Add WARN_UNUSED_RESULT to more static methods in (Byte|Wide)String.

Also fixes some usages that were not working as intended after the
conversion to static.

Change-Id: I18c18369754f6ca165f98999b5b80eecf6c76973
Reviewed-on: https://pdfium-review.googlesource.com/20590
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>

3 files changed, 12 insertions, 9 deletions

diff --git a/core/fxcrt/bytestring.h b/core/fxcrt/bytestring.h
index 6b167802d5..916820656d 100644
--- a/core/fxcrt/bytestring.h
+++ b/core/fxcrt/bytestring.h
@@ -64,7 +64,7 @@ class ByteString {
 
   void clear() { m_pData.Reset(); }
 
-  static ByteString FromUnicode(const WideString& str);
+  static ByteString FromUnicode(const WideString& str) WARN_UNUSED_RESULT;
 
   // Explicit conversion to C-style string.
   // Note: Any subsequent modification of |this| will invalidate the result.
diff --git a/core/fxcrt/widestring.h b/core/fxcrt/widestring.h
index 14621ec1a1..728ab35090 100644
--- a/core/fxcrt/widestring.h
+++ b/core/fxcrt/widestring.h
@@ -33,8 +33,9 @@ class WideString {
   using const_iterator = const CharType*;
   using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 
-  static WideString Format(const wchar_t* lpszFormat, ...);
-  static WideString FormatV(const wchar_t* lpszFormat, va_list argList);
+  static WideString Format(const wchar_t* lpszFormat, ...) WARN_UNUSED_RESULT;
+  static WideString FormatV(const wchar_t* lpszFormat,
+                            va_list argList) WARN_UNUSED_RESULT;
 
   WideString();
   WideString(const WideString& other);
@@ -58,13 +59,15 @@ class WideString {
 
   ~WideString();
 
-  static WideString FromLocal(const ByteStringView& str);
-  static WideString FromCodePage(const ByteStringView& str, uint16_t codepage);
+  static WideString FromLocal(const ByteStringView& str) WARN_UNUSED_RESULT;
+  static WideString FromCodePage(const ByteStringView& str,
+                                 uint16_t codepage) WARN_UNUSED_RESULT;
 
-  static WideString FromUTF8(const ByteStringView& str);
-  static WideString FromUTF16LE(const unsigned short* str, size_t len);
+  static WideString FromUTF8(const ByteStringView& str) WARN_UNUSED_RESULT;
+  static WideString FromUTF16LE(const unsigned short* str,
+                                size_t len) WARN_UNUSED_RESULT;
 
-  static size_t WStringLength(const unsigned short* str);
+  static size_t WStringLength(const unsigned short* str) WARN_UNUSED_RESULT;
 
   // Explicit conversion to C-style wide string.
   // Note: Any subsequent modification of |this| will invalidate the result.
diff --git a/core/fxcrt/widestring_unittest.cpp b/core/fxcrt/widestring_unittest.cpp
index 39337aa7a7..1673c8f069 100644
--- a/core/fxcrt/widestring_unittest.cpp
+++ b/core/fxcrt/widestring_unittest.cpp
@@ -1330,7 +1330,7 @@ TEST(WideString, FormatPrecision) {
 }
 
 TEST(WideString, FormatOutOfRangeChar) {
-  WideString::Format(L"unsupported char '%c'", 0x00FF00FF);
+  EXPECT_NE(L"", WideString::Format(L"unsupported char '%c'", 0x00FF00FF));
 }
 
 TEST(WideString, Empty) {