Build and type check

A build and type check compiles the code, or checks its types without running it, and reports each error with its place. Loops read it early and often: it catches a whole class of mistakes before any test runs.

What it sees

Whether the code is consistent with itself: names that resolve, types that match, modules that link. It comes at three speeds: diagnostics from a language server right after an edit, a type check, and a full build. It does not run the code, so it says nothing about whether the code behaves as it should.

Reading the signal

• No errors: the code builds, or its types check.
• Errors: each gives its file:line and a message, and the exit code is non-zero. Fix the first error first, as later ones often follow from it.
• A new suppression: a comment that tells the checker to ignore an error counts as a finding, even when the run passes.

A build can also fail for reasons outside the code: a missing dependency, a full disk, a cache in a bad state. Such a failure says nothing about the change. Read which kind it is before acting on it.