Do not modify mutability of simple bindings.

This commit removes the modification of the mutability of simple
bindings. While the mutability isn't used, it is important that it is
kept so that the input to procedural macros matches what the user wrote.
This commit also modifies the span of the binding mode so that it is
considered a compiler desugaring and won't be linted against for being
unused..

1 files changed, 21 insertions, 0 deletions

diff --git a/src/libsyntax/source_map.rs b/src/libsyntax/source_map.rs
index 08abbf5e8a4..215618bd09c 100644
--- a/src/libsyntax/source_map.rs
+++ b/src/libsyntax/source_map.rs
@@ -930,6 +930,27 @@ impl SourceMap {
 
         None
     }
+
+    /// Reuses the span but adds information like the kind of the desugaring and features that are
+    /// allowed inside this span.
+    pub fn mark_span_with_reason(
+        &self,
+        reason: hygiene::CompilerDesugaringKind,
+        span: Span,
+        allow_internal_unstable: Option<Lrc<[symbol::Symbol]>>,
+    ) -> Span {
+        let mark = Mark::fresh(Mark::root());
+        mark.set_expn_info(ExpnInfo {
+            call_site: span,
+            def_site: Some(span),
+            format: CompilerDesugaring(reason),
+            allow_internal_unstable,
+            allow_internal_unsafe: false,
+            local_inner_macros: false,
+            edition: hygiene::default_edition(),
+        });
+        span.with_ctxt(SyntaxContext::empty().apply_mark(mark))
+    }
 }
 
 impl SourceMapper for SourceMap {