From 932186d9c2046257c0a1fc38c1cecf7bc19736c3 Mon Sep 17 00:00:00 2001
From: Chayim Refael Friedman <chayimfr@gmail.com>
Date: Fri, 29 May 2026 01:16:22 +0300
Subject: [PATCH] Do not assume array destructuring assignments with rest
 pattern are constant-sized

We used to set a `slice: None`.
---
 crates/hir-def/src/expr_store/lower.rs               | 12 ++++++++++--
 .../src/handlers/mismatched_array_pat_len.rs         | 11 +++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/crates/hir-def/src/expr_store/lower.rs b/crates/hir-def/src/expr_store/lower.rs
index 21b5b199867f..b33b04e95ae4 100644
--- a/crates/hir-def/src/expr_store/lower.rs
+++ b/crates/hir-def/src/expr_store/lower.rs
@@ -1844,12 +1844,20 @@ impl<'db> ExprCollector<'db> {
                 }
 
                 let mut elements = e.exprs();
+                let mut rest_ptr = None;
                 let prefix = elements
                     .by_ref()
-                    .map_while(|elem| collect_possibly_rest(self, elem).left())
+                    .map_while(|elem| match collect_possibly_rest(self, elem.clone()) {
+                        Either::Left(elem) => Some(elem),
+                        Either::Right(()) => {
+                            rest_ptr = Some(AstPtr::new(&elem));
+                            None
+                        }
+                    })
                     .collect();
                 let suffix = elements.map(|elem| self.collect_expr_as_pat(elem)).collect();
-                self.alloc_pat_from_expr(Pat::Slice { prefix, slice: None, suffix }, syntax_ptr)
+                let slice = rest_ptr.map(|ptr| self.alloc_pat_from_expr(Pat::Rest, ptr));
+                self.alloc_pat_from_expr(Pat::Slice { prefix, slice, suffix }, syntax_ptr)
             }
             ast::Expr::CallExpr(e) => {
                 let path = collect_path(self, e.expr()?)?;
diff --git a/crates/ide-diagnostics/src/handlers/mismatched_array_pat_len.rs b/crates/ide-diagnostics/src/handlers/mismatched_array_pat_len.rs
index 8cae405c92ee..bd02ce6a02c7 100644
--- a/crates/ide-diagnostics/src/handlers/mismatched_array_pat_len.rs
+++ b/crates/ide-diagnostics/src/handlers/mismatched_array_pat_len.rs
@@ -111,4 +111,15 @@ fn f(arr: [i32; 3]) {
 "#,
         );
     }
+
+    #[test]
+    fn destructuring_assignment_array_rest() {
+        check_diagnostics(
+            r#"
+fn main() {
+    [..] = [1, 2, 3];
+}
+    "#,
+        );
+    }
 }