golang/go · error

error reading -outfilelist file

Error message

error reading -outfilelist file %q: %v

What it means

Thrown by 'go tool cover' readOutFileList when os.ReadFile fails on the path given to -outfilelist. The wrapped error includes the path and the underlying OS error (e.g. file not found, permission denied). The file is expected to contain one output path per line.

Solutions

1. Verify the -outfilelist path exists and is readable before invoking cover
2. Use an absolute path to avoid working-directory issues
3. Check file permissions if running under a restricted user/CI

Example fix

# before (path wrong / missing)
go tool cover -mode=set -pkgcfg=p.cfg -outfilelist=out.txt input.go
# after
go tool cover -mode=set -pkgcfg=p.cfg -outfilelist=/abs/path/out.txt input.go

# Validate outfilelist is readable before calling cover
if [ ! -r "$OUTFILELIST" ]; then echo "cannot read -outfilelist $OUTFILELIST" >&2; exit 2; fi

// Go caller of readOutFileList:
data, err := os.ReadFile(path)
if err != nil { return nil, fmt.Errorf("unreadable outfilelist %q: %w", path, err) }

When it happens

Trigger: `go tool cover -mode=set -pkgcfg=p.cfg -outfilelist=/nonexistent/files.txt input.go`, or pointing -outfilelist at an unreadable/permission-denied file.

Common situations: Wrong working directory producing a relative path that doesn't resolve. Stale path from a previous build. Permissions issue in CI sandboxes. Typo in the path.

Related errors

• error reading pkgconfig file
• can't read
• number of output files
• '-outfilelist' flag applicable only when -pkgcfg used
• please use '-outfilelist' flag instead of '-o'

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/efb628f9134403ea. Report an issue: GitHub.

Appendix: source

Thrown at src/cmd/cover/cover.go:211

			} else {
				if *outfilelist != "" {
					return fmt.Errorf("'-outfilelist' flag applicable only when -pkgcfg used")
				}
			}
			if flag.NArg() == 1 {
				return nil
			}
		}
	} else if flag.NArg() == 0 {
		return nil
	}
	return fmt.Errorf("too many arguments")
}

func readOutFileList(path string) ([]string, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("error reading -outfilelist file %q: %v", path, err)
	}
	return strings.Split(strings.TrimSpace(string(data)), "\n"), nil
}

func readPackageConfig(path string) error {
	data, err := os.ReadFile(path)
	if err != nil {
		return fmt.Errorf("error reading pkgconfig file %q: %v", path, err)
	}
	if err := json.Unmarshal(data, &pkgconfig); err != nil {
		return fmt.Errorf("error reading pkgconfig file %q: %v", path, err)
	}
	switch pkgconfig.Granularity {
	case "perblock":
		cgran = coverage.CtrGranularityPerBlock
	case "perfunc":
		cgran = coverage.CtrGranularityPerFunc
	default:

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