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|
use std::collections::HashMap;
use std::iter;
use quote::quote;
use syn::parse::{ParseStream, Result};
use syn::spanned::Spanned;
use syn::{
parse_quote, Error, Expr, FnArg, Ident, ImplItem, ImplItemMethod, ItemImpl,
Pat, Signature, Token,
};
fn collect_aliases(
imp: &mut ItemImpl,
) -> Result<HashMap<Ident, (Signature, Vec<Ident>)>> {
let mut alias_map = HashMap::new();
for item in &mut imp.items {
if let ImplItem::Method(function) = item {
let fn_name = function.sig.ident.clone();
let mut alias_attrs = function
.attrs
.drain_filter(|attr| attr.path.is_ident("alias"))
.collect::<Vec<_>>()
.into_iter();
if let Some(attr) = alias_attrs.next() {
let tgt: Ident = attr.parse_args()?;
alias_map
.entry(tgt)
.or_insert_with(|| (function.sig.clone(), Vec::new()))
.1
.push(fn_name);
}
if let Some(attr) = alias_attrs.next() {
return Err(Error::new(
attr.span(),
"expected at most one alias attribute",
));
}
}
}
Ok(alias_map)
}
fn parse_rulefn_sig(sig: &Signature) -> Result<(Ident, Ident)> {
let fn_name = sig.ident.clone();
// Get the name of the first (`input`) function argument
let input_arg = sig.inputs.first().ok_or_else(|| {
Error::new(
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",
)),
}
};
Ok((fn_name, input_arg))
}
fn apply_special_attrs(
function: &mut ImplItemMethod,
alias_map: &mut HashMap<Ident, (Signature, Vec<Ident>)>,
rule_enum: &Ident,
) -> Result<()> {
*function = parse_quote!(
#[allow(non_snake_case, dead_code)]
#function
);
let (fn_name, input_arg) = parse_rulefn_sig(&function.sig)?;
// `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 (child_rule, climber) =
attr.parse_args_with(|input: ParseStream| {
let child_rule: Ident = input.parse()?;
let _: Token![,] = input.parse()?;
let climber: Expr = input.parse()?;
Ok((child_rule, climber))
})?;
function.block = parse_quote!({
#function
#climber.climb(
#input_arg.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 let Some((_, aliases)) = alias_map.remove(&fn_name) {
let block = &function.block;
function.block = parse_quote!({
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<proc_macro2::TokenStream> {
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)| {
quote!(
#rule_enum::#src => stringify!(#tgt).to_string(),
)
})
.collect();
imp.items
.iter_mut()
.map(|item| match item {
ImplItem::Method(m) => {
apply_special_attrs(m, &mut alias_map, &rule_enum)
}
_ => Ok(()),
})
.collect::<Result<()>>()?;
// 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, (sig, srcs))| {
let mut sig = sig.clone();
sig.ident = tgt.clone();
let (_, input_arg) = parse_rulefn_sig(&sig)?;
Ok(ImplItem::Method(parse_quote!(
#sig {
match #input_arg.as_rule() {
#(#rule_enum::#srcs => Self::#srcs(#input_arg),)*
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::<Result<_>>()?;
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 PestConsumer for #ty #where_clause {
type Rule = #rule_enum;
fn rule_alias(rule: Self::Rule) -> String {
match rule {
#(#rule_alias_branches)*
r => format!("{:?}", r),
}
}
}
#imp
))
}
|
