packed -> C,packed

components/calendar/src/provider/chinese_based.rs

@@ -143,7 +143,7 @@ impl<'data> ChineseBasedCacheV1<'data> {
     derive(databake::Bake),
     databake(path = icu_calendar::provider),
 )]
-#[repr(packed)]
+#[repr(C, packed)]
 pub struct PackedChineseBasedYearInfo(pub u8, pub u8, pub u8);
 
 impl PackedChineseBasedYearInfo {

components/calendar/src/provider/islamic.rs

@@ -156,7 +156,7 @@ impl<'data> IslamicCacheV1<'data> {
     databake(path = icu_calendar::provider),
 )]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize))]
-#[repr(packed)]
+#[repr(C, packed)]
 pub struct PackedIslamicYearInfo(pub u8, pub u8);
 
 impl fmt::Debug for PackedIslamicYearInfo {

components/casemap/src/provider/exceptions_builder.rs

@@ -71,7 +71,7 @@ impl ExceptionHeader {
 /// In this struct the RESERVED bit is still allowed to be set, and it will produce a different
 /// exception header, but it will not have any other effects.
 #[derive(Copy, Clone, PartialEq, Eq, ULE)]
-#[repr(packed)]
+#[repr(C, packed)]
 pub struct ExceptionHeaderULE {
     slot_presence: SlotPresence,
     bits: ExceptionBitsULE,

utils/zerovec/derive/src/ule.rs

@@ -10,10 +10,10 @@ use syn::spanned::Spanned;
 use syn::{Data, DeriveInput, Error};
 
 pub fn derive_impl(input: &DeriveInput) -> TokenStream2 {
-    if !utils::has_valid_repr(&input.attrs, |r| r == "packed" || r == "transparent") {
+    if !utils::has_transparent_or_cpacked_repr(&input.attrs) {
         return Error::new(
             input.span(),
-            "derive(ULE) must be applied to a #[repr(packed)] or #[repr(transparent)] type",
+            "derive(ULE) must be applied to a #[repr(C, packed)] or #[repr(transparent)] type",
         )
         .to_compile_error();
     }

utils/zerovec/derive/src/utils.rs

@@ -21,6 +21,26 @@ pub fn has_valid_repr(attrs: &[Attribute], predicate: impl Fn(&Ident) -> bool +
     })
 }
 
+pub fn has_transparent_or_cpacked_repr(attrs: &[Attribute]) -> bool {
+    let mut found_transparent = false;
+    let mut found_packed = false;
+    let mut found_c = false;
+    for attr in attrs.iter().filter(|a| a.path().is_ident("repr")) {
+        if let Some(pieces) = attr.parse_args::<IdentListAttribute>().ok() {
+            for piece in pieces.idents.iter() {
+                if piece == "C" || piece == "c" {
+                    found_c = true;
+                } else if piece == "transparent" {
+                    found_transparent = true;
+                } else if piece == "packed" {
+                    found_packed = true;
+                }
+            }
+        }
+    }
+    (found_c && found_packed) || found_transparent
+}
+
 // An attribute that is a list of idents
 struct IdentListAttribute {
     idents: Punctuated<Ident, Token![,]>,
@@ -60,7 +80,7 @@ pub fn repr_for(f: &Fields) -> TokenStream2 {
     if f.len() == 1 {
         quote!(transparent)
     } else {
-        quote!(packed)
+        quote!(C, packed)
     }
 }
 

utils/zerovec/derive/src/varule.rs

@@ -15,10 +15,10 @@ pub fn derive_impl(
     input: &DeriveInput,
     custom_varule_validator: Option<TokenStream2>,
 ) -> TokenStream2 {
-    if !utils::has_valid_repr(&input.attrs, |r| r == "packed" || r == "transparent") {
+    if !utils::has_transparent_or_cpacked_repr(&input.attrs) {
         return Error::new(
             input.span(),
-            "derive(VarULE) must be applied to a #[repr(packed)] or #[repr(transparent)] type",
+            "derive(VarULE) must be applied to a #[repr(C, packed)] or #[repr(transparent)] type",
         )
         .to_compile_error();
     }