Use `Symbol` equality in `may_begin_with` and `parse_nt`.

src/libsyntax/ext/tt/macro_parser.rs

@@ -80,7 +80,7 @@
 use crate::parse::parser::{Parser, PathStyle};
 use crate::parse::token::{self, DocComment, Nonterminal, Token};
 use crate::print::pprust;
-use crate::symbol::kw;
+use crate::symbol::{kw, sym, Symbol};
 use crate::tokenstream::{DelimSpan, TokenStream};
 
 use errors::FatalError;
@@ -598,7 +598,7 @@ fn inner_parse_loop<'root, 'tt>(
                 TokenTree::MetaVarDecl(_, _, id) => {
                     // Built-in nonterminals never start with these tokens,
                     // so we can eliminate them from consideration.
-                    if may_begin_with(&*id.as_str(), token) {
+                    if may_begin_with(id.name, token) {
                         bb_items.push(item);
                     }
                 }
@@ -791,7 +791,7 @@ pub fn parse(
                 let match_cur = item.match_cur;
                 item.push_match(
                     match_cur,
-                    MatchedNonterminal(Lrc::new(parse_nt(&mut parser, span, &ident.as_str()))),
+                    MatchedNonterminal(Lrc::new(parse_nt(&mut parser, span, ident.name))),
                 );
                 item.idx += 1;
                 item.match_cur += 1;
@@ -819,7 +819,7 @@ fn get_macro_ident(token: &Token) -> Option<(Ident, bool)> {
 ///
 /// Returning `false` is a *stability guarantee* that such a matcher will *never* begin with that
 /// token. Be conservative (return true) if not sure.
-fn may_begin_with(name: &str, token: &Token) -> bool {
+fn may_begin_with(name: Symbol, token: &Token) -> bool {
     /// Checks whether the non-terminal may contain a single (non-keyword) identifier.
     fn may_be_ident(nt: &token::Nonterminal) -> bool {
         match *nt {
@@ -829,16 +829,16 @@ fn may_be_ident(nt: &token::Nonterminal) -> bool {
     }
 
     match name {
-        "expr" => token.can_begin_expr(),
-        "ty" => token.can_begin_type(),
-        "ident" => get_macro_ident(token).is_some(),
-        "literal" => token.can_begin_literal_or_bool(),
-        "vis" => match *token {
+        sym::expr => token.can_begin_expr(),
+        sym::ty => token.can_begin_type(),
+        sym::ident => get_macro_ident(token).is_some(),
+        sym::literal => token.can_begin_literal_or_bool(),
+        sym::vis => match *token {
             // The follow-set of :vis + "priv" keyword + interpolated
             Token::Comma | Token::Ident(..) | Token::Interpolated(_) => true,
             _ => token.can_begin_type(),
         },
-        "block" => match *token {
+        sym::block => match *token {
             Token::OpenDelim(token::Brace) => true,
             Token::Interpolated(ref nt) => match **nt {
                 token::NtItem(_)
@@ -852,7 +852,7 @@ fn may_be_ident(nt: &token::Nonterminal) -> bool {
             },
             _ => false,
         },
-        "path" | "meta" => match *token {
+        sym::path | sym::meta => match *token {
             Token::ModSep | Token::Ident(..) => true,
             Token::Interpolated(ref nt) => match **nt {
                 token::NtPath(_) | token::NtMeta(_) => true,
@@ -860,7 +860,7 @@ fn may_be_ident(nt: &token::Nonterminal) -> bool {
             },
             _ => false,
         },
-        "pat" => match *token {
+        sym::pat => match *token {
             Token::Ident(..) |               // box, ref, mut, and other identifiers (can stricten)
             Token::OpenDelim(token::Paren) |    // tuple pattern
             Token::OpenDelim(token::Bracket) |  // slice pattern
@@ -876,7 +876,7 @@ fn may_be_ident(nt: &token::Nonterminal) -> bool {
             Token::Interpolated(ref nt) => may_be_ident(nt),
             _ => false,
         },
-        "lifetime" => match *token {
+        sym::lifetime => match *token {
             Token::Lifetime(_) => true,
             Token::Interpolated(ref nt) => match **nt {
                 token::NtLifetime(_) | token::NtTT(_) => true,
@@ -903,34 +903,34 @@ fn may_be_ident(nt: &token::Nonterminal) -> bool {
 /// # Returns
 ///
 /// The parsed non-terminal.
-fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: &str) -> Nonterminal {
-    if name == "tt" {
+fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: Symbol) -> Nonterminal {
+    if name == sym::tt {
         return token::NtTT(p.parse_token_tree());
     }
     // check at the beginning and the parser checks after each bump
     p.process_potential_macro_variable();
     match name {
-        "item" => match panictry!(p.parse_item()) {
+        sym::item => match panictry!(p.parse_item()) {
             Some(i) => token::NtItem(i),
             None => {
                 p.fatal("expected an item keyword").emit();
                 FatalError.raise();
             }
         },
-        "block" => token::NtBlock(panictry!(p.parse_block())),
-        "stmt" => match panictry!(p.parse_stmt()) {
+        sym::block => token::NtBlock(panictry!(p.parse_block())),
+        sym::stmt => match panictry!(p.parse_stmt()) {
             Some(s) => token::NtStmt(s),
             None => {
                 p.fatal("expected a statement").emit();
                 FatalError.raise();
             }
         },
-        "pat" => token::NtPat(panictry!(p.parse_pat(None))),
-        "expr" => token::NtExpr(panictry!(p.parse_expr())),
-        "literal" => token::NtLiteral(panictry!(p.parse_literal_maybe_minus())),
-        "ty" => token::NtTy(panictry!(p.parse_ty())),
+        sym::pat => token::NtPat(panictry!(p.parse_pat(None))),
+        sym::expr => token::NtExpr(panictry!(p.parse_expr())),
+        sym::literal => token::NtLiteral(panictry!(p.parse_literal_maybe_minus())),
+        sym::ty => token::NtTy(panictry!(p.parse_ty())),
         // this could be handled like a token, since it is one
-        "ident" => if let Some((ident, is_raw)) = get_macro_ident(&p.token) {
+        sym::ident => if let Some((ident, is_raw)) = get_macro_ident(&p.token) {
             let span = p.span;
             p.bump();
             token::NtIdent(Ident::new(ident.name, span), is_raw)
@@ -939,10 +939,10 @@ fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: &str) -> Nonterminal {
             p.fatal(&format!("expected ident, found {}", &token_str)).emit();
             FatalError.raise()
         }
-        "path" => token::NtPath(panictry!(p.parse_path(PathStyle::Type))),
-        "meta" => token::NtMeta(panictry!(p.parse_meta_item())),
-        "vis" => token::NtVis(panictry!(p.parse_visibility(true))),
-        "lifetime" => if p.check_lifetime() {
+        sym::path => token::NtPath(panictry!(p.parse_path(PathStyle::Type))),
+        sym::meta => token::NtMeta(panictry!(p.parse_meta_item())),
+        sym::vis => token::NtVis(panictry!(p.parse_visibility(true))),
+        sym::lifetime => if p.check_lifetime() {
             token::NtLifetime(p.expect_lifetime().ident)
         } else {
             let token_str = pprust::token_to_string(&p.token);

src/libsyntax_pos/symbol.rs

@@ -252,6 +252,7 @@
         existential_type,
         expected,
         export_name,
+        expr,
         extern_absolute_paths,
         external_doc,
         extern_crate_item_prelude,
@@ -329,6 +330,7 @@
         issue,
         issue_5723_bootstrap,
         issue_tracker_base_url,
+        item,
         item_like_imports,
         iter,
         Iterator,
@@ -339,6 +341,7 @@
         lang,
         lang_items,
         lib,
+        lifetime,
         link,
         linkage,
         link_args,
@@ -347,6 +350,7 @@
         link_name,
         link_section,
         lint_reasons,
+        literal,
         local_inner_macros,
         log_syntax,
         loop_break_value,
@@ -435,6 +439,7 @@
         partial_cmp,
         PartialOrd,
         passes,
+        pat,
         path,
         pattern_parentheses,
         Pending,
@@ -578,6 +583,7 @@
         static_recursion,
         std,
         str,
+        stmt,
         stmt_expr_attributes,
         stop_after_dataflow,
         struct_field_attributes,
@@ -610,6 +616,7 @@
         Try,
         try_blocks,
         try_trait,
+        tt,
         tuple_indexing,
         ty,
         type_alias_enum_variants,