use std::collections::HashMap; use std::iter; use quote::quote; use syn::parse::{Parse, ParseStream, Result}; use syn::spanned::Spanned; use syn::{ parse_quote, Error, Expr, FnArg, Ident, ImplItem, ImplItemMethod, ItemImpl, LitBool, Pat, Token, }; mod kw { syn::custom_keyword!(shortcut); } struct AliasArgs { target: Ident, is_shortcut: bool, } struct PrecClimbArgs { child_rule: Ident, climber: Expr, } struct AliasSrc { ident: Ident, is_shortcut: bool, } struct ParsedFn<'a> { // Body of the function function: &'a mut ImplItemMethod, // Name of the function. fn_name: Ident, // Name of the first argument of the function, which should be of type `ParseInput`. input_arg: Ident, // List of aliases pointing to this function alias_srcs: Vec, } impl Parse for AliasArgs { fn parse(input: ParseStream) -> Result { let target = input.parse()?; let is_shortcut = if input.peek(Token![,]) { // #[alias(rule, shortcut = true)] let _: Token![,] = input.parse()?; let _: kw::shortcut = input.parse()?; let _: Token![=] = input.parse()?; let b: LitBool = input.parse()?; b.value } else { // #[alias(rule)] false }; Ok(AliasArgs { target, is_shortcut, }) } } impl Parse for PrecClimbArgs { fn parse(input: ParseStream) -> Result { let child_rule = input.parse()?; let _: Token![,] = input.parse()?; let climber = input.parse()?; Ok(PrecClimbArgs { child_rule, climber, }) } } fn collect_aliases( imp: &mut ItemImpl, ) -> Result>> { let functions = imp.items.iter_mut().flat_map(|item| match item { ImplItem::Method(m) => Some(m), _ => None, }); let mut alias_map = HashMap::new(); for function in functions { let fn_name = function.sig.ident.clone(); let mut alias_attrs = function .attrs .drain_filter(|attr| attr.path.is_ident("alias")) .collect::>() .into_iter(); if let Some(attr) = alias_attrs.next() { let args: AliasArgs = attr.parse_args()?; alias_map.entry(args.target).or_insert_with(Vec::new).push( AliasSrc { ident: fn_name, is_shortcut: args.is_shortcut, }, ); } if let Some(attr) = alias_attrs.next() { return Err(Error::new( attr.span(), "expected at most one alias attribute", )); } } Ok(alias_map) } fn parse_fn<'a>( function: &'a mut ImplItemMethod, alias_map: &mut HashMap>, ) -> Result> { let fn_name = function.sig.ident.clone(); // Get the name of the first (`input`) function argument let input_arg = function.sig.inputs.first().ok_or_else(|| { Error::new( function.sig.inputs.span(), "a rule function needs an `input` argument", ) })?; let input_arg = match &input_arg { FnArg::Receiver(_) => return Err(Error::new( input_arg.span(), "a rule function should not have a `self` argument", )), FnArg::Typed(input_arg) => match &*input_arg.pat{ Pat::Ident(ident) => ident.ident.clone(), _ => return Err(Error::new( input_arg.span(), "this argument should be a plain identifier instead of a pattern", )), } }; let alias_srcs = alias_map.remove(&fn_name).unwrap_or_else(Vec::new); Ok(ParsedFn { function, fn_name, input_arg, alias_srcs, }) } fn apply_special_attrs(f: &mut ParsedFn, rule_enum: &Ident) -> Result<()> { let function = &mut *f.function; let fn_name = &f.fn_name; let input_arg = &f.input_arg; *function = parse_quote!( #[allow(non_snake_case)] #function ); // `prec_climb` attr let prec_climb_attrs: Vec<_> = function .attrs .drain_filter(|attr| attr.path.is_ident("prec_climb")) .collect(); if prec_climb_attrs.len() > 1 { return Err(Error::new( prec_climb_attrs[1].span(), "expected at most one prec_climb attribute", )); } else if prec_climb_attrs.is_empty() { // do nothing } else { let attr = prec_climb_attrs.into_iter().next().unwrap(); let PrecClimbArgs { child_rule, climber, } = attr.parse_args()?; function.block = parse_quote!({ #function #climber.climb( #input_arg.as_pair().clone().into_inner(), |p| Self::#child_rule(#input_arg.with_pair(p)), |l, op, r| { #fn_name(#input_arg.clone(), l?, op, r?) }, ) }); // Remove the 3 last arguments to keep only the `input` one function.sig.inputs.pop(); function.sig.inputs.pop(); function.sig.inputs.pop(); // Check that an argument remains function.sig.inputs.first().ok_or_else(|| { Error::new( function.sig.inputs.span(), "a prec_climb function needs 4 arguments", ) })?; } // `alias` attr if !f.alias_srcs.is_empty() { let aliases = f.alias_srcs.iter().map(|src| &src.ident); let block = &function.block; function.block = parse_quote!({ let mut #input_arg = #input_arg; // While the current rule allows shortcutting, and there is a single child, and the // child can still be parsed by the current function, then skip to that child. while ::allows_shortcut(#input_arg.as_rule()) { if let Some(child) = #input_arg.single_child() { if &::rule_alias(child.as_rule()) == stringify!(#fn_name) { #input_arg = child; continue; } } break } match #input_arg.as_rule() { #(#rule_enum::#aliases => Self::#aliases(#input_arg),)* #rule_enum::#fn_name => #block, r => unreachable!( "make_parser: called {} on {:?}", stringify!(#fn_name), r ) } }); } Ok(()) } pub fn make_parser( attrs: proc_macro::TokenStream, input: proc_macro::TokenStream, ) -> Result { let rule_enum: Ident = syn::parse(attrs)?; let mut imp: ItemImpl = syn::parse(input)?; let mut alias_map = collect_aliases(&mut imp)?; let rule_alias_branches: Vec<_> = alias_map .iter() .flat_map(|(tgt, srcs)| iter::repeat(tgt).zip(srcs)) .map(|(tgt, src)| { let ident = &src.ident; quote!( #rule_enum::#ident => stringify!(#tgt).to_string(), ) }) .collect(); let shortcut_branches: Vec<_> = alias_map .iter() .flat_map(|(_tgt, srcs)| srcs) .map(|AliasSrc { ident, is_shortcut }| { quote!( #rule_enum::#ident => #is_shortcut, ) }) .collect(); let fn_map: HashMap = imp .items .iter_mut() .flat_map(|item| match item { ImplItem::Method(m) => Some(m), _ => None, }) .map(|method| { let mut f = parse_fn(method, &mut alias_map)?; apply_special_attrs(&mut f, &rule_enum)?; Ok((f.fn_name.clone(), f)) }) .collect::>()?; // Entries that remain in the alias map don't have a matching method, so we create one. let extra_fns: Vec<_> = alias_map .iter() .map(|(tgt, srcs)| { // Get the signature of one of the functions that has this alias. They should all have // essentially the same signature anyways. let f = fn_map.get(&srcs.first().unwrap().ident).unwrap(); let input_arg = f.input_arg.clone(); let mut sig = f.function.sig.clone(); sig.ident = tgt.clone(); let srcs = srcs.iter().map(|src| &src.ident); Ok(parse_quote!( #sig { match #input_arg.as_rule() { #(#rule_enum::#srcs => Self::#srcs(#input_arg),)* // We can't match on #rule_enum::#tgt since `tgt` might be an arbitrary // identifier. r if &format!("{:?}", r) == stringify!(#tgt) => return Err(#input_arg.error(format!( "make_parser: missing method for rule {}", stringify!(#tgt), ))), r => unreachable!( "make_parser: called {} on {:?}", stringify!(#tgt), r ) } } )) }) .collect::>()?; imp.items.extend(extra_fns); let ty = &imp.self_ty; let (impl_generics, _, where_clause) = imp.generics.split_for_impl(); Ok(quote!( impl #impl_generics pest_consume::PestConsumer for #ty #where_clause { type Rule = #rule_enum; fn rule_alias(rule: Self::Rule) -> String { match rule { #(#rule_alias_branches)* r => format!("{:?}", r), } } fn allows_shortcut(rule: Self::Rule) -> bool { match rule { #(#shortcut_branches)* _ => false, } } } #imp )) }