[clangd] Log dropped diagnostics.

[ilya-biryukov]

Summary

clangd drops diagnostics coming outside the main file, but it is still
useful to see that something went wrong in the logs.

[sammccall]

clangd/ClangdUnit.cpp

183

does Message include file:line? we probably want that in the log line.

187

Agree this is useful.

Have we turned off the diagnostics limit (or will we?) a misconfig of e.g. C vs C++ parsing of a header seems like it could produce 1000+ log lines from preamble that we should probably avoid somehow.
(Maybe even avoid paying to format)

[ilya-biryukov]

• Show location of dropped diagnostic.

clangd/ClangdUnit.cpp

183

No, it didn't include the line before. Now dumping the location too.

187

I don't think we have changed default clang behavior.
This look like a good use-case for introducing log levels.
This information is definitely too verbose most of the time, but very useful when debugging failures

clangd/ClangdUnit.cpp

 #include "clang/Lex/Preprocessor.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Serialization/ASTWriter.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/Format.h"
+#include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <chrono>
 
 using namespace clang::clangd;
 using namespace clang;
 
 namespace {
 
TextEdit toTextEdit(const FixItHint &FixIt, const SourceManager &M,
   Result.range = toRange(Lexer::makeFileCharRange(FixIt.RemoveRange, M, L), M);
   Result.newText = FixIt.CodeToInsert;
   return Result;
 }
 
 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())) {
+
+    SmallString<64> Location;
+    if (D.hasSourceManager() && D.getLocation().isValid()) {
+      auto &SourceMgr = D.getSourceManager();
+      auto Loc = SourceMgr.getFileLoc(D.getLocation());
+      llvm::raw_svector_ostream OS(Location);
+      Loc.print(OS, SourceMgr);
+    } else {
+      Location = "<no-loc>";
+    }
+
+    log(llvm::formatv("Ignored diagnostic outside main file. {0}: {1}",
+                      Location, 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));
   return std::move(Result);
 }
 
 class StoreDiagsConsumer : public DiagnosticConsumer {
 public: