cmd/go: go get with ... fails in module mode

[rsc]

This used to work and should ideally keep working.

$ go get -u github.com/google/codesearch/cmd/...
go: finding github.com/google/codesearch/cmd/... latest
go: finding github.com/google/codesearch/cmd latest
go: finding github.com/google/codesearch latest
go: downloading github.com/google/codesearch v0.0.0-20150617151851-a45d81b686e8
go: extracting github.com/google/codesearch v0.0.0-20150617151851-a45d81b686e8
go get github.com/google/codesearch/cmd/...: no matching versions for query "latest"
$ go list github.com/google/codesearch/...
go: warning: "github.com/google/codesearch/..." matched no packages

[thepudds]

There might be some overlap with #27215 (including #27215 (comment), which describes how the documentation uses go get golang.org/x/perf/cmd/..., but that example fails, unless you have first done something like go get golang.org/x/perf/cmd/benchstat).

[hxzhao527]

I think this caued by this

go/src/cmd/go/internal/modload/import.go

Lines 254 to 270 in 73fb3c3

	haveGoFiles = haveGoFilesCache.Do(dir, func() interface{} {
	f, err := os.Open(dir)
	if err != nil {
	return false
	}
	defer f.Close()
	names, _ := f.Readdirnames(-1)
	for _, name := range names {
	if strings.HasSuffix(name, ".go") {
	info, err := os.Stat(filepath.Join(dir, name))
	if err == nil && info.Mode().IsRegular() {
	return true
	}
	}
	}
	return false
	}).(bool)

when go get -u github.com/google/codesearch/cmd/..., dir is $GOPATH/pkg/mod/github.com/google/codesearch@v1.1.0/cmd/.... So os.Open will return error. And then no go source be throwed and get failed with not found.

I just motify this func to this:

haveGoFiles = haveGoFilesCache.Do(dir, func() interface{} {
		if strings.HasSuffix(dir, "/..."){
			dir = strings.TrimSuffix(dir, "/...")
			tmp, err := filepath.Glob(dir+"/**/*.go")
			if err != nil{
				return false
			}
			return len(tmp) > 0
		}
		f, err := os.Open(dir)
                ...

I did little test, to get

golang.org/x/tools/...
github.com/google/codesearch/cmd/...

And it works.

[gopherbot]

Change https://golang.org/cl/156757 mentions this issue: cmd/go: fix go get with ... fails in module mode

[mvdan]

@bcmills any chance this could be fixed in 1.12, or backported into a 1.12.x release at a later time?

It's great that with https://go-review.googlesource.com/c/go/+/148517, one can tell a program's users to install a specific version easily via GO111MODULE=on go get foo.com/bar@v1.2.3. However, it's a shame that GO111MODULE=on go get foo.com/bar/cmd/...@v1.2.3 doesn't work.

I realise the plan is to fix it in 1.13, but that would mean easy install instructions would be delayed by six months, as one can't expect users to run on betas or master.

[bcmills]

@mvdan, it's not obvious to me whether the fix will be small or simple enough to backport.

There have been two independent attempts so far, and both have some issues in the details of the semantics and implementation. (The interaction between wildcard-expansion and module resolution is, unfortunately, quite subtle.)

[gopherbot]

Change https://golang.org/cl/171138 mentions this issue: cmd/go: handle wildcards for unknown modules in "go get"