2 files changed, 139 insertions, 37 deletions

diff --git a/rust/qemu-api-macros/src/lib.rs b/rust/qemu-api-macros/src/lib.rs
index 74a8bc7..7ec2182 100644
--- a/rust/qemu-api-macros/src/lib.rs
+++ b/rust/qemu-api-macros/src/lib.rs
@@ -3,75 +3,81 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 use proc_macro::TokenStream;
-use proc_macro2::Span;
-use quote::{quote, quote_spanned};
+use quote::quote;
 use syn::{
-    parse_macro_input, parse_quote, punctuated::Punctuated, token::Comma, Data, DeriveInput, Field,
-    Fields, Ident, Type, Visibility,
+    parse_macro_input, parse_quote, punctuated::Punctuated, spanned::Spanned, token::Comma, Data,
+    DeriveInput, Field, Fields, Ident, Meta, Path, Token, Type, Variant, Visibility,
 };
 
-struct CompileError(String, Span);
+mod utils;
+use utils::MacroError;
 
-impl From<CompileError> for proc_macro2::TokenStream {
-    fn from(err: CompileError) -> Self {
-        let CompileError(msg, span) = err;
-        quote_spanned! { span => compile_error!(#msg); }
+fn get_fields<'a>(
+    input: &'a DeriveInput,
+    msg: &str,
+) -> Result<&'a Punctuated<Field, Comma>, MacroError> {
+    if let Data::Struct(s) = &input.data {
+        if let Fields::Named(fs) = &s.fields {
+            Ok(&fs.named)
+        } else {
+            Err(MacroError::Message(
+                format!("Named fields required for {}", msg),
+                input.ident.span(),
+            ))
+        }
+    } else {
+        Err(MacroError::Message(
+            format!("Struct required for {}", msg),
+            input.ident.span(),
+        ))
     }
 }
 
-fn is_c_repr(input: &DeriveInput, msg: &str) -> Result<(), CompileError> {
+fn is_c_repr(input: &DeriveInput, msg: &str) -> Result<(), MacroError> {
     let expected = parse_quote! { #[repr(C)] };
 
     if input.attrs.iter().any(|attr| attr == &expected) {
         Ok(())
     } else {
-        Err(CompileError(
+        Err(MacroError::Message(
             format!("#[repr(C)] required for {}", msg),
             input.ident.span(),
         ))
     }
 }
 
-#[proc_macro_derive(Object)]
-pub fn derive_object(input: TokenStream) -> TokenStream {
-    let input = parse_macro_input!(input as DeriveInput);
-    let name = input.ident;
+fn derive_object_or_error(input: DeriveInput) -> Result<proc_macro2::TokenStream, MacroError> {
+    is_c_repr(&input, "#[derive(Object)]")?;
+
+    let name = &input.ident;
+    let parent = &get_fields(&input, "#[derive(Object)]")?[0].ident;
+
+    Ok(quote! {
+        ::qemu_api::assert_field_type!(#name, #parent,
+            ::qemu_api::qom::ParentField<<#name as ::qemu_api::qom::ObjectImpl>::ParentType>);
 
-    let expanded = quote! {
         ::qemu_api::module_init! {
             MODULE_INIT_QOM => unsafe {
                 ::qemu_api::bindings::type_register_static(&<#name as ::qemu_api::qom::ObjectImpl>::TYPE_INFO);
             }
         }
-    };
-
-    TokenStream::from(expanded)
+    })
 }
 
-fn get_fields(input: &DeriveInput) -> Result<&Punctuated<Field, Comma>, CompileError> {
-    if let Data::Struct(s) = &input.data {
-        if let Fields::Named(fs) = &s.fields {
-            Ok(&fs.named)
-        } else {
-            Err(CompileError(
-                "Cannot generate offsets for unnamed fields.".to_string(),
-                input.ident.span(),
-            ))
-        }
-    } else {
-        Err(CompileError(
-            "Cannot generate offsets for union or enum.".to_string(),
-            input.ident.span(),
-        ))
-    }
+#[proc_macro_derive(Object)]
+pub fn derive_object(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    let expanded = derive_object_or_error(input).unwrap_or_else(Into::into);
+
+    TokenStream::from(expanded)
 }
 
 #[rustfmt::skip::macros(quote)]
-fn derive_offsets_or_error(input: DeriveInput) -> Result<proc_macro2::TokenStream, CompileError> {
+fn derive_offsets_or_error(input: DeriveInput) -> Result<proc_macro2::TokenStream, MacroError> {
     is_c_repr(&input, "#[derive(offsets)]")?;
 
     let name = &input.ident;
-    let fields = get_fields(&input)?;
+    let fields = get_fields(&input, "#[derive(offsets)]")?;
     let field_names: Vec<&Ident> = fields.iter().map(|f| f.ident.as_ref().unwrap()).collect();
     let field_types: Vec<&Type> = fields.iter().map(|f| &f.ty).collect();
     let field_vis: Vec<&Visibility> = fields.iter().map(|f| &f.vis).collect();
@@ -92,3 +98,73 @@ pub fn derive_offsets(input: TokenStream) -> TokenStream {
 
     TokenStream::from(expanded)
 }
+
+#[allow(non_snake_case)]
+fn get_repr_uN(input: &DeriveInput, msg: &str) -> Result<Path, MacroError> {
+    let repr = input.attrs.iter().find(|attr| attr.path().is_ident("repr"));
+    if let Some(repr) = repr {
+        let nested = repr.parse_args_with(Punctuated::<Meta, Token![,]>::parse_terminated)?;
+        for meta in nested {
+            match meta {
+                Meta::Path(path) if path.is_ident("u8") => return Ok(path),
+                Meta::Path(path) if path.is_ident("u16") => return Ok(path),
+                Meta::Path(path) if path.is_ident("u32") => return Ok(path),
+                Meta::Path(path) if path.is_ident("u64") => return Ok(path),
+                _ => {}
+            }
+        }
+    }
+
+    Err(MacroError::Message(
+        format!("#[repr(u8/u16/u32/u64) required for {}", msg),
+        input.ident.span(),
+    ))
+}
+
+fn get_variants(input: &DeriveInput) -> Result<&Punctuated<Variant, Comma>, MacroError> {
+    if let Data::Enum(e) = &input.data {
+        if let Some(v) = e.variants.iter().find(|v| v.fields != Fields::Unit) {
+            return Err(MacroError::Message(
+                "Cannot derive TryInto for enum with non-unit variants.".to_string(),
+                v.fields.span(),
+            ));
+        }
+        Ok(&e.variants)
+    } else {
+        Err(MacroError::Message(
+            "Cannot derive TryInto for union or struct.".to_string(),
+            input.ident.span(),
+        ))
+    }
+}
+
+#[rustfmt::skip::macros(quote)]
+fn derive_tryinto_or_error(input: DeriveInput) -> Result<proc_macro2::TokenStream, MacroError> {
+    let repr = get_repr_uN(&input, "#[derive(TryInto)]")?;
+
+    let name = &input.ident;
+    let variants = get_variants(&input)?;
+    let discriminants: Vec<&Ident> = variants.iter().map(|f| &f.ident).collect();
+
+    Ok(quote! {
+        impl core::convert::TryFrom<#repr> for #name {
+            type Error = #repr;
+
+            fn try_from(value: #repr) -> Result<Self, Self::Error> {
+                #(const #discriminants: #repr = #name::#discriminants as #repr;)*;
+                match value {
+                    #(#discriminants => Ok(Self::#discriminants),)*
+                    _ => Err(value),
+                }
+            }
+        }
+    })
+}
+
+#[proc_macro_derive(TryInto)]
+pub fn derive_tryinto(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    let expanded = derive_tryinto_or_error(input).unwrap_or_else(Into::into);
+
+    TokenStream::from(expanded)
+}
diff --git a/rust/qemu-api-macros/src/utils.rs b/rust/qemu-api-macros/src/utils.rs
new file mode 100644
index 0000000..02c91ae
--- /dev/null
+++ b/rust/qemu-api-macros/src/utils.rs
@@ -0,0 +1,26 @@
+// Procedural macro utilities.
+// Author(s): Paolo Bonzini <pbonzini@redhat.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use proc_macro2::Span;
+use quote::quote_spanned;
+
+pub enum MacroError {
+    Message(String, Span),
+    ParseError(syn::Error),
+}
+
+impl From<syn::Error> for MacroError {
+    fn from(err: syn::Error) -> Self {
+        MacroError::ParseError(err)
+    }
+}
+
+impl From<MacroError> for proc_macro2::TokenStream {
+    fn from(err: MacroError) -> Self {
+        match err {
+            MacroError::Message(msg, span) => quote_spanned! { span => compile_error!(#msg); },
+            MacroError::ParseError(err) => err.into_compile_error(),
+        }
+    }
+}