Go "inconsistent vendoring; run go mod vendor" - Fix in CI

When a vendor/ directory exists, Go builds from it and checks vendor/modules.txt against go.mod. If the two disagree, the build refuses rather than guess which is right.

What this error means

A build fails with inconsistent vendoring listing modules that differ between go.mod and vendor/modules.txt, ending with a go mod vendor hint. It means the vendor tree was not regenerated after a go.mod change.

go: inconsistent vendoring in /home/runner/work/app:
	github.com/foo/bar@v1.2.0: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
	To sync the vendor directory, run:
		go mod vendor

Common causes

vendor tree not regenerated

go.mod changed but go mod vendor was never re-run, so vendor/modules.txt is stale.

Partial vendor commit

Some vendored files or modules.txt were omitted from the commit, leaving the tree internally inconsistent.

How to fix it

Regenerate and commit the vendor tree

Run go mod vendor to rebuild vendor/ and vendor/modules.txt from go.mod.
Stage the entire vendor directory plus modules.txt and commit.

Terminal

go mod vendor
git add vendor go.mod go.sum

Verify the vendor tree in CI

Re-run go mod vendor and fail if it changes anything under vendor/.

.github/workflows/ci.yml

go mod vendor
git diff --exit-code vendor

How to prevent it

Re-run go mod vendor after any go.mod change.
Commit the whole vendor/ tree, not a subset.
Add a git diff --exit-code vendor guard to CI.