x/tools/cmd/goimports: put std, cmd packages in separate blocks

[jayconrod]

This came up in CL 228378 and many others. If we delete all the imports from src/cmd/go/internal/modload/modfile.go then run goimports, we should see cmd imports in a separate group from std imports:

import (
	"fmt"
	"io/ioutil"
	"path/filepath"

	"cmd/go/internal/base"
	"cmd/go/internal/cfg"
	"cmd/go/internal/modfetch"

	"golang.org/x/mod/modfile"
	"golang.org/x/mod/module"
	"golang.org/x/mod/semver"
)

Instead, all the std and cmd imports are grouped together.

import (
	"cmd/go/internal/base"
	"cmd/go/internal/cfg"
	"cmd/go/internal/modfetch"
	"fmt"
	"io/ioutil"
	"path/filepath"

	"golang.org/x/mod/modfile"
	"golang.org/x/mod/module"
	"golang.org/x/mod/semver"
)

goimports does the right thing if at least one cmd import is already in a separate group. It combines the groups when adding the first std or cmd import though.

[heschi]

To be clear, do you really want it in three sections, or do you just want cmd/ grouped with golang.org/x? Because the latter seems like a bug that should be fixed. The former would be more of a job for -local.

[bcmills]

The existing files in cmd/go mostly have it in three sections, so we would like to retain that.

But it looks like the existing files in cmd/compile make no such distinction. Perhaps we should reformat cmd to eliminate it too, and collapse down to only two sections.

[heschi]

Not sure what you'd like me to do here. I can change it so that cmd/ is grouped with golang.org, but -local is the only way to get three groups, and in general goimports will never merge groups, so if you want to collapse down to two you're going to have to give it some help.

[jayconrod]

After some discussion, we're leaning toward just combining std and cmd sections.

I was not at all aware of the -local flag, so it looks like that's there if we decide otherwise.

I'll close this. Looks like there's nothing to do on the goimports side.