Rollup merge of #133093 - est31:let_chains_tests, r=traviscross

Let chains tests

Filing this as this marks off two of the open issues in #132833:

* extending the tests for `move-guard-if-let-chain.rs` and `conflicting_bindings.rs` to have chains with multiple let's (one implementation could for example search for the first `let` and then terminate).
* An instance where a temporary lives shorter than with nested ifs, breaking compilation: #103476. This was fixed in the end by the if let rescoping work.

Closes #103476

tests/ui/pattern/usefulness/conflicting_bindings.rs

@@ -10,6 +10,8 @@ fn main() {
     //~^ ERROR: mutable more than once
     if let Some(ref mut y @ ref mut z) = x && true {}
     //~^ ERROR: mutable more than once
+    if let Some(_) = Some(()) && let Some(ref mut y @ ref mut z) = x && true {}
+    //~^ ERROR: mutable more than once
     while let Some(ref mut y @ ref mut z) = x {}
     //~^ ERROR: mutable more than once
     while let Some(ref mut y @ ref mut z) = x && true {}

tests/ui/pattern/usefulness/conflicting_bindings.stderr

@@ -31,7 +31,15 @@ LL |     if let Some(ref mut y @ ref mut z) = x && true {}
    |                 value is mutably borrowed by `y` here
 
 error: cannot borrow value as mutable more than once at a time
-  --> $DIR/conflicting_bindings.rs:13:20
+  --> $DIR/conflicting_bindings.rs:13:43
+   |
+LL |     if let Some(_) = Some(()) && let Some(ref mut y @ ref mut z) = x && true {}
+   |                                           ^^^^^^^^^   --------- value is mutably borrowed by `z` here
+   |                                           |
+   |                                           value is mutably borrowed by `y` here
+
+error: cannot borrow value as mutable more than once at a time
+  --> $DIR/conflicting_bindings.rs:15:20
    |
 LL |     while let Some(ref mut y @ ref mut z) = x {}
    |                    ^^^^^^^^^   --------- value is mutably borrowed by `z` here
@@ -39,7 +47,7 @@ LL |     while let Some(ref mut y @ ref mut z) = x {}
    |                    value is mutably borrowed by `y` here
 
 error: cannot borrow value as mutable more than once at a time
-  --> $DIR/conflicting_bindings.rs:15:20
+  --> $DIR/conflicting_bindings.rs:17:20
    |
 LL |     while let Some(ref mut y @ ref mut z) = x && true {}
    |                    ^^^^^^^^^   --------- value is mutably borrowed by `z` here
@@ -47,7 +55,7 @@ LL |     while let Some(ref mut y @ ref mut z) = x && true {}
    |                    value is mutably borrowed by `y` here
 
 error: cannot borrow value as mutable more than once at a time
-  --> $DIR/conflicting_bindings.rs:18:9
+  --> $DIR/conflicting_bindings.rs:20:9
    |
 LL |         ref mut y @ ref mut z => {}
    |         ^^^^^^^^^   --------- value is mutably borrowed by `z` here
@@ -55,12 +63,12 @@ LL |         ref mut y @ ref mut z => {}
    |         value is mutably borrowed by `y` here
 
 error: cannot borrow value as mutable more than once at a time
-  --> $DIR/conflicting_bindings.rs:21:24
+  --> $DIR/conflicting_bindings.rs:23:24
    |
 LL |         () if let Some(ref mut y @ ref mut z) = x => {}
    |                        ^^^^^^^^^   --------- value is mutably borrowed by `z` here
    |                        |
    |                        value is mutably borrowed by `y` here
 
-error: aborting due to 8 previous errors
+error: aborting due to 9 previous errors
 

tests/ui/rfcs/rfc-2294-if-let-guard/move-guard-if-let-chain.rs

@@ -94,4 +94,15 @@ fn use_in_arm_ok(c: bool) {
     };
 }
 
+fn use_in_same_chain(c: bool) {
+    let x: Box<_> = Box::new(1);
+
+    let v = (1, 2);
+
+    match v {
+        (1, 2) if let y = x && c && let z = x => false, //~ ERROR use of moved value: `x`
+        _ => true,
+    };
+}
+
 fn main() {}

tests/ui/rfcs/rfc-2294-if-let-guard/move-guard-if-let-chain.stderr

@@ -60,6 +60,22 @@ help: borrow this binding in the pattern to avoid moving the value
 LL |         (1, 2) if let ref y = x && c => false,
    |                       +++
 
-error: aborting due to 4 previous errors
+error[E0382]: use of moved value: `x`
+  --> $DIR/move-guard-if-let-chain.rs:103:41
+   |
+LL |     let x: Box<_> = Box::new(1);
+   |         - move occurs because `x` has type `Box<i32>`, which does not implement the `Copy` trait
+...
+LL |         (1, 2) if let y = x && c && let z = x => false,
+   |                       -                 ^ value used here after move
+   |                       |
+   |                       value moved here
+   |
+help: borrow this binding in the pattern to avoid moving the value
+   |
+LL |         (1, 2) if let ref y = x && c && let z = x => false,
+   |                       +++
+
+error: aborting due to 5 previous errors
 
 For more information about this error, try `rustc --explain E0382`.

tests/ui/rfcs/rfc-2497-if-let-chains/temporary-early-drop.rs

@@ -0,0 +1,25 @@
+// issue-103476
+//@ compile-flags: -Zlint-mir -Zunstable-options
+//@ edition: 2024
+//@ check-pass
+
+#![feature(let_chains)]
+#![allow(irrefutable_let_patterns)]
+
+struct Pd;
+
+impl Pd {
+    fn it(&self) -> It {
+        todo!()
+    }
+}
+
+pub struct It<'a>(Box<dyn Tr<'a>>);
+
+trait Tr<'a> {}
+
+fn f(m: Option<Pd>) {
+    if let Some(n) = m && let it = n.it() {};
+}
+
+fn main() {}