base,tests: Add a stringstream which tracks all log output.

Since gtest's SUCCEED() just throws away output sent to it, there needs
to be an alternative way to capture non-fatal warn, hack, or inform
messages. This change adds a stringstream called gtestLogOutput which
will accumulate all log messages so they can be inspected later. If you
want to see what output occurs as a result of a specific action, you can
flush out the stringstream with .str(""), perform that action, and then
check the stream's contents.

The stream also records the output of exiting logs like fatal and panic.
It's not 100% clear that these messages would be retrievable or useful,
but this at least maintains consistency between the two classes of
messages.

To avoid threading/locking issues, the stream is thread local. To
prevent tests from affecting each other and to make the output more
predictable for test assertions, it also automatically installs an event
hook which will be called each time a test starts which will clear out
the contents of the stream.

Change-Id: I9d6650feb77b676a5b2b1fc2542cdebf3c60ed34
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42181
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/base/gtest/logging.cc

@@ -25,6 +25,8 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include "base/gtest/logging.hh"
+
 #include <gtest/gtest.h>
 
 #include <array>
@@ -49,7 +51,12 @@ class GTestLogger : public Logger
     using Logger::Logger;
 
   protected:
-    void log(const Loc &loc, std::string s) override { SUCCEED() << s; }
+    void
+    log(const Loc &loc, std::string s) override
+    {
+        gtestLogOutput << s;
+        SUCCEED() << s;
+    }
 };
 
 class GTestExitLogger : public Logger
@@ -61,6 +68,7 @@ class GTestExitLogger : public Logger
     void
     log(const Loc &loc, std::string s) override
     {
+        gtestLogOutput << s;
         std::cerr << loc.file << ":" << loc.line << ": " << s;
     }
     // Throw an exception to escape down to the gtest framework.
@@ -75,6 +83,25 @@ GTestLogger hackLogger("hack: ");
 
 } // anonymous namespace
 
+thread_local GTestLogOutput gtestLogOutput;
+
+GTestLogOutput::EventHook::EventHook(GTestLogOutput &_stream) : stream(_stream)
+{
+    ::testing::UnitTest::GetInstance()->listeners().Append(this);
+}
+
+GTestLogOutput::EventHook::~EventHook()
+{
+    ::testing::UnitTest::GetInstance()->listeners().Release(this);
+}
+
+void
+GTestLogOutput::EventHook::OnTestStart(const ::testing::TestInfo &test_info)
+{
+    // Clear out the stream at the start of each test.
+    stream.str("");
+}
+
 Logger &Logger::getPanic() { return panicLogger; }
 Logger &Logger::getFatal() { return fatalLogger; }
 Logger &Logger::getWarn() { return warnLogger; }

src/base/gtest/logging.hh

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2021 Google Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <gtest/gtest.h>
+
+#include <sstream>
+
+class GTestLogOutput : public std::ostringstream
+{
+  private:
+    class EventHook : public ::testing::EmptyTestEventListener
+    {
+      private:
+        GTestLogOutput &stream;
+
+      public:
+        EventHook(GTestLogOutput &_stream);
+        ~EventHook();
+
+        void OnTestStart(const ::testing::TestInfo &test_info) override;
+    };
+
+    EventHook eventHook;
+
+  public:
+    template <typename ...Args>
+    GTestLogOutput(Args &&...args) :
+        std::ostringstream(std::forward<Args>(args)...), eventHook(*this)
+    {}
+};
+
+extern thread_local GTestLogOutput gtestLogOutput;