2 files changed, 322 insertions, 89 deletions

diff --git a/rust/qemu-api-macros/src/bits.rs b/rust/qemu-api-macros/src/bits.rs
new file mode 100644
index 0000000..5ba8475
--- /dev/null
+++ b/rust/qemu-api-macros/src/bits.rs
@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: MIT or Apache-2.0 or GPL-2.0-or-later
+
+// shadowing is useful together with "if let"
+#![allow(clippy::shadow_unrelated)]
+
+use proc_macro2::{
+    Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree, TokenTree as TT,
+};
+
+use crate::utils::MacroError;
+
+pub struct BitsConstInternal {
+    typ: TokenTree,
+}
+
+fn paren(ts: TokenStream) -> TokenTree {
+    TT::Group(Group::new(Delimiter::Parenthesis, ts))
+}
+
+fn ident(s: &'static str) -> TokenTree {
+    TT::Ident(Ident::new(s, Span::call_site()))
+}
+
+fn punct(ch: char) -> TokenTree {
+    TT::Punct(Punct::new(ch, Spacing::Alone))
+}
+
+/// Implements a recursive-descent parser that translates Boolean expressions on
+/// bitmasks to invocations of `const` functions defined by the `bits!` macro.
+impl BitsConstInternal {
+    // primary ::= '(' or ')'
+    //           | ident
+    //           | '!' ident
+    fn parse_primary(
+        &self,
+        tok: TokenTree,
+        it: &mut dyn Iterator<Item = TokenTree>,
+        out: &mut TokenStream,
+    ) -> Result<Option<TokenTree>, MacroError> {
+        let next = match tok {
+            TT::Group(ref g) => {
+                if g.delimiter() != Delimiter::Parenthesis && g.delimiter() != Delimiter::None {
+                    return Err(MacroError::Message("expected parenthesis".into(), g.span()));
+                }
+                let mut stream = g.stream().into_iter();
+                let Some(first_tok) = stream.next() else {
+                    return Err(MacroError::Message(
+                        "expected operand, found ')'".into(),
+                        g.span(),
+                    ));
+                };
+                let mut output = TokenStream::new();
+                // start from the lowest precedence
+                let next = self.parse_or(first_tok, &mut stream, &mut output)?;
+                if let Some(tok) = next {
+                    return Err(MacroError::Message(
+                        format!("unexpected token {tok}"),
+                        tok.span(),
+                    ));
+                }
+                out.extend(Some(paren(output)));
+                it.next()
+            }
+            TT::Ident(_) => {
+                let mut output = TokenStream::new();
+                output.extend([
+                    self.typ.clone(),
+                    TT::Punct(Punct::new(':', Spacing::Joint)),
+                    TT::Punct(Punct::new(':', Spacing::Joint)),
+                    tok,
+                ]);
+                out.extend(Some(paren(output)));
+                it.next()
+            }
+            TT::Punct(ref p) => {
+                if p.as_char() != '!' {
+                    return Err(MacroError::Message("expected operand".into(), p.span()));
+                }
+                let Some(rhs_tok) = it.next() else {
+                    return Err(MacroError::Message(
+                        "expected operand at end of input".into(),
+                        p.span(),
+                    ));
+                };
+                let next = self.parse_primary(rhs_tok, it, out)?;
+                out.extend([punct('.'), ident("invert"), paren(TokenStream::new())]);
+                next
+            }
+            _ => {
+                return Err(MacroError::Message("unexpected literal".into(), tok.span()));
+            }
+        };
+        Ok(next)
+    }
+
+    fn parse_binop<
+        F: Fn(
+            &Self,
+            TokenTree,
+            &mut dyn Iterator<Item = TokenTree>,
+            &mut TokenStream,
+        ) -> Result<Option<TokenTree>, MacroError>,
+    >(
+        &self,
+        tok: TokenTree,
+        it: &mut dyn Iterator<Item = TokenTree>,
+        out: &mut TokenStream,
+        ch: char,
+        f: F,
+        method: &'static str,
+    ) -> Result<Option<TokenTree>, MacroError> {
+        let mut next = f(self, tok, it, out)?;
+        while next.is_some() {
+            let op = next.as_ref().unwrap();
+            let TT::Punct(ref p) = op else { break };
+            if p.as_char() != ch {
+                break;
+            }
+
+            let Some(rhs_tok) = it.next() else {
+                return Err(MacroError::Message(
+                    "expected operand at end of input".into(),
+                    p.span(),
+                ));
+            };
+            let mut rhs = TokenStream::new();
+            next = f(self, rhs_tok, it, &mut rhs)?;
+            out.extend([punct('.'), ident(method), paren(rhs)]);
+        }
+        Ok(next)
+    }
+
+    // sub ::= primary ('-' primary)*
+    pub fn parse_sub(
+        &self,
+        tok: TokenTree,
+        it: &mut dyn Iterator<Item = TokenTree>,
+        out: &mut TokenStream,
+    ) -> Result<Option<TokenTree>, MacroError> {
+        self.parse_binop(tok, it, out, '-', Self::parse_primary, "difference")
+    }
+
+    // and ::= sub ('&' sub)*
+    fn parse_and(
+        &self,
+        tok: TokenTree,
+        it: &mut dyn Iterator<Item = TokenTree>,
+        out: &mut TokenStream,
+    ) -> Result<Option<TokenTree>, MacroError> {
+        self.parse_binop(tok, it, out, '&', Self::parse_sub, "intersection")
+    }
+
+    // xor ::= and ('&' and)*
+    fn parse_xor(
+        &self,
+        tok: TokenTree,
+        it: &mut dyn Iterator<Item = TokenTree>,
+        out: &mut TokenStream,
+    ) -> Result<Option<TokenTree>, MacroError> {
+        self.parse_binop(tok, it, out, '^', Self::parse_and, "symmetric_difference")
+    }
+
+    // or ::= xor ('|' xor)*
+    pub fn parse_or(
+        &self,
+        tok: TokenTree,
+        it: &mut dyn Iterator<Item = TokenTree>,
+        out: &mut TokenStream,
+    ) -> Result<Option<TokenTree>, MacroError> {
+        self.parse_binop(tok, it, out, '|', Self::parse_xor, "union")
+    }
+
+    pub fn parse(
+        it: &mut dyn Iterator<Item = TokenTree>,
+    ) -> Result<proc_macro2::TokenStream, MacroError> {
+        let mut pos = Span::call_site();
+        let mut typ = proc_macro2::TokenStream::new();
+
+        // Gobble everything up to an `@` sign, which is followed by a
+        // parenthesized expression; that is, all token trees except the
+        // last two form the type.
+        let next = loop {
+            let tok = it.next();
+            if let Some(ref t) = tok {
+                pos = t.span();
+            }
+            match tok {
+                None => break None,
+                Some(TT::Punct(ref p)) if p.as_char() == '@' => {
+                    let tok = it.next();
+                    if let Some(ref t) = tok {
+                        pos = t.span();
+                    }
+                    break tok;
+                }
+                Some(x) => typ.extend(Some(x)),
+            }
+        };
+
+        let Some(tok) = next else {
+            return Err(MacroError::Message(
+                "expected expression, do not call this macro directly".into(),
+                pos,
+            ));
+        };
+        let TT::Group(ref _group) = tok else {
+            return Err(MacroError::Message(
+                "expected parenthesis, do not call this macro directly".into(),
+                tok.span(),
+            ));
+        };
+        let mut out = TokenStream::new();
+        let state = Self {
+            typ: TT::Group(Group::new(Delimiter::None, typ)),
+        };
+
+        let next = state.parse_primary(tok, it, &mut out)?;
+
+        // A parenthesized expression is a single production of the grammar,
+        // so the input must have reached the last token.
+        if let Some(tok) = next {
+            return Err(MacroError::Message(
+                format!("unexpected token {tok}"),
+                tok.span(),
+            ));
+        }
+        Ok(out)
+    }
+}
diff --git a/rust/qemu-api-macros/src/lib.rs b/rust/qemu-api-macros/src/lib.rs
index eda0d46..c18bb4e 100644
--- a/rust/qemu-api-macros/src/lib.rs
+++ b/rust/qemu-api-macros/src/lib.rs
@@ -6,60 +6,54 @@ use proc_macro::TokenStream;
 use quote::quote;
 use syn::{
     parse_macro_input, parse_quote, punctuated::Punctuated, spanned::Spanned, token::Comma, Data,
-    DeriveInput, Field, Fields, FieldsUnnamed, Ident, Meta, Path, Token, Type, Variant, Visibility,
+    DeriveInput, Field, Fields, FieldsUnnamed, Ident, Meta, Path, Token, Variant,
 };
 
 mod utils;
 use utils::MacroError;
 
+mod bits;
+use bits::BitsConstInternal;
+
 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),
+    let Data::Struct(ref s) = &input.data else {
+        return Err(MacroError::Message(
+            format!("Struct required for {msg}"),
             input.ident.span(),
-        ))
-    }
+        ));
+    };
+    let Fields::Named(ref fs) = &s.fields else {
+        return Err(MacroError::Message(
+            format!("Named fields required for {msg}"),
+            input.ident.span(),
+        ));
+    };
+    Ok(&fs.named)
 }
 
 fn get_unnamed_field<'a>(input: &'a DeriveInput, msg: &str) -> Result<&'a Field, MacroError> {
-    if let Data::Struct(s) = &input.data {
-        let unnamed = match &s.fields {
-            Fields::Unnamed(FieldsUnnamed {
-                unnamed: ref fields,
-                ..
-            }) => fields,
-            _ => {
-                return Err(MacroError::Message(
-                    format!("Tuple struct required for {}", msg),
-                    s.fields.span(),
-                ))
-            }
-        };
-        if unnamed.len() != 1 {
-            return Err(MacroError::Message(
-                format!("A single field is required for {}", msg),
-                s.fields.span(),
-            ));
-        }
-        Ok(&unnamed[0])
-    } else {
-        Err(MacroError::Message(
-            format!("Struct required for {}", msg),
+    let Data::Struct(ref s) = &input.data else {
+        return Err(MacroError::Message(
+            format!("Struct required for {msg}"),
             input.ident.span(),
-        ))
+        ));
+    };
+    let Fields::Unnamed(FieldsUnnamed { ref unnamed, .. }) = &s.fields else {
+        return Err(MacroError::Message(
+            format!("Tuple struct required for {msg}"),
+            s.fields.span(),
+        ));
+    };
+    if unnamed.len() != 1 {
+        return Err(MacroError::Message(
+            format!("A single field is required for {msg}"),
+            s.fields.span(),
+        ));
     }
+    Ok(&unnamed[0])
 }
 
 fn is_c_repr(input: &DeriveInput, msg: &str) -> Result<(), MacroError> {
@@ -69,7 +63,7 @@ fn is_c_repr(input: &DeriveInput, msg: &str) -> Result<(), MacroError> {
         Ok(())
     } else {
         Err(MacroError::Message(
-            format!("#[repr(C)] required for {}", msg),
+            format!("#[repr(C)] required for {msg}"),
             input.ident.span(),
         ))
     }
@@ -82,7 +76,7 @@ fn is_transparent_repr(input: &DeriveInput, msg: &str) -> Result<(), MacroError>
         Ok(())
     } else {
         Err(MacroError::Message(
-            format!("#[repr(transparent)] required for {}", msg),
+            format!("#[repr(transparent)] required for {msg}"),
             input.ident.span(),
         ))
     }
@@ -160,33 +154,6 @@ pub fn derive_opaque(input: TokenStream) -> TokenStream {
     TokenStream::from(expanded)
 }
 
-#[rustfmt::skip::macros(quote)]
-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, "#[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();
-
-    Ok(quote! {
-	::qemu_api::with_offsets! {
-	    struct #name {
-		#(#field_vis #field_names: #field_types,)*
-	    }
-	}
-    })
-}
-
-#[proc_macro_derive(offsets)]
-pub fn derive_offsets(input: TokenStream) -> TokenStream {
-    let input = parse_macro_input!(input as DeriveInput);
-    let expanded = derive_offsets_or_error(input).unwrap_or_else(Into::into);
-
-    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"));
@@ -204,46 +171,74 @@ fn get_repr_uN(input: &DeriveInput, msg: &str) -> Result<Path, MacroError> {
     }
 
     Err(MacroError::Message(
-        format!("#[repr(u8/u16/u32/u64) required for {}", msg),
+        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(
+    let Data::Enum(ref e) = &input.data else {
+        return Err(MacroError::Message(
             "Cannot derive TryInto for union or struct.".to_string(),
             input.ident.span(),
-        ))
+        ));
+    };
+    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)
+}
+
+#[rustfmt::skip::macros(quote)]
+fn derive_tryinto_body(
+    name: &Ident,
+    variants: &Punctuated<Variant, Comma>,
+    repr: &Path,
+) -> Result<proc_macro2::TokenStream, MacroError> {
+    let discriminants: Vec<&Ident> = variants.iter().map(|f| &f.ident).collect();
+
+    Ok(quote! {
+        #(const #discriminants: #repr = #name::#discriminants as #repr;)*;
+        match value {
+            #(#discriminants => core::result::Result::Ok(#name::#discriminants),)*
+            _ => core::result::Result::Err(value),
+        }
+    })
 }
 
 #[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();
+    let body = derive_tryinto_body(name, get_variants(&input)?, &repr)?;
+    let errmsg = format!("invalid value for {name}");
 
     Ok(quote! {
+        impl #name {
+            #[allow(dead_code)]
+            pub const fn into_bits(self) -> #repr {
+                self as #repr
+            }
+
+            #[allow(dead_code)]
+            pub const fn from_bits(value: #repr) -> Self {
+                match ({
+                    #body
+                }) {
+                    Ok(x) => x,
+                    Err(_) => panic!(#errmsg)
+                }
+            }
+        }
         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),
-                }
+            #[allow(ambiguous_associated_items)]
+            fn try_from(value: #repr) -> Result<Self, #repr> {
+                #body
             }
         }
     })
@@ -256,3 +251,12 @@ pub fn derive_tryinto(input: TokenStream) -> TokenStream {
 
     TokenStream::from(expanded)
 }
+
+#[proc_macro]
+pub fn bits_const_internal(ts: TokenStream) -> TokenStream {
+    let ts = proc_macro2::TokenStream::from(ts);
+    let mut it = ts.into_iter();
+
+    let expanded = BitsConstInternal::parse(&mut it).unwrap_or_else(Into::into);
+    TokenStream::from(expanded)
+}