Handle let-else initializer edge case errors

compiler/rustc_ast/src/util/classify.rs

@@ -23,3 +23,30 @@ pub fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool {
             | ast::ExprKind::TryBlock(..)
     )
 }
+
+/// If an expression ends with `}`, returns the innermost expression ending in the `}`
+pub fn expr_trailing_brace(mut expr: &ast::Expr) -> Option<&ast::Expr> {
+    use ast::ExprKind::*;
+
+    loop {
+        match &expr.kind {
+            AddrOf(_, _, e)
+            | Assign(_, e, _)
+            | AssignOp(_, _, e)
+            | Binary(_, _, e)
+            | Box(e)
+            | Break(_, Some(e))
+            | Closure(.., e, _)
+            | Let(_, e, _)
+            | Range(_, Some(e), _)
+            | Ret(Some(e))
+            | Unary(_, e)
+            | Yield(Some(e)) => {
+                expr = e;
+            }
+            Async(..) | Block(..) | ForLoop(..) | If(..) | Loop(..) | Match(..) | Struct(..)
+            | TryBlock(..) | While(..) => break Some(expr),
+            _ => break None,
+        }
+    }
+}