lib: add Math.sumPrecise type definition (ES2025)

[Su Yiheng (827652549)]

Summary

Adds type definition for Math.sumPrecise which is part of the TC39 proposal-math-sum that reached Stage 4 on 2025-07-28, making it part of ES2026.

Changes

• New file: src/lib/esnext.math.d.ts — extends interface Math with sumPrecise
• Updated src/lib/esnext.d.ts — added /// <reference lib="esnext.math" />
• Updated src/lib/libs.json — registered esnext.math in the libs array
• Updated src/compiler/commandLineParser.ts — mapped esnext.math lib name to file
• Updated src/compiler/utilities.ts — added sumPrecise to ScriptTargetFeatures for helpful diagnostics

Why esnext, not es2025?

The proposal reached Stage 4 on 2025-07-28, one month after ES2025 was finalized (June 2025), so it will be included in ES2026. TypeScript does not have es2026 lib files yet, so esnext is the correct placement for now.

Runtime support

Runtime	Supported
Firefox 137+	✅
Safari 18.4 (JavaScriptCore)	✅
Bun	✅
V8 / Node.js / Chrome	❌ not yet

References

• TC39 Proposal: https://github.com/tc39/proposal-math-sum
• Stage 4 meeting notes: https://github.com/tc39/notes/blob/main/meetings/2025-07/july-28.md#mathsumprecise-for-stage-4
• MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sumPrecise

AI Disclosure

This PR was developed with AI assistance (Claude by Anthropic) for research, code generation, and verification against the TC39 spec, MDN, and runtime implementations.

Fixes #63427

[Su Yiheng (827652549)]

@microsoft-github-policy-service agree

[Copilot]

Pull request overview

Adds a new ESNext-by-feature library (esnext.math) to provide type definitions for Math.sumPrecise, and wires it through the lib registry / CLI parsing so it can be selected via --lib, with conformance + baseline coverage.

Changes:

• Added src/lib/esnext.math.d.ts to extend interface Math with sumPrecise(numbers: Iterable<number>): number.
• Registered esnext.math in the lib ecosystem (src/lib/libs.json, src/lib/esnext.d.ts, and src/compiler/commandLineParser.ts).
• Added diagnostics support and test coverage (new conformance test + updated baselines).

Reviewed changes

Copilot reviewed 14 out of 19 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/cases/conformance/esnext/mathSumPrecise.ts	New conformance test exercising Math.sumPrecise typing (positive + negative cases).
tests/baselines/reference/mathSumPrecise.types	New types baseline validating the inferred types for the conformance test.
tests/baselines/reference/mathSumPrecise.symbols	New symbols baseline validating symbol binding to lib.esnext.math.d.ts.
tests/baselines/reference/config/convertCompilerOptionsFromJson/Convert trailing-whitespace string option of libs to compiler-options with jsonSourceFile api.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/convertCompilerOptionsFromJson/Convert trailing-whitespace string option of libs to compiler-options with json api.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/convertCompilerOptionsFromJson/Convert incorrect option of libs to compiler-options with jsonSourceFile api.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/convertCompilerOptionsFromJson/Convert incorrect option of libs to compiler-options with json api.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/convertCompilerOptionsFromJson/Convert empty string option of libs to compiler-options with jsonSourceFile api.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/convertCompilerOptionsFromJson/Convert empty string option of libs to compiler-options with json api.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/convertCompilerOptionsFromJson/Convert empty string option of libs array to compiler-options with jsonSourceFile api.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/convertCompilerOptionsFromJson/Convert empty string option of libs array to compiler-options with json api.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/commandLineParsing/parseCommandLine/Parse invalid option of library flags.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/commandLineParsing/parseCommandLine/Parse --lib option with trailing white-space.js	Baseline update reflecting esnext.math in valid --lib values list.
tests/baselines/reference/config/commandLineParsing/parseCommandLine/Parse --lib option with extra comma.js	Baseline update reflecting esnext.math in valid --lib values list.
src/lib/libs.json	Registers esnext.math as a known lib for --lib parsing and ordering.
src/lib/esnext.math.d.ts	New lib fragment defining Math.sumPrecise.
src/lib/esnext.d.ts	Includes esnext.math in the aggregate esnext lib.
src/compiler/utilities.ts	Adds sumPrecise to ScriptTargetFeatures (used for “Try changing the 'lib' option to … or later” suggestions).
src/compiler/commandLineParser.ts	Maps esnext.math to lib.esnext.math.d.ts and adds it to the recognized --lib values list.

Files not reviewed (3)

• tests/baselines/reference/config/commandLineParsing/parseCommandLine/Parse --lib option with extra comma.js: Generated file
• tests/baselines/reference/config/commandLineParsing/parseCommandLine/Parse --lib option with trailing white-space.js: Generated file
• tests/baselines/reference/config/commandLineParsing/parseCommandLine/Parse invalid option of library flags.js: Generated file