Suggest add let when no let in refutable bindings

Signed-off-by: xizheyin <[email protected]>

Author: xizheyin

compiler/rustc_mir_build/src/errors.rs

@@ -1062,13 +1062,11 @@ pub(crate) enum SuggestLet {
         semi_span: Span,
         count: usize,
     },
-    #[suggestion(
-        mir_build_suggest_let_else,
-        code = " else {{ todo!() }}",
-        applicability = "has-placeholders"
-    )]
+    #[multipart_suggestion(mir_build_suggest_let_else, applicability = "has-placeholders")]
     Else {
-        #[primary_span]
+        #[suggestion_part(code = "let ")]
+        let_span: Option<Span>,
+        #[suggestion_part(code = " else {{ todo!() }}")]
         end_span: Span,
         count: usize,
     },

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -727,7 +727,14 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
             let_suggestion = Some(if bindings.is_empty() {
                 SuggestLet::If { start_span, semi_span, count }
             } else {
-                SuggestLet::Else { end_span, count }
+                let let_span = if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
+                    && !snippet.trim_start().starts_with("let")
+                {
+                    Some(start_span)
+                } else {
+                    None
+                };
+                SuggestLet::Else { let_span, end_span, count }
             });
         };
 

tests/ui/let-else/suggest-with-let-issue-145548.stderr

@@ -9,8 +9,8 @@ LL |     Some(x) = Some(1);
    = note: the matched value is of type `Option<i32>`
 help: you might want to use `let else` to handle the variant that isn't matched
    |
-LL |     Some(x) = Some(1) else { todo!() };
-   |                       ++++++++++++++++
+LL |     let Some(x) = Some(1) else { todo!() };
+   |     +++                   ++++++++++++++++
 
 error[E0005]: refutable pattern in local binding
   --> $DIR/suggest-with-let-issue-145548.rs:11:9