mbe: metavar expressions: Use symbols rather than ident.as_str()

Identify metavariable functions by using named symbols rather than
string comparisons.

Author: joshtriplett

compiler/rustc_expand/src/mbe/metavar_expr.rs

@@ -5,7 +5,7 @@ use rustc_ast_pretty::pprust;
 use rustc_errors::{Applicability, PResult};
 use rustc_macros::{Decodable, Encodable};
 use rustc_session::parse::ParseSess;
-use rustc_span::{Ident, Span, Symbol};
+use rustc_span::{Ident, Span, Symbol, sym};
 
 use crate::errors;
 
@@ -69,15 +69,15 @@ impl MetaVarExpr {
         }
 
         let mut iter = args.iter();
-        let rslt = match ident.as_str() {
-            "concat" => parse_concat(&mut iter, psess, outer_span, ident.span)?,
-            "count" => parse_count(&mut iter, psess, ident.span)?,
-            "ignore" => {
+        let rslt = match ident.name {
+            sym::concat => parse_concat(&mut iter, psess, outer_span, ident.span)?,
+            sym::count => parse_count(&mut iter, psess, ident.span)?,
+            sym::ignore => {
                 eat_dollar(&mut iter, psess, ident.span)?;
                 MetaVarExpr::Ignore(parse_ident(&mut iter, psess, ident.span)?)
             }
-            "index" => MetaVarExpr::Index(parse_depth(&mut iter, psess, ident.span)?),
-            "len" => MetaVarExpr::Len(parse_depth(&mut iter, psess, ident.span)?),
+            sym::index => MetaVarExpr::Index(parse_depth(&mut iter, psess, ident.span)?),
+            sym::len => MetaVarExpr::Len(parse_depth(&mut iter, psess, ident.span)?),
             _ => {
                 let err = errors::MveUnrecognizedExpr {
                     span: ident.span,
@@ -119,14 +119,13 @@ fn check_trailing_tokens<'psess>(
     }
 
     // `None` for max indicates the arg count must be exact, `Some` indicates a range is accepted.
-    let (min_or_exact_args, max_args) = match ident.as_str() {
-        "concat" => panic!("concat takes unlimited tokens but didn't eat them all"),
-        "ignore" => (1, None),
+    let (min_or_exact_args, max_args) = match ident.name {
+        sym::concat => panic!("concat takes unlimited tokens but didn't eat them all"),
+        sym::ignore => (1, None),
         // 1 or 2 args
-        "count" => (1, Some(2)),
+        sym::count => (1, Some(2)),
         // 0 or 1 arg
-        "index" => (0, Some(1)),
-        "len" => (0, Some(1)),
+        sym::index | sym::len => (0, Some(1)),
         other => unreachable!("unknown MVEs should be rejected earlier (got `{other}`)"),
     };