feat: check a project with TypeScript 7 by alexander-akait · Pull Request #391 · webpack/diagnostics-webpack-plugin

alexander-akait · 2026-10-23T14:47:21Z

Summary

typescript@latest is now 7.0.2, a native compiler with no compiler API in JavaScript: import("typescript") yields only { version, versionMajorMinor }. On main, the TypeScript check therefore fails outright with TS 7, with "Directory import … is not supported" when given a path and a TypeError with the bare name.

This PR runs the check on TS 7 through the API it ships, typescript/unstable/async. The new code is in src/checks/typescript-native.js.

Detection:
- loadNative() reads the package's package.json. For major ≥ 7 it imports unstable/async, through the package's own exports.
- Otherwise the existing path runs unchanged. A path to a module rather than a package, such as a test mock, also counts as classic.
A process of its own:
- The API spawns the native compiler, so threads doesn't apply.
- One client is kept per check and compiler: closed on shutdown or watchClose, or after a one-shot build.
Rebuilds: updateSnapshot() is handed webpack's modifiedFiles and removedFiles, split into changed, created and deleted, so nothing is read again to find out what changed. The previous snapshot is disposed.
Diagnostics:
- Config-file, program, syntactic, global, declaration (when declaration or composite is set) and semantic diagnostics, honouring diagnosticOptions, and deduplicated.
- Each is described as worker results already are, so ignoreDiagnostics, reportAs, formatter and outputReport work unchanged.
- The default output is byte-for-byte what TypeScript 6's formatDiagnosticsWithColorAndContext prints for the bad fixture.
Unsupported, and reported as such rather than ignored: build, a mode that writes, and compiler options written in the plugin. The native API reads a project as its config file describes it.
Peer range: widened to ^5.0.0 || ^6.0.0 || ^7.0.0.

Measurements

600 .ts files (bench-heavy), one TypeScript check, default options.

	one-shot wall	webpack process CPU	webpack process peak RSS	watch: first build, then 3 rebuilds
TypeScript 6.0.3	3.47 / 3.54 s	6.4–6.5 s	382–384 MB	3.9 / 2.4 / 1.0 / 1.2 s
TypeScript 7.0.2 (this PR)	1.55 / 1.38 s	0.6–0.8 s	107–109 MB	1.4 / 0.7 / 0.7 / 0.7 s

The native compiler's own CPU isn't in the webpack-process column. Measured alone with tsc -p --noEmit, the native compiler takes 1.1–1.3 s user + 0.4 s sys on this project, against 4.8 + 0.3 s for TypeScript 6.

Tests and tooling

The typescript7 alias: TS 7 is installed for the tests as typescript7@npm:typescript@7.0.2. Its bin is also named tsc and took over node_modules/.bin/tsc, so build:types and lint:types now run the repository's own TypeScript by path (node ./node_modules/typescript/bin/tsc).
test/typescript/native.test.js covers:
- loading only for TS ≥ 7 packages;
- a clean project;
- a type error, with location, code frame and a file nothing imports;
- ignoreDiagnostics;
- diagnosticOptions;
- a formatter written in the configuration;
- the unsupported options;
- a watch rebuild that fixes an error.
Lint, types, schema lint, prettier, cspell and the full suite (338 tests) pass locally.

Generated by Claude Code

Summary by CodeRabbit

New Features
- Added support for TypeScript 7, including compiler diagnostics during initial checks and watch-mode rebuilds.
Documentation
- Added TypeScript 7 setup guidance and performance comparisons.
- Documented limitations: build mode, writing mode, and compiler options configured directly in the plugin are not supported. Set compiler options in your TypeScript configuration file instead.

TypeScript 7 is a native compiler with no compiler API in JavaScript: importing it yields its version and nothing else, so the TypeScript check could not run at all. The check now drives the native compiler through the API it ships (typescript/unstable/async), in a process of its own that stays open while webpack watches and is told which files webpack saw change. Diagnostics are printed as tsc --pretty prints them. build, a writing mode, and compiler options written in the plugin are reported as unsupported, since the native API reads a project as its config file describes it. TypeScript 7 is installed for the tests under the typescript7 alias. Its bin is also named tsc, so the scripts run the repository's own TypeScript by path. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01App18sYbe6Vf6HDCjCXbvf

linux-foundation-easycla · 2026-10-23T14:47:32Z

✅ Unknown (51d5bfe, 743af82)
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/easycla

socket-security · 2026-10-23T14:47:59Z

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	typescript@7.0.2

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alexander-akait · 2026-10-23T14:53:25Z

EasyCLA fails because the commits carry a Co-Authored-By: Claude trailer that maps to no GitHub account. It is not a code failure. Whether to drop the trailer or accept the check is for the maintainers to decide, so I haven't rewritten history.

Generated by Claude Code

coderabbitai · 2026-10-23T14:53:34Z

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README.md

Walkthrough

The TypeScript check now uses TypeScript 7’s native asynchronous API when available. The new implementation manages compiler clients and snapshots, collects and formats diagnostics, and handles watch rebuilds. It rejects build mode, output-writing modes, and plugin-level compiler options. Package metadata, documentation, and tests now cover TypeScript 7 support.

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to 51d5b

TypeScript 7 users may be misdirected when configuring the check. Clarify the guidance before merging; the documented issue does not establish a runtime failure.

Pre-merge checks: 5

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Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: adding support for checking projects with TypeScript 7.
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01App18sYbe6Vf6HDCjCXbvf

coderabbitai Bot reviewed Oct 23, 2026

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Comment thread README.md Outdated

docs: say compiler options, not build or mode, belong in tsconfig.json

743af82

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01App18sYbe6Vf6HDCjCXbvf

alexander-akait closed this Oct 23, 2026

alexander-akait mentioned this pull request Oct 23, 2026

feat: TypeScript 7.1 support, one place for compiler-lived state, shared TypeScript runs #392

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feat: check a project with TypeScript 7 - #391

feat: check a project with TypeScript 7#391
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