transpile: Propagate cast of EnumConstant to its own integral type

Author: Rua

c2rust-transpile/src/translator/enums.rs

@@ -163,7 +163,7 @@ 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

@@ -3104,10 +3104,10 @@ impl<'c> Translation<'c> {
                 // If the variable is actually an `EnumConstant`, we need to add a cast to the
                 // expected integral type.
                 if let &CDeclKind::EnumConstant { .. } = decl {
-                    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));
@@ -3551,6 +3551,18 @@ impl<'c> Translation<'c> {
                         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.snap

@@ -33,9 +33,8 @@ 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.snap

@@ -34,9 +34,8 @@ 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