diff --git a/lldb/unittests/TestingSupport/CMakeLists.txt b/lldb/unittests/TestingSupport/CMakeLists.txt
--- a/lldb/unittests/TestingSupport/CMakeLists.txt
+++ b/lldb/unittests/TestingSupport/CMakeLists.txt
@@ -2,6 +2,7 @@
add_lldb_library(lldbUtilityHelpers
MockTildeExpressionResolver.cpp
TestUtilities.cpp
+ TestStderrLogger.cpp
LINK_LIBS
lldbUtility
@@ -14,3 +15,4 @@
add_subdirectory(Host)
add_subdirectory(Symbol)
+add_subdirectory(tests)
diff --git a/lldb/unittests/TestingSupport/TestStderrLogger.h b/lldb/unittests/TestingSupport/TestStderrLogger.h
new file mode 100644
--- /dev/null
+++ b/lldb/unittests/TestingSupport/TestStderrLogger.h
@@ -0,0 +1,89 @@
+//===- TestStderrLogger.h ---------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_UNITTESTS_TESTINGSUPPORT_TESTUTILITIES_H
+#define LLDB_UNITTESTS_TESTINGSUPPORT_TESTUTILITIES_H
+
+#include "lldb/Utility/LLDBLog.h"
+#include "llvm/Support/Threading.h"
+
+namespace lldb_private {
+
+// Map categories to their name. This is not exposed at the moment so we hard
+// code it this way.
+template <typename Cat> llvm::StringRef ChannelName() = delete;
+template <> llvm::StringRef ChannelName<LLDBLog>();
+
+/// Scoped logger to dump everything logged through LLDB's logging macros, such
+/// as LLDB_LOGF, to stderr.
+///
+/// This is meant as a local debugging tool to see what is logged. You almost
+/// certainly want to remove use of this class before submitting your change.
+///
+/// Usage:
+///
+/// TEST(Foo, ThingWorks) {
+/// auto logger = ScopedLogger("lldb", {"all"});
+/// ...
+/// <calls to LLDB_LOGF(...) will go to stderr>
+/// ...
+/// }
+/// TEST(Foo, OtherThingWorks) {
+/// ...
+/// <calls to LLDB_LOGF(...) will not be logged anywhere>
+/// ...
+/// }
+///
+/// This has some limitations because logging is not uniform, so some things
+/// don't work well or are hard coded in an unfortunate way.
+/// - There isn't a mapping from the channel enum to the string used to enable
+/// it. See ChannelName<T> above.
+/// - There isn't a uniform way to Register/Unregister log types, and
+/// registering it twice is fatal. We have to be careful to only register it
+/// once, and even then, make sure you aren't calling code that registers it.
+/// - This does not remember what logging might have been enabled when it
+/// started, so it completely disables logging when the scope goes out.
+class TestStderrLogger {
+ class TestStderrLogCloser {
+ public:
+ TestStderrLogCloser(llvm::StringRef channel,
+ llvm::ArrayRef<const char *> categories,
+ uint32_t log_options, llvm::raw_ostream &os);
+ ~TestStderrLogCloser();
+ };
+
+ static void Init();
+
+ static std::vector<const char *> CategoriesForMask(const Log::Channel &chan,
+ Log::MaskType mask);
+
+public:
+ /// Example usage:
+ /// auto log = TestStderrLogger::Scoped("lldb", {"ast", "break"});
+ static TestStderrLogCloser Scoped(llvm::StringRef channel,
+ llvm::ArrayRef<const char *> categories,
+ uint32_t log_options = 0,
+ llvm::raw_ostream &os = llvm::errs());
+
+ /// Example usage:
+ /// auto log = TestStderrLogger::Scoped(LLDBLog::AST | LLDBLog::Breakpoints);
+ template <typename Cat>
+ static TestStderrLogCloser Scoped(Cat mask, uint32_t log_options = 0,
+ llvm::raw_ostream &os = llvm::errs()) {
+ static_assert(
+ std::is_same<Log::MaskType, std::underlying_type_t<Cat>>::value);
+ Init();
+ return Scoped(ChannelName<Cat>(),
+ CategoriesForMask(LogChannelFor<Cat>(), Log::MaskType(mask)),
+ log_options, os);
+ }
+};
+
+} // namespace lldb_private
+
+#endif
diff --git a/lldb/unittests/TestingSupport/TestStderrLogger.cpp b/lldb/unittests/TestingSupport/TestStderrLogger.cpp
new file mode 100644
--- /dev/null
+++ b/lldb/unittests/TestingSupport/TestStderrLogger.cpp
@@ -0,0 +1,61 @@
+//===-- TestStderrLogger.cpp ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "TestStderrLogger.h"
+
+using namespace lldb_private;
+
+class OstreamLogHandler : public LogHandler {
+public:
+ OstreamLogHandler(llvm::raw_ostream &os) : os(os) {}
+ void Emit(llvm::StringRef message) override {
+ os << std::string_view(message);
+ }
+
+private:
+ llvm::raw_ostream &os;
+};
+
+template <> llvm::StringRef lldb_private::ChannelName<LLDBLog>() {
+ return "lldb";
+}
+
+TestStderrLogger::TestStderrLogCloser::TestStderrLogCloser(
+ llvm::StringRef channel, llvm::ArrayRef<const char *> categories,
+ uint32_t log_options, llvm::raw_ostream &os) {
+ auto log_stream_sp = std::make_shared<OstreamLogHandler>(os);
+ Log::EnableLogChannel(log_stream_sp, /*log_options=*/0, channel, categories,
+ llvm::errs());
+}
+
+TestStderrLogger::TestStderrLogCloser::~TestStderrLogCloser() {
+ Log::DisableAllLogChannels();
+}
+
+void TestStderrLogger::Init() {
+ static llvm::once_flag g_once_flag;
+ llvm::call_once(g_once_flag, []() { lldb_private::InitializeLldbChannel(); });
+}
+
+TestStderrLogger::TestStderrLogCloser
+TestStderrLogger::Scoped(llvm::StringRef channel,
+ llvm::ArrayRef<const char *> categories,
+ uint32_t log_options, llvm::raw_ostream &os) {
+ Init();
+ return TestStderrLogger::TestStderrLogCloser(channel, categories, log_options,
+ os);
+}
+std::vector<const char *>
+TestStderrLogger::CategoriesForMask(const Log::Channel &chan,
+ Log::MaskType mask) {
+ std::vector<const char *> categories;
+ for (const auto &c : chan.categories)
+ if (mask & c.flag)
+ categories.push_back(c.name.data());
+ return categories;
+}
diff --git a/lldb/unittests/TestingSupport/tests/CMakeLists.txt b/lldb/unittests/TestingSupport/tests/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/lldb/unittests/TestingSupport/tests/CMakeLists.txt
@@ -0,0 +1,9 @@
+# Note: "TestingSupportTests" already exists in LLVM. Prefix with "LLDB" to
+# make it unique.
+add_lldb_unittest(LLDBTestingSupportTests
+ TestStderrLoggerTest.cpp
+
+ LINK_LIBS
+ lldbUtilityHelpers
+ )
+
\ No newline at end of file
diff --git a/lldb/unittests/TestingSupport/tests/TestStderrLoggerTest.cpp b/lldb/unittests/TestingSupport/tests/TestStderrLoggerTest.cpp
new file mode 100644
--- /dev/null
+++ b/lldb/unittests/TestingSupport/tests/TestStderrLoggerTest.cpp
@@ -0,0 +1,59 @@
+//===-- TestStderrLoggerTest.cpp ------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "TestingSupport/TestStderrLogger.h"
+#include "gtest/gtest.h"
+
+using namespace lldb_private;
+using namespace lldb;
+
+TEST(TestStderrLoggerTest, Strings) {
+ LLDB_LOG(GetLog(LLDBLog::AST), "This won't be logged");
+ {
+ auto logger = TestStderrLogger::Scoped("lldb", {"ast"});
+ LLDB_LOG(GetLog(LLDBLog::AST), "This will be logged");
+ }
+ LLDB_LOG(GetLog(LLDBLog::AST), "This won't be logged either");
+}
+
+TEST(TestStderrLoggerTest, Special) {
+ EXPECT_EQ(1, 2);
+ {
+ auto logger = TestStderrLogger::Scoped("lldb", {"all"});
+ LLDB_LOG(GetLog(LLDBLog::Breakpoints), "break is part of all");
+ }
+ {
+ auto logger = TestStderrLogger::Scoped("lldb", {"default"});
+ LLDB_LOG(GetLog(LLDBLog::AST), "ast is not part of default");
+ LLDB_LOG(GetLog(LLDBLog::Breakpoints), "break is part of default");
+ }
+}
+
+TEST(TestStderrLoggerTest, Enums) {
+ auto logger = TestStderrLogger::Scoped(LLDBLog::AST | LLDBLog::Breakpoints);
+ LLDB_LOG(GetLog(LLDBLog::AST), "AST lines are logged");
+ LLDB_LOG(GetLog(LLDBLog::Breakpoints), "Breakpoint lines are logged");
+ LLDB_LOG(GetLog(LLDBLog::Unwind), "Unwind lines are not logged");
+}
+
+TEST(TestStderrLoggerTest, SwitchSource) {
+ std::string log_dest;
+ llvm::raw_string_ostream ostream_dest(log_dest);
+
+ {
+ auto logger = TestStderrLogger::Scoped("lldb", {"ast"}, /*log_options=*/0,
+ ostream_dest);
+ LLDB_LOG(GetLog(LLDBLog::AST), "This goes to a stream");
+ }
+
+ {
+ auto logger = TestStderrLogger::Scoped("lldb", {"ast"});
+ LLDB_LOG(GetLog(LLDBLog::AST), "This goes to stderr");
+ }
+ EXPECT_EQ(log_dest, "This goes to a stream\n");
+}