[clangd] Fix auto expand not work on "const au^to s = 123;"

[hokein]

as discussed, this is an issue of selection tree (selection tree should give the AutoTypeLoc on const aut^o).

clang-tools-extra/clangd/refactor/tweaks/ExpandAutoType.cpp

 REGISTER_TWEAK(ExpandAutoType)
 
 std::string ExpandAutoType::title() const { return "Expand auto type"; }
 
 bool ExpandAutoType::prepare(const Selection& Inputs) {
   CachedLocation = llvm::None;
   if (auto *Node = Inputs.ASTSelection.commonAncestor()) {
     if (auto *TypeNode = Node->ASTNode.get<TypeLoc>()) {
-      if (const AutoTypeLoc Result = TypeNode->getAs<AutoTypeLoc>()) {
+      auto Node = *TypeNode;
+      // Skip any qualifiers (e.g. const) around auto.
+      if (const auto QTL = Node.getAs<QualifiedTypeLoc>())
+        Node = QTL.getUnqualifiedLoc();
+      if (const AutoTypeLoc Result = Node.getAs<AutoTypeLoc>())
         CachedLocation = Result;
-      }
-    }
-  }
   return (bool) CachedLocation;
 }
 
 Expected<Tweak::Effect> ExpandAutoType::apply(const Selection& Inputs) {
   auto& SrcMgr = Inputs.AST.getASTContext().getSourceManager();
 
   llvm::Optional<clang::QualType> DeducedType =
       getDeducedType(Inputs.AST, CachedLocation->getBeginLoc());

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

TEST(TweakTest, ExpandAutoType) {
   // replace array types
   Input = R"cpp(
     au^to x = "test";
   )cpp";
   Output = R"cpp(
     const char * x = "test";
   )cpp";
   checkTransform(ID, Input, Output);
+
+  // qualified auto type
+  Input = R"cpp(
+    class Foo {};
+    const au^to x = Foo();
+  )cpp";
+  Output = R"cpp(
+    class Foo {};
+    const Foo x = Foo();
+  )cpp";
+  checkTransform(ID, Input, Output);
+
+  Input = R"cpp(
+    volatile au^to x = 1;
+  )cpp";
+  Output = R"cpp(
+    volatile int x = 1;
+  )cpp";
+  checkTransform(ID, Input, Output);
+
+  Input = R"cpp(
+    class Foo {};
+    const au^to *x = new Foo();
+  )cpp";
+  Output = R"cpp(
+    class Foo {};
+    const Foo *x = new Foo();
+  )cpp";
+  checkTransform(ID, Input, Output);
 }
 
 } // namespace
 } // namespace clangd
 } // namespace clang