golang/go · warning

repo changed

Error message

repo changed

What it means

CheckReuse repoSum branch: both old and current RepoSum are populated but differ. The repository's content fingerprint changed, indicating upstream history was rewritten, the remote is a different clone, or the sum algorithm differs.

Source

Thrown at src/cmd/go/internal/modfetch/codehost/vcs.go:416

			return fmt.Errorf("looking up hash: %v", err)
		}
		return fmt.Errorf("hash changed") // weird but maybe they made a tag
	}

	if old.Ref != "" && old.RepoSum == "" {
		hash, err := r.lookupRef(ctx, old.Ref)
		if err == nil && hash != "" && hash == old.Hash {
			return nil
		}
	}

	r.repoSumOnce.Do(func() { r.loadRepoSum(ctx) })
	if r.repoSum != "" {
		if old.RepoSum == "" {
			return fmt.Errorf("non-specific origin")
		}
		if old.RepoSum != r.repoSum {
			return fmt.Errorf("repo changed")
		}
		return nil
	}
	return fmt.Errorf("vcs %s: CheckReuse: %w", r.cmd.vcs, errors.ErrUnsupported)
}

func (r *vcsRepo) Tags(ctx context.Context, prefix string) (*Tags, error) {
	unlock, err := r.mu.Lock()
	if err != nil {
		return nil, err
	}
	defer unlock()

	r.tagsOnce.Do(func() { r.loadTags(ctx) })
	tags := &Tags{
		Origin: r.repoSumOrigin(ctx),
		List:   []Tag{},
	}

View on GitHub (pinned to b6b368adc5)

Solutions

  1. Confirm the upstream change is intentional (check the VCS for recent force-pushes/rebases).
  2. `go clean -modcache` to discard the stale sum and re-establish a baseline against the current remote.
  3. Pin the module to a specific version tag so the same commit is always resolved.
  4. If using a mirror, ensure all clients point at the same mirror consistently.
Defensive patterns

Strategy: fallback

Validate before calling

func repoSumStable(oldSum, currentSum string) bool {
    return oldSum != "" && oldSum == currentSum
}

Try / catch

if err := repo.CheckReuse(ctx, old, subdir); err != nil {
    if strings.Contains(err.Error(), "repo changed") {
        // history rewritten upstream — re-baseline the cache
    }
}

Prevention

When it happens

Trigger: old.RepoSum != r.repoSum after loadRepoSum completes — the repo's deterministic content hash diverged from what was cached.

Common situations: Upstream rebased or force-pushed history; the module is served from a mirror whose content differs from the originally-cached remote; hg repository reorganisation affecting the goreposum.py output.

Related errors

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/a63824b493715b0d. Report an issue: GitHub.