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/23732Reviewed-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)
+		}
+	}
+}