Pass a slice instead of a Vec to transcribe.

It avoids some unnecessary allocations.

Author: nnethercote

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -263,14 +263,14 @@ fn generic_extension<'cx, 'tt>(
 
                 // Ignore the delimiters on the RHS.
                 let rhs = match &rhses[i] {
-                    mbe::TokenTree::Delimited(_, delimited) => delimited.tts.to_vec(),
+                    mbe::TokenTree::Delimited(_, delimited) => &delimited.tts,
                     _ => cx.span_bug(sp, "malformed macro rhs"),
                 };
                 let arm_span = rhses[i].span();
 
                 let rhs_spans = rhs.iter().map(|t| t.span()).collect::<Vec<_>>();
                 // rhs has holes ( `$id` and `$(...)` that need filled)
-                let mut tts = match transcribe(cx, &named_matches, rhs, transparency) {
+                let mut tts = match transcribe(cx, &named_matches, &rhs, transparency) {
                     Ok(tts) => tts,
                     Err(mut err) => {
                         err.emit();

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -85,7 +85,7 @@ impl<'a> Iterator for Frame<'a> {
 pub(super) fn transcribe<'a>(
     cx: &ExtCtxt<'a>,
     interp: &FxHashMap<MacroRulesNormalizedIdent, NamedMatch>,
-    src: Vec<mbe::TokenTree>,
+    src: &[mbe::TokenTree],
     transparency: Transparency,
 ) -> PResult<'a, TokenStream> {
     // Nothing for us to transcribe...