Mojo: Add logging macros (and supporting code) for use in mojo/public/cpp.

mojo/public/cpp/environment/logging.h

Index: mojo/public/cpp/environment/logging.h
diff --git a/mojo/public/cpp/environment/logging.h b/mojo/public/cpp/environment/logging.h
new file mode 100644
index 0000000000000000000000000000000000000000..a3e2cef42938c759c898e576b8dc54c1e980cbcf
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+++ b/mojo/public/cpp/environment/logging.h
@@ -0,0 +1,87 @@
+// Copyright 2014 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.
+
+// Logging macros, similar to Chromium's base/logging.h, except with |MOJO_|
+// prefixes and missing some features (notably |CHECK_EQ()|, etc.).
+
+// TODO(vtl): It's weird that this is in the environment directory, since its
+// implementation (in environment/lib) is meant to be used by any implementation
+// of the environment.
+
+#ifndef MOJO_PUBLIC_CPP_ENVIRONMENT_LOGGING_H_
+#define MOJO_PUBLIC_CPP_ENVIRONMENT_LOGGING_H_
+
+#include <sstream>
+
+#include "mojo/public/c/environment/logger.h"
+#include "mojo/public/cpp/environment/environment.h"
+#include "mojo/public/cpp/system/macros.h"
+
+#define MOJO_LOG_STREAM(level) \
+    ::mojo::internal::LogMessage(__FILE__, __LINE__, \
+                                 MOJO_LOG_LEVEL_ ## level).stream()
+
+#define MOJO_LAZY_LOG_STREAM(level, condition) \
+    !(condition) ? \
+        (void) 0 : \
+        ::mojo::internal::VoidifyOstream() & MOJO_LOG_STREAM(level)
+
+#define MOJO_SHOULD_LOG(level) \
+    (MOJO_LOG_LEVEL_ ## level >= \
+     ::mojo::Environment::GetDefaultLogger()->GetMinimumLogLevel())
+
+#define MOJO_LOG(level) \
+    MOJO_LAZY_LOG_STREAM(level, MOJO_SHOULD_LOG(level))
+
+#define MOJO_LOG_IF(level, condition) \
+    MOJO_LAZY_LOG_STREAM(level, MOJO_SHOULD_LOG(level) && (condition))
+
+#define MOJO_CHECK(condition) \
+    MOJO_LAZY_LOG_STREAM(FATAL, !(condition)) \
+        << "Check failed: " #condition ". "
+
+// Note: For non-debug builds, |MOJO_DLOG_IF()| *eliminates* (i.e., doesn't
+// compile) the condition, whereas |MOJO_DCHECK()| "neuters" the condition
+// (i.e., compiles, but doesn't evaluate).
+#ifdef NDEBUG
+
+#define MOJO_DLOG(level) MOJO_LAZY_LOG_STREAM(level, false)
+#define MOJO_DLOG_IF(level, condition) MOJO_LAZY_LOG_STREAM(level, false)
+#define MOJO_DCHECK(condition) MOJO_LAZY_LOG_STREAM(FATAL, false && (condition))
+
+#else
+
+#define MOJO_DLOG(level) MOJO_LOG(level)
+#define MOJO_DLOG_IF(level, condition) MOJO_LOG_IF(level, condition)
+#define MOJO_DCHECK(condition) MOJO_CHECK(condition)
+
+#endif  // NDEBUG
+
+namespace mojo {
+namespace internal {
+
+class LogMessage {
+ public:
+  LogMessage(const char* file, int line, MojoLogLevel log_level);
+  ~LogMessage();
+
+  std::ostream& stream() { return stream_; }
+
+ private:
+  const MojoLogLevel log_level_;
+  std::ostringstream stream_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(LogMessage);
+};
+
+// Used to ignore a stream.
+struct VoidifyOstream {
+  // Use & since it has precedence lower than << but higher than ?:.
+  void operator&(std::ostream&) {}
+};
+
+}  // namespace internal
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_ENVIRONMENT_LOGGING_H_