Re-wrap Rust pattern in a Group

After removing the brackets, we still want a group with delimiter None.
Because the `spacing` of the last token of the pattern is passed
through, it can conflict with the following `=` in the expansion and
cause an error like rust-lang/rust#107420

peg-macros/translate.rs

@@ -1,3 +1,4 @@
+use proc_macro2::Delimiter;
 use proc_macro2::{Group, Ident, Literal, Span, TokenStream, TokenTree};
 use std::collections::{HashMap, HashSet};
 
@@ -511,6 +512,8 @@ fn compile_pattern_expr(
             (pattern_group.stream(), success_res, failure_res)
         };
 
+    let pattern = Group::new(Delimiter::None, pattern);
+
     quote_spanned! { span =>
         match ::peg::ParseElem::parse_elem(__input, __pos) {
             ::peg::RuleResult::Matched(__next, #result_name) => match #result_name {

tests/run-pass/pattern.rs

@@ -4,6 +4,8 @@ peg::parser!( grammar test() for str {
 
     pub rule capture() -> char = ['a'..='z']
     pub rule capture2() -> (char, char) = a:['a'..='z'] b:['0'..='9'] { (a, b) }
+
+    pub rule open_range() -> char = ['a'..]
 });
 
 fn main() {