`ts-r-check`

Type checker. Replaces tsc.

Pre-alpha
Works from source

ts-r-check type-checks a TypeScript project and prints diagnostics in tsc’s format, with tsc’s error codes. It never writes JavaScript or declaration files: it is the tsc --noEmit step of a build. It is the least finished part of ts-r, and it follows one rule: no false positives first.

Check all five projects, total wall timeShorter is faster. Pre-release build, real app.

ts-r-check1,936 ms
tsc 7.0.23,044 ms

1.6× faster type checks

What switching looks like

Nothing is on npm yet. Once it is, switching looks like this: ts-r-check reads the config you already have, so the change is to the command, not the project.

package.json

  "scripts": {
-   "typecheck": "tsc --noEmit -p tsconfig.json",
+   "typecheck": "ts-r-check --noEmit -p tsconfig.json",
  }

What works, and what doesn’t yet

Works today

Loading the project from tsconfig.json, including extends, with tsc’s config diagnostics
Module resolution that matches tsc’s on every resolution of the reference app
Assignability, calls and overloads, generics and inference, unions and narrowing
keyof, mapped, conditional and literal types; classes, declarations and unused-code checks
tsc’s output in both plain and pretty form, with tsc’s exit codes

Not yet

JSX element and attribute types
Evolving arrays (let xs = [])
Implicit any in binding patterns (TS7031) and this parameter checks
Reverse mapped types
TypeScript syntax errors in .js files (TS8xxx)

Measured

Every run, on the same reference app as the home page, with the command and commit that recorded it.

ts-r-check against tsc 7.0.2

Type checking five public projects from the command line, cold (no saved history), against TypeScript 7.0.2's native tsc. These repos do not type-check cleanly under TypeScript 7, and ts-r-check does not report the same diagnostics as tsc on them yet: it reports extra ones on all five (27 on date-fns to 1,333 on RxJS in the last comparison) and misses some of tsc's. It also skips checks it does not implement yet, so these times will move as the checker grows.

Check all five projects, total wall timeShorter is faster, in ms

ts-r
Other tools

ts-r-check1,936 ms
tsc 7.0.23,044 ms

Cold check, wall timeShorter is faster, in ms

tRPC packages/server108 ms
date-fns pkgs/core226 ms
RxJS packages/rxjs462 ms
TypeORM packages/typeorm548 ms
Playwright592 ms

Cold check, peak memoryShorter is faster, in MB

tRPC packages/server117 MB
date-fns pkgs/core216 MB
RxJS packages/rxjs458 MB
TypeORM packages/typeorm377 MB
Playwright463 MB

Warm runs, and each repo's own TypeScript
Project	ts-r-check, saved history, nothing changed	The repo's own tsc
tRPC	23 ms	1,130 ms
date-fns	78 ms	324 ms
RxJS	57 ms	2,468 ms
TypeORM	126 ms	3,915 ms
Playwright	40 ms	4,754 ms

How we measured

Measured: Wall time with hyperfine (cargo xtask bench --repos), median of 5 runs; peak RSS of one extra run. Every tool checks the same wrapper tsconfig (noEmit, not incremental)
Machine: Apple M-series MacBook (macOS arm64, 16 cores, 48 GB), shared with other jobs while measuring; release build, 4 threads
Software: ts-r-check release build; TypeScript 7.0.2 (native tsc) pinned in bench/package.json; each repo's own TypeScript
Input: tRPC, date-fns, RxJS, TypeORM and Playwright at the commits pinned in bench/repos.toml
Command: cargo xtask bench --fetch-repos --repos trpc,date-fns,rxjs,typeorm,playwright && cargo xtask bench --repos trpc,date-fns,rxjs,typeorm,playwright --memory check-
Recorded in: commit 9c3a371

Correctness

Compared with the tool ts-r-check replaces, on its own tests and on real code.

Module resolution100%
63,958 of 63,958 resolutions match (0 differences)
Every resolution in tsc --traceResolution for 24 tsconfig files of private-app. Commit 856e43d.
tsconfig loading100%
49 of 49 configs match tsc --showConfig exactly
private-app tsconfig files. Commit 856e43d.
Binder diagnostics90.0%
398 of 442 tests match exactly; 1,683 of 1,789 expected diagnostics found
tsc 7.0.2 baselines for the binder's error codes. Commit 16a6b7e.
Type checker58.0%
58.0% of 13,398 conformance test variants exact; 937 variants with a diagnostic tsc does not report
tsc 7.0.2 conformance baselines. Commit aaa5051.

Command line

An excerpt of ts-r-check --help. You can also run it through the launcher as ts-r check.

Next to tsc

ts-r-check reads the same tsconfig.json and prints the same format, so editor problem matchers and CI annotations that parse tsc’s output work unchanged. An error from ts-r-check is very likely one tsc reports too, but a clean run doesn’t mean tsc is clean. Keep tsc in CI until ts-r-check covers the features your project uses.

ts-r-check --help

usage: ts-r-check -p tsconfig.json [--noEmit] [--pretty false] [--threads N]