Fix more disabled MSVC warnings, base/ edition.

base/logging.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_LOGGING_H_
 #define BASE_LOGGING_H_
 
 #include <cassert>
 #include <string>
 #include <cstring>
@@ skipping 600 matching lines @@
 #define COMPACT_GOOGLE_LOG_DCHECK COMPACT_GOOGLE_LOG_INFO
 const LogSeverity LOG_DCHECK = LOG_INFO;
 
 #endif  // DCHECK_IS_ON
 
 // DCHECK et al. make sure to reference |condition| regardless of
 // whether DCHECKs are enabled; this is so that we don't get unused
 // variable warnings if the only use of a variable is in a DCHECK.
 // This behavior is different from DLOG_IF et al.
 
-#define DCHECK(condition)                                         \
-  LAZY_STREAM(LOG_STREAM(DCHECK), DCHECK_IS_ON && !(condition))   \
+#define DCHECK(condition)                                               \
+  LAZY_STREAM(LOG_STREAM(DCHECK), DCHECK_IS_ON ? !(condition) : false)  \

[brettw, 2014/10/01 17:54:07]

I don't follow the reason for this change.

[Peter Kasting, 2014/10/01 19:30:21]

My explanatory comment from an earlier patchset (
https://codereview.chromium.org/596103002/diff/1/base/logging.h#newcode622 ):
"This form of the macro eliminates "unused variable" warnings compared to the
other form."

More specifically, since && short-circuits, MSVC doesn't consider the old form
to have "referenced" |condition| as desired when DCHECK_IS_ON is known at
compile time to be false.  Using ?: instead ensures the compiler considers
|condition| to have been referenced in all cases, while preserving the property
that it isn't actually evaluated when DCHECKs are off.

(I ran into these warnings and found a number of helpful pages online noting
that the ?: form was a solution that worked across compilers.)

   << "Check failed: " #condition ". "
 
-#define DPCHECK(condition)                                        \
-  LAZY_STREAM(PLOG_STREAM(DCHECK), DCHECK_IS_ON && !(condition))  \
+#define DPCHECK(condition)                                              \
+  LAZY_STREAM(PLOG_STREAM(DCHECK), DCHECK_IS_ON ? !(condition) : false) \
   << "Check failed: " #condition ". "
 
 // Helper macro for binary operators.
 // Don't use this macro directly in your code, use DCHECK_EQ et al below.
 #define DCHECK_OP(name, op, val1, val2)                         \
   if (DCHECK_IS_ON)                                             \
     if (std::string* _result =                                  \
         logging::Check##name##Impl((val1), (val2),              \
                                    #val1 " " #op " " #val2))    \
       logging::LogMessage(                                      \
@@ skipping 253 matching lines @@
 #elif NOTIMPLEMENTED_POLICY == 5
 #define NOTIMPLEMENTED() do {\
   static bool logged_once = false;\
   LOG_IF(ERROR, !logged_once) << NOTIMPLEMENTED_MSG;\
   logged_once = true;\
 } while(0);\
 EAT_STREAM_PARAMETERS
 #endif
 
 #endif  // BASE_LOGGING_H_