Introduce `TtHandle` and use it in `TokenSet`.

This removes the last use of `<mbe::TokenTree as Clone>`. It also
removes two trivial methods on `Delimited`.

3 files changed, 111 insertions, 53 deletions

diff --git a/compiler/rustc_expand/src/mbe.rs b/compiler/rustc_expand/src/mbe.rs
index f78f8460dcf..845d1ff5b51 100644
--- a/compiler/rustc_expand/src/mbe.rs
+++ b/compiler/rustc_expand/src/mbe.rs
@@ -26,18 +26,6 @@ struct Delimited {
     tts: Vec<TokenTree>,
 }
 
-impl Delimited {
-    /// Returns a `self::TokenTree` with a `Span` corresponding to the opening delimiter.
-    fn open_tt(&self, span: DelimSpan) -> TokenTree {
-        TokenTree::token(token::OpenDelim(self.delim), span.open)
-    }
-
-    /// Returns a `self::TokenTree` with a `Span` corresponding to the closing delimiter.
-    fn close_tt(&self, span: DelimSpan) -> TokenTree {
-        TokenTree::token(token::CloseDelim(self.delim), span.close)
-    }
-}
-
 #[derive(PartialEq, Encodable, Decodable, Debug)]
 struct SequenceRepetition {
     /// The sequence of token trees
diff --git a/compiler/rustc_expand/src/mbe/macro_parser.rs b/compiler/rustc_expand/src/mbe/macro_parser.rs
index b5f56d7d6dc..74b8450f756 100644
--- a/compiler/rustc_expand/src/mbe/macro_parser.rs
+++ b/compiler/rustc_expand/src/mbe/macro_parser.rs
@@ -142,10 +142,13 @@ pub(super) fn compute_locs(sess: &ParseSess, matcher: &[TokenTree]) -> Vec<Match
                     locs.push(MatcherLoc::Token { token: token.clone() });
                 }
                 TokenTree::Delimited(span, delimited) => {
+                    let open_token = Token::new(token::OpenDelim(delimited.delim), span.open);
+                    let close_token = Token::new(token::CloseDelim(delimited.delim), span.close);
+
                     locs.push(MatcherLoc::Delimited);
-                    inner(sess, &[delimited.open_tt(*span)], locs, next_metavar, seq_depth);
+                    locs.push(MatcherLoc::Token { token: open_token });
                     inner(sess, &delimited.tts, locs, next_metavar, seq_depth);
-                    inner(sess, &[delimited.close_tt(*span)], locs, next_metavar, seq_depth);
+                    locs.push(MatcherLoc::Token { token: close_token });
                 }
                 TokenTree::Sequence(_, seq) => {
                     // We can't determine `idx_first_after` and construct the final
diff --git a/compiler/rustc_expand/src/mbe/macro_rules.rs b/compiler/rustc_expand/src/mbe/macro_rules.rs
index c9a06728856..f9d24eeadd0 100644
--- a/compiler/rustc_expand/src/mbe/macro_rules.rs
+++ b/compiler/rustc_expand/src/mbe/macro_rules.rs
@@ -8,7 +8,7 @@ use crate::mbe::macro_parser::{MatchedSeq, MatchedTokenTree, MatcherLoc};
 use crate::mbe::transcribe::transcribe;
 
 use rustc_ast as ast;
-use rustc_ast::token::{self, NonterminalKind, Token, TokenKind::*};
+use rustc_ast::token::{self, NonterminalKind, Token, TokenKind, TokenKind::*};
 use rustc_ast::tokenstream::{DelimSpan, TokenStream};
 use rustc_ast::{NodeId, DUMMY_NODE_ID};
 use rustc_ast_pretty::pprust;
@@ -658,18 +658,18 @@ fn check_matcher(
 // that do not try to inject artificial span information. My plan is
 // to try to catch such cases ahead of time and not include them in
 // the precomputed mapping.)
-struct FirstSets {
+struct FirstSets<'tt> {
     // this maps each TokenTree::Sequence `$(tt ...) SEP OP` that is uniquely identified by its
     // span in the original matcher to the First set for the inner sequence `tt ...`.
     //
     // If two sequences have the same span in a matcher, then map that
     // span to None (invalidating the mapping here and forcing the code to
     // use a slow path).
-    first: FxHashMap<Span, Option<TokenSet>>,
+    first: FxHashMap<Span, Option<TokenSet<'tt>>>,
 }
 
-impl FirstSets {
-    fn new(tts: &[mbe::TokenTree]) -> FirstSets {
+impl<'tt> FirstSets<'tt> {
+    fn new(tts: &'tt [mbe::TokenTree]) -> FirstSets<'tt> {
         use mbe::TokenTree;
 
         let mut sets = FirstSets { first: FxHashMap::default() };
@@ -679,7 +679,7 @@ impl FirstSets {
         // walks backward over `tts`, returning the FIRST for `tts`
         // and updating `sets` at the same time for all sequence
         // substructure we find within `tts`.
-        fn build_recur(sets: &mut FirstSets, tts: &[TokenTree]) -> TokenSet {
+        fn build_recur<'tt>(sets: &mut FirstSets<'tt>, tts: &'tt [TokenTree]) -> TokenSet<'tt> {
             let mut first = TokenSet::empty();
             for tt in tts.iter().rev() {
                 match *tt {
@@ -687,11 +687,14 @@ impl FirstSets {
                     | TokenTree::MetaVar(..)
                     | TokenTree::MetaVarDecl(..)
                     | TokenTree::MetaVarExpr(..) => {
-                        first.replace_with(tt.clone());
+                        first.replace_with(TtHandle::TtRef(tt));
                     }
                     TokenTree::Delimited(span, ref delimited) => {
                         build_recur(sets, &delimited.tts);
-                        first.replace_with(delimited.open_tt(span));
+                        first.replace_with(TtHandle::from_token_kind(
+                            token::OpenDelim(delimited.delim),
+                            span.open,
+                        ));
                     }
                     TokenTree::Sequence(sp, ref seq_rep) => {
                         let subfirst = build_recur(sets, &seq_rep.tts);
@@ -715,7 +718,7 @@ impl FirstSets {
                         // token could be the separator token itself.
 
                         if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
-                            first.add_one_maybe(TokenTree::Token(sep.clone()));
+                            first.add_one_maybe(TtHandle::from_token(sep.clone()));
                         }
 
                         // Reverse scan: Sequence comes before `first`.
@@ -741,7 +744,7 @@ impl FirstSets {
 
     // walks forward over `tts` until all potential FIRST tokens are
     // identified.
-    fn first(&self, tts: &[mbe::TokenTree]) -> TokenSet {
+    fn first(&self, tts: &'tt [mbe::TokenTree]) -> TokenSet<'tt> {
         use mbe::TokenTree;
 
         let mut first = TokenSet::empty();
@@ -752,11 +755,14 @@ impl FirstSets {
                 | TokenTree::MetaVar(..)
                 | TokenTree::MetaVarDecl(..)
                 | TokenTree::MetaVarExpr(..) => {
-                    first.add_one(tt.clone());
+                    first.add_one(TtHandle::TtRef(tt));
                     return first;
                 }
                 TokenTree::Delimited(span, ref delimited) => {
-                    first.add_one(delimited.open_tt(span));
+                    first.add_one(TtHandle::from_token_kind(
+                        token::OpenDelim(delimited.delim),
+                        span.open,
+                    ));
                     return first;
                 }
                 TokenTree::Sequence(sp, ref seq_rep) => {
@@ -775,7 +781,7 @@ impl FirstSets {
                     // If the sequence contents can be empty, then the first
                     // token could be the separator token itself.
                     if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
-                        first.add_one_maybe(TokenTree::Token(sep.clone()));
+                        first.add_one_maybe(TtHandle::from_token(sep.clone()));
                     }
 
                     assert!(first.maybe_empty);
@@ -803,6 +809,62 @@ impl FirstSets {
     }
 }
 
+// Most `mbe::TokenTree`s are pre-existing in the matcher, but some are defined
+// implicitly, such as opening/closing delimiters and sequence repetition ops.
+// This type encapsulates both kinds. It implements `Clone` while avoiding the
+// need for `mbe::TokenTree` to implement `Clone`.
+#[derive(Debug)]
+enum TtHandle<'tt> {
+    /// This is used in most cases.
+    TtRef(&'tt mbe::TokenTree),
+
+    /// This is only used for implicit token trees. The `mbe::TokenTree` *must*
+    /// be `mbe::TokenTree::Token`. No other variants are allowed. We store an
+    /// `mbe::TokenTree` rather than a `Token` so that `get()` can return a
+    /// `&mbe::TokenTree`.
+    Token(mbe::TokenTree),
+}
+
+impl<'tt> TtHandle<'tt> {
+    fn from_token(tok: Token) -> Self {
+        TtHandle::Token(mbe::TokenTree::Token(tok))
+    }
+
+    fn from_token_kind(kind: TokenKind, span: Span) -> Self {
+        TtHandle::from_token(Token::new(kind, span))
+    }
+
+    // Get a reference to a token tree.
+    fn get(&'tt self) -> &'tt mbe::TokenTree {
+        match self {
+            TtHandle::TtRef(tt) => tt,
+            TtHandle::Token(token_tt) => &token_tt,
+        }
+    }
+}
+
+impl<'tt> PartialEq for TtHandle<'tt> {
+    fn eq(&self, other: &TtHandle<'tt>) -> bool {
+        self.get() == other.get()
+    }
+}
+
+impl<'tt> Clone for TtHandle<'tt> {
+    fn clone(&self) -> Self {
+        match self {
+            TtHandle::TtRef(tt) => TtHandle::TtRef(tt),
+
+            // This variant *must* contain a `mbe::TokenTree::Token`, and not
+            // any other variant of `mbe::TokenTree`.
+            TtHandle::Token(mbe::TokenTree::Token(tok)) => {
+                TtHandle::Token(mbe::TokenTree::Token(tok.clone()))
+            }
+
+            _ => unreachable!(),
+        }
+    }
+}
+
 // A set of `mbe::TokenTree`s, which may include `TokenTree::Match`s
 // (for macro-by-example syntactic variables). It also carries the
 // `maybe_empty` flag; that is true if and only if the matcher can
@@ -814,12 +876,12 @@ impl FirstSets {
 //
 // (Notably, we must allow for *-op to occur zero times.)
 #[derive(Clone, Debug)]
-struct TokenSet {
-    tokens: Vec<mbe::TokenTree>,
+struct TokenSet<'tt> {
+    tokens: Vec<TtHandle<'tt>>,
     maybe_empty: bool,
 }
 
-impl TokenSet {
+impl<'tt> TokenSet<'tt> {
     // Returns a set for the empty sequence.
     fn empty() -> Self {
         TokenSet { tokens: Vec::new(), maybe_empty: true }
@@ -827,15 +889,15 @@ impl TokenSet {
 
     // Returns the set `{ tok }` for the single-token (and thus
     // non-empty) sequence [tok].
-    fn singleton(tok: mbe::TokenTree) -> Self {
-        TokenSet { tokens: vec![tok], maybe_empty: false }
+    fn singleton(tt: TtHandle<'tt>) -> Self {
+        TokenSet { tokens: vec![tt], maybe_empty: false }
     }
 
     // Changes self to be the set `{ tok }`.
     // Since `tok` is always present, marks self as non-empty.
-    fn replace_with(&mut self, tok: mbe::TokenTree) {
+    fn replace_with(&mut self, tt: TtHandle<'tt>) {
         self.tokens.clear();
-        self.tokens.push(tok);
+        self.tokens.push(tt);
         self.maybe_empty = false;
     }
 
@@ -848,17 +910,17 @@ impl TokenSet {
     }
 
     // Adds `tok` to the set for `self`, marking sequence as non-empy.
-    fn add_one(&mut self, tok: mbe::TokenTree) {
-        if !self.tokens.contains(&tok) {
-            self.tokens.push(tok);
+    fn add_one(&mut self, tt: TtHandle<'tt>) {
+        if !self.tokens.contains(&tt) {
+            self.tokens.push(tt);
         }
         self.maybe_empty = false;
     }
 
     // Adds `tok` to the set for `self`. (Leaves `maybe_empty` flag alone.)
-    fn add_one_maybe(&mut self, tok: mbe::TokenTree) {
-        if !self.tokens.contains(&tok) {
-            self.tokens.push(tok);
+    fn add_one_maybe(&mut self, tt: TtHandle<'tt>) {
+        if !self.tokens.contains(&tt) {
+            self.tokens.push(tt);
         }
     }
 
@@ -870,9 +932,9 @@ impl TokenSet {
     // setting of the empty flag of `self`. If `other` is guaranteed
     // non-empty, then `self` is marked non-empty.
     fn add_all(&mut self, other: &Self) {
-        for tok in &other.tokens {
-            if !self.tokens.contains(tok) {
-                self.tokens.push(tok.clone());
+        for tt in &other.tokens {
+            if !self.tokens.contains(tt) {
+                self.tokens.push(tt.clone());
             }
         }
         if !other.maybe_empty {
@@ -892,14 +954,14 @@ impl TokenSet {
 //
 // Requires that `first_sets` is pre-computed for `matcher`;
 // see `FirstSets::new`.
-fn check_matcher_core(
+fn check_matcher_core<'tt>(
     sess: &ParseSess,
     features: &Features,
     def: &ast::Item,
-    first_sets: &FirstSets,
-    matcher: &[mbe::TokenTree],
-    follow: &TokenSet,
-) -> TokenSet {
+    first_sets: &FirstSets<'tt>,
+    matcher: &'tt [mbe::TokenTree],
+    follow: &TokenSet<'tt>,
+) -> TokenSet<'tt> {
     use mbe::TokenTree;
 
     let mut last = TokenSet::empty();
@@ -938,12 +1000,15 @@ fn check_matcher_core(
                     // followed by anything against SUFFIX.
                     continue 'each_token;
                 } else {
-                    last.replace_with(token.clone());
+                    last.replace_with(TtHandle::TtRef(token));
                     suffix_first = build_suffix_first();
                 }
             }
             TokenTree::Delimited(span, ref d) => {
-                let my_suffix = TokenSet::singleton(d.close_tt(span));
+                let my_suffix = TokenSet::singleton(TtHandle::from_token_kind(
+                    token::CloseDelim(d.delim),
+                    span.close,
+                ));
                 check_matcher_core(sess, features, def, first_sets, &d.tts, &my_suffix);
                 // don't track non NT tokens
                 last.replace_with_irrelevant();
@@ -967,7 +1032,7 @@ fn check_matcher_core(
                 let mut new;
                 let my_suffix = if let Some(sep) = &seq_rep.separator {
                     new = suffix_first.clone();
-                    new.add_one_maybe(TokenTree::Token(sep.clone()));
+                    new.add_one_maybe(TtHandle::from_token(sep.clone()));
                     &new
                 } else {
                     &suffix_first
@@ -994,9 +1059,11 @@ fn check_matcher_core(
 
         // Now `last` holds the complete set of NT tokens that could
         // end the sequence before SUFFIX. Check that every one works with `suffix`.
-        for token in &last.tokens {
-            if let TokenTree::MetaVarDecl(span, name, Some(kind)) = *token {
+        for tt in &last.tokens {
+            if let &TokenTree::MetaVarDecl(span, name, Some(kind)) = tt.get() {
                 for next_token in &suffix_first.tokens {
+                    let next_token = next_token.get();
+
                     // Check if the old pat is used and the next token is `|`
                     // to warn about incompatibility with Rust 2021.
                     // We only emit this lint if we're parsing the original