[unsage] Fix missing transmute in function pointer cast

Fixes test fn_ptr_typedef_cast.c

Author: nunoplopes

cpp2rust/converter/converter.cpp

@@ -2039,12 +2039,29 @@ void Converter::ConvertParamTy(clang::QualType param_type, clang::Expr *expr) {
   if (param_type->isReferenceType()) {
     PushExprKind push(*this, ExprKind::AddrOf);
     ConvertVarInit(param_type, expr);
+  } else if (FunctionPointerCastNeedsTransmute() &&
+             param_type->isFunctionPointerType() &&
+             expr->getType()->isFunctionPointerType() &&
+             !IsCastRedundantInRust(expr, param_type)) {
+    ConvertFunctionPointerTransmute(expr, param_type);
+    return;
   } else {
     ConvertVarInit(param_type, expr);
   }
   ConvertParamTyPointerCastIfNeeded(param_type, expr);
 }
 
+void Converter::ConvertFunctionPointerTransmute(clang::Expr *expr,
+                                                clang::QualType type) {
+  StrCat("std::mem::transmute::<");
+  Convert(expr->getType());
+  StrCat(',');
+  Convert(type);
+  StrCat(">(");
+  Convert(expr);
+  StrCat(')');
+}
+
 void Converter::ConvertParamTyPointerCastIfNeeded(clang::QualType param_type,
                                                   clang::Expr *expr) {
   if (!param_type->isPointerType() || !expr->getType()->isPointerType() ||
@@ -2625,13 +2642,7 @@ bool Converter::VisitExplicitCastExpr(clang::ExplicitCastExpr *expr) {
     }
     if (type->isFunctionPointerType() ||
         sub_expr->getType()->isFunctionPointerType()) {
-      StrCat("std::mem::transmute::<");
-      Convert(sub_expr->getType());
-      StrCat(',');
-      Convert(type);
-      StrCat(">(");
-      Convert(sub_expr);
-      StrCat(')');
+      ConvertFunctionPointerTransmute(sub_expr, type);
       return false;
     }
     if (type->isEnumeralType() && !sub_expr->getType()->isEnumeralType()) {

cpp2rust/converter/converter.h

@@ -318,6 +318,10 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
   virtual void ConvertParamTyPointerCastIfNeeded(clang::QualType param_type,
                                                  clang::Expr *expr);
 
+  virtual bool FunctionPointerCastNeedsTransmute() const { return true; }
+
+  void ConvertFunctionPointerTransmute(clang::Expr *expr, clang::QualType type);
+
   void EmitHoistedArgs(CallInfo &info);
 
   void EmitArgList(const CallInfo &info);

cpp2rust/converter/models/converter_refcount.h

@@ -114,6 +114,7 @@ class ConverterRefCount final : public Converter {
 
   // FnPtr does not implement Copy
   bool FunctionPointerImplementsCopy() const override { return false; }
+  bool FunctionPointerCastNeedsTransmute() const override { return false; }
 
   bool VisitCallExpr(clang::CallExpr *expr) override;
 

tests/unit/fn_ptr_typedef_cast.c

@@ -1,4 +1,3 @@
-// XFAIL: unsafe
 #include <assert.h>
 #include <stddef.h>
 

tests/unit/out/unsafe/fn_ptr_typedef_cast.rs

@@ -28,7 +28,10 @@ unsafe fn main_0() -> i32 {
     assert!(((((unsafe { call_with_ulong_0(Some(same_type_1),) }) == (4_u64)) as i32) != 0));
     assert!(
         ((((unsafe {
-            call_with_ulong_0(Some(via_size_t_param_2) as Option<unsafe fn(u64) -> u64>)
+            call_with_ulong_0(std::mem::transmute::<
+                Option<unsafe fn(usize) -> u64>,
+                Option<unsafe fn(u64) -> u64>,
+            >(Some(via_size_t_param_2)))
         }) == (4_u64)) as i32)
             != 0)
     );