[clang][libclang] Report auto function parameters as CXType_Auto

Author: dev-priyanshu15

clang/test/Index/auto-function-param.cpp

@@ -12,3 +12,13 @@ int bar(auto p) {
 
 // CHECK: FunctionDecl=bar:{{.*}} CXType_FunctionProto
 // CHECK: ParmDecl=p:{{.*}} CXType_Auto
+// C++20 constrained auto parameter
+template<typename T>
+concept Integral = __is_integral(T);
+
+int baz(Integral auto q) {
+  return q;
+}
+
+// CHECK: FunctionDecl=baz:{{.*}} CXType_FunctionProto
+// CHECK: ParmDecl=q:{{.*}} CXType_Auto

clang/tools/libclang/CXType.cpp

@@ -150,13 +150,11 @@ CXType cxtype::MakeCXType(QualType T, CXTranslationUnit TU) {
       return MakeCXType(PTT->getInnerType(), TU);
     }
 
-    // Handle auto in function parameters
+    // Handle auto in function parameters (including constrained auto)
     if (auto *TTP = T->getAs<TemplateTypeParmType>()) {
       auto *D = TTP->getDecl();
       if (D && D->isImplicit()) {
-        if (auto *TC = D->getTypeConstraint(); !TC) {
-          TK = CXType_Auto;
-        }
+        TK = CXType_Auto;
       }
     }