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

[PiotrZSL]

Summary

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

[PiotrZSL]

Add call to DiagnosticEngine::hasSourceManager()

[aaron.ballman]

LGTM!

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

if (ExternalDiagEngine) {
     forwardDiagnostic(Info);
   } else {
     ClangTidyDiagnosticRenderer Converter(
         Context.getLangOpts(), &Context.DiagEngine->getDiagnosticOptions(),
         Errors.back());
     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());
   }
 
   if (Info.hasSourceManager())
     checkFilters(Info.getLocation(), Info.getSourceManager());
 
   Context.DiagEngine->Clear();

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

 // RUN: not clang-tidy -checks='-*,modernize-use-override' %T/diagnostics/nonexistent.cpp -- 2>&1 | FileCheck -check-prefix=CHECK1 -implicit-check-not='{{warning:|error:}}' %s
 // RUN: not clang-tidy -checks='-*,clang-diagnostic-*,google-explicit-constructor' %T/diagnostics/input.cpp -- -fan-unknown-option 2>&1 | FileCheck -check-prefix=CHECK2 -implicit-check-not='{{warning:|error:}}' %s
 // RUN: not clang-tidy -checks='-*,google-explicit-constructor,clang-diagnostic-literal-conversion' %T/diagnostics/input.cpp -- -fan-unknown-option 2>&1 | FileCheck -check-prefix=CHECK3 -implicit-check-not='{{warning:|error:}}' %s
 // RUN: clang-tidy -checks='-*,modernize-use-override,clang-diagnostic-macro-redefined' %T/diagnostics/input.cpp -- -DMACRO_FROM_COMMAND_LINE 2>&1 | FileCheck -check-prefix=CHECK4 -implicit-check-not='{{warning:|error:}}' %s
 // RUN: not clang-tidy -checks='-*,clang-diagnostic-*,google-explicit-constructor' %T/diagnostics/input.cpp 2>&1 | FileCheck -check-prefix=CHECK5 -implicit-check-not='{{warning:|error:}}' %s
 // 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]
 // CHECK1: error: unable to handle compilation{{.*}} [clang-diagnostic-error]
 // CHECK2: error: unknown argument: '-fan-unknown-option' [clang-diagnostic-error]
 // CHECK3: error: unknown argument: '-fan-unknown-option' [clang-diagnostic-error]
 // CHECK5: error: unknown argument: '-fan-option-from-compilation-database' [clang-diagnostic-error]
 

 // CHECK7-NOT: :[[@LINE-2]]:9: warning: 'MACRO_FROM_COMMAND_LINE' macro redefined
 
 #ifdef COMPILATION_ERROR
 void f(int a) {
   &(a + 1);
   // 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