cmd/go: match go-import package prefixes by slash

The existing implementation for path collision resolution would
incorrectly determine that:

    example.org/aa

collides with:

    example.org/a

This change splits by slash rather than comparing on a byte-by-byte
basis.

Fixes: #15947

Change-Id: I18b3aaafbc787c81253203cf1328bb3c4420a0c4
Reviewed-on: https://go-review.googlesource.com/23732
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/cmd/go/vcs.go

@@ -779,15 +779,31 @@ type metaImport struct {
// errNoMatch is returned from matchGoImport when there's no applicable match.
var errNoMatch = errors.New("no import match")

func splitPathHasPrefix(path, prefix []string) bool {
	if len(path) < len(prefix) {
		return false
	}
	for i, p := range prefix {
		if path[i] != p {
			return false
		}
	}
	return true
}

// matchGoImport returns the metaImport from imports matching importPath.
// An error is returned if there are multiple matches.
// errNoMatch is returned if none match.
func matchGoImport(imports []metaImport, importPath string) (_ metaImport, err error) {
	match := -1
	imp := strings.Split(importPath, "/")
	for i, im := range imports {
		if !strings.HasPrefix(importPath, im.Prefix) {
		pre := strings.Split(im.Prefix, "/")

		if !splitPathHasPrefix(imp, pre) {
			continue
		}

		if match != -1 {
			err = fmt.Errorf("multiple meta tags match import path %q", importPath)
			return

src/cmd/go/vcs_test.go

@@ -5,6 +5,7 @@
package main

import (
	"errors"
	"internal/testenv"
	"io/ioutil"
	"os"
@@ -227,3 +228,96 @@ func TestIsSecure(t *testing.T) {
		}
	}
}

func TestMatchGoImport(t *testing.T) {
	tests := []struct {
		imports []metaImport
		path    string
		mi      metaImport
		err     error
	}{
		{
			imports: []metaImport{
				{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
			},
			path: "example.com/user/foo",
			mi:   metaImport{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
		},
		{
			imports: []metaImport{
				{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
			},
			path: "example.com/user/foo/",
			mi:   metaImport{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
		},
		{
			imports: []metaImport{
				{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
				{Prefix: "example.com/user/fooa", VCS: "git", RepoRoot: "https://example.com/repo/target"},
			},
			path: "example.com/user/foo",
			mi:   metaImport{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
		},
		{
			imports: []metaImport{
				{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
				{Prefix: "example.com/user/fooa", VCS: "git", RepoRoot: "https://example.com/repo/target"},
			},
			path: "example.com/user/fooa",
			mi:   metaImport{Prefix: "example.com/user/fooa", VCS: "git", RepoRoot: "https://example.com/repo/target"},
		},
		{
			imports: []metaImport{
				{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
				{Prefix: "example.com/user/foo/bar", VCS: "git", RepoRoot: "https://example.com/repo/target"},
			},
			path: "example.com/user/foo/bar",
			err:  errors.New("should not be allowed to create nested repo"),
		},
		{
			imports: []metaImport{
				{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
				{Prefix: "example.com/user/foo/bar", VCS: "git", RepoRoot: "https://example.com/repo/target"},
			},
			path: "example.com/user/foo/bar/baz",
			err:  errors.New("should not be allowed to create nested repo"),
		},
		{
			imports: []metaImport{
				{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
				{Prefix: "example.com/user/foo/bar", VCS: "git", RepoRoot: "https://example.com/repo/target"},
			},
			path: "example.com/user/foo/bar/baz/qux",
			err:  errors.New("should not be allowed to create nested repo"),
		},
		{
			imports: []metaImport{
				{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
				{Prefix: "example.com/user/foo/bar", VCS: "git", RepoRoot: "https://example.com/repo/target"},
			},
			path: "example.com/user/foo/bar/baz/",
			err:  errors.New("should not be allowed to create nested repo"),
		},
		{
			imports: []metaImport{
				{Prefix: "example.com/user/foo", VCS: "git", RepoRoot: "https://example.com/repo/target"},
				{Prefix: "example.com/user/foo/bar", VCS: "git", RepoRoot: "https://example.com/repo/target"},
			},
			path: "example.com",
			err:  errors.New("pathologically short path"),
		},
	}

	for _, test := range tests {
		mi, err := matchGoImport(test.imports, test.path)
		if mi != test.mi {
			t.Errorf("unexpected metaImport; got %v, want %v", mi, test.mi)
		}

		got := err
		want := test.err
		if (got == nil) != (want == nil) {
			t.Errorf("unexpected error; got %v, want %v", got, want)
		}
	}
}