Pass a Symbol to check_name, emit_feature_err, and related functions.

src/libsyntax_ext/format.rs

@@ -12,7 +12,7 @@ use syntax::ext::build::AstBuilder;
 use syntax::feature_gate;
 use syntax::parse::token;
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::{Symbol, sym};
 use syntax::tokenstream;
 use syntax_pos::{MultiSpan, Span, DUMMY_SP};
 
@@ -711,12 +711,12 @@ pub fn expand_format_args_nl<'cx>(
     //if !ecx.ecfg.enable_allow_internal_unstable() {
 
     // For some reason, the only one that actually works for `println` is the first check
-    if !sp.allows_unstable("format_args_nl") // the span is marked as `#[allow_insternal_unsable]`
+    if !sp.allows_unstable(sym::format_args_nl) // the span is marked `#[allow_insternal_unsable]`
         && !ecx.ecfg.enable_allow_internal_unstable()  // NOTE: when is this enabled?
         && !ecx.ecfg.enable_format_args_nl()  // enabled using `#[feature(format_args_nl]`
     {
         feature_gate::emit_feature_err(&ecx.parse_sess,
-                                       "format_args_nl",
+                                       sym::format_args_nl,
                                        sp,
                                        feature_gate::GateIssue::Language,
                                        feature_gate::EXPLAIN_FORMAT_ARGS_NL);