Capture scrutinee of if let guards correctly

Previously we were always capturing by value.

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -664,10 +664,12 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
         );
         self.walk_pat(discr_place, arm.pat, arm.guard.is_some());
 
-        if let Some(hir::Guard::If(e)) = arm.guard {
+        match arm.guard {
-            self.consume_expr(e)
+            Some(hir::Guard::If(ref e)) => self.consume_expr(e),
-        } else if let Some(hir::Guard::IfLet(ref l)) = arm.guard {
+            Some(hir::Guard::IfLet(ref l)) => {
-            self.consume_expr(l.init)
+                self.walk_local(l.init, l.pat, None, |t| t.borrow_expr(l.init, ty::ImmBorrow))
+            }
+            None => {}
         }
 
         self.consume_expr(arm.body);

tests/ui/closures/2229_closure_analysis/match/if-let-guards-errors.e2018.stderr

@@ -0,0 +1,33 @@
+error[E0505]: cannot move out of `value` because it is borrowed
+  --> $DIR/if-let-guards-errors.rs:16:13
+   |
+LL |     let f = |x: &E| {
+   |             ------- borrow of `value` occurs here
+LL |         match &x {
+LL |             E::Number(_) if let E::Number(ref mut n) = *value => { }
+   |                                                        ------ borrow occurs due to use in closure
+...
+LL |     let x = value;
+   |             ^^^^^ move out of `value` occurs here
+LL |
+LL |     drop(f);
+   |          - borrow later used here
+
+error[E0382]: use of moved value: `value`
+  --> $DIR/if-let-guards-errors.rs:28:13
+   |
+LL | fn if_let_move(value: Box<E>) {
+   |                ----- move occurs because `value` has type `Box<E>`, which does not implement the `Copy` trait
+LL |     let f = |x: &E| {
+   |             ------- value moved into closure here
+LL |         match &x {
+LL |             E::Number(_) if let E::String(s) = *value => { }
+   |                                                ------ variable moved due to use in closure
+...
+LL |     let x = value;
+   |             ^^^^^ value used here after move
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0382, E0505.
+For more information about an error, try `rustc --explain E0382`.

tests/ui/closures/2229_closure_analysis/match/if-let-guards-errors.e2021.stderr

@@ -0,0 +1,33 @@
+error[E0505]: cannot move out of `value` because it is borrowed
+  --> $DIR/if-let-guards-errors.rs:16:13
+   |
+LL |     let f = |x: &E| {
+   |             ------- borrow of `*value` occurs here
+LL |         match &x {
+LL |             E::Number(_) if let E::Number(ref mut n) = *value => { }
+   |                                                        ------ borrow occurs due to use in closure
+...
+LL |     let x = value;
+   |             ^^^^^ move out of `value` occurs here
+LL |
+LL |     drop(f);
+   |          - borrow later used here
+
+error[E0382]: use of moved value: `value`
+  --> $DIR/if-let-guards-errors.rs:28:13
+   |
+LL | fn if_let_move(value: Box<E>) {
+   |                ----- move occurs because `value` has type `Box<E>`, which does not implement the `Copy` trait
+LL |     let f = |x: &E| {
+   |             ------- value moved into closure here
+LL |         match &x {
+LL |             E::Number(_) if let E::String(s) = *value => { }
+   |                                                ------ variable moved due to use in closure
+...
+LL |     let x = value;
+   |             ^^^^^ value used here after move
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0382, E0505.
+For more information about an error, try `rustc --explain E0382`.

tests/ui/closures/2229_closure_analysis/match/if-let-guards-errors.rs

@@ -0,0 +1,37 @@
+// Check the if let guards don't force capture by value
+// revisions: e2018 e2021
+//[e2018] edition:2018
+//[e2021] edition:2021
+
+#![feature(if_let_guard)]
+#![allow(irrefutable_let_patterns)]
+
+fn if_let_ref_mut(mut value: Box<E>) {
+    let f = |x: &E| {
+        match &x {
+            E::Number(_) if let E::Number(ref mut n) = *value => { }
+            _ => {}
+        }
+    };
+    let x = value;
+    //~^ ERROR cannot move out of `value` because it is borrowed
+    drop(f);
+}
+
+fn if_let_move(value: Box<E>) {
+    let f = |x: &E| {
+        match &x {
+            E::Number(_) if let E::String(s) = *value => { }
+            _ => {}
+        }
+    };
+    let x = value;
+    //~^ ERROR use of moved value: `value`
+}
+
+enum E {
+    String(String),
+    Number(i32),
+}
+
+fn main() {}

tests/ui/closures/2229_closure_analysis/match/if-let-guards.rs

@@ -0,0 +1,55 @@
+// Check the if let guards don't force capture by value
+// revisions: e2018 e2021
+// check-pass
+//[e2018] edition:2018
+//[e2021] edition:2021
+
+#![feature(if_let_guard)]
+#![allow(irrefutable_let_patterns)]
+
+fn if_let_underscore(value: Box<E>) {
+    |x: &E| {
+        match &x {
+            E::Number(_) if let _ = *value => { }
+            _ => {}
+        }
+    };
+    let x = value;
+}
+
+fn if_let_copy(value: Box<E>) {
+    |x: &E| {
+        match &x {
+            E::Number(_) if let E::Number(n) = *value => { }
+            _ => {}
+        }
+    };
+    let x = value;
+}
+
+fn if_let_ref(value: Box<E>) {
+    |x: &E| {
+        match &x {
+            E::Number(_) if let E::Number(ref n) = *value => { }
+            _ => {}
+        }
+    };
+    let x = value;
+}
+
+fn if_let_ref_mut(mut value: Box<E>) {
+    |x: &E| {
+        match &x {
+            E::Number(_) if let E::Number(ref mut n) = *value => { }
+            _ => {}
+        }
+    };
+    let x = value;
+}
+
+enum E {
+    String(String),
+    Number(i32),
+}
+
+fn main() {}