
(#23030) (Boshen)
- 325c94f codegen: Tighten conditional-type and constructor-type
whitespace when minifying (#23033) (Boshen)
- 95dd3a2 parser: Report `import type` alias to a non-external reference
in the parser (#23032) (Boshen)
- 90180b8 codegen: Drop space after `:` in function return type when
minifying (#23028) (Boshen)
- 6da876e parser: Report `abstract` private class field in the parser
(#23029) (Boshen)
- 28467ce codegen: Don't emit space before a postfix update operand when
minifying (#23027) (Boshen)
- cb29926 codegen: Drop redundant space after `export default` when
minifying (#23024) (Boshen)
- 62965ae codegen: Drop redundant space after `else` when minifying
(#23025) (Boshen)
- 989230a parser: Report compound assignment to non-simple target in the
parser (#23022) (Boshen)
- 06f367c parser: Report `super.#field` private access in the parser
(#23014) (Boshen)
- 184edef codegen: Print space before `const`/`declare` enum modifier
(#23013) (Boshen)
- 4d722e0 parser: Report duplicate switch `default` clause in the parser
(#23012) (Boshen)
- 597ed85 codegen: Parenthesize `let`/`async` for-of head target
(#23008) (Boshen)
- 8b631bf codegen: Remove stray space before mapped type value colon
(#23010) (Boshen)
- c08407e codegen: Don't over-parenthesize `in` inside an arrow in a
for-init (#23009) (Boshen)
- 600cd6f codegen: Parenthesize lower-precedence
`TSInstantiationExpression` operand (#23007) (Boshen)
- 187e1a5 codegen: Don't leak space after comment-only JSX expression
container (#23006) (Boshen)
- 294c473 codegen: Don't over-parenthesize `TSTypeAssertion` operand
(#23004) (Boshen)
- 786d96f codegen: Give `TSTypeAssertion` unary precedence (#23002)
(Boshen)
- 1295882 parser: Report `new.target` and `import.meta` syntax errors in
the parser (#23003) (Boshen)
- d727b6b codegen: Parenthesize `await` expression as base of `**`
(#23001) (Boshen)
- 67dfa08 codegen: Keep parentheses around `new` callees containing a
call (#22997) (Boshen)
- 17e7cf3 parser: Disallow unerasable `as`/`satisfies` assertions
(#22986) (Boshen)
- beb46d3 parser: Commit to module goal on decorated exports (#22941)
(Boshen)
- 49e63f7 isolated-declarations: Require annotations for satisfies
initializers (#22898) (camc314)
- 8c93601 isolated-declarations: Allow unknown enum initializer in
non-const enum (#22900) (camc314)

### ⚡ Performance

- 7d89909 parser: Peek instead of lookahead for yield disambiguation
(#23071) (Boshen)
- bf872f0 parser: Skip arrow lookahead for a parenthesized literal
(#23070) (Boshen)
- d19fc54 parser: Guard type-argument speculation behind an angle-token
check (#23069) (Boshen)
- 8eb5507 parser: Skip redundant member-rest re-scan on call entry
(#23068) (Boshen)
- 883dfc1 parser: Skip parse_call_expression_rest when no call follows
(#23063) (Boshen)
- b171153 parser: Peek before the await-using lookahead (#23059)
(Boshen)
- 56f21bd parser: Use peek_token for the TS `asserts` type predicate
(#23058) (Boshen)
- 68805ac parser: Use peek_token instead of checkpoint/rewind for
single-token decisions (#23056) (Boshen)
- 1f9d8eb ast: `AstBuilder::template_element_escape_raw` avoid
allocation if no escape required (#23053) (overlookmotel)
- 502b04d semantic: Move cold function redeclaration handling into
`#[cold]` function (#22973) (overlookmotel)

### 📚 Documentation

- 275d318 napi/minifier: Point `target` to oxc docs (#23102) (camc314)

Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com>
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