Implement destructuring assignment for structs and slices

Co-authored-by: varkor <github@varkor.com>

Author: fanzier

clippy_lints/src/utils/ast_utils.rs

@@ -107,6 +107,15 @@ pub fn eq_expr_opt(l: &Option<P<Expr>>, r: &Option<P<Expr>>) -> bool {
     both(l, r, |l, r| eq_expr(l, r))
 }
 
+pub fn eq_struct_rest(l: &StructRest, r: &StructRest) -> bool {
+    match (l, r) {
+        (StructRest::Base(lb), StructRest::Base(rb)) => eq_expr(lb, rb),
+        (StructRest::Rest(_), StructRest::Rest(_)) => true,
+        (StructRest::None, StructRest::None) => true,
+        _ => false,
+    }
+}
+
 pub fn eq_expr(l: &Expr, r: &Expr) -> bool {
     use ExprKind::*;
     if !over(&l.attrs, &r.attrs, |l, r| eq_attr(l, r)) {
@@ -150,7 +159,7 @@ pub fn eq_expr(l: &Expr, r: &Expr) -> bool {
         (Path(lq, lp), Path(rq, rp)) => both(lq, rq, |l, r| eq_qself(l, r)) && eq_path(lp, rp),
         (MacCall(l), MacCall(r)) => eq_mac_call(l, r),
         (Struct(lp, lfs, lb), Struct(rp, rfs, rb)) => {
-            eq_path(lp, rp) && eq_expr_opt(lb, rb) && unordered_over(lfs, rfs, |l, r| eq_field(l, r))
+            eq_path(lp, rp) && eq_struct_rest(lb, rb) && unordered_over(lfs, rfs, |l, r| eq_field(l, r))
         },
         _ => false,
     }

tests/ui/crashes/ice-6250.stderr

@@ -1,3 +1,14 @@
+error[E0658]: destructuring assignments are unstable
+  --> $DIR/ice-6250.rs:12:25
+   |
+LL |         Some(reference) = cache.data.get(key) {
+   |         --------------- ^
+   |         |
+   |         cannot assign to this expression
+   |
+   = note: see issue #71126 <https://github.com/rust-lang/rust/issues/71126> for more information
+   = help: add `#![feature(destructuring_assignment)]` to the crate attributes to enable
+
 error[E0601]: `main` function not found in crate `ice_6250`
   --> $DIR/ice-6250.rs:4:1
    |
@@ -10,18 +21,22 @@ LL | |     }
 LL | | }
    | |_^ consider adding a `main` function to `$DIR/ice-6250.rs`
 
+error[E0308]: mismatched types
+  --> $DIR/ice-6250.rs:12:14
+   |
+LL |         Some(reference) = cache.data.get(key) {
+   |              ^^^^^^^^^
+   |              |
+   |              expected integer, found `&i32`
+   |              help: consider dereferencing the borrow: `*reference`
+
 error[E0308]: mismatched types
   --> $DIR/ice-6250.rs:12:9
    |
 LL |         Some(reference) = cache.data.get(key) {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `bool`, found `()`
-   |
-help: you might have meant to use pattern matching
-   |
-LL |         let Some(reference) = cache.data.get(key) {
-   |         ^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0308, E0601.
+Some errors have detailed explanations: E0308, E0601, E0658.
 For more information about an error, try `rustc --explain E0308`.