golang/go · error

too many arguments

Error message

too many arguments

What it means

Thrown by 'go tool cover' parseFlags as a catch-all when, in source-instrumentation mode (-mode set), more than one input file is given WITHOUT -pkgcfg. Without -pkgcfg the tool only supports a single source file; multiple files require the -pkgcfg package workflow.

Source

Thrown at src/cmd/cover/cover.go:205

					return fmt.Errorf("number of output files (%d) not equal to number of input files (%d)", numOutputs, numInputs)
				}
				if err := readPackageConfig(*pkgcfg); err != nil {
					return err
				}
				return nil
			} 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)
	}

View on GitHub (pinned to b6b368adc5)

Solutions

1. Pass exactly one .go file when not using -pkgcfg
2. For multi-file packages, use the -pkgcfg + -outfilelist workflow (normally driven by `go build -cover`)

Example fix

# before
go tool cover -mode=set a.go b.go
# after (single file)
go tool cover -mode=set a.go
# or use the package workflow via the go command:
go build -cover ./...

# Without -pkgcfg, allow exactly one input
if [ -z "$PKGCFG" ] && [ "$#" -ne 1 ]; then
  echo "single-file mode needs exactly one input; use -pkgcfg for packages" >&2; exit 2
fi

When it happens

Trigger: `go tool cover -mode=set a.go b.go` (two files, no -pkgcfg).

Common situations: Trying to instrument a whole package directly with `go tool cover` instead of through the go command. Passing a glob that expands to multiple files.

Related errors

• too many options
• -var: %q is not a valid identifier
• unknown -mode %v
• missing source file(s)
• please use '-outfilelist' flag instead of '-o'

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/c10238bf84f67514. Report an issue: GitHub.