Rollup merge of #144439 - xizheyin:symbol-rs, r=petrochenkov

Introduce ModernIdent type to unify macro 2.0 hygiene handling

This pr introduce ModernIdent type to unify macro 2.0 hygiene handling

1. Added ModernIdent type. Wraps Ident and automatically calls `normalize_to_macros_2_0()`
2. Unified identifier normalization. Replaced scattered ident.normalize_to_macros_2_0() calls with ModernIdent::new(ident)

r? ````@petrochenkov````

compiler/rustc_span/src/lib.rs

@@ -66,7 +66,8 @@ pub use span_encoding::{DUMMY_SP, Span};
 
 pub mod symbol;
 pub use symbol::{
-    ByteSymbol, Ident, MacroRulesNormalizedIdent, STDLIB_STABLE_CRATES, Symbol, kw, sym,
+    ByteSymbol, Ident, MacroRulesNormalizedIdent, Macros20NormalizedIdent, STDLIB_STABLE_CRATES,
+    Symbol, kw, sym,
 };
 
 mod analyze_source_file;

compiler/rustc_span/src/symbol.rs

@@ -3,6 +3,7 @@
 //! type, and vice versa.
 
 use std::hash::{Hash, Hasher};
+use std::ops::Deref;
 use std::{fmt, str};
 
 use rustc_arena::DroplessArena;
@@ -2563,16 +2564,17 @@ impl fmt::Display for IdentPrinter {
 }
 
 /// An newtype around `Ident` that calls [Ident::normalize_to_macro_rules] on
-/// construction.
-// FIXME(matthewj, petrochenkov) Use this more often, add a similar
-// `ModernIdent` struct and use that as well.
+/// construction for "local variable hygiene" comparisons.
+///
+/// Use this type when you need to compare identifiers according to macro_rules hygiene.
+/// This ensures compile-time safety and avoids manual normalization calls.
 #[derive(Copy, Clone, Eq, PartialEq, Hash)]
 pub struct MacroRulesNormalizedIdent(Ident);
 
 impl MacroRulesNormalizedIdent {
     #[inline]
     pub fn new(ident: Ident) -> Self {
-        Self(ident.normalize_to_macro_rules())
+        MacroRulesNormalizedIdent(ident.normalize_to_macro_rules())
     }
 }
 
@@ -2588,6 +2590,48 @@ impl fmt::Display for MacroRulesNormalizedIdent {
     }
 }
 
+/// An newtype around `Ident` that calls [Ident::normalize_to_macros_2_0] on
+/// construction for "item hygiene" comparisons.
+///
+/// Identifiers with same string value become same if they came from the same macro 2.0 macro
+/// (e.g., `macro` item, but not `macro_rules` item) and stay different if they came from
+/// different macro 2.0 macros.
+#[derive(Copy, Clone, Eq, PartialEq, Hash)]
+pub struct Macros20NormalizedIdent(pub Ident);
+
+impl Macros20NormalizedIdent {
+    #[inline]
+    pub fn new(ident: Ident) -> Self {
+        Macros20NormalizedIdent(ident.normalize_to_macros_2_0())
+    }
+
+    // dummy_span does not need to be normalized, so we can use `Ident` directly
+    pub fn with_dummy_span(name: Symbol) -> Self {
+        Macros20NormalizedIdent(Ident::with_dummy_span(name))
+    }
+}
+
+impl fmt::Debug for Macros20NormalizedIdent {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.0, f)
+    }
+}
+
+impl fmt::Display for Macros20NormalizedIdent {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.0, f)
+    }
+}
+
+/// By impl Deref, we can access the wrapped Ident as if it were a normal Ident
+/// such as `norm_ident.name` instead of `norm_ident.0.name`.
+impl Deref for Macros20NormalizedIdent {
+    type Target = Ident;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
 /// An interned UTF-8 string.
 ///
 /// Internally, a `Symbol` is implemented as an index, and all operations