Rollup merge of #100115 - obeis:issue-99910, r=cjgillot

Suggest removing `let` if `const let` or `let const` is used

Closes #99910

2 files changed, 26 insertions, 0 deletions

diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index c6dd5e7fda3..83fab0829a1 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -1162,6 +1162,16 @@ impl<'a> Parser<'a> {
                     Applicability::MaybeIncorrect,
                 )
                 .emit();
+        } else if self.eat_keyword(kw::Let) {
+            let span = self.prev_token.span;
+            self.struct_span_err(const_span.to(span), "`const` and `let` are mutually exclusive")
+                .span_suggestion(
+                    const_span.to(span),
+                    "remove `let`",
+                    "const",
+                    Applicability::MaybeIncorrect,
+                )
+                .emit();
         }
     }
 
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 51bd9d2d386..6990d0782b7 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -247,6 +247,22 @@ impl<'a> Parser<'a> {
     /// Parses a local variable declaration.
     fn parse_local(&mut self, attrs: AttrVec) -> PResult<'a, P<Local>> {
         let lo = self.prev_token.span;
+
+        if self.token.is_keyword(kw::Const) && self.look_ahead(1, |t| t.is_ident()) {
+            self.struct_span_err(
+                lo.to(self.token.span),
+                "`const` and `let` are mutually exclusive",
+            )
+            .span_suggestion(
+                lo.to(self.token.span),
+                "remove `let`",
+                "const",
+                Applicability::MaybeIncorrect,
+            )
+            .emit();
+            self.bump();
+        }
+
         let (pat, colon) = self.parse_pat_before_ty(None, RecoverComma::Yes, "`let` bindings")?;
 
         let (err, ty) = if colon {