[clangd] Only emit default error/fatal diagnostices from included files.

[hokein]

Summary

This would avoid adding too much noise when there is a "-Wall" in the
compile command.

[sammccall]

Thanks!

clang-tools-extra/clangd/Diagnostics.cpp

127–129

"especially" suggests there are other cases where we we report non-default errors, but I'm not sure there are.

Maybe just "Use default severity to avoid noise with -Werror".

[hokein]

Address comments.

clang-tools-extra/clangd/Diagnostics.cpp

Range diagnosticRange(const clang::Diagnostic &D, const LangOptions &L) {
   }
   return halfOpenToRange(M, R);
 }
 
 // Returns whether the \p D is modified.
 bool adjustDiagFromHeader(Diag &D, const clang::Diagnostic &Info,
                           const LangOptions &LangOpts) {
   // We only report diagnostics with at least error severity from headers.
-  if (D.Severity < DiagnosticsEngine::Level::Error)
+  // Use default severity to avoid noise with -Werror.
+  if (!Info.getDiags()->getDiagnosticIDs()->isDefaultMappingAsError(
+          Info.getID()))
     return false;
 
   const SourceManager &SM = Info.getSourceManager();
   const SourceLocation &DiagLoc = SM.getExpansionLoc(Info.getLocation());
   SourceLocation IncludeInMainFile;
   auto GetIncludeLoc = [&SM](SourceLocation SLoc) {
     return SM.getIncludeLoc(SM.getFileID(SLoc));
   };

 
 void StoreDiags::HandleDiagnostic(DiagnosticsEngine::Level DiagLevel,
                                   const clang::Diagnostic &Info) {
   DiagnosticConsumer::HandleDiagnostic(DiagLevel, Info);
 
   if (Info.getLocation().isInvalid()) {
     // Handle diagnostics coming from command-line arguments. The source manager
     // is *not* available at this point, so we cannot use it.
-    if (DiagLevel < DiagnosticsEngine::Level::Error) {
+    if (!Info.getDiags()->getDiagnosticIDs()->isDefaultMappingAsError(
+            Info.getID())) {
       IgnoreDiagnostics::log(DiagLevel, Info);
       return; // non-errors add too much noise, do not show them.
     }
 
     flushLastDiag();
 
     LastDiag = Diag();
     LastDiag->ID = Info.getID();

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

TEST(DiagsInHeaders, OnlyErrorOrFatal) {
   TU.AdditionalFiles = {{"a.h", std::string(Header.code())}};
   EXPECT_THAT(TU.build().getDiagnostics(),
               UnorderedElementsAre(AllOf(
                   Diag(Main.range(), "in included file: C++ requires "
                                      "a type specifier for all declarations"),
                   WithNote(Diag(Header.range(), "error occurred here")))));
 }
 
+TEST(DiagsInHeaders, OnlyDefaultErrorOrFatal) {
+  Annotations Main(R"cpp(
+    #include [["a.h"]] // get unused "foo" warning when building preamble.
+    )cpp");
+  Annotations Header(R"cpp(
+    namespace { void foo() {} }
+    void func() {foo();} ;)cpp");
+  TestTU TU = TestTU::withCode(Main.code());
+  TU.AdditionalFiles = {{"a.h", std::string(Header.code())}};
+  // promote warnings to errors.
+  TU.ExtraArgs = {"-Werror", "-Wunused"};
+  EXPECT_THAT(TU.build().getDiagnostics(), IsEmpty());
+}
+
 TEST(DiagsInHeaders, FromNonWrittenSources) {
   Annotations Main(R"cpp(
     #include [["a.h"]]
     void foo() {})cpp");
   Annotations Header(R"cpp(
     int x = 5/0;
     int b = [[FOO]]; // error-ok)cpp");
   TestTU TU = TestTU::withCode(Main.code());