[clangd] Keep go-to-definition working at the end of an identifier (fixes #194)

[nridge]

By the way, may I get permissions to assign issues to myself (and make other such metadata changes to issues) on github?

[hokein]

In D70727#1760485, @nridge wrote:

By the way, may I get permissions to assign issues to myself (and make other such metadata changes to issues) on github?

sure, we just sent you an invitation to the clangd org.

clang-tools-extra/clangd/XRefs.cpp

153

this looks a hacky workaround, I assume it may introduce other regression issues.

I think https://reviews.llvm.org/D70773 and https://reviews.llvm.org/D70807 should fix most annoying cases (function call).

[nridge]

In D70727#1763781, @hokein wrote:

In D70727#1760485, @nridge wrote:

By the way, may I get permissions to assign issues to myself (and make other such metadata changes to issues) on github?

sure, we just sent you an invitation to the clangd org.

Thanks!

[nridge]

clang-tools-extra/clangd/XRefs.cpp

153

Fair enough! Will abandon this patch.

clang-tools-extra/clangd/XRefs.cpp

SymbolLocation getPreferredLocation(const Location &ASTLoc,
   Symbol ASTSym, IdxSym;
   ASTSym.ID = IdxSym.ID = SymbolID("dummy_id");
   ASTSym.CanonicalDeclaration = toIndexLocation(ASTLoc, Scratch);
   IdxSym.CanonicalDeclaration = IdxLoc;
   auto Merged = mergeSymbol(ASTSym, IdxSym);
   return Merged.CanonicalDeclaration;
 }
 
-std::vector<const Decl *> getDeclAtPosition(ParsedAST &AST, SourceLocation Pos,
-                                            DeclRelationSet Relations) {
-  FileID FID;
-  unsigned Offset;
-  std::tie(FID, Offset) = AST.getSourceManager().getDecomposedSpellingLoc(Pos);
+std::vector<const Decl *> getDeclAtOffset(ParsedAST &AST, unsigned Offset,
   SelectionTree Selection(AST.getASTContext(), AST.getTokens(), Offset);
   std::vector<const Decl *> Result;
   if (const SelectionTree::Node *N = Selection.commonAncestor()) {
     auto Decls = targetDecl(N->ASTNode, Relations);
     Result.assign(Decls.begin(), Decls.end());
   }
   return Result;
 }
 
+std::vector<const Decl *> getDeclAtPosition(ParsedAST &AST, SourceLocation Pos,
+                                            DeclRelationSet Relations) {
+  FileID FID;
+  unsigned Offset;
+  std::tie(FID, Offset) = AST.getSourceManager().getDecomposedSpellingLoc(Pos);
+  std::vector<const Decl *> Result = getDeclAtOffset(AST, Offset, Relations);
+  // If no declaration was found at this offset, try the previous offset.
+  // This compensates for the fact that SelectionTree interprets an offset
+  // as applying to the character after rather than the character before,
+  // allowing go-to-definition to work at the end of an identifier.
+  if (Result.empty() && Offset > 0) {
+    Result = getDeclAtOffset(AST, Offset - 1, Relations);
+  }
+  return Result;
+}
+
 llvm::Optional<Location> makeLocation(ASTContext &AST, SourceLocation TokLoc,
                                       llvm::StringRef TUPath) {
   const SourceManager &SourceMgr = AST.getSourceManager();
   const FileEntry *F = SourceMgr.getFileEntryForID(SourceMgr.getFileID(TokLoc));
   if (!F)
     return None;
   auto FilePath = getCanonicalPath(F, SourceMgr);
   if (!FilePath) {

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

const char *Tests[] = {
       R"cpp(
         struct X {
           X& [[operator]]++() {}
         };
         void foo(X& x) {
           +^+x;
         }
       )cpp",
+
+      R"cpp(// End of identifier (definition)
+        void [[func]]^() {}
+      )cpp",
+
+      R"cpp(// End of identifier (reference)
+        void [[func]]() {}
+        void test() {
+          func^();
+        }
+      )cpp",
   };
   for (const char *Test : Tests) {
     Annotations T(Test);
     llvm::Optional<Range> WantDecl;
     llvm::Optional<Range> WantDef;
     if (!T.ranges().empty())
       WantDecl = WantDef = T.range();
     if (!T.ranges("decl").empty())