Avoid copying in TrimRight() and TrimLeft() if possible.

core/fxcrt/fx_basic_wstring_unittest.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/fxcrt/include/fx_basic.h"
 #include "testing/fx_string_testhelpers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 TEST(fxcrt, WideStringOperatorSubscript) {
   // CFX_WideString includes the NUL terminator for non-empty strings.
@@ skipping 454 matching lines @@
 
   CFX_WideString empty;
   empty.TrimRight(L"ERP");
   EXPECT_EQ(L"", empty);
   empty.TrimRight(L'E');
   EXPECT_EQ(L"", empty);
   empty.TrimRight();
   EXPECT_EQ(L"", empty);
 }
 
+TEST(fxcrt, WideStringTrimRightCopies) {
+  {
+    // With a single reference, no copy takes place.
+    CFX_WideString fred(L"  FRED  ");
+    const FX_WCHAR* old_buffer = fred.c_str();
+    fred.TrimRight();
+    EXPECT_EQ(L"  FRED", fred);
+    EXPECT_EQ(old_buffer, fred.c_str());
+  }
+  {
+    // With multiple references, we must copy.
+    CFX_WideString fred(L"  FRED  ");
+    CFX_WideString other_fred = fred;
+    const FX_WCHAR* old_buffer = fred.c_str();
+    fred.TrimRight();
+    EXPECT_EQ(L"  FRED", fred);
+    EXPECT_EQ(L"  FRED  ", other_fred);
+    EXPECT_NE(old_buffer, fred.c_str());
+  }
+  {
+    // With multiple references, but no modifications, no copy.
+    CFX_WideString fred(L"FRED");
+    CFX_WideString other_fred = fred;
+    const FX_WCHAR* old_buffer = fred.c_str();
+    fred.TrimRight();
+    EXPECT_EQ(L"FRED", fred);
+    EXPECT_EQ(L"FRED", other_fred);
+    EXPECT_EQ(old_buffer, fred.c_str());
+  }
+}
+
 TEST(fxcrt, WideStringTrimLeft) {
   CFX_WideString fred(L"  FRED  ");
   fred.TrimLeft();
   EXPECT_EQ(L"FRED  ", fred);
   fred.TrimLeft(L'E');
   EXPECT_EQ(L"FRED  ", fred);
   fred.TrimLeft(L'F');
   EXPECT_EQ(L"RED  ", fred);
   fred.TrimLeft(L"ERP");
   EXPECT_EQ(L"D  ", fred);
 
   CFX_WideString blank(L"   ");
   blank.TrimLeft(L"ERP");
   EXPECT_EQ(L"   ", blank);
   blank.TrimLeft(L'E');
   EXPECT_EQ(L"   ", blank);
   blank.TrimLeft();
   EXPECT_EQ(L"", blank);
 
   CFX_WideString empty;
   empty.TrimLeft(L"ERP");
   EXPECT_EQ(L"", empty);
   empty.TrimLeft(L'E');
   EXPECT_EQ(L"", empty);
   empty.TrimLeft();
   EXPECT_EQ(L"", empty);
 }
 
+TEST(fxcrt, WideStringTrimLeftCopies) {
+  {
+    // With a single reference, no copy takes place.
+    CFX_WideString fred(L"  FRED  ");
+    const FX_WCHAR* old_buffer = fred.c_str();
+    fred.TrimLeft();
+    EXPECT_EQ(L"FRED  ", fred);
+    EXPECT_EQ(old_buffer, fred.c_str());
+  }
+  {
+    // With multiple references, we must copy.
+    CFX_WideString fred(L"  FRED  ");
+    CFX_WideString other_fred = fred;
+    const FX_WCHAR* old_buffer = fred.c_str();
+    fred.TrimLeft();
+    EXPECT_EQ(L"FRED  ", fred);
+    EXPECT_EQ(L"  FRED  ", other_fred);
+    EXPECT_NE(old_buffer, fred.c_str());
+  }
+  {
+    // With multiple references, but no modifications, no copy.
+    CFX_WideString fred(L"FRED");
+    CFX_WideString other_fred = fred;
+    const FX_WCHAR* old_buffer = fred.c_str();
+    fred.TrimLeft();
+    EXPECT_EQ(L"FRED", fred);
+    EXPECT_EQ(L"FRED", other_fred);
+    EXPECT_EQ(old_buffer, fred.c_str());
+  }
+}
+
 TEST(fxcrt, WideStringUTF16LE_Encode) {
   struct UTF16LEEncodeCase {
     CFX_WideString ws;
     CFX_ByteString bs;
   } utf16le_encode_cases[] = {
       {L"", CFX_ByteString("\0\0", 2)},
       {L"abc", CFX_ByteString("a\0b\0c\0\0\0", 8)},
       {L"abcdef", CFX_ByteString("a\0b\0c\0d\0e\0f\0\0\0", 14)},
       {L"abc\0def", CFX_ByteString("a\0b\0c\0\0\0", 8)},
       {L"\xaabb\xccdd", CFX_ByteString("\xbb\xaa\xdd\xcc\0\0", 6)},
@@ skipping 226 matching lines @@
   }
 }
 
 TEST(fxcrt, EmptyWideString) {
   CFX_WideString empty_str;
   EXPECT_TRUE(empty_str.IsEmpty());
   EXPECT_EQ(0, empty_str.GetLength());
   const FX_WCHAR* cstr = empty_str.c_str();
   EXPECT_EQ(0, FXSYS_wcslen(cstr));
 }