transpile: Propagate cast of EnumConstant to its own integral type

Author: Rua

c2rust-transpile/src/translator/enums.rs

@@ -142,7 +142,7 @@ impl<'c> Translation<'c> {
         type_enum_id == constant_enum_id
     }
 
-    fn enum_integral_type(&self, enum_id: CEnumId) -> CQualTypeId {
+    pub fn enum_integral_type(&self, enum_id: CEnumId) -> CQualTypeId {
         match self.ast_context[enum_id].kind {
             CDeclKind::Enum {
                 integral_type: Some(integral_type),

c2rust-transpile/src/translator/mod.rs

@@ -3053,11 +3053,10 @@ impl<'c> Translation<'c> {
                     CDeclKind::EnumConstant { .. } => {
                         // If the variable is actually an `EnumConstant`, we need to add a cast to
                         // the expected integral type.
-                        if !self.enum_constant_matches_type(
-                            override_ty.unwrap_or(qual_ty).ctype,
-                            decl_id,
-                        ) {
-                            val = self.convert_cast_from_enum(qual_ty.ctype, val)?;
+                        let target_type_id = override_ty.unwrap_or(qual_ty);
+
+                        if !self.enum_constant_matches_type(target_type_id.ctype, decl_id) {
+                            val = self.convert_cast_from_enum(target_type_id.ctype, val)?;
                         }
 
                         return Ok(WithStmts::new_val(val));
@@ -3597,6 +3596,18 @@ impl<'c> Translation<'c> {
                 if self.enum_constant_matches_type(target_type_id.ctype, decl_id) {
                     return true;
                 }
+
+                let source_enum_id = self.ast_context.parents[&decl_id];
+                let source_integral_type_id = self.enum_integral_type(source_enum_id);
+                let target_type_resolved_id = self
+                    .ast_context
+                    .resolve_type_id_no_typedef(target_type_id.ctype);
+
+                // Likewise, if we are casting to the inner integral type of the enum, then
+                // translate the enum constant directly as that.
+                if target_type_resolved_id == source_integral_type_id.ctype {
+                    return true;
+                }
             }
         }
 

c2rust-transpile/tests/snapshots/snapshots__transpile@enums.c.2021.clang15.snap

@@ -41,9 +41,8 @@ pub unsafe extern "C" fn test_enums() {
     let mut e: Foo = Foo1;
     let mut enum_enum: ::core::ffi::c_int =
         (e as ::core::ffi::c_uint == foo as ::core::ffi::c_uint) as ::core::ffi::c_int;
-    let mut enum_constant: ::core::ffi::c_int = (e as ::core::ffi::c_uint
-        == Foo0 as ::core::ffi::c_int as ::core::ffi::c_uint)
-        as ::core::ffi::c_int;
+    let mut enum_constant: ::core::ffi::c_int =
+        (e as ::core::ffi::c_uint == Foo0 as ::core::ffi::c_uint) as ::core::ffi::c_int;
     let mut wrong_enum_enum: ::core::ffi::c_int =
         (e as ::core::ffi::c_uint == bar as ::core::ffi::c_uint) as ::core::ffi::c_int;
     let mut wrong_enum_constant: ::core::ffi::c_int = (e as ::core::ffi::c_uint

c2rust-transpile/tests/snapshots/snapshots__transpile@enums.c.2024.clang15.snap

@@ -42,9 +42,8 @@ pub unsafe extern "C" fn test_enums() {
     let mut e: Foo = Foo1;
     let mut enum_enum: ::core::ffi::c_int =
         (e as ::core::ffi::c_uint == foo as ::core::ffi::c_uint) as ::core::ffi::c_int;
-    let mut enum_constant: ::core::ffi::c_int = (e as ::core::ffi::c_uint
-        == Foo0 as ::core::ffi::c_int as ::core::ffi::c_uint)
-        as ::core::ffi::c_int;
+    let mut enum_constant: ::core::ffi::c_int =
+        (e as ::core::ffi::c_uint == Foo0 as ::core::ffi::c_uint) as ::core::ffi::c_int;
     let mut wrong_enum_enum: ::core::ffi::c_int =
         (e as ::core::ffi::c_uint == bar as ::core::ffi::c_uint) as ::core::ffi::c_int;
     let mut wrong_enum_constant: ::core::ffi::c_int = (e as ::core::ffi::c_uint