EndSourceFile() for preprocessor before diagnstic client

The comment for `DiagnosticConsumer::BeginSourceFile()` states that "diagnostics with source range information are required to only be emitted in between BeginSourceFile() and EndSourceFile().". While working on some upcoming changes to the static analyzer, we hit some crashes when diagnostics were reported from the `EndOfMainFile` callback in the preprocessor. This turned out to be because `FrontEndAction::EndSourceFile()` notifies the diagnostic clients of the end of the source file before it notifies the preprocessor. Thus, the diagnostics from the preprocessor callback are reported when the diagnostic client is no longer expecting any diagnostics.

The fix is to swap the order of the `EndSourceFile()` calls so that the preprocessor is notified first.

I've added asserts to the `ClangTidyDiagnosticConsumer` to catch unexpected diagnostics outside of a source file, which catches the problem in current tests.

Author: dbartol

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

@@ -360,6 +360,8 @@ getFixIt(const tooling::Diagnostic &Diagnostic, bool AnyFix) {
 
 void ClangTidyDiagnosticConsumer::HandleDiagnostic(
     DiagnosticsEngine::Level DiagLevel, const Diagnostic &Info) {
+  assert(InSourceFile || Info.getLocation().isInvalid());  // A diagnostic should not be reported outside of a BeginSourceFile()/EndSourceFile() pair if it has a source location.
+
   if (LastErrorWasIgnored && DiagLevel == DiagnosticsEngine::Note)
     return;
 

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

@@ -292,6 +292,21 @@ class ClangTidyDiagnosticConsumer : public DiagnosticConsumer {
   void HandleDiagnostic(DiagnosticsEngine::Level DiagLevel,
                         const Diagnostic &Info) override;
 
+  void BeginSourceFile(const LangOptions &LangOpts,
+                               const Preprocessor *PP = nullptr) override {
+    DiagnosticConsumer::BeginSourceFile(LangOpts, PP);
+    
+    assert(!InSourceFile);
+    InSourceFile = true;
+  }
+    
+  void EndSourceFile() override {
+    assert(InSourceFile);
+    InSourceFile = false;
+      
+    DiagnosticConsumer::EndSourceFile();
+  }
+
   // Retrieve the diagnostics that were captured.
   std::vector<ClangTidyError> take();
 
@@ -326,6 +341,7 @@ class ClangTidyDiagnosticConsumer : public DiagnosticConsumer {
   bool LastErrorRelatesToUserCode = false;
   bool LastErrorPassesLineFilter = false;
   bool LastErrorWasIgnored = false;
+  bool InSourceFile = false;
 };
 
 } // end namespace tidy

clang/lib/Frontend/FrontendAction.cpp

@@ -1243,13 +1243,15 @@ llvm::Error FrontendAction::Execute() {
 void FrontendAction::EndSourceFile() {
   CompilerInstance &CI = getCompilerInstance();
 
-  // Inform the diagnostic client we are done with this source file.
-  CI.getDiagnosticClient().EndSourceFile();
-
   // Inform the preprocessor we are done.
   if (CI.hasPreprocessor())
     CI.getPreprocessor().EndSourceFile();
 
+  // Inform the diagnostic client we are done with this source file.
+  // Do this after notifying the preprocessor, so that end-of-file preprocessor
+  // callbacks can report diagnostics.
+  CI.getDiagnosticClient().EndSourceFile();
+
   // Finalize the action.
   EndSourceFileAction();