Index: clangd/ClangdUnit.cpp
===================================================================
--- clangd/ClangdUnit.cpp
+++ clangd/ClangdUnit.cpp
@@ -178,15 +178,18 @@
 llvm::Optional<DiagWithFixIts> toClangdDiag(const clang::Diagnostic &D,
                                             DiagnosticsEngine::Level Level,
                                             const LangOptions &LangOpts) {
+  SmallString<64> Message;
+  D.FormatDiagnostic(Message);
+
   if (!D.hasSourceManager() || !D.getLocation().isValid() ||
-      !D.getSourceManager().isInMainFile(D.getLocation()))
+      !D.getSourceManager().isInMainFile(D.getLocation())) {
+    log("Ignored diagnostic outside main file: " + Twine(Message));
     return llvm::None;
+  }
 
   DiagWithFixIts Result;
   Result.Diag.range = diagnosticRange(D, LangOpts);
   Result.Diag.severity = getSeverity(Level);
-  SmallString<64> Message;
-  D.FormatDiagnostic(Message);
   Result.Diag.message = Message.str();
   for (const FixItHint &Fix : D.getFixItHints())
     Result.FixIts.push_back(toTextEdit(Fix, D.getSourceManager(), LangOpts));