[clang][libclang] Fix auto function parameter type reporting

When auto is used as a function parameter type, clang-c API was
incorrectly reporting it as TypeRef with kind unexposed instead of
reporting it as CXType_Auto.

The issue was that CursorVisitor did not have a handler for AutoTypeLoc,
so it fell back to default behavior which resulted in unexposed types.

Add VisitAutoTypeLoc method to properly handle auto type locations in
function parameters. This brings consistency with how auto is handled
in variable declarations.

Fixes issue #172072

Author: dev-priyanshu15

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

@@ -0,0 +1,14 @@
+// Test case for auto function parameter reported as CXType_Auto
+// This test verifies that auto parameters in function declarations
+// are properly reported as CXType_Auto in the libclang C API
+// See issue #172072
+
+// RUN: c-index-test -test-type %s | FileCheck %s
+
+// Function with auto parameter
+int bar(auto p) {
+  return p;
+}
+
+// CHECK: FunctionDecl=bar:{{.*}} CXType_FunctionProto
+// CHECK: ParmDecl=p:{{.*}} CXType_Auto

clang/tools/libclang/CIndex.cpp

@@ -1789,6 +1789,15 @@ bool CursorVisitor::VisitAdjustedTypeLoc(AdjustedTypeLoc TL) {
   return Visit(TL.getOriginalLoc());
 }
 
+bool CursorVisitor::VisitAutoTypeLoc(AutoTypeLoc TL) {
+  // AutoTypeLoc represents the location of an auto type specifier.
+  // We do not visit children because the auto type itself is complete.
+  // This handler ensures that auto function parameters are properly
+  // reported as CXType_Auto in the libclang C API, rather than being
+  // incorrectly reported as TypeRef/unexposed.
+  return false;
+}
+
 bool CursorVisitor::VisitDeducedTemplateSpecializationTypeLoc(
     DeducedTemplateSpecializationTypeLoc TL) {
   if (VisitTemplateName(TL.getTypePtr()->getTemplateName(),

clang/tools/libclang/CXType.cpp

@@ -150,6 +150,16 @@ CXType cxtype::MakeCXType(QualType T, CXTranslationUnit TU) {
       return MakeCXType(PTT->getInnerType(), TU);
     }
 
+    // Handle auto in function parameters
+    if (auto *TTP = T->getAs<TemplateTypeParmType>()) {
+      auto *D = TTP->getDecl();
+      if (D && D->isImplicit()) {
+        if (auto *TC = D->getTypeConstraint(); !TC) {
+          TK = CXType_Auto;
+        }
+      }
+    }
+
     ASTContext &Ctx = cxtu::getASTUnit(TU)->getASTContext();
     if (Ctx.getLangOpts().ObjC) {
       QualType UnqualT = T.getUnqualifiedType();