dagger/dagger · error

stage before delta: %w

Error message

stage before delta: %w

What it means

materializeDeltaFiles copies the before-side paths (modified candidates plus removed files when detecting renames) from beforeDir into the staging tmpBefore tree; failure is wrapped as "stage before delta: %w". It means the delta files on the "before" side could not be copied out for git comparison.

Source

Thrown at core/changeset_delta.go:86

		}
		defer os.RemoveAll(tmpRoot)
		tmpBefore := filepath.Join(tmpRoot, "before")
		tmpAfter := filepath.Join(tmpRoot, "after")

		// Modified files exist at the same path on both sides, so they can
		// never participate in rename pairing; stage them only when numstat
		// needs their content.
		var beforePaths, afterPaths []string
		if materializeModified {
			beforePaths = slices.Clone(modified)
			afterPaths = slices.Clone(modified)
		}
		if detectRenames {
			beforePaths = append(beforePaths, delta.removedFiles...)
			afterPaths = append(afterPaths, delta.addedFiles...)
		}
		if err := materializeDeltaFiles(ctx, beforeDir, tmpBefore, beforePaths); err != nil {
			return nil, nil, fmt.Errorf("stage before delta: %w", err)
		}
		if err := materializeDeltaFiles(ctx, afterDir, tmpAfter, afterPaths); err != nil {
			return nil, nil, fmt.Errorf("stage after delta: %w", err)
		}

		if detectRenames {
			gitFC, err := compareDirectories(ctx, tmpBefore, tmpAfter)
			if err != nil {
				return nil, nil, fmt.Errorf("compare delta files: %w", err)
			}
			fc.Added = gitFC.Added
			fc.Removed = gitFC.Removed
			fc.Renamed = gitFC.Renamed
		}
		if withStats {
			stats, err = compareDirectoriesNumStat(ctx, tmpBefore, tmpAfter)
			if err != nil {
				return nil, nil, fmt.Errorf("numstat delta files: %w", err)

View on GitHub (pinned to 82ba2681db)

Solutions

1. Check the wrapped cause for the specific path that failed to copy
2. Ensure the before/after trees are not modified concurrently (snapshot them)
3. Verify disk space in TMPDIR; staging duplicates the delta content
4. Retry once the tree is stable

for _, p := range beforePaths {
  if _, err := os.Stat(filepath.Join(beforeDir, p)); err != nil { return fmt.Errorf("before path %s: %w", p, err) }
}

if err != nil {
  return fmt.Errorf("staging before-side files failed: %w", err)
}

When it happens

Trigger: computeChangesetPathsDelta with rename detection or stats enabled, when copying beforeDir paths fails: a listed path vanished from beforeDir, permission denied, source file read error, or context cancellation mid-copy.

Common situations: Tree mutated between collectChangesetDelta and staging (file removed/renamed concurrently); unreadable file due to permission changes; disk full while writing the staging copy.

Related errors

• stage after delta: %w
• compute paths: %w
• copy changed paths: %w
• collect delta: %w
• verify modified files: %w

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/0b8e49e86b8d01de. Report an issue: GitHub.