fix(es/optimization): preserve JSON numeric values by magic-akari · Pull Request #12051 · swc-project/swc

magic-akari · 2026-07-21T11:20:52Z

Description:

The JSON parse optimization had a number fast path that cast through i64. That path could be unsafe for out-of-range values and for -0, changing observable results.

This PR keeps the optimization but only uses the i64 path when safe: when the number is an integer within i64 range and does not alter the zero sign.
Other finite numbers are serialized via serde_json::Number::from_f64, and non-finite handling is updated so NaN is rejected while ±Infinity is emitted as ±2e308.

Related issue (if exists):

fix(es/ast): support hashing non-finite numbers #12043
- fix(es/codegen): emit non-finite numeric literals #12047

codspeed-hq · 2026-07-21T11:36:57Z

Merging this PR will not alter performance

✅ 200 untouched benchmarks
⏩ 61 skipped benchmarks¹

_{Comparing fix/json-number-serialization (83df80f) with main (b830786)}

61 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. ↩

changeset-bot · 2026-07-21T13:41:50Z

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changeset-bot · 2026-07-21T13:41:52Z

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**Description:** ECMAScript bitwise NOT first applies `ToInt32`, including wraparound for out-of-range numbers. Folding with direct Rust casts does not reproduce those conversions at the boundaries. This PR delegates numeric bitwise NOT folding to the existing `JsNumber` implementation and adds coverage for boundary, wraparound, and very large values. The simplifier now uses the same number semantics as the rest of the optimizer. **Related issue (if exists):** - Close: #12062 --- - #12043 - #12047 - #12050 - #12048 - #12051 - #12052 - #12053 - #12054 - #12055 - #12056 - #12057 - **#12058** (current) - #12049 - #12059 - #12060

**Description:** Several property-key optimizations rely on Rust number formatting or eagerly parse strings as numbers. This can merge distinct ECMAScript keys, including `Infinity` and `inf`, `-0` and `0`, or `"01"` and `"1"`. This PR introduces shared canonical-index parsing and ECMAScript number-to-string conversion, then uses them across property-key transforms, literal folding, and TypeScript name extraction. Each path now preserves property-key identity before optimizing it. **Related issue (if exists):** - Close: #12061 --- - #12043 - #12047 - **#12050** (current) - #12048 - #12051 - #12052 - #12053 - #12054 - #12055 - #12056 - #12057 - #12058 - #12049 - #12059 - #12060

…12049) **Description:** Enum evaluation currently rebuilds computed `NaN` and infinity values as identifiers. That turns numeric constants into apparent references and loses number-literal semantics as values move through the TypeScript transform and fast-DTS evaluators. This PR keeps computed enum numbers as `Number` literals in both paths, applies JavaScript number stringification when names are required, and corrects modulo evaluation for non-finite operands. **Related issue (if exists):** - #12043 - #12047 - #12050 - #12048 - #12051 - #12052 - #12053 - #12054 - #12055 - #12056 - #12057 - #12058 - **#12049** (current) - #12059 - #12060 Co-authored-by: Donny/강동윤 <kdy.1997.dev@gmail.com>

**Description:** `Number#toString(radix)` folding currently converts integer values through `u128`. Unsafe integers can already have rounded representations, so this conversion can produce digits that do not match JavaScript for non-power-of-two radices. This PR restricts radix folding to safe integers, with a separate exact path for supported power-of-two radices below the `u128` bound. Values outside those limits remain for runtime evaluation. **Related issue (if exists):** - #12043 - #12047 - #12050 - #12048 - #12051 - #12052 - #12053 - #12054 - #12055 - #12056 - **#12057** (current) - #12058 - #12049 - #12059 - #12060

**Description:** `Array(length)` throws a `RangeError` when the length is fractional or otherwise invalid. Folding every small numeric length into an array literal suppresses that observable exception. This PR requires candidate lengths to be integers before applying the literal-folding optimization and adds runtime coverage for invalid lengths. Valid small arrays are still folded as before. **Related issue (if exists):** - #12043 - #12047 - #12050 - #12048 - #12051 - #12052 - #12053 - #12054 - #12055 - **#12056** (current) - #12057 - #12058 - #12049 - #12059 - #12060

**Description:** Computed `arguments` properties are currently parsed or cast directly as numeric indices. Non-canonical names and invalid indices can therefore be mistaken for parameter positions and replaced incorrectly. This PR resolves `arguments` slots through the shared canonical-index parser and ECMAScript number-to-string conversion before substituting parameters. An access is optimized only when its property denotes the same canonical argument index. **Related issue (if exists):** - Closes: #12066 --- - #12043 - #12047 - #12050 - #12048 - #12051 - **#12052** (current) - #12053 - #12054 - #12055 - #12056 - #12057 - #12058 - #12049 - #12059 - #12060

**Description:** `String.fromCharCode` applies ECMAScript `ToUint16` to every argument. The current floor-and-cast folding path does not match that behavior for negative, wrapping, or non-finite inputs. This PR adds `JsNumber::to_uint16` and uses it before folding ASCII `String.fromCharCode` results. Boundary coverage keeps the optimization limited to values whose output can be produced safely. **Related issue (if exists):** - #12043 - #12047 - #12050 - #12048 - #12051 - #12052 - #12053 - #12054 - **#12055** (current) - #12056 - #12057 - #12058 - #12049 - #12059 - #12060

**Description:** Enum template evaluation currently reads raw template source and converts atoms lossily. Escapes, interpolation, and lone surrogates can therefore diverge from the cooked JavaScript string used at runtime. This PR evaluates template quasis and static template member keys from cooked WTF-8 values in both the transform and fast-DTS paths. Lookup and concatenation retain lone surrogates without changing the surrounding enum evaluation model. **Related issue (if exists):** - #12043 - #12047 - #12050 - #12048 - #12051 - #12052 - #12053 - #12054 - #12055 - #12056 - #12057 - #12058 - #12049 - **#12059** (current) - #12060

**Description:** JavaScript string property indexing uses UTF-16 code units. Existing constant folding checked string-literal indices against WTF-8 byte length, which can treat out-of-bounds indices as valid for non-ASCII BMP characters, astral characters, and lone surrogates. In the expression simplifier, that mismatch could also reach an `unreachable!` branch. This PR validates and reads string-literal indices using UTF-16 code units in both the minifier and expression simplifier. It preserves the WTF-8 byte-length check as a fast upper-bound rejection, folds valid indices to the correct code unit, and handles UTF-16 out-of-bounds indices according to each pass's existing semantics. Coverage includes BMP non-ASCII characters, astral surrogate pairs, and lone surrogates. The change was verified with: - `cargo test -p swc_ecma_minifier -p swc_ecma_transforms_optimization` - `(cd crates/swc_ecma_minifier && ./scripts/exec.sh)` - `cargo fmt --all` - `cargo clippy --all --all-targets -- -D warnings` **Related issue (if exists):** - #12043 - #12047 - #12050 - #12048 - #12051 - #12052 - #12053 - **#12054** (current) - #12055 - #12056 - #12057 - #12058 - #12049 - #12059 - #12060

**Description:** The optimizer currently represents `NaN` and infinities in several forms, including identifiers, divisions, and numeric literals. As these forms move through multiple optimization passes, they can be folded inconsistently and acquire incorrect truthiness or stringification. This PR canonicalizes non-finite optimization results as raw-free `Lit::Num` values. Minifier and simplifier helpers then preserve ECMAScript behavior for these numbers, while codegen remains responsible for choosing valid output syntax. **Related issue (if exists):** - #12043 - #12047 - #12050 - **#12048** (current) - #12051 - #12052 - #12053 - #12054 - #12055 - #12056 - #12057 - #12058 - #12049 - #12059 - #12060

magic-akari force-pushed the fix/non-finite-number-minifier branch from c4b8684 to 1b7c67a Compare July 21, 2026 13:41

magic-akari force-pushed the fix/json-number-serialization branch from ed9a2ee to 6bb3e34 Compare July 21, 2026 13:41

magic-akari force-pushed the fix/non-finite-number-minifier branch from 1b7c67a to 7477945 Compare July 22, 2026 04:26

magic-akari force-pushed the fix/json-number-serialization branch from 6bb3e34 to 4cffc5d Compare July 22, 2026 04:26

magic-akari force-pushed the fix/non-finite-number-minifier branch from 7477945 to c2b4b09 Compare July 22, 2026 10:45

magic-akari force-pushed the fix/json-number-serialization branch from 4cffc5d to 208c6c3 Compare July 22, 2026 11:04

magic-akari force-pushed the fix/non-finite-number-minifier branch from c2b4b09 to 3f6379d Compare July 23, 2026 05:06

magic-akari force-pushed the fix/json-number-serialization branch from 208c6c3 to eb7dc46 Compare July 23, 2026 05:06

Base automatically changed from fix/non-finite-number-minifier to main July 24, 2026 07:33

fix(es/optimization): preserve JSON numeric values

83df80f

magic-akari force-pushed the fix/json-number-serialization branch from eb7dc46 to 83df80f Compare July 24, 2026 08:11

magic-akari marked this pull request as ready for review July 24, 2026 09:30

magic-akari requested review from a team as code owners July 24, 2026 09:30

Donny/강동윤 (kdy1) approved these changes Jul 28, 2026

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Donny/강동윤 (kdy1) merged commit 667af8c into main Jul 28, 2026
363 of 366 checks passed

Donny/강동윤 (kdy1) deleted the fix/json-number-serialization branch July 28, 2026 12:26

github-actions Bot modified the milestones: Planned, v1.15.47 Jul 28, 2026

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fix(es/optimization): preserve JSON numeric values - #12051

fix(es/optimization): preserve JSON numeric values#12051
Donny/강동윤 (kdy1) merged 1 commit into
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fix/json-number-serialization

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