[Clang] Retain the angle loci for invented template parameters of constraints (#92104)

Clangd uses it to determine whether the argument is within the selection
range.

Fixes https://github.com/clangd/clangd/issues/2033

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

@@ -589,6 +589,12 @@ TEST(SelectionTest, CommonAncestor) {
         auto x = [[ns::^C<int>]];
       )cpp",
        "ConceptReference"},
+      {R"cpp(
+        template <typename T, typename K>
+        concept D = true;
+        template <typename T> void g(D<[[^T]]> auto abc) {}
+      )cpp",
+       "TemplateTypeParmTypeLoc"},
   };
 
   for (const Case &C : Cases) {

clang/lib/Sema/SemaType.cpp

@@ -3099,7 +3099,8 @@ InventTemplateParameter(TypeProcessingState &state, QualType T,
       // The 'auto' appears in the decl-specifiers; we've not finished forming
       // TypeSourceInfo for it yet.
       TemplateIdAnnotation *TemplateId = D.getDeclSpec().getRepAsTemplateId();
-      TemplateArgumentListInfo TemplateArgsInfo;
+      TemplateArgumentListInfo TemplateArgsInfo(TemplateId->LAngleLoc,
+                                                TemplateId->RAngleLoc);
       bool Invalid = false;
       if (TemplateId->LAngleLoc.isValid()) {
         ASTTemplateArgsPtr TemplateArgsPtr(TemplateId->getTemplateArgs(),

clang/test/AST/ast-dump-concepts.cpp

@@ -107,3 +107,16 @@ auto FooFunc(C auto V) -> C decltype(auto) {
 }
 
 }
+
+namespace constraint_auto_params {
+
+template <class T, class K>
+concept C = true;
+
+template<class T>
+void g(C<T> auto Foo) {}
+
+// CHECK: TemplateTypeParmDecl {{.*}} depth 0 index 1 Foo:auto
+// CHECK-NEXT: `-ConceptSpecializationExpr {{.*}} <col:8, col:11>
+
+}