[clangd] Tag clang-tidy diagnostics: modernize-*=deprecated, misc-unused-*=unneccesary

clang-tools-extra/clangd/Diagnostics.cpp

static const auto *UnusedDiags = new llvm::DenseSet<unsigned>{
       diag::warn_unused_template,
       diag::warn_unused_variable,
   };
   if (DeprecatedDiags->contains(D.ID)) {
     D.Tags.push_back(DiagnosticTag::Deprecated);
   } else if (UnusedDiags->contains(D.ID)) {
     D.Tags.push_back(DiagnosticTag::Unnecessary);
   }
-  // FIXME: Set tags for tidy-based diagnostics too.
+  if (D.Source == Diag::ClangTidy) {
+    if (llvm::StringRef(D.Name).starts_with("misc-unused-"))
+      D.Tags.push_back(DiagnosticTag::Unnecessary);
+    if (llvm::StringRef(D.Name).starts_with("modernize-"))
+      D.Tags.push_back(DiagnosticTag::Deprecated);
+  }
 }
 } // namespace
 
 llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const DiagBase &D) {
   OS << "[";
   if (!D.InsideMainFile)
     OS << D.File << ":";
   OS << D.Range.start << "-" << D.Range.end << "] ";

 }
 
 std::vector<Diag> StoreDiags::take(const clang::tidy::ClangTidyContext *Tidy) {
   // Do not forget to emit a pending diagnostic if there is one.
   flushLastDiag();
 
   // Fill in name/source now that we have all the context needed to map them.
   for (auto &Diag : Output) {
-    setTags(Diag);
     if (const char *ClangDiag = getDiagnosticCode(Diag.ID)) {
       // Warnings controlled by -Wfoo are better recognized by that name.
       StringRef Warning = DiagnosticIDs::getWarningOptionForDiag(Diag.ID);
       if (!Warning.empty()) {
         Diag.Name = ("-W" + Warning).str();
       } else {
         StringRef Name(ClangDiag);
         // Almost always an error, with a name like err_enum_class_reference.
         // Drop the err_ prefix for brevity.
         Name.consume_front("err_");
         Diag.Name = std::string(Name);
       }
       Diag.Source = Diag::Clang;
-      continue;
-    }
-    if (Tidy != nullptr) {
+    } else if (Tidy != nullptr) {
       std::string TidyDiag = Tidy->getCheckName(Diag.ID);
       if (!TidyDiag.empty()) {
         Diag.Name = std::move(TidyDiag);
         Diag.Source = Diag::ClangTidy;
         // clang-tidy bakes the name into diagnostic messages. Strip it out.
         // It would be much nicer to make clang-tidy not do this.
         auto CleanMessage = [&](std::string &Msg) {
           StringRef Rest(Msg);
           if (Rest.consume_back("]") && Rest.consume_back(Diag.Name) &&
               Rest.consume_back(" ["))
             Msg.resize(Rest.size());
         };
         CleanMessage(Diag.Message);
         for (auto &Note : Diag.Notes)
           CleanMessage(Note.Message);
         for (auto &Fix : Diag.Fixes)
           CleanMessage(Fix.Message);
-        continue;
       }
     }
+    setTags(Diag);
   }
   // Deduplicate clang-tidy diagnostics -- some clang-tidy checks may emit
   // duplicated messages due to various reasons (e.g. the check doesn't handle
   // template instantiations well; clang-tidy alias checks).
   std::set<std::pair<Range, std::string>> SeenDiags;
   llvm::erase_if(Output, [&](const Diag &D) {
     return !SeenDiags.emplace(D.Range, D.Message).second;
   });

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

TEST(Diagnostics, Tags) {
   })cpp");
   TU.Code = Test.code().str();
   EXPECT_THAT(*TU.build().getDiagnostics(),
               UnorderedElementsAre(
                   AllOf(Diag(Test.range("unused"), "unused variable 'x'"),
                         withTag(DiagnosticTag::Unnecessary)),
                   AllOf(Diag(Test.range("deprecated"), "'bar' is deprecated"),
                         withTag(DiagnosticTag::Deprecated))));
+
+  Test = Annotations(R"cpp(
+    $typedef[[typedef int INT]];
+  )cpp");
+  TU.Code = Test.code();
+  TU.ClangTidyProvider = addTidyChecks("modernize-use-using");
+  EXPECT_THAT(
+      *TU.build().getDiagnostics(),
+      UnorderedElementsAre(
+          AllOf(Diag(Test.range("typedef"), "use 'using' instead of 'typedef'"),
+                withTag(DiagnosticTag::Deprecated))));
 }
 
 TEST(DiagnosticsTest, IncludeCleaner) {
   Annotations Test(R"cpp(
 $fix[[  $diag[[#include "unused.h"]]
 ]]
   #include "used.h"