Fix glob cache conflict when excludes=nil and excludes=[]string{}

Performing the same glob twice, once with excludes=nil and once
with excludes=[]string{} would hit the same entry in the glob
cache (since the glob filename would be the same), but fail
the verifyGlob check because DeepEqual considers []string(nil)
and []string{} to be different.  Use a manual array check
instead.

Test: glob_test.go
Change-Id: If0d4fe80163a871077b7276e1b4a3e888a4a4898

Blueprints

@@ -23,6 +23,7 @@ bootstrap_go_package {
     ],
     testSrcs: [
         "context_test.go",
+        "glob_test.go",
         "ninja_strings_test.go",
         "ninja_writer_test.go",
         "splice_modules_test.go",

glob.go

@@ -17,7 +17,6 @@ package blueprint
 import (
 	"crypto/md5"
 	"fmt"
-	"reflect"
 	"sort"
 	"strings"
 )
@@ -34,9 +33,15 @@ func verifyGlob(fileName, pattern string, excludes []string, g GlobPath) {
 	if pattern != g.Pattern {
 		panic(fmt.Errorf("Mismatched patterns %q and %q for glob file %q", pattern, g.Pattern, fileName))
 	}
-	if !reflect.DeepEqual(g.Excludes, excludes) {
+	if len(excludes) != len(g.Excludes) {
 		panic(fmt.Errorf("Mismatched excludes %v and %v for glob file %q", excludes, g.Excludes, fileName))
 	}
+
+	for i := range excludes {
+		if g.Excludes[i] != excludes[i] {
+			panic(fmt.Errorf("Mismatched excludes %v and %v for glob file %q", excludes, g.Excludes, fileName))
+		}
+	}
 }
 
 func (c *Context) glob(pattern string, excludes []string) ([]string, error) {

glob_test.go

@@ -0,0 +1,55 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package blueprint
+
+import "testing"
+
+func TestGlobCache(t *testing.T) {
+	ctx := NewContext()
+	ctx.MockFileSystem(map[string][]byte{
+		"Blueprints": nil,
+		"a/a":        nil,
+		"a/b":        nil,
+	})
+
+	// Test a simple glob with no excludes
+	matches, err := ctx.glob("a/*", nil)
+	if err != nil {
+		t.Error("unexpected error", err)
+	}
+	if len(matches) != 2 || matches[0] != "a/a" || matches[1] != "a/b" {
+		t.Error(`expected ["a/a", "a/b"], got`, matches)
+	}
+
+	// Test the same glob with an empty excludes array to make sure
+	// excludes=nil does not conflict with excludes=[]string{} in the
+	// cache.
+	matches, err = ctx.glob("a/*", []string{})
+	if err != nil {
+		t.Error("unexpected error", err)
+	}
+	if len(matches) != 2 || matches[0] != "a/a" || matches[1] != "a/b" {
+		t.Error(`expected ["a/a", "a/b"], got`, matches)
+	}
+
+	// Test the same glob with a different excludes array
+	matches, err = ctx.glob("a/*", []string{"a/b"})
+	if err != nil {
+		t.Error("unexpected error", err)
+	}
+	if len(matches) != 1 || matches[0] != "a/a" {
+		t.Error(`expected ["a/a"], got`, matches)
+	}
+}