Add Log.h to replace all uses of iostream

On Android iostream doesn't appear in logcat, the system log that's
often used for printf debugging. Introduce Chromium/ANGLE like logging
that looks like the following:

  InfoLog() << stuff << stuff;

This makes sure the message is put in logcat on Android and removes
static initializers from <iostream>

BUG=dawn:286

Change-Id: Ie0d018f49bcac1a7b740739a6e59d45ae6728638
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/14102
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: David Turner <digit@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>

src/common/Assert.cpp

@@ -13,14 +13,13 @@
 // limitations under the License.
 
 #include "common/Assert.h"
-
-#include <iostream>
+#include "common/Log.h"
 
 void HandleAssertionFailure(const char* file,
                             const char* function,
                             int line,
                             const char* condition) {
-    std::cerr << "Assertion failure at " << file << ":" << line << " (" << function
-              << "): " << condition << std::endl;
+    ErrorLog() << "Assertion failure at " << file << ":" << line << " (" << function
+               << "): " << condition;
     DAWN_BREAKPOINT();
 }

src/common/BUILD.gn

@@ -90,6 +90,8 @@ if (is_win || is_linux || is_mac || is_fuchsia || is_android) {
       "DynamicLib.cpp",
       "DynamicLib.h",
       "HashUtils.h",
+      "Log.cpp",
+      "Log.h",
       "Math.cpp",
       "Math.h",
       "Platform.h",
@@ -116,5 +118,8 @@ if (is_win || is_linux || is_mac || is_fuchsia || is_android) {
         "../../third_party:vulkan_headers",
       ]
     }
+    if (is_android) {
+      libs = [ "log" ]
+    }
   }
 }

src/common/Log.cpp

@@ -0,0 +1,112 @@
+// Copyright 2019 The Dawn Authors
+//
+// 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.
+
+#include "common/Log.h"
+
+#include "common/Assert.h"
+#include "common/Platform.h"
+
+#include <cstdio>
+
+#if defined(DAWN_PLATFORM_ANDROID)
+#    include <android/log.h>
+#endif
+
+namespace {
+
+    const char* SeverityName(LogSeverity severity) {
+        switch (severity) {
+            case LogSeverity::Debug:
+                return "Debug";
+            case LogSeverity::Info:
+                return "Info";
+            case LogSeverity::Warning:
+                return "Warning";
+            case LogSeverity::Error:
+                return "Error";
+            default:
+                UNREACHABLE();
+                return "";
+        }
+    }
+
+#if defined(DAWN_PLATFORM_ANDROID)
+    android_LogPriority AndroidLogPriority(LogSeverity severity) {
+        switch (severity) {
+            case LogSeverity::Debug:
+                return ANDROID_LOG_INFO;
+            case LogSeverity::Info:
+                return ANDROID_LOG_INFO;
+            case LogSeverity::Warning:
+                return ANDROID_LOG_WARN;
+            case LogSeverity::Error:
+                return ANDROID_LOG_ERROR;
+            default:
+                UNREACHABLE();
+                return ANDROID_LOG_ERROR;
+        }
+    }
+#endif  // defined(DAWN_PLATFORM_ANDROID)
+
+}  // anonymous namespace
+
+LogMessage::LogMessage(LogSeverity severity) : mSeverity(severity) {
+}
+
+LogMessage::~LogMessage() {
+    std::string fullMessage = mStream.str();
+
+    // If this message has been moved, its stream is empty.
+    if (fullMessage.empty()) {
+        return;
+    }
+
+    const char* severityName = SeverityName(mSeverity);
+
+    FILE* outputStream = stdout;
+    if (mSeverity == LogSeverity::Warning || mSeverity == LogSeverity::Error) {
+        outputStream = stderr;
+    }
+
+#if defined(DAWN_PLATFORM_ANDROID)
+    android_LogPriority androidPriority = AndroidLogPriority(mSeverity);
+    __android_log_print(androidPriority, "Dawn", "%s: %s\n", severityName, fullMessage.c_str());
+#else   // defined(DAWN_PLATFORM_ANDROID)
+    // Note: we use fprintf because <iostream> includes static initializers.
+    fprintf(outputStream, "%s: %s\n", severityName, fullMessage.c_str());
+    fflush(outputStream);
+#endif  // defined(DAWN_PLATFORM_ANDROID)
+}
+
+LogMessage DebugLog() {
+    return {LogSeverity::Debug};
+}
+
+LogMessage InfoLog() {
+    return {LogSeverity::Info};
+}
+
+LogMessage WarningLog() {
+    return {LogSeverity::Warning};
+}
+
+LogMessage ErrorLog() {
+    return {LogSeverity::Error};
+}
+
+LogMessage DebugLog(const char* file, const char* function, int line) {
+    LogMessage message = DebugLog();
+    message << file << ":" << line << "(" << function << ")";
+    return message;
+}

src/common/Log.h

@@ -0,0 +1,90 @@
+// Copyright 2019 The Dawn Authors
+//
+// 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.
+
+#ifndef COMMON_LOG_H_
+#define COMMON_LOG_H_
+
+// Dawn targets shouldn't use iostream or printf directly for several reasons:
+//  - iostream adds static initializers which we want to avoid.
+//  - printf and iostream don't show up in logcat on Android so printf debugging doesn't work but
+//  log-message debugging does.
+//  - log severity helps provide intent compared to a printf.
+//
+// Logging should in general be avoided: errors should go through the regular WebGPU error reporting
+// mechanism and others form of logging should (TODO: eventually) go through the logging dependency
+// injection, so for example they show up in Chromium's about:gpu page. Nonetheless there are some
+// cases where logging is necessary and when this file was first introduced we needed to replace all
+// uses of iostream so we could see them in Android's logcat.
+//
+// Regular logging is done using the [Debug|Info|Warning|Error]Log() function this way:
+//
+//   InfoLog() << things << that << ostringstream << supports; // No need for a std::endl or "\n"
+//
+// It creates a LogMessage object that isn't stored anywhere and gets its destructor called
+// immediately which outputs the stored ostringstream in the right place.
+//
+// This file also contains DAWN_DEBUG for "printf debugging" which works on Android and
+// additionally outputs the file, line and function name. Use it this way:
+//
+//   // Pepper this throughout code to get a log of the execution
+//   DAWN_DEBUG();
+//
+//   // Get more information
+//   DAWN_DEBUG() << texture.GetFormat();
+
+#include <sstream>
+
+// Log levels mostly used to signal intent where the log message is produced and used to route the
+// message to the correct output.
+enum class LogSeverity {
+    Debug,
+    Info,
+    Warning,
+    Error,
+};
+
+// Essentially an ostringstream that will print itself in its destructor.
+class LogMessage {
+  public:
+    LogMessage(LogSeverity severity);
+    ~LogMessage();
+
+    LogMessage(LogMessage&& other) = default;
+    LogMessage& operator=(LogMessage&& other) = default;
+
+    template <typename T>
+    LogMessage& operator<<(T&& value) {
+        mStream << value;
+        return *this;
+    }
+
+  private:
+    LogMessage(const LogMessage& other) = delete;
+    LogMessage& operator=(const LogMessage& other) = delete;
+
+    LogSeverity mSeverity;
+    std::ostringstream mStream;
+};
+
+// Short-hands to create a LogMessage with the respective severity.
+LogMessage DebugLog();
+LogMessage InfoLog();
+LogMessage WarningLog();
+LogMessage ErrorLog();
+
+// DAWN_DEBUG is a helper macro that creates a DebugLog and outputs file/line/function information
+LogMessage DebugLog(const char* file, const char* function, int line);
+#define DAWN_DEBUG() DebugLog(__FILE__, __func__, __LINE__)
+
+#endif  // COMMON_LOG_H_