add suggestion to add mut or const after &raw

Author: rmehri01

compiler/rustc_parse/messages.ftl

@@ -764,6 +764,8 @@ parse_suffixed_literal_in_attribute = suffixed literals are not allowed in attri
 
 parse_sugg_add_let_for_stmt = you might have meant to introduce a new binding
 
+parse_sugg_add_mut_or_const_in_raw_ref = you might have meant to use a raw reference
+
 parse_sugg_add_semi = add `;` here
 parse_sugg_change_inner_attr_to_outer = to annotate the {$item}, change the attribute from inner to outer style
 

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1303,6 +1303,22 @@ impl<'a> Parser<'a> {
         Err(e)
     }
 
+    /// When writing `&raw` that is missing the following `mut` or `const`, we will
+    /// encounter a parse error when encountering the next expression.
+    pub(super) fn suggest_add_mut_or_const_in_raw_ref(&mut self, e: &mut Diag<'_>, expr: &P<Expr>) {
+        if let ExprKind::AddrOf(ast::BorrowKind::Ref, ast::Mutability::Not, r) = &expr.kind
+            && let ast::ExprKind::Path(_, p) = &r.kind
+            && *p == Symbol::intern("raw")
+        {
+            e.span_suggestions(
+                expr.span.shrink_to_hi(),
+                fluent::parse_sugg_add_mut_or_const_in_raw_ref,
+                [" mut".to_string(), " const".to_string()],
+                Applicability::HasPlaceholders,
+            );
+        }
+    }
+
     /// Suggest add the missing `let` before the identifier in stmt
     /// `a: Ty = 1` -> `let a: Ty = 1`
     pub(super) fn suggest_add_missing_let_for_stmt(&mut self, err: &mut Diag<'a>) {

compiler/rustc_parse/src/parser/expr.rs

@@ -1581,7 +1581,10 @@ impl<'a> Parser<'a> {
                 ExprKind::Array(exprs)
             } else {
                 // Vector with one element
-                self.expect(close)?;
+                self.expect(close).map_err(|mut e| {
+                    self.suggest_add_mut_or_const_in_raw_ref(&mut e, &first_expr);
+                    e
+                })?;
                 ExprKind::Array(thin_vec![first_expr])
             }
         };

compiler/rustc_parse/src/parser/stmt.rs

@@ -897,6 +897,7 @@ impl<'a> Parser<'a> {
                                 res?
                             } else {
                                 res.unwrap_or_else(|mut e| {
+                                    self.suggest_add_mut_or_const_in_raw_ref(&mut e, expr);
                                     self.recover_missing_dot(&mut e);
                                     let guar = e.emit();
                                     self.recover_stmt();
@@ -920,6 +921,7 @@ impl<'a> Parser<'a> {
                     LocalKind::Init(expr) | LocalKind::InitElse(expr, _) => {
                         self.check_mistyped_turbofish_with_multiple_type_params(e, expr).map_err(
                             |mut e| {
+                                self.suggest_add_mut_or_const_in_raw_ref(&mut e, expr);
                                 self.recover_missing_dot(&mut e);
                                 e
                             },