Introduce `sym::dummy` and `Ident::dummy`.

The idea is to identify cases of symbols/identifiers that are not
expected to be used. There isn't a perfectly sharp line between "dummy"
and "not dummy", but I think it's useful nonetheless.

2 files changed, 3 insertions, 4 deletions

diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
index 0e6b0bab082..35541bb04bd 100644
--- a/compiler/rustc_attr_parsing/src/context.rs
+++ b/compiler/rustc_attr_parsing/src/context.rs
@@ -9,7 +9,6 @@ use rustc_errors::{DiagCtxtHandle, Diagnostic};
 use rustc_feature::Features;
 use rustc_hir::{AttrArgs, AttrItem, AttrPath, Attribute, HashIgnoredAttrId};
 use rustc_session::Session;
-use rustc_span::symbol::kw;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};
 
 use crate::attributes::allow_unstable::{AllowConstFnUnstableParser, AllowInternalUnstableParser};
@@ -338,7 +337,7 @@ impl<'sess> AttributeParser<'sess> {
                         "expr in place where literal is expected (builtin attr parsing)",
                     );
                     ast::MetaItemLit {
-                        symbol: kw::Empty,
+                        symbol: sym::dummy,
                         suffix: None,
                         kind: ast::LitKind::Err(guar),
                         span: DUMMY_SP,
diff --git a/compiler/rustc_attr_parsing/src/parser.rs b/compiler/rustc_attr_parsing/src/parser.rs
index f0cce26f4e2..a8a1460591c 100644
--- a/compiler/rustc_attr_parsing/src/parser.rs
+++ b/compiler/rustc_attr_parsing/src/parser.rs
@@ -12,7 +12,7 @@ use rustc_ast::{AttrArgs, DelimArgs, Expr, ExprKind, LitKind, MetaItemLit, Norma
 use rustc_ast_pretty::pprust;
 use rustc_errors::DiagCtxtHandle;
 use rustc_hir::{self as hir, AttrPath};
-use rustc_span::symbol::{Ident, kw};
+use rustc_span::symbol::{Ident, kw, sym};
 use rustc_span::{ErrorGuaranteed, Span, Symbol};
 
 pub struct SegmentIterator<'a> {
@@ -360,7 +360,7 @@ fn expr_to_lit(dcx: DiagCtxtHandle<'_>, expr: &Expr, span: Span) -> MetaItemLit
             span,
             "expr in place where literal is expected (builtin attr parsing)",
         );
-        MetaItemLit { symbol: kw::Empty, suffix: None, kind: LitKind::Err(guar), span }
+        MetaItemLit { symbol: sym::dummy, suffix: None, kind: LitKind::Err(guar), span }
     }
 }