From 6f32a2814745d227189bfcca273594b76769d8ea Mon Sep 17 00:00:00 2001
From: Mads Marquart <mads@marquart.dk>
Date: Mon, 17 Jan 2022 18:48:46 +0100
Subject: [PATCH] Add initial derive(Encode, RefEncode) implementation

---
 objc2-encode/tests/test_derive.rs | 25 ++++++++++
 objc2-proc-macros/src/derive.rs   | 76 ++++++++++++++++++++++++++-----
 objc2-proc-macros/src/lib.rs      |  1 +
 objc2-proc-macros/src/utils.rs    | 30 ++++++++++++
 4 files changed, 121 insertions(+), 11 deletions(-)
 create mode 100644 objc2-proc-macros/src/utils.rs

diff --git a/objc2-encode/tests/test_derive.rs b/objc2-encode/tests/test_derive.rs
index ae2abbb7f..fe9f7f308 100644
--- a/objc2-encode/tests/test_derive.rs
+++ b/objc2-encode/tests/test_derive.rs
@@ -20,3 +20,28 @@ fn cgpoint() {
     assert_eq!(CGPoint::ENCODING, enc);
     assert_eq!(CGPoint::ENCODING_REF, Encoding::Pointer(&enc));
 }
+
+#[derive(Encode, RefEncode)]
+#[repr(transparent)]
+struct Transparent {
+    _inner: usize,
+}
+
+#[test]
+fn transparent() {
+    assert_eq!(Transparent::ENCODING, usize::ENCODING);
+    assert_eq!(Transparent::ENCODING_REF, usize::ENCODING_REF);
+}
+
+#[derive(Encode, RefEncode)]
+#[repr(usize)]
+enum MyEnum {
+    _A = 1,
+    _B = 2,
+}
+
+#[test]
+fn enum_repr() {
+    assert_eq!(MyEnum::ENCODING, usize::ENCODING);
+    assert_eq!(MyEnum::ENCODING_REF, usize::ENCODING_REF);
+}
diff --git a/objc2-proc-macros/src/derive.rs b/objc2-proc-macros/src/derive.rs
index 4ee6aab4e..db1c9e97e 100644
--- a/objc2-proc-macros/src/derive.rs
+++ b/objc2-proc-macros/src/derive.rs
@@ -1,24 +1,78 @@
 use proc_macro::TokenStream;
 use quote::quote;
-use syn::DeriveInput;
+use syn::{Data, DeriveInput};
+
+use crate::utils::get_repr;
 
 pub(crate) fn impl_encode(ast: &DeriveInput) -> TokenStream {
-    let name = &ast.ident;
-    let gen = quote! {
-        unsafe impl ::objc2_encode::Encode for #name {
-            const ENCODING: ::objc2_encode::Encoding<'static> = ::objc2_encode::Encoding::Struct(
-                stringify!(#name),
-                &[CGFloat::ENCODING, CGFloat::ENCODING],
-            );
+    let DeriveInput {
+        ident, data, attrs, ..
+    } = ast;
+
+    let repr = match get_repr(&attrs) {
+        Some(repr) => repr,
+        None => panic!("Missing repr"),
+    };
+
+    let encoding = match data {
+        Data::Struct(data) => {
+            let fields = data
+                .fields
+                .iter()
+                .map(|field| &field.ty)
+                .collect::<Vec<_>>();
+            match &*repr.to_string() {
+                "transparent" => {
+                    let field = fields[0];
+                    assert_eq!(fields.len(), 1, "Expected one item");
+                    quote!(<#field as ::objc2_encode::Encode>::ENCODING)
+                }
+                "C" => {
+                    quote!(
+                        ::objc2_encode::Encoding::Struct(
+                            stringify!(#ident),
+                            &[#(<#fields as ::objc2_encode::Encode>::ENCODING),*],
+                        )
+                    )
+                }
+                _ => panic!("Unknown repr"),
+            }
         }
+        Data::Enum(_) => {
+            let ty = match &*repr.to_string() {
+                "usize" => quote! { core::primitive::usize },
+                "isize" => quote! { core::primitive::isize },
+                "u64" => quote! { core::primitive::u64 },
+                "i64" => quote! { core::primitive::i64 },
+                "u32" => quote! { core::primitive::u32 },
+                "i32" => quote! { core::primitive::i32 },
+                "u16" => quote! { core::primitive::u16 },
+                "i16" => quote! { core::primitive::i16 },
+                "u8" => quote! { core::primitive::u8 },
+                "i8" => quote! { core::primitive::i8 },
+                _ => panic!("Unknown repr"),
+            };
+            quote! { <#ty as ::objc2_encode::Encode>::ENCODING }
+        }
+        Data::Union(_) => unimplemented!(),
     };
-    gen.into()
+
+    // TODO: Generics
+    quote! {
+        unsafe impl ::objc2_encode::Encode for #ident {
+            const ENCODING: ::objc2_encode::Encoding<'static> = #encoding;
+        }
+    }
+    .into()
 }
 
 pub(crate) fn impl_ref_encode(ast: &DeriveInput) -> TokenStream {
-    let name = &ast.ident;
+    let DeriveInput { ident, .. } = ast;
+    // TODO: Generics
+    // TODO: Objects
+
     let gen = quote! {
-        unsafe impl ::objc2_encode::RefEncode for #name {
+        unsafe impl ::objc2_encode::RefEncode for #ident {
             const ENCODING_REF: ::objc2_encode::Encoding<'static> = ::objc2_encode::Encoding::Pointer(
                 &<Self as ::objc2_encode::Encode>::ENCODING
             );
diff --git a/objc2-proc-macros/src/lib.rs b/objc2-proc-macros/src/lib.rs
index 9572d3d60..5f13e13c5 100644
--- a/objc2-proc-macros/src/lib.rs
+++ b/objc2-proc-macros/src/lib.rs
@@ -20,6 +20,7 @@ extern "C" {}
 use proc_macro::TokenStream;
 
 mod derive;
+mod utils;
 
 /// TODO
 #[proc_macro_derive(Encode)]
diff --git a/objc2-proc-macros/src/utils.rs b/objc2-proc-macros/src/utils.rs
new file mode 100644
index 000000000..571392922
--- /dev/null
+++ b/objc2-proc-macros/src/utils.rs
@@ -0,0 +1,30 @@
+use syn::{Attribute, Ident, Meta, NestedMeta};
+
+// Taken from `nom-derive`:
+// https://github.com/rust-bakery/nom-derive/blob/5315891a0016b15094d4d0201f7d3ac803e4fc57/nom-derive-impl/src/enums.rs#L60-L90
+pub(crate) fn get_repr(attrs: &[Attribute]) -> Option<Ident> {
+    for attr in attrs {
+        if let Ok(Meta::List(metalist)) = attr.parse_meta() {
+            if let Some(ident) = metalist.path.get_ident() {
+                if ident == "repr" {
+                    for n in metalist.nested.iter() {
+                        match n {
+                            NestedMeta::Meta(meta) => match meta {
+                                Meta::Path(path) => {
+                                    if let Some(word) = path.get_ident() {
+                                        return Some(word.clone());
+                                    } else {
+                                        panic!("unsupported nested type for 'repr'")
+                                    }
+                                }
+                                _ => panic!("unsupported nested type for 'repr'"),
+                            },
+                            _ => panic!("unsupported meta type for 'repr'"),
+                        }
+                    }
+                }
+            }
+        }
+    }
+    None
+}