format octal integer literals consistently about gofumpt

[mvdan]

I agree. Where possible, we should enforce the new syntax.

There is only one wrinkle - this syntax requires Go 1.13 or later as a toolchain and on go.mod, so forcing this on a module that has go 1.12 or earlier on their go.mod would break the module.

I think a direction for gofumpt could be to start being module-aware, even if it's only optionally. Then we can make better decisions like "are these imports from the main module", or "can we use this language feature", among many other questions that gofmt can't have an answer to.

[mvdan]

Another option is that, since we only support the latest two major Go versions, we can wait a few more months and then just start enforcing this all the time.

If someone is stuck on Go 1.12 or earlier, they can simply pin an older version of gofumpt.

[twpayne]

The last two major Go versions are Go 1.13 and Go 1.14, and the 0o prefix was introduced in Go 1.13 so can we implement this now or am I missing something?

[mvdan]

Yes, we could in theory do it now. In practice, I'd prefer to wait a bit longer to not annoy too many people. 1.12 is still maintained by the Go project until 1.15 is out, and some users are slow to upgrade.

[twpayne]

OK.

Would you consider either of the following?

• Making this behavior configurable with a command line flag?
• An abomination of a PR that uses the go1.15 build flag to automatically enable and disable this behavior, allowing the user to enable it manually by enabling the go1.15 build tag when compiling with Go 1.14. I cringe horribly just thinking about it, but it does work.

[mvdan]

I don't think this feature warrants a command line flag. Like I mentioned before, the correct way to do the right thing would be to look at go.mod, but that would first require refactoring the tool a bit to be module-aware.

However, I'm OK with adding a "go version" argument to the internal API. That way, once the external tool starts grabbing the version from go.mod, it can pass the version along. The same could apply to other tools like gopls, if they integrate the gofumpt internals in the future.

For now, we can just make our gofumpt tool always pass go 1.15. The format should be a string, matching what go list -m -json shows for a module:

$ go list -m -json
{
	"Path": "mvdan.cc/sh/v3",
	"Main": true,
	"Dir": "/home/mvdan/src/sh",
	"GoMod": "/home/mvdan/src/sh/go.mod",
	"GoVersion": "1.14"
}

Semver comparisons would be a bit awkward, but you can reuse https://godoc.org/golang.org/x/mod/semver.