1 files changed, 111 insertions, 0 deletions
diff --git a/dhall_proc_macros/src/make_parser.rs b/dhall_proc_macros/src/make_parser.rs
new file mode 100644
index 0000000..268a639
--- /dev/null
+++ b/dhall_proc_macros/src/make_parser.rs
@@ -0,0 +1,111 @@
+use quote::quote;
+use syn::parse::{ParseStream, Result};
+use syn::spanned::Spanned;
+use syn::{
+    parse_quote, Error, Expr, FnArg, Ident, ImplItem, ImplItemMethod, ItemImpl,
+    Pat, Token,
+};
+
+fn apply_special_attrs(function: &mut ImplItemMethod) -> Result<()> {
+    *function = parse_quote!(
+        #[allow(non_snake_case, dead_code)]
+        #function
+    );
+
+    let recognized_attrs: Vec<_> = function
+        .attrs
+        .drain_filter(|attr| attr.path.is_ident("prec_climb"))
+        .collect();
+
+    let name = function.sig.ident.clone();
+
+    if recognized_attrs.is_empty() {
+        // do nothing
+    } else if recognized_attrs.len() > 1 {
+        return Err(Error::new(
+            recognized_attrs[1].span(),
+            "expected a single prec_climb attribute",
+        ));
+    } else {
+        let attr = recognized_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))
+            })?;
+
+        // Get the name of the first (`input`) function argument
+        let first_arg = function.sig.inputs.first().ok_or_else(|| {
+            Error::new(
+                function.sig.inputs.span(),
+                "a prec_climb function needs 4 arguments",
+            )
+        })?;
+        let first_arg = match &first_arg {
+            FnArg::Receiver(_) => return Err(Error::new(
+                first_arg.span(),
+                "a prec_climb function should not have a `self` argument",
+            )),
+            FnArg::Typed(first_arg) =>   match &*first_arg.pat{
+                Pat::Ident(ident) => &ident.ident,
+                _ => return Err(Error::new(
+                    first_arg.span(),
+                    "this argument should be a plain identifier instead of a pattern",
+                )),
+            }
+        };
+
+        function.block = parse_quote!({
+            #function
+
+            #climber.climb(
+                #first_arg.pair.clone().into_inner(),
+                |p| Self::#child_rule(#first_arg.with_pair(p)),
+                |l, op, r| {
+                    #name(#first_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",
+            )
+        })?;
+    }
+
+    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)?;
+    imp.items
+        .iter_mut()
+        .map(|item| match item {
+            ImplItem::Method(m) => apply_special_attrs(m),
+            _ => Ok(()),
+        })
+        .collect::<Result<()>>()?;
+
+    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 RuleEnum = #rule_enum;
+        }
+
+        #imp
+    ))
+}