The project's type checker

Where a language checks its types with a program separate from its build, this tool is that checker, with the settings the project gives it. Which checker that is, and how strict, is found in the project, not assumed.

Finding it

Look in CI and the task file for a type-check step, then for the checker's config (tsconfig.json, mypy.ini, pyrightconfig.json, or a [tool.mypy] or [tool.pyright] section in pyproject.toml) and its version in the dev dependencies. Where the compiler checks types as part of the build (Go, Rust, Java), the build is the type check.

Using it

• Run it as CI does: tsc --noEmit, mypy, pyright, with the project's config and strictness, not the checker's defaults.
• The pinned version: a new release of the checker can find new errors in code that did not change.
• New suppressions too: the checker does not report a new # type: ignore, @ts-ignore or @ts-expect-error, so they are read from the diff; mypy --warn-unused-ignores reports the ones no longer needed.

Examples: tsc --noEmit (TypeScript), mypy and Pyright (Python), Sorbet (Ruby).