ir: Fall back to get the cursors from the type if we find no param decls.

It seems libclang sometimes doesn't expose the right paramdecl cursors.

This should be reported upstream, but it's easy enough to workaround. It
loses the parameter names which is a bit unfortunate but...

Fixes #1778

Author: emilio

src/ir/function.rs

@@ -311,7 +311,7 @@ fn args_from_ty_and_cursor(
     cursor: &clang::Cursor,
     ctx: &mut BindgenContext,
 ) -> Vec<(Option<String>, TypeId)> {
-    let cursor_args = cursor.args().unwrap().into_iter();
+    let cursor_args = cursor.args().unwrap_or_default().into_iter();
     let type_args = ty.args().unwrap_or_default().into_iter();
 
     // Argument types can be found in either the cursor or the type, but argument names may only be
@@ -421,7 +421,16 @@ impl FunctionSig {
                     }
                     CXChildVisit_Continue
                 });
-                args
+
+                if args.is_empty() {
+                    // FIXME(emilio): Sometimes libclang doesn't expose the
+                    // right AST for functions tagged as stdcall and such...
+                    //
+                    // https://bugs.llvm.org/show_bug.cgi?id=45919
+                    args_from_ty_and_cursor(&ty, &cursor, ctx)
+                } else {
+                    args
+                }
             }
         };
 

tests/expectations/tests/function-typedef-stdcall.rs

@@ -0,0 +1,19 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+pub type PFN_VIGEM_X360_NOTIFICATION = ::std::option::Option<
+    unsafe extern "C" fn(
+        arg1: *mut ::std::os::raw::c_void,
+        arg2: *mut ::std::os::raw::c_void,
+        arg3: ::std::os::raw::c_uchar,
+        arg4: ::std::os::raw::c_uchar,
+        arg5: ::std::os::raw::c_uchar,
+        arg6: *mut ::std::os::raw::c_void,
+    ),
+>;

tests/expectations/tests/objc_property_fnptr.rs

@@ -46,7 +46,11 @@ pub trait IFoo: Sized + std::ops::Deref {
     unsafe fn setFunc_(
         self,
         func: ::std::option::Option<
-            unsafe extern "C" fn() -> ::std::os::raw::c_int,
+            unsafe extern "C" fn(
+                arg1: ::std::os::raw::c_char,
+                arg2: ::std::os::raw::c_short,
+                arg3: f32,
+            ) -> ::std::os::raw::c_int,
         >,
     ) where
         <Self as std::ops::Deref>::Target: objc::Message + Sized,

tests/headers/function-typedef-stdcall.h

@@ -0,0 +1,12 @@
+typedef
+    void __stdcall
+    EVT_VIGEM_X360_NOTIFICATION(
+        void* Client,
+        void* Target,
+        unsigned char LargeMotor,
+        unsigned char SmallMotor,
+        unsigned char LedNumber,
+        void* UserData
+    );
+
+typedef EVT_VIGEM_X360_NOTIFICATION *PFN_VIGEM_X360_NOTIFICATION;