[clang-tidy] Fix crash when diagnostic is emit with invalid location

Fix crash when diagnostic is emit with invalid location,
but with attached valid ranges. Diagnostic can contain
invalid location, but SourceManager attached to it still
can be valid, use it in such case or fallback to known
SourceManager.

Fixes: #64602

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D157649

(cherry picked from commit efd44f8)

clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp

@@ -436,8 +436,11 @@ void ClangTidyDiagnosticConsumer::HandleDiagnostic(
     SmallString<100> Message;
     Info.FormatDiagnostic(Message);
     FullSourceLoc Loc;
-    if (Info.getLocation().isValid() && Info.hasSourceManager())
+    if (Info.hasSourceManager())
       Loc = FullSourceLoc(Info.getLocation(), Info.getSourceManager());
+    else if (Context.DiagEngine->hasSourceManager())
+      Loc = FullSourceLoc(Info.getLocation(),
+                          Context.DiagEngine->getSourceManager());
     Converter.emitDiagnostic(Loc, DiagLevel, Message, Info.getRanges(),
                              Info.getFixItHints());
   }

clang-tools-extra/test/clang-tidy/infrastructure/diagnostic.cpp

@@ -25,6 +25,7 @@
 // RUN: not clang-tidy -checks='-*,modernize-use-override' %T/diagnostics/input.cpp -- -DCOMPILATION_ERROR 2>&1 | FileCheck -check-prefix=CHECK6 -implicit-check-not='{{warning:|error:}}' %s
 // RUN: clang-tidy -checks='-*,modernize-use-override,clang-diagnostic-macro-redefined' %s -- -DMACRO_FROM_COMMAND_LINE -std=c++20 | FileCheck -check-prefix=CHECK4 -implicit-check-not='{{warning:|error:}}' %s
 // RUN: clang-tidy -checks='-*,modernize-use-override,clang-diagnostic-macro-redefined,clang-diagnostic-literal-conversion' %s -- -DMACRO_FROM_COMMAND_LINE -std=c++20 -Wno-macro-redefined | FileCheck --check-prefix=CHECK7 -implicit-check-not='{{warning:|error:}}' %s
+// RUN: not clang-tidy -checks='-*,modernize-use-override' %s -- -std=c++20 -DPR64602 | FileCheck -check-prefix=CHECK8 -implicit-check-not='{{warning:|error:}}' %s
 
 // CHECK1: error: no input files [clang-diagnostic-error]
 // CHECK1: error: no such file or directory: '{{.*}}nonexistent.cpp' [clang-diagnostic-error]
@@ -54,3 +55,18 @@ void f(int a) {
   // CHECK6: :[[@LINE-1]]:3: error: cannot take the address of an rvalue of type 'int' [clang-diagnostic-error]
 }
 #endif
+
+#ifdef PR64602 // Should not crash
+template <class T = void>
+struct S
+{
+    auto foo(auto);
+};
+
+template <>
+auto S<>::foo(auto)
+{
+    return 1;
+}
+// CHECK8: error: template parameter list matching the non-templated nested type 'S<>' should be empty ('template<>') [clang-diagnostic-error]
+#endif