go/build: fix field mismatch in unkeyed struct literal

Fixes #9409

Change-Id: I2404cd8bf3ebb07f4b6a2b3e1d58ab69b9f1e8d8
Reviewed-on: https://go-review.googlesource.com/2040
Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/go/build/build.go

@@ -688,7 +688,11 @@ Found:
 			p.Name = pkg
 			firstFile = name
 		} else if pkg != p.Name {
-			return p, &MultiplePackageError{p.Dir, []string{firstFile, name}, []string{p.Name, pkg}}
+			return p, &MultiplePackageError{
+				Dir:      p.Dir,
+				Packages: []string{p.Name, pkg},
+				Files:    []string{firstFile, name},
+			}
 		}
 		if pf.Doc != nil && p.Doc == "" {
 			p.Doc = doc.Synopsis(pf.Doc.Text())

src/go/build/build_test.go

@@ -94,9 +94,18 @@ func TestEmptyFolderImport(t *testing.T) {
 
 func TestMultiplePackageImport(t *testing.T) {
 	_, err := Import(".", "testdata/multi", 0)
-	if _, ok := err.(*MultiplePackageError); !ok {
+	mpe, ok := err.(*MultiplePackageError)
+	if !ok {
 		t.Fatal(`Import("testdata/multi") did not return MultiplePackageError.`)
 	}
+	want := &MultiplePackageError{
+		Dir:      "testdata/multi",
+		Packages: []string{"main", "test_package"},
+		Files:    []string{"file.go", "file_appengine.go"},
+	}
+	if !reflect.DeepEqual(mpe, want) {
+		t.Errorf("got %#v; want %#v", mpe, want)
+	}
 }
 
 func TestLocalDirectory(t *testing.T) {