[Frontend] Check diagnostics in generated sources

The previous commit added support for checking diagnostics in other
buffers, enabling diagnostic verification for e.g. macro expansions.
Because the diagnostics are in a different buffer, there is no error for
not marking them as "expected". This commit expands the scope to
include generated sources originating in code in any checked buffer, to
help make sure that errors aren't accidentally missed.

Author: hnrklssn

lib/Frontend/DiagnosticVerifier.cpp

@@ -594,7 +594,7 @@ static void validatePrefixList(ArrayRef<std::string> prefixes) {
   }
 }
 
-bool parseTargetBufferName(StringRef &MatchStart, StringRef &Out, size_t &TextStartIdx) {
+static bool parseTargetBufferName(StringRef &MatchStart, StringRef &Out, size_t &TextStartIdx) {
   StringRef Offs = MatchStart.slice(0, TextStartIdx);
 
   size_t LineIndex = Offs.find(':');
@@ -1217,8 +1217,19 @@ DiagnosticVerifier::Result DiagnosticVerifier::verifyFile(unsigned BufferID) {
   auto CapturedDiagIter = CapturedDiagnostics.begin();
   while (CapturedDiagIter != CapturedDiagnostics.end()) {
     if (CapturedDiagIter->SourceBufferID != BufferID) {
-      ++CapturedDiagIter;
-      continue;
+      if (!CapturedDiagIter->SourceBufferID) {
+        ++CapturedDiagIter;
+        continue;
+      }
+
+      // Diagnostics attached to generated sources originating in this
+      // buffer also count as part of this buffer for this purpose.
+      const GeneratedSourceInfo *GSI =
+          SM.getGeneratedSourceInfo(CapturedDiagIter->SourceBufferID.value());
+      if (!GSI || !llvm::find(GSI->ancestors, BufferID)) {
+        ++CapturedDiagIter;
+        continue;
+      }
     }
 
     HadUnexpectedDiag = true;