[clangd] Handle AttributedTypeLoc in SelectionTree (#163926)

This ensures a method name continues to target the method's
declaration even if the method's type uses an attribute. Before
this change, the AttributedTypeLoc would claim the method name.

Fixes clangd/clangd#2488

Author: quanzhuo

clang-tools-extra/clangd/Selection.cpp

@@ -958,6 +958,18 @@ class SelectionVisitor : public RecursiveASTVisitor<SelectionVisitor> {
         claimRange(SourceRange(FTL.getLParenLoc(), FTL.getEndLoc()), Result);
         return;
       }
+      if (auto ATL = TL->getAs<AttributedTypeLoc>()) {
+        // For attributed function types like `int foo() [[attr]]`, the
+        // AttributedTypeLoc's range includes the function name. We want to
+        // allow the function name to be associated with the FunctionDecl
+        // rather than the AttributedTypeLoc, so we only claim the attribute
+        // range itself.
+        if (ATL.getModifiedLoc().getAs<FunctionTypeLoc>()) {
+          // Only claim the attribute's source range, not the whole type.
+          claimRange(ATL.getLocalSourceRange(), Result);
+          return;
+        }
+      }
     }
     claimRange(getSourceRange(N), Result);
   }

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

@@ -311,6 +311,19 @@ TEST(SelectionTest, CommonAncestor) {
       {"[[void foo^()]];", "FunctionProtoTypeLoc"},
       {"[[^void foo^()]];", "FunctionDecl"},
       {"[[void ^foo()]];", "FunctionDecl"},
+      // Tricky case: with function attributes, the AttributedTypeLoc's range
+      // includes the function name, but we want the name to be associated with
+      // the CXXMethodDecl.
+      {"struct X { [[const int* ^Get() const <:[clang::lifetimebound]:> "
+       "{return nullptr;}]]; };",
+       "CXXMethodDecl"},
+      // When the cursor is on the attribute itself, we should select the
+      // AttributedTypeLoc. Note: Due to a bug or deliberate quirk in the AST
+      // modeling of AttributedTypeLoc, its range ends at the attribute name
+      // token, not including the closing brackets ":>:>".
+      {"struct X { const [[int* Foo() const <:<:clang::life^timebound]]:>:> "
+       "{return nullptr;}; };",
+       "AttributedTypeLoc"},
       // Tricky case: two VarDecls share a specifier.
       {"[[int ^a]], b;", "VarDecl"},
       {"[[int a, ^b]];", "VarDecl"},