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

This is related to golang/go#15947.

This ports https://golang.org/cl/23732 (June 2016)
from cmd/go to this repository.

Change-Id: I9960556bd19775b433d4eecc0ecca3f09ce1368b
Reviewed-on: https://go-review.googlesource.com/119935
Reviewed-by: Ian Lance Taylor <iant@golang.org>

go/vcs/vcs.go

@@ -603,15 +603,28 @@ type metaImport struct {
 // errNoMatch is returned from matchGoImport when there's no applicable match.
 var errNoMatch = errors.New("no import match")
 
+// pathPrefix reports whether sub is a prefix of s,
+// only considering entire path components.
+func pathPrefix(s, sub string) bool {
+	// strings.HasPrefix is necessary but not sufficient.
+	if !strings.HasPrefix(s, sub) {
+		return false
+	}
+	// The remainder after the prefix must either be empty or start with a slash.
+	rem := s[len(sub):]
+	return rem == "" || rem[0] == '/'
+}
+
 // 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
 	for i, im := range imports {
-		if !strings.HasPrefix(importPath, im.Prefix) {
+		if !pathPrefix(importPath, im.Prefix) {
 			continue
 		}
+
 		if match != -1 {
 			err = fmt.Errorf("multiple meta tags match import path %q", importPath)
 			return

go/vcs/vcs_test.go

@@ -5,6 +5,7 @@
 package vcs
 
 import (
+	"errors"
 	"io/ioutil"
 	"os"
 	"path"
@@ -184,3 +185,96 @@ func TestValidateRepoRoot(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)
+		}
+	}
+}