internal: Use boxed slices instead ovecs in decl macros

crates/mbe/src/benchmark.rs

@@ -79,7 +79,7 @@ fn invocation_fixtures(rules: &FxHashMap<String, DeclarativeMacro>) -> Vec<(Stri
     let mut res = Vec::new();
 
     for (name, it) in rules {
-        for rule in &it.rules {
+        for rule in it.rules.iter() {
             // Generate twice
             for _ in 0..2 {
                 // The input are generated by filling the `Op` randomly.

crates/mbe/src/lib.rs

@@ -104,7 +104,7 @@ impl fmt::Display for ExpandError {
 /// and `$()*` have special meaning (see `Var` and `Repeat` data structures)
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct DeclarativeMacro {
-    rules: Vec<Rule>,
+    rules: Box<[Rule]>,
     /// Highest id of the token we have in TokenMap
     shift: Shift,
     // This is used for correctly determining the behavior of the pat fragment
@@ -217,7 +217,7 @@ impl DeclarativeMacro {
             validate(lhs)?;
         }
 
-        Ok(DeclarativeMacro { rules, shift: Shift::new(tt), is_2021 })
+        Ok(DeclarativeMacro { rules: rules.into_boxed_slice(), shift: Shift::new(tt), is_2021 })
     }
 
     /// The new, unstable `macro m {}` flavor.
@@ -250,7 +250,7 @@ impl DeclarativeMacro {
             validate(lhs)?;
         }
 
-        Ok(DeclarativeMacro { rules, shift: Shift::new(tt), is_2021 })
+        Ok(DeclarativeMacro { rules: rules.into_boxed_slice(), shift: Shift::new(tt), is_2021 })
     }
 
     pub fn expand(&self, tt: &tt::Subtree) -> ExpandResult<tt::Subtree> {

crates/mbe/src/parser.rs

@@ -20,7 +20,7 @@ use crate::{tt, tt_iter::TtIter, ParseError};
 /// Stuff to the right is a [`MetaTemplate`] template which is used to produce
 /// output.
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub(crate) struct MetaTemplate(pub(crate) Vec<Op>);
+pub(crate) struct MetaTemplate(pub(crate) Box<[Op]>);
 
 impl MetaTemplate {
     pub(crate) fn parse_pattern(pattern: &tt::Subtree) -> Result<MetaTemplate, ParseError> {
@@ -44,7 +44,7 @@ impl MetaTemplate {
             res.push(op);
         }
 
-        Ok(MetaTemplate(res))
+        Ok(MetaTemplate(res.into_boxed_slice()))
     }
 }