Remove needless indirection through Rc

NamedMatch is already cheap to clone due to Lrc's inside.

Author: Mark-Simulacrum

src/libsyntax/ext/tt/macro_parser.rs

@@ -92,7 +92,6 @@ use rustc_data_structures::sync::Lrc;
 use std::collections::hash_map::Entry::{Occupied, Vacant};
 use std::mem;
 use std::ops::{Deref, DerefMut};
-use std::rc::Rc;
 
 // To avoid costly uniqueness checks, we require that `MatchSeq` always has a nonempty body.
 
@@ -280,7 +279,7 @@ pub enum ParseResult<T> {
 
 /// A `ParseResult` where the `Success` variant contains a mapping of `Ident`s to `NamedMatch`es.
 /// This represents the mapping of metavars to the token trees they bind to.
-pub type NamedParseResult = ParseResult<FxHashMap<Ident, Rc<NamedMatch>>>;
+pub type NamedParseResult = ParseResult<FxHashMap<Ident, NamedMatch>>;
 
 /// Count how many metavars are named in the given matcher `ms`.
 pub fn count_names(ms: &[TokenTree]) -> usize {
@@ -373,7 +372,7 @@ fn nameize<I: Iterator<Item = NamedMatch>>(
         sess: &ParseSess,
         m: &TokenTree,
         res: &mut I,
-        ret_val: &mut FxHashMap<Ident, Rc<NamedMatch>>,
+        ret_val: &mut FxHashMap<Ident, NamedMatch>,
     ) -> Result<(), (syntax_pos::Span, String)> {
         match *m {
             TokenTree::Sequence(_, ref seq) => for next_m in &seq.tts {
@@ -390,8 +389,7 @@ fn nameize<I: Iterator<Item = NamedMatch>>(
             TokenTree::MetaVarDecl(sp, bind_name, _) => {
                 match ret_val.entry(bind_name) {
                     Vacant(spot) => {
-                        // FIXME(simulacrum): Don't construct Rc here
-                        spot.insert(Rc::new(res.next().unwrap()));
+                        spot.insert(res.next().unwrap());
                     }
                     Occupied(..) => {
                         return Err((sp, format!("duplicated bind name: {}", bind_name)))

src/libsyntax/ext/tt/macro_rules.rs

@@ -308,7 +308,7 @@ pub fn compile(
     let mut valid = true;
 
     // Extract the arguments:
-    let lhses = match *argument_map[&lhs_nm] {
+    let lhses = match argument_map[&lhs_nm] {
         MatchedSeq(ref s, _) => s
             .iter()
             .map(|m| {
@@ -335,7 +335,7 @@ pub fn compile(
         _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs"),
     };
 
-    let rhses = match *argument_map[&rhs_nm] {
+    let rhses = match argument_map[&rhs_nm] {
         MatchedSeq(ref s, _) => s
             .iter()
             .map(|m| {

src/libsyntax/ext/tt/transcribe.rs

@@ -12,7 +12,6 @@ use smallvec::{smallvec, SmallVec};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
 use std::mem;
-use std::rc::Rc;
 
 /// An iterator over the token trees in a delimited token tree (`{ ... }`) or a sequence (`$(...)`).
 enum Frame {
@@ -65,9 +64,9 @@ impl Iterator for Frame {
 /// `transcribe` would return a `TokenStream` containing `println!("{}", stringify!(bar));`.
 ///
 /// Along the way, we do some additional error checking.
-pub fn transcribe(
+pub(super) fn transcribe(
     cx: &ExtCtxt<'_>,
-    interp: &FxHashMap<Ident, Rc<NamedMatch>>,
+    interp: &FxHashMap<Ident, NamedMatch>,
     src: Vec<quoted::TokenTree>,
 ) -> TokenStream {
     // Nothing for us to transcribe...
@@ -212,7 +211,7 @@ pub fn transcribe(
                 // Find the matched nonterminal from the macro invocation, and use it to replace
                 // the meta-var.
                 if let Some(cur_matched) = lookup_cur_matched(ident, interp, &repeats) {
-                    if let MatchedNonterminal(ref nt) = *cur_matched {
+                    if let MatchedNonterminal(ref nt) = cur_matched {
                         // FIXME #2887: why do we apply a mark when matching a token tree meta-var
                         // (e.g. `$x:tt`), but not when we are matching any other type of token
                         // tree?
@@ -273,18 +272,17 @@ pub fn transcribe(
 /// See the definition of `repeats` in the `transcribe` function. `repeats` is used to descend
 /// into the right place in nested matchers. If we attempt to descend too far, the macro writer has
 /// made a mistake, and we return `None`.
-fn lookup_cur_matched(
+fn lookup_cur_matched<'a>(
     ident: Ident,
-    interpolations: &FxHashMap<Ident, Rc<NamedMatch>>,
+    interpolations: &'a FxHashMap<Ident, NamedMatch>,
     repeats: &[(usize, usize)],
-) -> Option<Rc<NamedMatch>> {
+) -> Option<&'a NamedMatch> {
     interpolations.get(&ident).map(|matched| {
-        let mut matched = matched.clone();
+        let mut matched = matched;
         for &(idx, _) in repeats {
-            let m = matched.clone();
-            match *m {
+            match matched {
                 MatchedNonterminal(_) => break,
-                MatchedSeq(ref ads, _) => matched = Rc::new(ads[idx].clone()),
+                MatchedSeq(ref ads, _) => matched = ads.get(idx).unwrap(),
             }
         }
 
@@ -343,7 +341,7 @@ impl LockstepIterSize {
 /// multiple nested matcher sequences.
 fn lockstep_iter_size(
     tree: &quoted::TokenTree,
-    interpolations: &FxHashMap<Ident, Rc<NamedMatch>>,
+    interpolations: &FxHashMap<Ident, NamedMatch>,
     repeats: &[(usize, usize)],
 ) -> LockstepIterSize {
     use quoted::TokenTree;
@@ -360,7 +358,7 @@ fn lockstep_iter_size(
         }
         TokenTree::MetaVar(_, name) | TokenTree::MetaVarDecl(_, name, _) => {
             match lookup_cur_matched(name, interpolations, repeats) {
-                Some(matched) => match *matched {
+                Some(matched) => match matched {
                     MatchedNonterminal(_) => LockstepIterSize::Unconstrained,
                     MatchedSeq(ref ads, _) => LockstepIterSize::Constraint(ads.len(), name),
                 },