go: flag: clean up error message

What version of Go are you using (`go version`)?

go version go1.9.7 linux/amd64 (but it affects basically all versions of go).

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (`go env`)?

GOHOSTARCH=“amd64” GOHOSTOS=“linux”

What did you do?

Provide a non-numerical input for an integer flag yields the following error:

invalid value "donut" for flag -cpu-quota: strconv.ParseInt: parsing "donut": invalid syntax

What did you expect to see?

--cpuquota is expecting an integer

Something more user-friendly. Currently, the error message must be interpreted by the user and should guide users a bit more in a direction to solve the issue. See https://github.com/projectatomic/buildah/issues/673 as an example.

What did you see instead?

invalid value "donut" for flag -cpu-quota: strconv.ParseInt: parsing "donut": invalid syntax

Proposal

I want to suggest two options:

Update the error messages (e.g., for integer flags https://golang.org/src/flag/flag.go?s=8120:8324#L912).
Expose public error types (e.g., ErrInvalidValue and ErrInvalidBoolen) that can be used by users of the flag package (e.g., urfave/cli).

About this issue

Original URL
State: closed
Created 6 years ago
Comments: 19 (15 by maintainers)

Most upvoted comments

If you want to look at the registered flags and make a new flag parser, do that. Don’t try to parse the parser errors - just do a fresh parse. See rsc.io/getopt for an example.

rsc on Oct 16, 2018