Go "build failed" - Read the First Compiler Error in CI

go build stopped with a non-zero exit. The cause is the first file.go:line:col: <error> line in the output -- a type mismatch, an undefined identifier, or a package that could not be found.

What this error means

The job ends with one or more ./file.go:NN:CC: ... compiler errors and the build step exits non-zero. Compile errors are deterministic; a failure that only mentions a dependency download and clears on re-run is a transient fetch, not a code error.

# example.com/app/handler
./handler.go:18:14: undefined: parseRequst
./handler.go:24:9: cannot use n (variable of type int) as string value in return statement

Common causes

A real compile error

An undefined identifier, a type mismatch, an unused import, or a wrong return type makes the compiler reject the package. The first file:line error names exactly what is wrong.

Missing or unresolved dependency

A package import that is not in go.mod, or a module that failed to download, stops the build before compilation completes.

How to fix it

Fix the first compiler error

Scroll to the first file.go:line:col: error -- later errors are often cascades of it.
Reproduce locally with go build ./....
Correct the named symbol or type, then rebuild until clean.

Terminal

go build ./...

Resolve missing dependencies first

Run go mod tidy so go.mod/go.sum match the imports.
Run go mod download to fetch modules before the build step.
Confirm actions/checkout and setup-go ran before any go command.

.github/workflows/ci.yml

- uses: actions/checkout@v4
- uses: actions/setup-go@v5
- run: go mod download && go build ./...

How to prevent it

Run go vet ./... and go build ./... locally before pushing.
Keep go.mod tidy so missing-import failures surface early.
On Latchkey, self-healing managed runners auto-retry transient module-download failures so a flaky proxy fetch does not fail the build on its own.