Require a repr attribute

Author: meithecatte

enumflags_derive/src/lib.rs

@@ -159,10 +159,12 @@ fn gen_enumflags(ident: &Ident, item: &DeriveInput, data: &DataEnum)
     let variants = data.variants.iter().map(|v| &v.ident);
     let variants_len = data.variants.len();
     let names = std::iter::repeat(&ident);
-    let ty = extract_repr(&item.attrs)?
-        .unwrap_or_else(|| Ident::new("usize", span));
 
     let deferred = verify_flag_values(ident, data.variants.iter())?;
+
+    let ty = extract_repr(&item.attrs)?
+        .ok_or_else(|| syn::Error::new_spanned(&ident,
+                        "repr attribute missing. Add #[repr(u64)] or a similar attribute to specify the size of the bitfield."))?;
     let std_path = quote_spanned!(span => ::enumflags2::_internal::core);
     let all = if variants_len == 0 {
         quote!(0)

src/lib.rs

@@ -9,8 +9,8 @@
 //! use enumflags2::{bitflags, BitFlags};
 //!
 //! #[bitflags]
-//! #[derive(Copy, Clone, Debug, PartialEq)]
 //! #[repr(u8)]
+//! #[derive(Copy, Clone, Debug, PartialEq)]
 //! enum Test {
 //!     A = 0b0001,
 //!     B = 0b0010,
@@ -105,6 +105,7 @@ pub trait BitFlag: Copy + Clone + 'static + _internal::RawBitFlags {
     /// ```
     /// # use enumflags2::{bitflags, BitFlags};
     /// #[bitflags]
+    /// #[repr(u8)]
     /// #[derive(Clone, Copy, PartialEq, Eq)]
     /// enum MyFlag {
     ///     One = 1 << 0,
@@ -134,6 +135,7 @@ pub trait BitFlag: Copy + Clone + 'static + _internal::RawBitFlags {
     /// ```
     /// # use enumflags2::{bitflags, BitFlags};
     /// #[bitflags]
+    /// #[repr(u8)]
     /// #[derive(Clone, Copy, PartialEq, Eq)]
     /// enum MyFlag {
     ///     One = 1 << 0,
@@ -289,6 +291,7 @@ where
     /// ```
     /// # use enumflags2::{bitflags, BitFlags};
     /// #[bitflags]
+    /// #[repr(u8)]
     /// #[derive(Clone, Copy, PartialEq, Eq)]
     /// enum MyFlag {
     ///     One = 1 << 0,
@@ -315,6 +318,7 @@ where
     /// ```
     /// # use enumflags2::{bitflags, BitFlags};
     /// #[bitflags]
+    /// #[repr(u8)]
     /// #[derive(Clone, Copy, PartialEq, Eq)]
     /// enum MyFlag {
     ///     One = 1 << 0,

test_suite/ui/overlapping_flags.rs

@@ -1,4 +1,5 @@
 #[enumflags2::bitflags]
+#[repr(u8)]
 #[derive(Copy, Clone)]
 enum Foo {
     SomeFlag = 1 << 0,

test_suite/ui/overlapping_flags.stderr

@@ -1,7 +1,7 @@
 error[E0081]: discriminant value `1` already exists
- --> $DIR/overlapping_flags.rs:5:23
+ --> $DIR/overlapping_flags.rs:6:23
   |
-4 |     SomeFlag = 1 << 0,
+5 |     SomeFlag = 1 << 0,
   |                ------ first use of `1`
-5 |     OverlappingFlag = 1 << 0,
+6 |     OverlappingFlag = 1 << 0,
   |                       ^^^^^^ enum already has `1`