golang/go · error

can't read %q: %v

Error message

can't read %q: %v

What it means

Thrown by 'go tool cover' html.go when os.ReadFile fails on the source file located for a coverage profile entry during HTML report generation. The wrapped error names the profile's FileName and the underlying read error. findFile has already resolved the path, so failure means the resolved file is missing or unreadable.

Source

Thrown at src/cmd/cover/html.go:48

	var d templateData

	dirs, err := findPkgs(profiles)
	if err != nil {
		return err
	}

	for _, profile := range profiles {
		fn := profile.FileName
		if profile.Mode == "set" {
			d.Set = true
		}
		file, err := findFile(dirs, fn)
		if err != nil {
			return err
		}
		src, err := os.ReadFile(file)
		if err != nil {
			return fmt.Errorf("can't read %q: %v", fn, err)
		}
		var buf strings.Builder
		err = htmlGen(&buf, src, profile.Boundaries(src))
		if err != nil {
			return err
		}
		d.Files = append(d.Files, &templateFile{
			Name:     fn,
			Body:     template.HTML(buf.String()),
			Coverage: percentCovered(profile),
		})
	}

	var out *os.File
	if outfile == "" {
		var dir string
		dir, err = os.MkdirTemp("", "cover")
		if err != nil {

View on GitHub (pinned to b6b368adc5)

Solutions

1. Regenerate the profile in the current source tree before producing the HTML report
2. Run `go tool cover -html` from the same module root as the test
3. Check read permissions on the source tree

Example fix

# before
go tool cover -html=stale.out
# after
go test -coverprofile=c.out ./...
go tool cover -html=c.out -o coverage.html

# Confirm every profile file is readable before -html
for f in $(awk '{print $1}' c.out | cut -d: -f1); do
  [ -r "$f" ] || echo "missing/unreadable: $f"
done

When it happens

Trigger: `go tool cover -html=profile.out` where a referenced source file no longer exists at the resolved location (findFile returned a path but ReadFile failed).

Common situations: Source files deleted/moved after the profile was generated. Running -html in a different checkout. Permission-denied on source files. Generated files (`.cover.go`) cleaned up. Stale profile.

Related errors

• error reading -outfilelist file %q: %v
• error reading pkgconfig file %q: %v
• did not find package for %s in go list output
• too many options
• -var: %q is not a valid identifier

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/087c339faedd08a6. Report an issue: GitHub.