fix handling of const and size type generics when generating Index impls

crates/fayalite-proc-macros-impl/src/fold.rs

@@ -230,6 +230,7 @@ forward_fold!(syn::Path => fold_path);
 forward_fold!(syn::Type => fold_type);
 forward_fold!(syn::TypePath => fold_type_path);
 forward_fold!(syn::WherePredicate => fold_where_predicate);
+no_op_fold!(proc_macro2::Span);
 no_op_fold!(syn::parse::Nothing);
 no_op_fold!(syn::token::Brace);
 no_op_fold!(syn::token::Bracket);

crates/fayalite-proc-macros-impl/src/hdl_type_common.rs

@@ -8,11 +8,12 @@ use syn::{
     punctuated::{Pair, Punctuated},
     spanned::Spanned,
     token::{Brace, Bracket, Paren},
-    AngleBracketedGenericArguments, Attribute, ConstParam, Expr, ExprIndex, ExprPath, ExprTuple,
-    Field, FieldMutability, Fields, FieldsNamed, FieldsUnnamed, GenericArgument, GenericParam,
-    Generics, Ident, ImplGenerics, Index, ItemStruct, Path, PathArguments, PathSegment,
-    PredicateType, QSelf, Token, Turbofish, Type, TypeGenerics, TypeGroup, TypeParam, TypeParen,
-    TypePath, TypeTuple, Visibility, WhereClause, WherePredicate,
+    AngleBracketedGenericArguments, Attribute, Block, ConstParam, Expr, ExprBlock, ExprGroup,
+    ExprIndex, ExprParen, ExprPath, ExprTuple, Field, FieldMutability, Fields, FieldsNamed,
+    FieldsUnnamed, GenericArgument, GenericParam, Generics, Ident, ImplGenerics, Index, ItemStruct,
+    Path, PathArguments, PathSegment, PredicateType, QSelf, Stmt, Token, Turbofish, Type,
+    TypeGenerics, TypeGroup, TypeParam, TypeParen, TypePath, TypeTuple, Visibility, WhereClause,
+    WherePredicate,
 };
 
 crate::options! {
@@ -113,6 +114,230 @@ macro_rules! parse_failed {
     }};
 }
 
+#[derive(Copy, Clone, Debug)]
+pub(crate) enum ExprDelimiter {
+    Group(syn::token::Group),
+    Brace(Brace),
+    Paren(Paren),
+}
+
+impl_fold! {
+    enum ExprDelimiter<> {
+        Group(syn::token::Group),
+        Brace(Brace),
+        Paren(Paren),
+    }
+}
+
+impl ExprDelimiter {
+    pub(crate) fn surround<F: FnOnce(&mut TokenStream)>(self, tokens: &mut TokenStream, f: F) {
+        match self {
+            ExprDelimiter::Group(v) => v.surround(tokens, f),
+            ExprDelimiter::Brace(v) => v.surround(tokens, f),
+            ExprDelimiter::Paren(v) => v.surround(tokens, f),
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct ParsedExprDelimited {
+    pub(crate) delim: ExprDelimiter,
+    pub(crate) expr: Box<ParsedExpr>,
+}
+
+impl_fold! {
+    struct ParsedExprDelimited<> {
+        delim: ExprDelimiter,
+        expr: Box<ParsedExpr>,
+    }
+}
+
+impl From<ParsedExprDelimited> for Expr {
+    fn from(value: ParsedExprDelimited) -> Self {
+        let ParsedExprDelimited { delim, expr } = value;
+        let expr = expr.into();
+        match delim {
+            ExprDelimiter::Group(group_token) => Expr::Group(ExprGroup {
+                attrs: vec![],
+                group_token,
+                expr: Box::new(expr),
+            }),
+            ExprDelimiter::Brace(brace_token) => Expr::Block(ExprBlock {
+                attrs: vec![],
+                label: None,
+                block: Block {
+                    brace_token,
+                    stmts: vec![Stmt::Expr(expr, None)],
+                },
+            }),
+            ExprDelimiter::Paren(paren_token) => Expr::Paren(ExprParen {
+                attrs: vec![],
+                paren_token,
+                expr: Box::new(expr),
+            }),
+        }
+    }
+}
+
+impl ToTokens for ParsedExprDelimited {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        let Self { delim, expr } = self;
+        delim.surround(tokens, |tokens| expr.to_tokens(tokens));
+    }
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct ParsedExprNamedParamConst {
+    pub(crate) ident: Ident,
+    pub(crate) param_index: usize,
+}
+
+impl_fold! {
+    struct ParsedExprNamedParamConst<> {
+        ident: Ident,
+        param_index: usize,
+    }
+}
+
+impl ToTokens for ParsedExprNamedParamConst {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        let Self {
+            ident,
+            param_index: _,
+        } = self;
+        ident.to_tokens(tokens);
+    }
+}
+
+impl From<ParsedExprNamedParamConst> for Expr {
+    fn from(value: ParsedExprNamedParamConst) -> Self {
+        Expr::Path(ExprPath {
+            attrs: vec![],
+            qself: None,
+            path: value.ident.into(),
+        })
+    }
+}
+
+#[derive(Clone, Debug)]
+pub(crate) enum ParsedExpr {
+    Delimited(ParsedExprDelimited),
+    NamedParamConst(ParsedExprNamedParamConst),
+    Other(Box<Expr>),
+}
+
+impl ParsedExpr {
+    pub(crate) fn named_param_const(mut self: &Self) -> Option<&ParsedExprNamedParamConst> {
+        loop {
+            match self {
+                ParsedExpr::Delimited(ParsedExprDelimited { expr, .. }) => self = &**expr,
+                ParsedExpr::NamedParamConst(retval) => return Some(retval),
+                ParsedExpr::Other(_) => return None,
+            }
+        }
+    }
+}
+
+impl_fold! {
+    enum ParsedExpr<> {
+        Delimited(ParsedExprDelimited),
+        NamedParamConst(ParsedExprNamedParamConst),
+        Other(Box<Expr>),
+    }
+}
+
+impl ToTokens for ParsedExpr {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        match self {
+            ParsedExpr::Delimited(v) => v.to_tokens(tokens),
+            ParsedExpr::NamedParamConst(v) => v.to_tokens(tokens),
+            ParsedExpr::Other(v) => v.to_tokens(tokens),
+        }
+    }
+}
+
+impl From<ParsedExpr> for Expr {
+    fn from(value: ParsedExpr) -> Self {
+        match value {
+            ParsedExpr::Delimited(expr) => expr.into(),
+            ParsedExpr::NamedParamConst(expr) => expr.into(),
+            ParsedExpr::Other(expr) => *expr,
+        }
+    }
+}
+
+impl From<Box<ParsedExpr>> for Expr {
+    fn from(value: Box<ParsedExpr>) -> Self {
+        (*value).into()
+    }
+}
+
+impl ParseTypes<Expr> for ParsedExpr {
+    fn parse_types(input: &mut Expr, parser: &mut TypesParser<'_>) -> Result<Self, ParseFailed> {
+        match input {
+            Expr::Block(ExprBlock {
+                attrs,
+                label: None,
+                block: Block { brace_token, stmts },
+            }) if attrs.is_empty() && stmts.len() == 1 => {
+                if let Stmt::Expr(expr, None) = &mut stmts[0] {
+                    return Ok(ParsedExpr::Delimited(ParsedExprDelimited {
+                        delim: ExprDelimiter::Brace(*brace_token),
+                        expr: Box::new(parser.parse(expr)?),
+                    }));
+                }
+            }
+            Expr::Group(ExprGroup {
+                attrs,
+                group_token,
+                expr,
+            }) if attrs.is_empty() => {
+                return Ok(ParsedExpr::Delimited(ParsedExprDelimited {
+                    delim: ExprDelimiter::Group(*group_token),
+                    expr: parser.parse(expr)?,
+                }))
+            }
+            Expr::Paren(ExprParen {
+                attrs,
+                paren_token,
+                expr,
+            }) if attrs.is_empty() => {
+                return Ok(ParsedExpr::Delimited(ParsedExprDelimited {
+                    delim: ExprDelimiter::Paren(*paren_token),
+                    expr: parser.parse(expr)?,
+                }))
+            }
+            Expr::Path(ExprPath {
+                attrs,
+                qself: None,
+                path,
+            }) if attrs.is_empty() => {
+                if let Some((param_index, ident)) = parser.get_named_param(path) {
+                    return Ok(Self::NamedParamConst(
+                        match parser.generics().params[param_index] {
+                            ParsedGenericParam::Const(_) => ParsedExprNamedParamConst {
+                                ident: ident.clone(),
+                                param_index,
+                            },
+                            ParsedGenericParam::Type(ParsedTypeParam { ref ident, .. })
+                            | ParsedGenericParam::SizeType(ParsedSizeTypeParam {
+                                ref ident, ..
+                            }) => {
+                                parser
+                                    .errors
+                                    .error(ident, "type provided when a constant was expected");
+                                return Err(ParseFailed);
+                            }
+                        },
+                    ));
+                }
+            }
+            _ => {}
+        }
+        Ok(ParsedExpr::Other(Box::new(input.clone())))
+    }
+}
+
 #[derive(Copy, Clone, Debug)]
 pub(crate) enum TypeDelimiter {
     Group(syn::token::Group),
@@ -214,13 +439,13 @@ impl ParseTypes<TypeTuple> for ParsedTypeTuple {
 #[derive(Debug, Clone)]
 pub(crate) enum ParsedGenericArgument {
     Type(ParsedType),
-    Const(Expr),
+    Const(ParsedExpr),
 }
 
 impl_fold! {
     enum ParsedGenericArgument<> {
         Type(ParsedType),
-        Const(Expr),
+        Const(ParsedExpr),
     }
 }
 
@@ -246,20 +471,16 @@ impl ParseTypes<GenericArgument> for ParsedGenericArgument {
                         ty = &**elem;
                     }
                     if let Type::Path(TypePath { qself: None, path }) = ty {
-                        if let Some(ident) = path.get_ident() {
-                            if let Some(&param_index) =
-                                parser.generics.param_name_to_index_map.get(ident)
-                            {
+                        if let Some((param_index, ident)) = parser.get_named_param(path) {
                             match parser.generics.params[param_index] {
-                                    ParsedGenericParam::Type(_)
-                                    | ParsedGenericParam::SizeType(_) => {}
+                                ParsedGenericParam::Type(_) | ParsedGenericParam::SizeType(_) => {}
                                 ParsedGenericParam::Const(_) => {
-                                        return Ok(Self::Const(Expr::Path(ExprPath {
-                                            attrs: vec![],
-                                            qself: None,
-                                            path: path.clone(),
-                                        })));
-                                    }
+                                    return Ok(Self::Const(ParsedExpr::NamedParamConst(
+                                        ParsedExprNamedParamConst {
+                                            ident: ident.clone(),
+                                            param_index,
+                                        },
+                                    )));
                                 }
                             }
                         }
@@ -267,7 +488,7 @@ impl ParseTypes<GenericArgument> for ParsedGenericArgument {
                 }
                 Ok(Self::Type(parser.parse(ty)?))
             }
-            GenericArgument::Const(expr) => Ok(Self::Const(expr.clone())),
+            GenericArgument::Const(expr) => Ok(Self::Const(parser.parse(expr)?)),
             _ => parse_failed!(parser, arg, "expected type or const generic argument"),
         }
     }
@@ -277,7 +498,7 @@ impl From<ParsedGenericArgument> for GenericArgument {
     fn from(value: ParsedGenericArgument) -> Self {
         match value {
             ParsedGenericArgument::Type(ty) => Self::Type(ty.into()),
-            ParsedGenericArgument::Const(expr) => Self::Const(expr),
+            ParsedGenericArgument::Const(expr) => Self::Const(expr.into()),
         }
     }
 }
@@ -496,7 +717,7 @@ impl ToTokens for ParsedTypeNamedParam {
 pub(crate) struct ParsedTypeConstUsize {
     pub(crate) const_usize: known_items::ConstUsize,
     pub(crate) lt_token: Token![<],
-    pub(crate) value: Box<Expr>,
+    pub(crate) value: ParsedExpr,
     pub(crate) gt_token: Token![>],
 }
 
@@ -504,7 +725,7 @@ impl_fold! {
     struct ParsedTypeConstUsize<> {
         const_usize: known_items::ConstUsize,
         lt_token: Token![<],
-        value: Box<Expr>,
+        value: ParsedExpr,
         gt_token: Token![>],
     }
 }
@@ -518,7 +739,7 @@ impl From<ParsedTypeConstUsize> for Path {
             gt_token,
         } = value;
         let path = const_usize.path;
-        let args = Punctuated::from_iter([GenericArgument::Const(*value)]);
+        let args = Punctuated::from_iter([GenericArgument::Const(value.into())]);
         let args = AngleBracketedGenericArguments {
             colon2_token: Some(Token![::](lt_token.span)),
             lt_token,
@@ -544,13 +765,17 @@ impl From<ParsedTypeConstUsize> for Type {
 }
 
 impl MakeHdlTypeExpr for ParsedTypeConstUsize {
-    fn make_hdl_type_expr(&self, _context: &MakeHdlTypeExprContext) -> Expr {
+    fn make_hdl_type_expr(&self, context: &MakeHdlTypeExprContext) -> Expr {
+        if let Some(named_param_const) = self.value.named_param_const() {
+            named_param_const.make_hdl_type_expr(context)
+        } else {
             Expr::Path(ExprPath {
                 attrs: vec![],
                 qself: None,
                 path: self.clone().into(),
             })
         }
+    }
 }
 
 impl ToTokens for ParsedTypeConstUsize {
@@ -606,7 +831,7 @@ impl ParsedTypeConstUsize {
         Ok(Ok(Self {
             const_usize,
             lt_token,
-            value: Box::new(value),
+            value,
             gt_token,
         }))
     }
@@ -694,7 +919,7 @@ macro_rules! make_parsed_type_or_const {
                 let $type_arg = Box::new(ParsedType::ConstUsize(ParsedTypeConstUsize {
                     const_usize: known_items::ConstUsize($span),
                     lt_token: Token![<]($span),
-                    value: Box::new($const_arg.clone()),
+                    value: $const_arg.clone(),
                     gt_token: Token![>]($span),
                 }));
                 ($type_arg, Some(Box::new($const_arg)))
@@ -887,7 +1112,7 @@ macro_rules! make_parsed_type_or_const {
                     let mut args = Punctuated::new();
                     $(
                         args.push((
-                            ($(|| GenericArgument::Const(*$const_arg),)?
+                            ($(|| GenericArgument::Const($const_arg.into()),)?
                             || GenericArgument::Type($type_arg.into()),
                         ).0)());
                         $(args.push_punct($separator);)?
@@ -1010,7 +1235,7 @@ make_parsed_type_or_const! {
         #[separator]
         comma_token: Token![,],
         #[const]
-        const_len: Option<Box<Expr>>,
+        const_len: Option<Box<ParsedExpr>>,
         #[type(default = |span| ParsedType::DynSize(known_items::DynSize(span)))]
         type_len: Box<ParsedType>,
         gt_token: Token![>],
@@ -1024,7 +1249,7 @@ make_parsed_type_or_const! {
         uint_type: known_items::UIntType,
         lt_token: Token![<],
         #[const]
-        const_width: Option<Box<Expr>>,
+        const_width: Option<Box<ParsedExpr>>,
         #[type(default = |span| ParsedType::DynSize(known_items::DynSize(span)))]
         type_width: Box<ParsedType>,
         gt_token: Token![>],
@@ -1038,7 +1263,7 @@ make_parsed_type_or_const! {
         uint_type: known_items::SIntType,
         lt_token: Token![<],
         #[const]
-        const_width: Option<Box<Expr>>,
+        const_width: Option<Box<ParsedExpr>>,
         #[type(default = |span| ParsedType::DynSize(known_items::DynSize(span)))]
         type_width: Box<ParsedType>,
         gt_token: Token![>],
@@ -1207,17 +1432,7 @@ impl ParseTypes<Path> for ParsedType {
             },
             args,
         };
-        if let Some(ident) = named.path.get_ident() {
-            if let Some(&param_index) = parser.generics().param_name_to_index_map.get(ident) {
-                if parser
-                    .cur_param_index
-                    .is_some_and(|cur_param_index| param_index >= cur_param_index)
-                {
-                    parser.errors.error(
-                        parser.generics().params[param_index].ident(),
-                        "cannot use forward declared identifier in generic parameter defaults",
-                    );
-                }
+        if let Some((param_index, ident)) = parser.get_named_param(&named.path) {
             return Ok(Self::NamedParam(
                 match parser.generics().params[param_index] {
                     ParsedGenericParam::Type(_) => {
@@ -1241,7 +1456,6 @@ impl ParseTypes<Path> for ParsedType {
                 },
             ));
         }
-        }
         let named = match ParsedTypeArray::try_from_named(named, parser)? {
             Ok(v) => return Ok(Self::Array(v)),
             Err(named) => named,
@@ -1489,6 +1703,18 @@ impl<'a> TypesParser<'a> {
     pub(crate) fn parse<T: ParseTypes<I>, I>(&mut self, input: &mut I) -> Result<T, ParseFailed> {
         T::parse_types(input, self)
     }
+    pub(crate) fn get_named_param<'b>(&mut self, path: &'b Path) -> Option<(usize, &'b Ident)> {
+        let ident = path.get_ident()?;
+        let param_index = *self.generics().param_name_to_index_map.get(ident)?;
+        if self
+            .cur_param_index
+            .is_some_and(|cur_param_index| param_index >= cur_param_index)
+        {
+            self.errors
+                .error(path, "cannot use forward declared identifier here");
+        }
+        Some((param_index, ident))
+    }
 }
 
 pub(crate) trait ParseTypes<I>: Sized {
@@ -2311,7 +2537,7 @@ impl ParsedGenerics {
     ) {
         if self.params.is_empty() {
             let target_expr = target_expr(&MakeHdlTypeExprContext {
-                type_arg_values: vec![],
+                named_param_values: vec![],
                 is_const: true,
             });
             quote_spanned! {ident.span()=>
@@ -2364,36 +2590,40 @@ impl ParsedGenerics {
                     .clone()
                     .into()
             };
-            let next_generics = if is_last {
+            let make_next_target_args = |next_arg: Option<GenericArgument>| {
+                let generics = if is_last {
                     &final_generics
                 } else {
                     &generics_accumulation_types[next_param_count].generics
                 };
+                let type_generics = generics.split_for_impl().1;
+                let turbofish = type_generics.as_turbofish();
+                let mut retval: AngleBracketedGenericArguments = parse_quote! { #turbofish };
+                if let Some(next_arg) = next_arg {
+                    *retval.args.last_mut().unwrap() = next_arg;
+                }
+                retval
+            };
             let (cur_impl_generics, cur_type_generics, cur_where_clause) =
                 cur_generics.split_for_impl();
-            let (_next_impl_generics, next_type_generics, _next_where_clause) =
-                next_generics.split_for_impl();
-            let next_turbofish = next_type_generics.as_turbofish();
-            let mut next_target_expr = |context: &MakeHdlTypeExprContext| -> Expr {
-                if is_last {
-                    target_expr(context)
-                } else {
-                    let args = &context.type_arg_values[..next_param_count];
-                    parse_quote_spanned! {ident.span()=>
-                        #next_target #next_turbofish(#(#args),*)
-                    }
-                }
-            };
             match next_param {
                 ParsedGenericParam::Type(ParsedTypeParam {
                     ident: param_ident,
                     default,
                     ..
                 }) => {
-                    let mut generics = next_generics.clone();
+                    let next_generics = if is_last {
+                        &final_generics
+                    } else {
+                        &generics_accumulation_types[next_param_count].generics
+                    };
+                    let (_next_impl_generics, next_type_generics, _next_where_clause) =
+                        next_generics.split_for_impl();
+                    let next_turbofish = next_type_generics.as_turbofish();
                     let mut param: Expr = parse_quote_spanned! {ident.span()=>
                         __param
                     };
+                    let mut generics = next_generics.clone();
                     let mut index_type = param_ident.clone();
                     if let Some((_, default)) = default {
                         index_type = format_ident!("__Param", span = ident.span());
@@ -2402,24 +2632,34 @@ impl ParsedGenerics {
                             #index_type: ::fayalite::ty::TypeOrDefault<#default, Type = #param_ident>
                         });
                         let default_expr = default.make_hdl_type_expr(&MakeHdlTypeExprContext {
-                            type_arg_values: self_members[..param_count].to_vec(),
+                            named_param_values: self_members[..param_count].to_vec(),
                             is_const: false,
                         });
                         param = parse_quote_spanned! {ident.span()=>
                             ::fayalite::ty::TypeOrDefault::get(__param, || #default_expr)
                         };
-                        let output_expr = next_target_expr(&MakeHdlTypeExprContext {
-                            type_arg_values: self_members[..param_count]
+                        let context = MakeHdlTypeExprContext {
+                            named_param_values: self_members[..param_count]
                                 .iter()
                                 .cloned()
                                 .chain([default_expr])
                                 .collect(),
                             is_const: false,
-                        });
-                        let mut next_target_args: AngleBracketedGenericArguments =
-                            parse_quote! { #next_type_generics };
-                        *next_target_args.args.last_mut().unwrap() =
-                            GenericArgument::Type(default.clone().into());
+                        };
+                        let output_expr = {
+                            let next_turbofish = next_type_generics.as_turbofish();
+                            if is_last {
+                                target_expr(&context)
+                            } else {
+                                let args = &context.named_param_values[..next_param_count];
+                                parse_quote_spanned! {ident.span()=>
+                                    #next_target #next_turbofish(#(#args),*)
+                                }
+                            }
+                        };
+                        let next_target_args = make_next_target_args(Some(GenericArgument::Type(
+                            default.clone().into(),
+                        )));
                         quote_spanned! {ident.span()=>
                             impl #cur_impl_generics ::fayalite::ty::FillInDefaultedGenerics
                             for #cur_target #cur_type_generics
@@ -2436,14 +2676,22 @@ impl ParsedGenerics {
                         .to_tokens(tokens);
                     }
                     let (impl_generics, _type_generics, where_clause) = generics.split_for_impl();
-                    let output_expr = next_target_expr(&MakeHdlTypeExprContext {
-                        type_arg_values: self_members[..param_count]
+                    let context = MakeHdlTypeExprContext {
+                        named_param_values: self_members[..param_count]
                             .iter()
                             .cloned()
                             .chain([param])
                             .collect(),
                         is_const: false,
-                    });
+                    };
+                    let output_expr = if is_last {
+                        target_expr(&context)
+                    } else {
+                        let args = &context.named_param_values[..next_param_count];
+                        parse_quote_spanned! {ident.span()=>
+                            #next_target #next_turbofish(#(#args),*)
+                        }
+                    };
                     quote_spanned! {ident.span()=>
                         #[allow(non_upper_case_globals)]
                         #[automatically_derived]
@@ -2468,9 +2716,9 @@ impl ParsedGenerics {
                     default,
                     ..
                 }) => {
-                    if bounds.KnownSize.is_none() {
-                        let output_expr = next_target_expr(&MakeHdlTypeExprContext {
-                            type_arg_values: self_members[..param_count]
+                    {
+                        let context = MakeHdlTypeExprContext {
+                            named_param_values: self_members[..param_count]
                                 .iter()
                                 .cloned()
                                 .chain([parse_quote_spanned! {ident.span()=>
@@ -2478,80 +2726,42 @@ impl ParsedGenerics {
                                 }])
                                 .collect(),
                             is_const: false,
-                        });
-                        let mut next_target_args: AngleBracketedGenericArguments =
-                            parse_quote! { #next_type_generics };
-                        *next_target_args.args.last_mut().unwrap() = parse_quote_spanned! {ident.span()=>
-                            ::fayalite::int::DynSize
                         };
-                        quote_spanned! {ident.span()=>
-                            #[allow(non_upper_case_globals)]
-                            #[automatically_derived]
-                            impl #cur_impl_generics ::fayalite::__std::ops::Index<::fayalite::__std::primitive::usize>
-                            for #cur_target #cur_type_generics
-                            #cur_where_clause
-                            {
-                                type Output = #next_target #next_target_args;
-
-                                fn index(
-                                    &self,
-                                    __param: ::fayalite::__std::primitive::usize,
-                                ) -> &Self::Output {
-                                    ::fayalite::intern::Interned::<_>::into_inner(
-                                        ::fayalite::intern::Intern::intern_sized(#output_expr),
-                                    )
+                        let next_target_args =
+                            make_next_target_args(Some(parse_quote_spanned! {ident.span()=>
+                                <#param_ident as ::fayalite::int::SizeType>::Size
+                            }));
+                        let output_expr = if is_last {
+                            target_expr(&context)
+                        } else {
+                            let args = &context.named_param_values[..next_param_count];
+                            parse_quote_spanned! {ident.span()=>
+                                #next_target #next_target_args(#(#args),*)
                             }
-                            }
-                        }
-                        .to_tokens(tokens);
-                    }
-                    {
-                        let output_expr = next_target_expr(&MakeHdlTypeExprContext {
-                            type_arg_values: self_members[..param_count]
-                                .iter()
-                                .cloned()
-                                .chain([parse_quote_spanned! {ident.span()=>
-                                    __param
-                                }])
-                                .collect(),
-                            is_const: false,
-                        });
+                        };
                         let mut next_generics = cur_generics.clone();
                         next_generics
                             .params
                             .push(parse_quote_spanned! {ident.span()=>
-                                const #param_ident: ::fayalite::__std::primitive::usize
+                                #param_ident: ::fayalite::int::SizeType
                             });
-                        let known_size = bounds
-                            .KnownSize
-                            .clone()
-                            .unwrap_or_else(|| known_items::KnownSize(ident.span()));
                         next_generics.make_where_clause().predicates.push(
                             parse_quote_spanned! {ident.span()=>
-                                ::fayalite::util::ConstUsize<#param_ident>: #known_size
+                                <#param_ident as ::fayalite::int::SizeType>::Size: #bounds
                             },
                         );
-                        let (next_impl_generics, next_type_generics, next_where_clause) =
+                        let (next_impl_generics, _next_type_generics, next_where_clause) =
                             next_generics.split_for_impl();
-                        let mut next_target_args: AngleBracketedGenericArguments =
-                            parse_quote! { #next_type_generics };
-                        *next_target_args.args.last_mut().unwrap() = parse_quote_spanned! {ident.span()=>
-                            ::fayalite::util::ConstUsize<#param_ident>
-                        };
                         quote_spanned! {ident.span()=>
                             #[allow(non_upper_case_globals)]
                             #[automatically_derived]
-                            impl #next_impl_generics ::fayalite::__std::ops::Index<
-                                ::fayalite::util::ConstUsize<#param_ident>,
-                            > for #cur_target #cur_type_generics
+                            impl #next_impl_generics ::fayalite::__std::ops::Index<#param_ident>
+                            for #cur_target #cur_type_generics
                             #next_where_clause
                             {
                                 type Output = #next_target #next_target_args;
 
-                                fn index(
-                                    &self,
-                                    __param: ::fayalite::util::ConstUsize<#param_ident>,
-                                ) -> &Self::Output {
+                                fn index(&self, __param: #param_ident) -> &Self::Output {
                                     ::fayalite::intern::Interned::<_>::into_inner(
                                         ::fayalite::intern::Intern::intern_sized(#output_expr),
                                     )
@@ -2565,7 +2775,71 @@ impl ParsedGenerics {
                         todo!();
                     }
                 }
-                ParsedGenericParam::Const(_) => todo!(),
+                ParsedGenericParam::Const(ParsedConstParam {
+                    attrs: _,
+                    options: _,
+                    const_token,
+                    ident: param_ident,
+                    colon_token,
+                    ty: ParsedConstGenericType::Usize(ty),
+                    bounds: ParsedConstParamWhereBounds { bounds, .. },
+                }) => {
+                    let context = MakeHdlTypeExprContext {
+                        named_param_values: self_members[..param_count]
+                            .iter()
+                            .cloned()
+                            .chain([parse_quote_spanned! {ident.span()=>
+                                __param
+                            }])
+                            .collect(),
+                        is_const: false,
+                    };
+                    let next_target_args =
+                        make_next_target_args(Some(parse_quote! { #param_ident }));
+                    let output_expr = if is_last {
+                        target_expr(&context)
+                    } else {
+                        let args = &context.named_param_values[..next_param_count];
+                        parse_quote_spanned! {ident.span()=>
+                            #next_target #next_target_args(#(#args),*)
+                        }
+                    };
+                    let mut next_generics = cur_generics.clone();
+                    next_generics
+                        .params
+                        .push(parse_quote! { #const_token #param_ident #colon_token #ty });
+                    next_generics
+                        .params
+                        .push(parse_quote_spanned! {ident.span()=>
+                            __Param: ::fayalite::int::SizeType<
+                                Size = ::fayalite::util::ConstUsize<#param_ident>,
+                            >
+                        });
+                    next_generics.make_where_clause().predicates.push(
+                        parse_quote_spanned! {ident.span()=>
+                            ::fayalite::util::ConstUsize<#param_ident>: ::fayalite::int::Size<SizeType = __Param> + #bounds
+                        },
+                    );
+                    let (next_impl_generics, _next_type_generics, next_where_clause) =
+                        next_generics.split_for_impl();
+                    quote_spanned! {ident.span()=>
+                        #[allow(non_upper_case_globals)]
+                        #[automatically_derived]
+                        impl #next_impl_generics ::fayalite::__std::ops::Index<__Param>
+                        for #cur_target #cur_type_generics
+                        #next_where_clause
+                        {
+                            type Output = #next_target #next_target_args;
+
+                            fn index(&self, __param: __Param) -> &Self::Output {
+                                ::fayalite::intern::Interned::<_>::into_inner(
+                                    ::fayalite::intern::Intern::intern_sized(#output_expr),
+                                )
+                            }
+                        }
+                    }
+                    .to_tokens(tokens);
+                }
             };
         }
     }
@@ -3145,7 +3419,8 @@ impl ToTokens for ParsedGenericsWhereClause<'_> {
         let mut where_token = |span: Span| -> Option<Token![where]> {
             mem::replace(&mut need_where_token, false).then(|| Token![where](span))
         };
-        for param in self.generics.params.iter().take(self.param_count) {
+        for param in self.generics.params.pairs().take(self.param_count) {
+            let (param, comma_token) = param.into_tuple();
             match param {
                 ParsedGenericParam::Type(ParsedTypeParam {
                     ident,
@@ -3156,7 +3431,7 @@ impl ToTokens for ParsedGenericsWhereClause<'_> {
                     if let Some(static_type) = &bounds.StaticType {
                         where_token(static_type.span).to_tokens(tokens);
                         quote_spanned! {static_type.span=>
-                            <#ident as ::fayalite::ty::Type>::MaskType #colon_token #static_type,
+                            <#ident as ::fayalite::ty::Type>::MaskType #colon_token #static_type #comma_token
                         }
                         .to_tokens(tokens);
                     }
@@ -3182,6 +3457,7 @@ impl ToTokens for ParsedGenericsWhereClause<'_> {
                     gt_token.to_tokens(tokens);
                     colon_token.to_tokens(tokens);
                     bounds.to_tokens(tokens);
+                    comma_token.to_tokens(tokens);
                 }
             }
         }
@@ -3649,7 +3925,7 @@ impl From<MaybeParsed<ParsedFieldsNamed, FieldsNamed>> for FieldsNamed {
 
 #[derive(Debug)]
 pub(crate) struct MakeHdlTypeExprContext {
-    pub(crate) type_arg_values: Vec<Expr>,
+    pub(crate) named_param_values: Vec<Expr>,
     pub(crate) is_const: bool,
 }
 
@@ -3694,6 +3970,28 @@ impl MakeHdlTypeExpr for known_items::DynSize {
     }
 }
 
+impl MakeHdlTypeExpr for ParsedExprDelimited {
+    fn make_hdl_type_expr(&self, context: &MakeHdlTypeExprContext) -> Expr {
+        self.expr.make_hdl_type_expr(context)
+    }
+}
+
+impl MakeHdlTypeExpr for ParsedExprNamedParamConst {
+    fn make_hdl_type_expr(&self, context: &MakeHdlTypeExprContext) -> Expr {
+        context.named_param_values[self.param_index].clone()
+    }
+}
+
+impl MakeHdlTypeExpr for ParsedExpr {
+    fn make_hdl_type_expr(&self, context: &MakeHdlTypeExprContext) -> Expr {
+        match self {
+            ParsedExpr::Delimited(expr) => expr.make_hdl_type_expr(context),
+            ParsedExpr::NamedParamConst(expr) => expr.make_hdl_type_expr(context),
+            ParsedExpr::Other(expr) => (**expr).clone(),
+        }
+    }
+}
+
 impl MakeHdlTypeExpr for ParsedTypeDelimited {
     fn make_hdl_type_expr(&self, context: &MakeHdlTypeExprContext) -> Expr {
         self.elem.make_hdl_type_expr(context)
@@ -3743,7 +4041,7 @@ impl MakeHdlTypeExpr for ParsedGenericArgument {
     fn make_hdl_type_expr(&self, context: &MakeHdlTypeExprContext) -> Expr {
         match self {
             ParsedGenericArgument::Type(v) => v.make_hdl_type_expr(context),
-            ParsedGenericArgument::Const(v) => v.clone(),
+            ParsedGenericArgument::Const(v) => v.make_hdl_type_expr(context),
         }
     }
 }
@@ -3759,13 +4057,13 @@ impl MakeHdlTypeExpr for ParsedTypeNamedParam {
 
 impl MakeHdlTypeExpr for ParsedTypeNamedParamType {
     fn make_hdl_type_expr(&self, context: &MakeHdlTypeExprContext) -> Expr {
-        context.type_arg_values[self.param_index].clone()
+        context.named_param_values[self.param_index].clone()
     }
 }
 
 impl MakeHdlTypeExpr for ParsedTypeNamedParamSizeType {
     fn make_hdl_type_expr(&self, context: &MakeHdlTypeExprContext) -> Expr {
-        context.type_arg_values[self.param_index].clone()
+        context.named_param_values[self.param_index].clone()
     }
 }
 

crates/fayalite/src/array.rs

@@ -3,7 +3,7 @@
 
 use crate::{
     expr::{ops::ArrayIndex, Expr, ToExpr},
-    int::{DynSize, KnownSize, Size},
+    int::{DynSize, KnownSize, Size, SizeType, DYN_SIZE},
     intern::{Intern, Interned, LazyInterned},
     module::transform::visit::{Fold, Folder, Visit, Visitor},
     source_location::SourceLocation,
@@ -27,10 +27,7 @@ impl<T: Type, Len: Size> std::fmt::Debug for ArrayType<T, Len> {
     }
 }
 
-pub type Array<
-    T = CanonicalType,
-    const LEN: usize = { <DynSize as crate::util::GenericConstUsize>::VALUE },
-> = ArrayType<T, ConstUsize<LEN>>;
+pub type Array<T = CanonicalType, const LEN: usize = DYN_SIZE> = ArrayType<T, ConstUsize<LEN>>;
 
 #[allow(non_upper_case_globals)]
 pub const Array: ArrayWithoutGenerics = ArrayWithoutGenerics;
@@ -214,21 +211,10 @@ pub struct ArrayWithoutLen<T: Type> {
     element: T,
 }
 
-impl<T: Type> Index<usize> for ArrayWithoutLen<T> {
-    type Output = Array<T>;
+impl<T: Type, L: SizeType> Index<L> for ArrayWithoutLen<T> {
+    type Output = ArrayType<T, L::Size>;
 
-    fn index(&self, len: usize) -> &Self::Output {
-        Interned::<_>::into_inner(Intern::intern_sized(Array::new_dyn(self.element, len)))
-    }
-}
-
-impl<T: Type, const LEN: usize> Index<ConstUsize<LEN>> for ArrayWithoutLen<T>
-where
-    ConstUsize<LEN>: KnownSize,
-{
-    type Output = Array<T, LEN>;
-
-    fn index(&self, len: ConstUsize<LEN>) -> &Self::Output {
-        Interned::<_>::into_inner(Intern::intern_sized(Array::new(self.element, len)))
+    fn index(&self, len: L) -> &Self::Output {
+        Interned::<_>::into_inner(Intern::intern_sized(ArrayType::new(self.element, len)))
     }
 }

crates/fayalite/src/int.rs

@@ -25,6 +25,7 @@ use std::{
 mod sealed {
     pub trait BoolOrIntTypeSealed {}
     pub trait SizeSealed {}
+    pub trait SizeTypeSealed {}
 }
 
 pub const DYN_SIZE: usize = !0;
@@ -59,6 +60,12 @@ macro_rules! known_widths {
 
 known_widths!([2 2 2 2 2 2 2 2 2]);
 
+pub trait SizeType:
+    sealed::SizeTypeSealed + Copy + Ord + std::hash::Hash + std::fmt::Debug + Send + Sync + 'static
+{
+    type Size: Size<SizeType = Self>;
+}
+
 pub trait Size:
     sealed::SizeSealed + Copy + Ord + std::hash::Hash + std::fmt::Debug + Send + Sync + 'static
 {
@@ -76,7 +83,14 @@ pub trait Size:
         + TryFrom<Vec<Expr<Element>>>
         + Into<Vec<Expr<Element>>>;
     const KNOWN_VALUE: Option<usize>;
-    type SizeType: Copy + Ord + std::hash::Hash + std::fmt::Debug + Send + Sync + 'static;
+    type SizeType: SizeType<Size = Self>
+        + Copy
+        + Ord
+        + std::hash::Hash
+        + std::fmt::Debug
+        + Send
+        + Sync
+        + 'static;
     fn as_usize(size_type: Self::SizeType) -> usize;
     fn try_from_usize(v: usize) -> Option<Self::SizeType>;
     #[track_caller]
@@ -85,6 +99,12 @@ pub trait Size:
     }
 }
 
+impl sealed::SizeTypeSealed for usize {}
+
+impl SizeType for usize {
+    type Size = DynSize;
+}
+
 impl Size for DynSize {
     type ArrayMatch<Element: Type> = Box<[Expr<Element>]>;
     const KNOWN_VALUE: Option<usize> = None;
@@ -101,6 +121,15 @@ impl Size for DynSize {
 
 impl<const VALUE: usize> sealed::SizeSealed for ConstUsize<VALUE> {}
 
+impl<const VALUE: usize> sealed::SizeTypeSealed for ConstUsize<VALUE> {}
+
+impl<const VALUE: usize> SizeType for ConstUsize<VALUE>
+where
+    ConstUsize<VALUE>: KnownSize,
+{
+    type Size = ConstUsize<VALUE>;
+}
+
 impl<const VALUE: usize> Size for ConstUsize<VALUE>
 where
     ConstUsize<VALUE>: KnownSize,
@@ -138,9 +167,7 @@ macro_rules! impl_int {
             }
         }
 
-        pub type $pretty_name<
-            const WIDTH: usize = { <DynSize as crate::util::GenericConstUsize>::VALUE },
-        > = $name<ConstUsize<WIDTH>>;
+        pub type $pretty_name<const WIDTH: usize = DYN_SIZE> = $name<ConstUsize<WIDTH>>;
 
         #[allow(non_upper_case_globals)]
         pub const $pretty_name: $generic_name = $generic_name;
@@ -269,21 +296,10 @@ macro_rules! impl_int {
         #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, Default)]
         pub struct $generic_name;
 
-        impl Index<usize> for $generic_name {
-            type Output = $name;
+        impl<Width: SizeType> Index<Width> for $generic_name {
+            type Output = $name<Width::Size>;
 
-            fn index(&self, width: usize) -> &Self::Output {
-                Interned::<_>::into_inner(Intern::intern_sized($name::new_dyn(width)))
-            }
-        }
-
-        impl<const WIDTH: usize> Index<ConstUsize<WIDTH>> for $generic_name
-        where
-            ConstUsize<WIDTH>: KnownSize,
-        {
-            type Output = $pretty_name<WIDTH>;
-
-            fn index(&self, width: ConstUsize<WIDTH>) -> &Self::Output {
+            fn index(&self, width: Width) -> &Self::Output {
                 Interned::<_>::into_inner(Intern::intern_sized($name::new(width)))
             }
         }

crates/fayalite/tests/hdl_types.rs

@@ -1,16 +1,22 @@
 // SPDX-License-Identifier: LGPL-3.0-or-later
 // See Notices.txt for copyright information
-use fayalite::{
-    array::ArrayType,
-    hdl,
-    int::{IntType, Size, UInt},
-};
+use fayalite::prelude::*;
 
 #[hdl(outline_generated)]
-pub struct S<T: IntType, Len: Size> {
+pub struct S<T, Len: Size, T2> {
     pub a: T,
     b: UInt<3>,
     pub(crate) c: ArrayType<UInt<1>, Len>,
+    pub d: T2,
+}
+
+//#[cfg(todo)]
+#[hdl(outline_generated)]
+pub struct S3<const LEN: usize, T> {
+    pub a: T,
+    b: UInt<3>,
+    pub(crate) c: Array<UInt<1>, LEN>,
+    pub d: S<T, ConstUsize<LEN>, ()>,
 }
 
 #[hdl(outline_generated)]