From b898cc666ffb36431398c9cae1fdf5911f3129d2 Mon Sep 17 00:00:00 2001
From: Pierre Avital <pierre.avital@me.com>
Date: Sat, 22 Jun 2024 11:15:22 +0200
Subject: [PATCH] Start work on #[repr(C, uX)] enums

---
 stabby-macros/src/enums.rs | 87 ++++++++++++++++++++++++++++++--------
 1 file changed, 70 insertions(+), 17 deletions(-)

diff --git a/stabby-macros/src/enums.rs b/stabby-macros/src/enums.rs
index 894338a..5b2728e 100644
--- a/stabby-macros/src/enums.rs
+++ b/stabby-macros/src/enums.rs
@@ -53,6 +53,33 @@ impl syn::parse::Parse for Repr {
         }
     }
 }
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub struct FullRepr {
+    repr: Option<Repr>,
+    is_c: bool,
+}
+impl syn::parse::Parse for FullRepr {
+    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+        let mut this = FullRepr {
+            repr: None,
+            is_c: false,
+        };
+        while !input.is_empty() {
+            match input.parse()? {
+                Repr::C => this.is_c = true,
+                repr => match this.repr {
+                    None => this.repr = Some(repr),
+                    Some(r) if repr == r => {}
+                    _ => return Err(input.error("Determinants may only have one representation. You can use `#[repr(C, u8)]` to use a u8 as determinant while ensuring all variants have their data in C layout.")),
+                },
+            }
+            if !input.is_empty() {
+                let _: syn::token::Comma = input.parse()?;
+            }
+        }
+        Ok(this)
+    }
+}
 
 pub fn stabby(
     attrs: Vec<Attribute>,
@@ -63,7 +90,7 @@ pub fn stabby(
 ) -> TokenStream {
     let st = crate::tl_mod();
     let unbound_generics = &generics.params;
-    let mut repr = None;
+    let mut repr: Option<FullRepr> = None;
     let repr_ident = quote::format_ident!("repr");
     let mut new_attrs = Vec::with_capacity(attrs.len());
     for a in attrs {
@@ -77,6 +104,15 @@ pub fn stabby(
             new_attrs.push(a)
         }
     }
+    if matches!(
+        repr,
+        Some(FullRepr {
+            repr: Some(Repr::Stabby),
+            is_c: true
+        })
+    ) {
+        panic!("#[repr(C)] and #[repr(stabby)] connot be combined")
+    }
     if data.variants.is_empty() {
         todo!("empty enums are not supported by stabby YET")
     }
@@ -87,20 +123,29 @@ pub fn stabby(
     let mut report = Vec::new();
     for variant in variants {
         match &variant.fields {
+            syn::Fields::Named(f) if matches!(repr, Some(FullRepr { is_c: true, .. })) => {
+                todo!("stabby support for named fields is undergoing implementation...")
+            }
             syn::Fields::Named(_) => {
-                panic!("stabby does not support named fields in enum variants")
+                panic!("stabby only supports named fields in #[repr(C, uX)] enums");
             }
             syn::Fields::Unnamed(f) => {
-                assert_eq!(
-                    f.unnamed.len(),
-                    1,
-                    "stabby only supports one field per enum variant"
-                );
-                has_non_empty_fields = true;
-                let f = f.unnamed.first().unwrap();
-                let ty = &f.ty;
-                layout = quote!(#st::Union<#layout, core::mem::ManuallyDrop<#ty>>);
-                report.push((variant.ident.to_string(), ty));
+                if f.unnamed.len() != 1 && matches!(repr, Some(FullRepr { is_c: true, .. })) {
+                    todo!(
+                        "stabby support for multiple fields per enum is restricted to named fields"
+                    )
+                } else {
+                    assert_eq!(
+                        f.unnamed.len(),
+                        1,
+                        "stabby only supports multiple fields per enum variant in #[repr(C, uX)] enums"
+                    );
+                    has_non_empty_fields = true;
+                    let f = f.unnamed.first().unwrap();
+                    let ty = &f.ty;
+                    layout = quote!(#st::Union<#layout, core::mem::ManuallyDrop<#ty>>);
+                    report.push((variant.ident.to_string(), ty));
+                }
             }
             syn::Fields::Unit => {
                 report.push((variant.ident.to_string(), &unit));
@@ -108,10 +153,13 @@ pub fn stabby(
         }
     }
     let report = crate::report(&report);
-    let repr = match repr {
+    let reprstr = match repr
+        .as_ref()
+        .and_then(|r| if r.is_c { Some(Repr::C) } else { r.repr })
+    {
         None | Some(Repr::Stabby) => {
             if !has_non_empty_fields {
-                panic!("Your enum doesn't have any field with values: use #[repr(C)] or #[repr(u*)] instead")
+                panic!("Your enum doesn't have any field with values: use #[repr(C)] or (preferably) #[repr(u*)] instead")
             }
             return repr_stabby(
                 &new_attrs,
@@ -135,13 +183,18 @@ pub fn stabby(
         Some(Repr::I64) => "i64",
         Some(Repr::Isize) => "isize",
     };
-    let reprid = quote::format_ident!("{}", repr);
+    let reprid = quote::format_ident!("{}", reprstr);
+    let reprattr = if repr.map_or(false, |r| r.is_c) {
+        quote!(#[repr(C, #reprid)])
+    } else {
+        quote!(#[repr(#reprid)])
+    };
     layout = quote!(#st::Tuple<#reprid, #layout>);
     let sident = format!("{ident}");
     let (report, report_bounds) = report;
     quote! {
         #(#new_attrs)*
-        #[repr(#reprid)]
+        #reprattr
         #vis enum #ident #generics {
             #variants
         }
@@ -159,7 +212,7 @@ pub fn stabby(
                 module: #st::str::Str::new(core::module_path!()),
                 fields: unsafe {#st::StableLike::new(#report)},
                 version: 0,
-                tyty: #st::report::TyTy::Enum(#st::str::Str::new(#repr)),
+                tyty: #st::report::TyTy::Enum(#st::str::Str::new(#reprstr)),
             };
             const ID: u64 = #st::report::gen_id(Self::REPORT);
         }