[clangd] Get rid of unnecssary source transformations in locateMacroAt

[kadircet]

Summary

All callers are already passing spelling locations to locateMacroAt.
Also there's no point at looking at macro expansion for figuring out undefs as
it is forbidden to have PP directives inside macro bodies.
Also fixes a bug when the previous sourcelocation is unavailable.

[hokein]

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

440

nit: the trailing ; seems not needed.

[kadircet]

• Drop semicolon

clang-tools-extra/clangd/SourceCode.h

 EligibleRegion getEligiblePoints(llvm::StringRef Code,
                                  llvm::StringRef FullyQualifiedName,
                                  const format::FormatStyle &Style);
 
 struct DefinedMacro {
   llvm::StringRef Name;
   const MacroInfo *Info;
 };
-/// Gets the macro at a specified \p Loc.
+/// Gets the macro at a specified \p Loc. It must be a spelling location and
+/// point to the beginning of identifier.
 llvm::Optional<DefinedMacro> locateMacroAt(SourceLocation Loc,
                                            Preprocessor &PP);
 
 /// Infers whether this is a header from the FileName and LangOpts (if
 /// presents).
 bool isHeaderFile(llvm::StringRef FileName,
                   llvm::Optional<LangOptions> LangOpts = llvm::None);
 
 /// Returns true if the given location is in a generated protobuf file.
 bool isProtoFile(SourceLocation Loc, const SourceManager &SourceMgr);
 
 } // namespace clangd
 } // namespace clang
 #endif

clang-tools-extra/clangd/SourceCode.cpp

llvm::StringSet<> collectWords(llvm::StringRef Content) {
   }
   Flush();
 
   return Result;
 }
 
 llvm::Optional<DefinedMacro> locateMacroAt(SourceLocation Loc,
                                            Preprocessor &PP) {
+  assert(Loc.isFileID());
   const auto &SM = PP.getSourceManager();
   const auto &LangOpts = PP.getLangOpts();
   Token Result;
-  if (Lexer::getRawToken(SM.getSpellingLoc(Loc), Result, SM, LangOpts, false))
+  if (Lexer::getRawToken(Loc, Result, SM, LangOpts, false))
     return None;
   if (Result.is(tok::raw_identifier))
     PP.LookUpIdentifierInfo(Result);
   IdentifierInfo *IdentifierInfo = Result.getIdentifierInfo();
   if (!IdentifierInfo || !IdentifierInfo->hadMacroDefinition())
     return None;
 
-  std::pair<FileID, unsigned int> DecLoc = SM.getDecomposedExpansionLoc(Loc);
   // Get the definition just before the searched location so that a macro
-  // referenced in a '#undef MACRO' can still be found.
-  SourceLocation BeforeSearchedLocation =
-      SM.getMacroArgExpandedLocation(SM.getLocForStartOfFile(DecLoc.first)
-                                         .getLocWithOffset(DecLoc.second - 1));
-  MacroDefinition MacroDef =
-      PP.getMacroDefinitionAtLoc(IdentifierInfo, BeforeSearchedLocation);
+  // referenced in a '#undef MACRO' can still be found. Note that we only do
+  // that if Loc is not pointing at start of file.
+  if (SM.getLocForStartOfFile(SM.getFileID(Loc)) != Loc)
+    Loc = Loc.getLocWithOffset(-1);
+  MacroDefinition MacroDef = PP.getMacroDefinitionAtLoc(IdentifierInfo, Loc);
   if (auto *MI = MacroDef.getMacroInfo())
     return DefinedMacro{IdentifierInfo->getName(), MI};
   return None;
 }
 
 llvm::Expected<std::string> Edit::apply() const {
   return tooling::applyAllReplacements(InitialCode, Replacements);
 }

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

TEST(SourceCodeTests, GetMacros) {
   ASSERT_TRUE(bool(CurLoc));
   const auto *Id = syntax::spelledIdentifierTouching(*CurLoc, AST.getTokens());
   ASSERT_TRUE(Id);
   auto Result = locateMacroAt(Id->location(), AST.getPreprocessor());
   ASSERT_TRUE(Result);
   EXPECT_THAT(*Result, MacroName("MACRO"));
 }
 
+TEST(SourceCodeTests, WorksAtBeginOfFile) {
+  Annotations Code("^MACRO");
+  TestTU TU = TestTU::withCode(Code.code());
+  TU.HeaderCode = "#define MACRO int x;";
+  auto AST = TU.build();
+  auto CurLoc = sourceLocationInMainFile(AST.getSourceManager(), Code.point());
+  ASSERT_TRUE(bool(CurLoc));
+  const auto *Id = syntax::spelledIdentifierTouching(*CurLoc, AST.getTokens());
+  ASSERT_TRUE(Id);
+  auto Result = locateMacroAt(Id->location(), AST.getPreprocessor());
+  ASSERT_TRUE(Result);
+  EXPECT_THAT(*Result, MacroName("MACRO"));
+}
+
 TEST(SourceCodeTests, IsInsideMainFile){
   TestTU TU;
   TU.HeaderCode = R"cpp(
     #define DEFINE_CLASS(X) class X {};
     #define DEFINE_YY DEFINE_CLASS(YY)
 
     class Header1 {};
     DEFINE_CLASS(Header2)