ts-r-check: type checker

ts-r-check type-checks a TypeScript project and prints diagnostics in tsc's format, with tsc's error codes. Like tsc, it also writes the project's JavaScript, source maps and declaration files unless noEmit is set; pass --noEmit to only check, as with tsc --noEmit.

The checker is the least finished part of ts-r. Read Status before you rely on it.

#How to read its results

The checker follows one rule: no false positives first. When it meets something it doesn't implement yet, it gives that expression a silent type that is never reported. So:

• An error from ts-r-check is very likely an error tsc reports too.
• A clean run from ts-r-check does not mean tsc is clean. It can miss errors.

Keep tsc in CI until ts-r-check covers the features your project uses.

#What works today

• Loading the project from tsconfig.json, including extends, with tsc's config diagnostics such as TS6053.
• Module resolution that matches tsc's: 63,958 resolutions across 24 private-app configs, 0 mismatches.
• Assignability, calls and overloads, generics and inference, unions and narrowing, type operators (keyof, mapped, conditional and literal types), classes and declarations, and unused-code checks. Errors such as TS2322, TS2304, TS2307 and TS7006 print with tsc's wording.
• tsc's output in both plain and pretty form.

#Not yet

• Regular expression pattern errors: only the flags of a regex literal are checked, so errors such as TS1507 and TS1515 aren't reported. Octal escapes in strings (TS1487) aren't reported either.
• Some inference: contextual types that flow through a reverse mapped type print wider than tsc's (number | T["a"] where tsc prints number).
• Some relation and narrowing results differ from tsc's, mostly in TS2322, TS2339 and TS2345: 434 of tsc's 12,750 conformance test variants (3.4%) don't match exactly.

The full list is in ts_r_checker's notes.

#Command line

usage: ts-r-check [-p tsconfig.json] [options]

--help lists every option. It accepts tsc 7's command line; the flags below are the common ones.

Pretty output is the default on a terminal. It adds code frames and a Found N errors in M files. line. Paths are relative to the current directory, and output is sorted by path, then position. Config diagnostics print first.

Exit codes follow tsc:

You can also run it through the launcher as ts-r check.

#Lib files

ts-r-check needs TypeScript's lib.*.d.ts files. It looks in this order:

1. The directory in TS_R_LIB_DIR.
2. A lib/ directory next to the executable (or ../lib).
3. target/upstream/typescript/tsc/internal/bundled/libs in a source checkout, after cargo xtask upstream sync --minimal.

See Getting started for the source setup.

#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. It also takes tsc's --build and --watch, and writes the same output files. Running both and comparing their output is a good way to try it; ts-r-build makes bundles.

For stricter checks than tsc's, see Sound mode.

#Measured

Against tsc 7.0.2:

Most extra diagnostics in the ecosystem run are TS2344, TS2305, TS2694 and TS2304. Some of the 220 conformance extras are runner artefacts, such as tests for module kinds tsc 7 removed, which have no baseline.

Speed and memory on public projects (cargo xtask bench --repos, cold check, no history; Apple M-series shared laptop, median of 5, peak memory of one run):

With its saved history and nothing changed, ts-r-check takes 23 to 126 ms on the same projects. These repos don't type-check cleanly under TypeScript 7, and ts-r-check doesn't report the same diagnostics as tsc on them yet: it reports extra ones on all five (from a few dozen on date-fns to over a thousand on RxJS) and misses some of tsc's. ts-r also skips work it doesn't implement yet, so these numbers will move as the checker grows.

Method and commits: check, ecosystem and correctness.