[Support] Fix crash in install_bad_alloc_error_handler (#83160)

Previously, the function `install_bad_alloc_error_handler` was asserting that a bad_alloc error handler was not already installed. However, it was actually checking for the fatal-error handler, not for the bad_alloc error handler, causing an assertion failure if a fatal-error handler was already installed.

Fixes #83040

Author: fabianbs96

llvm/lib/Support/ErrorHandling.cpp

@@ -130,7 +130,8 @@ void llvm::install_bad_alloc_error_handler(fatal_error_handler_t handler,
 #if LLVM_ENABLE_THREADS == 1
   std::lock_guard<std::mutex> Lock(BadAllocErrorHandlerMutex);
 #endif
-  assert(!ErrorHandler && "Bad alloc error handler already registered!\n");
+  assert(!BadAllocErrorHandler &&
+         "Bad alloc error handler already registered!\n");
   BadAllocErrorHandler = handler;
   BadAllocErrorHandlerUserData = user_data;
 }

llvm/unittests/Support/ErrorTest.cpp

@@ -1132,4 +1132,30 @@ TEST(Error, moveInto) {
   }
 }
 
+TEST(Error, FatalBadAllocErrorHandlersInteraction) {
+  auto ErrorHandler = [](void *Data, const char *, bool) {};
+  install_fatal_error_handler(ErrorHandler, nullptr);
+  // The following call should not crash; previously, a bug in
+  // install_bad_alloc_error_handler asserted that no fatal-error handler is
+  // installed already.
+  install_bad_alloc_error_handler(ErrorHandler, nullptr);
+
+  // Don't interfere with other tests.
+  remove_fatal_error_handler();
+  remove_bad_alloc_error_handler();
+}
+
+TEST(Error, BadAllocFatalErrorHandlersInteraction) {
+  auto ErrorHandler = [](void *Data, const char *, bool) {};
+  install_bad_alloc_error_handler(ErrorHandler, nullptr);
+  // The following call should not crash; related to
+  // FatalBadAllocErrorHandlersInteraction: Ensure that the error does not occur
+  // in the other direction.
+  install_fatal_error_handler(ErrorHandler, nullptr);
+
+  // Don't interfere with other tests.
+  remove_fatal_error_handler();
+  remove_bad_alloc_error_handler();
+}
+
 } // namespace