[clangd] Make use of diagnostic tags for some clang diags

[kadircet]

Summary

It is not great to list diag ids by hand, but I don't see any other
solution unless diagnostics are annotated with these explicitly, which is a
bigger change in clang and I am not sure if would be worth it.

Diagnostics handled by this patch is by no means exhaustive, there might be
other checks that don't mention "unused"/"deprecated" in their names. But it
feels like this should be enough to catch common diagnostics and can be extended
over time.

[kadircet]

• Fix base

[sammccall]

clang-tools-extra/clangd/Diagnostics.cpp

330

I think it might be nicer if this took a clangd::Diag& and added the tags to it, then we could naturally group the clang-tidy list along with the main clang diag list (I don't think having them separately serves anyone well)

331

nit: static const auto& DeprecatedDiags = *new llvm::DenseSet<unsigned>{...

This suppresses destruction

clang-tools-extra/clangd/Diagnostics.h

110

Maybe SmallVector or even Optional since this is 0-1 integers in practice?

clang-tools-extra/clangd/Protocol.cpp

1457

keep ordering consistent with the header? so before Diagnostic

[kadircet]

• Address comments

clang-tools-extra/clangd/Diagnostics.h

 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/SourceLocation.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Support/JSON.h"
 #include "llvm/Support/SourceMgr.h"
 #include <cassert>
 #include <functional>
 #include <memory>
 #include <string>
 #include <utility>
enum DiagSource {
     Clang,
     ClangTidy,
     ClangdConfig,
   } Source = Unknown;
   /// Elaborate on the problem, usually pointing to a related piece of code.
   std::vector<Note> Notes;
   /// *Alternative* fixes for this diagnostic, one should be chosen.
   std::vector<Fix> Fixes;
+  llvm::SmallVector<DiagnosticTag, 1> Tags;
 };
 llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Diag &D);
 
 Diag toDiag(const llvm::SMDiagnostic &, Diag::DiagSource Source);
 
 /// Conversion to LSP diagnostics. Formats the error message of each diagnostic
 /// to include all its notes. Notes inside main file are also provided as
 /// separate diagnostics with their corresponding fixits. Notes outside main

clang-tools-extra/clangd/Diagnostics.cpp

 #include "clang/Lex/Lexer.h"
 #include "clang/Lex/Token.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/Capacity.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cstddef>
+#include <vector>
 
 namespace clang {
 namespace clangd {
 namespace {
 
 const char *getDiagnosticCode(unsigned ID) {
   switch (ID) {
 #define DIAG(ENUM, CLASS, DEFAULT_MAPPING, DESC, GROPU, SFINAE, NOWERROR,      \
std::string noteMessage(const Diag &Main, const DiagBase &Note,
   // original diagnostic, then emit the main diagnostic to give context.
   if (!Opts.EmitRelatedLocations) {
     OS << "\n\n";
     printDiag(OS, Main);
   }
   OS.flush();
   return capitalize(std::move(Result));
 }
+
+void setTags(clangd::Diag &D) {
+  static const auto *DeprecatedDiags = new llvm::DenseSet<unsigned>{
+      diag::warn_access_decl_deprecated,
+      diag::warn_atl_uuid_deprecated,
+      diag::warn_deprecated,
+      diag::warn_deprecated_altivec_src_compat,
+      diag::warn_deprecated_comma_subscript,
+      diag::warn_deprecated_compound_assign_volatile,
+      diag::warn_deprecated_copy,
+      diag::warn_deprecated_copy_with_dtor,
+      diag::warn_deprecated_copy_with_user_provided_copy,
+      diag::warn_deprecated_copy_with_user_provided_dtor,
+      diag::warn_deprecated_def,
+      diag::warn_deprecated_increment_decrement_volatile,
+      diag::warn_deprecated_message,
+      diag::warn_deprecated_redundant_constexpr_static_def,
+      diag::warn_deprecated_register,
+      diag::warn_deprecated_simple_assign_volatile,
+      diag::warn_deprecated_string_literal_conversion,
+      diag::warn_deprecated_this_capture,
+      diag::warn_deprecated_volatile_param,
+      diag::warn_deprecated_volatile_return,
+      diag::warn_deprecated_volatile_structured_binding,
+      diag::warn_opencl_attr_deprecated_ignored,
+      diag::warn_property_method_deprecated,
+      diag::warn_vector_mode_deprecated,
+  };
+  static const auto *UnusedDiags = new llvm::DenseSet<unsigned>{
+      diag::warn_opencl_attr_deprecated_ignored,
+      diag::warn_pragma_attribute_unused,
+      diag::warn_unused_but_set_parameter,
+      diag::warn_unused_but_set_variable,
+      diag::warn_unused_comparison,
+      diag::warn_unused_const_variable,
+      diag::warn_unused_exception_param,
+      diag::warn_unused_function,
+      diag::warn_unused_label,
+      diag::warn_unused_lambda_capture,
+      diag::warn_unused_local_typedef,
+      diag::warn_unused_member_function,
+      diag::warn_unused_parameter,
+      diag::warn_unused_private_field,
+      diag::warn_unused_property_backing_ivar,
+      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.
+}
 } // 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 << "] ";
 
for (auto &Note : D.Notes) {
       DiagnosticRelatedInformation RelInfo;
       RelInfo.location.range = Note.Range;
       RelInfo.location.uri =
           URIForFile::canonicalize(*Note.AbsFile, File.file());
       RelInfo.message = noteMessage(D, Note, Opts);
       Main.relatedInformation->push_back(std::move(RelInfo));
     }
   }
+  Main.tags = D.Tags;
   OutFn(std::move(Main), D.Fixes);
 
   // If we didn't emit the notes as relatedLocations, emit separate diagnostics
   // so the user can find the locations easily.
   if (!Opts.EmitRelatedLocations)
     for (auto &Note : D.Notes) {
       if (!Note.InsideMainFile)
         continue;

 }
 
 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.
if (Tidy != nullptr) {
         continue;
       }
     }
   }
   // 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) {
+  llvm::erase_if(Output, [&](const Diag &D) {
     return !SeenDiags.emplace(D.Range, D.Message).second;
   });
   return std::move(Output);
 }
 
 void StoreDiags::BeginSourceFile(const LangOptions &Opts,
                                  const Preprocessor *PP) {
   LangOpts = Opts;

clang-tools-extra/clangd/Protocol.h

 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_PROTOCOL_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_PROTOCOL_H
 
 #include "URI.h"
 #include "index/SymbolID.h"
 #include "support/MemoryTree.h"
 #include "clang/Index/IndexSymbol.h"
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/JSON.h"
 #include "llvm/Support/raw_ostream.h"
 #include <bitset>
 #include <memory>
 #include <string>
 #include <vector>
 
 namespace clang {

 struct DiagnosticRelatedInformation {
   /// The location of this related diagnostic information.
   Location location;
   /// The message of this related diagnostic information.
   std::string message;
 };
 llvm::json::Value toJSON(const DiagnosticRelatedInformation &);
 
+enum DiagnosticTag {
+  /// Unused or unnecessary code.
+  ///
+  /// Clients are allowed to render diagnostics with this tag faded out instead
+  /// of having an error squiggle.
+  Unnecessary = 1,
+  /// Deprecated or obsolete code.
+  ///
+  /// Clients are allowed to rendered diagnostics with this tag strike through.
+  Deprecated = 2,
+};
+llvm::json::Value toJSON(DiagnosticTag Tag);
+
 struct CodeAction;
 struct Diagnostic {
   /// The range at which the message applies.
   Range range;
 
   /// The diagnostic's severity. Can be omitted. If omitted it is up to the
   /// client to interpret diagnostics as error, warning, info or hint.
   int severity = 0;
 
   /// The diagnostic's code. Can be omitted.
   std::string code;
 
   /// A human-readable string describing the source of this
   /// diagnostic, e.g. 'typescript' or 'super lint'.
   std::string source;
 
   /// The diagnostic's message.
   std::string message;
 
+  /// Additional metadata about the diagnostic.
+  llvm::SmallVector<DiagnosticTag, 1> tags;
+
   /// An array of related diagnostic information, e.g. when symbol-names within
   /// a scope collide all definitions can be marked via this property.
   llvm::Optional<std::vector<DiagnosticRelatedInformation>> relatedInformation;
 
   /// The diagnostic's category. Can be omitted.
   /// An LSP extension that's used to send the name of the category over to the
   /// client. The category typically describes the compilation stage during
   /// which the issue was produced, e.g. "Semantic Issue" or "Parse Issue".

clang-tools-extra/clangd/Protocol.cpp

 
 llvm::json::Value toJSON(const DiagnosticRelatedInformation &DRI) {
   return llvm::json::Object{
       {"location", DRI.location},
       {"message", DRI.message},
   };
 }
 
+llvm::json::Value toJSON(DiagnosticTag Tag) { return static_cast<int>(Tag); }
+
 llvm::json::Value toJSON(const Diagnostic &D) {
   llvm::json::Object Diag{
       {"range", D.range},
       {"severity", D.severity},
       {"message", D.message},
   };
   if (D.category)
     Diag["category"] = *D.category;
   if (D.codeActions)
     Diag["codeActions"] = D.codeActions;
   if (!D.code.empty())
     Diag["code"] = D.code;
   if (!D.source.empty())
     Diag["source"] = D.source;
   if (D.relatedInformation)
     Diag["relatedInformation"] = *D.relatedInformation;
   if (!D.data.empty())
     Diag["data"] = llvm::json::Object(D.data);
+  if (!D.tags.empty())
+    Diag["tags"] = llvm::json::Array{D.tags};
   // FIXME: workaround for older gcc/clang
   return std::move(Diag);
 }
 
 bool fromJSON(const llvm::json::Value &Params, Diagnostic &R,
               llvm::json::Path P) {
   llvm::json::ObjectMapper O(Params, P);
   if (!O)
std::function<void(const ASTNode &, unsigned)> Print = [&](const ASTNode &N,
     OS << "\n";
     for (const ASTNode &C : N.children)
       Print(C, Level + 1);
   };
   Print(Root, 0);
   return OS;
 }
 
 } // namespace clangd
 } // namespace clang

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

 }
 
 ::testing::Matcher<const Diag &>
 WithNote(::testing::Matcher<Note> NoteMatcher1,
          ::testing::Matcher<Note> NoteMatcher2) {
   return Field(&Diag::Notes, UnorderedElementsAre(NoteMatcher1, NoteMatcher2));
 }
 
+::testing::Matcher<const Diag &>
+WithTag(::testing::Matcher<DiagnosticTag> TagMatcher) {
+  return Field(&Diag::Tags, Contains(TagMatcher));
+}
+
 MATCHER_P2(Diag, Range, Message,
            "Diag at " + llvm::to_string(Range) + " = [" + Message + "]") {
   return arg.Range == Range && arg.Message == Message;
 }
 
 MATCHER_P3(Fix, Range, Replacement, Message,
            "Fix " + llvm::to_string(Range) + " => " +
                ::testing::PrintToString(Replacement) + " = [" + Message + "]") {

 TEST(DiagnosticsTest, ToLSP) {
   URIForFile MainFile =
       URIForFile::canonicalize(testPath("foo/bar/main.cpp"), "");
   URIForFile HeaderFile =
       URIForFile::canonicalize(testPath("foo/bar/header.h"), "");
 
   clangd::Diag D;
   D.ID = clang::diag::err_undeclared_var_use;
+  D.Tags = {DiagnosticTag::Unnecessary};
   D.Name = "undeclared_var_use";
   D.Source = clangd::Diag::Clang;
   D.Message = "something terrible happened";
   D.Range = {pos(1, 2), pos(3, 4)};
   D.InsideMainFile = true;
   D.Severity = DiagnosticsEngine::Error;
   D.File = "foo/bar/main.cpp";
   D.AbsFile = std::string(MainFile.file());
TEST(DiagnosticsTest, ToLSP) {
   MainLSP.source = "clang";
   MainLSP.message =
       R"(Something terrible happened (fix available)
 
 main.cpp:6:7: remark: declared somewhere in the main file
 
 ../foo/baz/header.h:10:11:
 note: declared somewhere in the header file)";
+  MainLSP.tags = {DiagnosticTag::Unnecessary};
 
   clangd::Diagnostic NoteInMainLSP;
   NoteInMainLSP.range = NoteInMain.Range;
   NoteInMainLSP.severity = getSeverity(DiagnosticsEngine::Remark);
   NoteInMainLSP.message = R"(Declared somewhere in the main file
 
 main.cpp:2:3: error: something terrible happened)";
 
TU.ExtraArgs = {"-Wnewline-eof"};
     Annotations Code("#define FOO[[]]");
     TU.Code = Code.code().str();
     auto AST = TU.build();
     EXPECT_THAT(
         *AST.getDiagnostics(),
         testing::Contains(Diag(Code.range(), "no newline at end of file")));
   }
 }
+
+TEST(Diagnostics, Tags) {
+  TestTU TU;
+  TU.ExtraArgs = {"-Wunused", "-Wdeprecated"};
+  Annotations Test(R"cpp(
+  void bar() __attribute__((deprecated));
+  void foo() {
+    int $unused[[x]];
+    $deprecated[[bar]]();
+  })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))));
+}
 } // namespace
 } // namespace clangd
 } // namespace clang