Auto merge of #96268 - jackh726:remove-mutable_borrow_reservation_conflict-lint, r=nikomatsakis

Remove mutable_borrow_reservation_conflict lint and allow the code pattern

This was the only breaking issue with the NLL stabilization PR. Lang team decided to go ahead and allow this.

r? `@nikomatsakis`
Closes #59159
Closes #56254

17 files changed, 76 insertions, 276 deletions

diff --git a/src/test/ui/borrowck/suggest-local-var-imm-and-mut.nll.stderr b/src/test/ui/borrowck/suggest-local-var-imm-and-mut.nll.stderr
index 2ba0b6b28aa..eb934e7b72b 100644
--- a/src/test/ui/borrowck/suggest-local-var-imm-and-mut.nll.stderr
+++ b/src/test/ui/borrowck/suggest-local-var-imm-and-mut.nll.stderr
@@ -7,23 +7,12 @@ LL |             self.foo(self.bar());
    |             |    |   mutable borrow occurs here
    |             |    immutable borrow later used by call
    |             immutable borrow occurs here
-   |
-help: try adding a local storing this argument...
-  --> $DIR/suggest-local-var-imm-and-mut.rs:12:22
-   |
-LL |             self.foo(self.bar());
-   |                      ^^^^^^^^^^
-help: ...and then using that local as the argument to this call
-  --> $DIR/suggest-local-var-imm-and-mut.rs:12:13
-   |
-LL |             self.foo(self.bar());
-   |             ^^^^^^^^^^^^^^^^^^^^
 
 error[E0502]: cannot borrow `*self` as mutable because it is also borrowed as immutable
-  --> $DIR/suggest-local-var-imm-and-mut.rs:24:39
+  --> $DIR/suggest-local-var-imm-and-mut.rs:24:29
    |
 LL |             Self::foo(self, Self::bar(self));
-   |             --------- ----            ^^^^ mutable borrow occurs here
+   |             --------- ----  ^^^^^^^^^^^^^^^ mutable borrow occurs here
    |             |         |
    |             |         immutable borrow occurs here
    |             immutable borrow later used by call
diff --git a/src/test/ui/borrowck/two-phase-cannot-nest-mut-self-calls.stderr b/src/test/ui/borrowck/two-phase-cannot-nest-mut-self-calls.stderr
index 85c7159952f..a89bb941532 100644
--- a/src/test/ui/borrowck/two-phase-cannot-nest-mut-self-calls.stderr
+++ b/src/test/ui/borrowck/two-phase-cannot-nest-mut-self-calls.stderr
@@ -13,23 +13,6 @@ LL | |
 LL | |         0
 LL | |     });
    | |______- immutable borrow occurs here
-   |
-help: try adding a local storing this argument...
-  --> $DIR/two-phase-cannot-nest-mut-self-calls.rs:16:9
-   |
-LL |         vec.push(2);
-   |         ^^^^^^^^^^^
-help: ...and then using that local as the argument to this call
-  --> $DIR/two-phase-cannot-nest-mut-self-calls.rs:14:5
-   |
-LL | /     vec.get({
-LL | |
-LL | |         vec.push(2);
-LL | |
-LL | |
-LL | |         0
-LL | |     });
-   | |______^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.base.stderr b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.base.stderr
new file mode 100644
index 00000000000..cbbbde61917
--- /dev/null
+++ b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.base.stderr
@@ -0,0 +1,25 @@
+error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
+  --> $DIR/two-phase-reservation-sharing-interference-2.rs:19:5
+   |
+LL |     let shared = &v;
+   |                  -- immutable borrow occurs here
+LL | 
+LL |     v.extend(shared);
+   |     ^^------^^^^^^^^
+   |     | |
+   |     | immutable borrow later used by call
+   |     mutable borrow occurs here
+
+error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
+  --> $DIR/two-phase-reservation-sharing-interference-2.rs:27:5
+   |
+LL |     v.extend(&v);
+   |     ^^------^--^
+   |     | |      |
+   |     | |      immutable borrow occurs here
+   |     | immutable borrow later used by call
+   |     mutable borrow occurs here
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0502`.
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2015.stderr b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2015.stderr
index 6cff53399ca..69c3d7915e4 100644
--- a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2015.stderr
+++ b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2015.stderr
@@ -20,22 +20,6 @@ LL |     v.extend(&v);
    |     | immutable borrow later used by call
    |     mutable borrow occurs here
 
-warning: cannot borrow `v` as mutable because it is also borrowed as immutable
-  --> $DIR/two-phase-reservation-sharing-interference-2.rs:40:5
-   |
-LL |     let shared = &v;
-   |                  -- immutable borrow occurs here
-LL | 
-LL |     v.push(shared.len());
-   |     ^^^^^^^------------^
-   |     |      |
-   |     |      immutable borrow later used here
-   |     mutable borrow occurs here
-   |
-   = note: `#[warn(mutable_borrow_reservation_conflict)]` on by default
-   = warning: this borrowing pattern was not meant to be accepted, and may become a hard error in the future
-   = note: for more information, see issue #59159 <https://github.com/rust-lang/rust/issues/59159>
-
-error: aborting due to 2 previous errors; 1 warning emitted
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0502`.
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2018.stderr b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2018.stderr
index 6cff53399ca..69c3d7915e4 100644
--- a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2018.stderr
+++ b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.migrate2018.stderr
@@ -20,22 +20,6 @@ LL |     v.extend(&v);
    |     | immutable borrow later used by call
    |     mutable borrow occurs here
 
-warning: cannot borrow `v` as mutable because it is also borrowed as immutable
-  --> $DIR/two-phase-reservation-sharing-interference-2.rs:40:5
-   |
-LL |     let shared = &v;
-   |                  -- immutable borrow occurs here
-LL | 
-LL |     v.push(shared.len());
-   |     ^^^^^^^------------^
-   |     |      |
-   |     |      immutable borrow later used here
-   |     mutable borrow occurs here
-   |
-   = note: `#[warn(mutable_borrow_reservation_conflict)]` on by default
-   = warning: this borrowing pattern was not meant to be accepted, and may become a hard error in the future
-   = note: for more information, see issue #59159 <https://github.com/rust-lang/rust/issues/59159>
-
-error: aborting due to 2 previous errors; 1 warning emitted
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0502`.
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll.stderr b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll.stderr
new file mode 100644
index 00000000000..cbbbde61917
--- /dev/null
+++ b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll.stderr
@@ -0,0 +1,25 @@
+error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
+  --> $DIR/two-phase-reservation-sharing-interference-2.rs:19:5
+   |
+LL |     let shared = &v;
+   |                  -- immutable borrow occurs here
+LL | 
+LL |     v.extend(shared);
+   |     ^^------^^^^^^^^
+   |     | |
+   |     | immutable borrow later used by call
+   |     mutable borrow occurs here
+
+error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
+  --> $DIR/two-phase-reservation-sharing-interference-2.rs:27:5
+   |
+LL |     v.extend(&v);
+   |     ^^------^--^
+   |     | |      |
+   |     | |      immutable borrow occurs here
+   |     | immutable borrow later used by call
+   |     mutable borrow occurs here
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0502`.
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll2015.stderr b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll2015.stderr
index 0ae6fe78c6a..69c3d7915e4 100644
--- a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll2015.stderr
+++ b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll2015.stderr
@@ -5,9 +5,9 @@ LL |     let shared = &v;
    |                  -- immutable borrow occurs here
 LL | 
 LL |     v.extend(shared);
-   |     ^^^^^^^^^------^
-   |     |        |
-   |     |        immutable borrow later used here
+   |     ^^------^^^^^^^^
+   |     | |
+   |     | immutable borrow later used by call
    |     mutable borrow occurs here
 
 error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
@@ -20,18 +20,6 @@ LL |     v.extend(&v);
    |     | immutable borrow later used by call
    |     mutable borrow occurs here
 
-error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
-  --> $DIR/two-phase-reservation-sharing-interference-2.rs:40:5
-   |
-LL |     let shared = &v;
-   |                  -- immutable borrow occurs here
-LL | 
-LL |     v.push(shared.len());
-   |     ^^^^^^^------------^
-   |     |      |
-   |     |      immutable borrow later used here
-   |     mutable borrow occurs here
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0502`.
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll2018.stderr b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll2018.stderr
index 0ae6fe78c6a..69c3d7915e4 100644
--- a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll2018.stderr
+++ b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.nll2018.stderr
@@ -5,9 +5,9 @@ LL |     let shared = &v;
    |                  -- immutable borrow occurs here
 LL | 
 LL |     v.extend(shared);
-   |     ^^^^^^^^^------^
-   |     |        |
-   |     |        immutable borrow later used here
+   |     ^^------^^^^^^^^
+   |     | |
+   |     | immutable borrow later used by call
    |     mutable borrow occurs here
 
 error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
@@ -20,18 +20,6 @@ LL |     v.extend(&v);
    |     | immutable borrow later used by call
    |     mutable borrow occurs here
 
-error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
-  --> $DIR/two-phase-reservation-sharing-interference-2.rs:40:5
-   |
-LL |     let shared = &v;
-   |                  -- immutable borrow occurs here
-LL | 
-LL |     v.push(shared.len());
-   |     ^^^^^^^------------^
-   |     |      |
-   |     |      immutable borrow later used here
-   |     mutable borrow occurs here
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0502`.
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.rs b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.rs
index 14f687c2378..3e125869ef1 100644
--- a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.rs
+++ b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-2.rs
@@ -1,50 +1,39 @@
-// Test for #56254, we previously allowed the last example on the 2018
-// edition. Make sure that we now emit a warning in that case and an error for
-// everyone else.
+// Test for #56254. The last example originally failed with the ast checker, was
+// accidentally allowed under migrate/nll, then linted against in migrate mode
+// but disallowed under NLL. Now, we accept it everywhere.
 
 //ignore-compare-mode-nll
 //ignore-compare-mode-polonius
 
-//revisions: migrate2015 migrate2018 nll2015 nll2018
+//revisions: base nll
 
 //[migrate2018] edition:2018
 //[nll2018] edition:2018
 
-#![cfg_attr(any(nll2015, nll2018), feature(nll))]
+#![cfg_attr(nll, feature(nll))]
 
 fn double_conflicts() {
     let mut v = vec![0, 1, 2];
     let shared = &v;
 
     v.extend(shared);
-    //[migrate2015]~^ ERROR cannot borrow `v` as mutable
-    //[nll2015]~^^ ERROR cannot borrow `v` as mutable
-    //[migrate2018]~^^^ ERROR cannot borrow `v` as mutable
-    //[nll2018]~^^^^ ERROR cannot borrow `v` as mutable
+    //[base]~^ ERROR cannot borrow `v` as mutable
+    //[nll]~^^ ERROR cannot borrow `v` as mutable
 }
 
 fn activation_conflict() {
     let mut v = vec![0, 1, 2];
 
     v.extend(&v);
-    //[migrate2015]~^ ERROR cannot borrow `v` as mutable
-    //[nll2015]~^^ ERROR cannot borrow `v` as mutable
-    //[migrate2018]~^^^ ERROR cannot borrow `v` as mutable
-    //[nll2018]~^^^^ ERROR cannot borrow `v` as mutable
+    //[base]~^ ERROR cannot borrow `v` as mutable
+    //[nll]~^^ ERROR cannot borrow `v` as mutable
 }
 
-fn reservation_conflict() {
+fn reservation_allowed() {
     let mut v = vec![0, 1, 2];
     let shared = &v;
 
     v.push(shared.len());
-    //[nll2015]~^ ERROR cannot borrow `v` as mutable
-    //[nll2018]~^^ ERROR cannot borrow `v` as mutable
-    //[migrate2015]~^^^ WARNING cannot borrow `v` as mutable
-    //[migrate2015]~| WARNING may become a hard error in the future
-
-    //[migrate2018]~^^^^^^ WARNING cannot borrow `v` as mutable
-    //[migrate2018]~| WARNING may become a hard error in the future
 }
 
 fn main() {}
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-future-compat-lint.nll.stderr b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-future-compat-lint.nll.stderr
deleted file mode 100644
index 52e8de3c4ac..00000000000
--- a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-future-compat-lint.nll.stderr
+++ /dev/null
@@ -1,39 +0,0 @@
-error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
-  --> $DIR/two-phase-reservation-sharing-interference-future-compat-lint.rs:13:9
-   |
-LL |         let shared = &v;
-   |                      -- immutable borrow occurs here
-LL | 
-LL |         v.push(shared.len());
-   |         ^^^^^^^------------^
-   |         |      |
-   |         |      immutable borrow later used here
-   |         mutable borrow occurs here
-
-error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
-  --> $DIR/two-phase-reservation-sharing-interference-future-compat-lint.rs:24:9
-   |
-LL |         let shared = &v;
-   |                      -- immutable borrow occurs here
-LL | 
-LL |         v.push(shared.len());
-   |         ^^^^^^^------------^
-   |         |      |
-   |         |      immutable borrow later used here
-   |         mutable borrow occurs here
-
-error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable
-  --> $DIR/two-phase-reservation-sharing-interference-future-compat-lint.rs:37:9
-   |
-LL |         let shared = &v;
-   |                      -- immutable borrow occurs here
-LL | 
-LL |         v.push(shared.len());
-   |         ^^^^^^^------------^
-   |         |      |
-   |         |      immutable borrow later used here
-   |         mutable borrow occurs here
-
-error: aborting due to 3 previous errors
-
-For more information about this error, try `rustc --explain E0502`.
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-future-compat-lint.rs b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-future-compat-lint.rs
deleted file mode 100644
index 0e1d77ace3f..00000000000
--- a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-future-compat-lint.rs
+++ /dev/null
@@ -1,43 +0,0 @@
-// Check that the future-compat-lint for the reservation conflict is
-// handled like any other lint.
-
-// edition:2018
-
-mod future_compat_allow {
-    #![allow(mutable_borrow_reservation_conflict)]
-
-    fn reservation_conflict() {
-        let mut v = vec![0, 1, 2];
-        let shared = &v;
-
-        v.push(shared.len());
-    }
-}
-
-mod future_compat_warn {
-    #![warn(mutable_borrow_reservation_conflict)]
-
-    fn reservation_conflict() {
-        let mut v = vec![0, 1, 2];
-        let shared = &v;
-
-        v.push(shared.len());
-        //~^ WARNING cannot borrow `v` as mutable
-        //~| WARNING may become a hard error in the future
-    }
-}
-
-mod future_compat_deny {
-    #![deny(mutable_borrow_reservation_conflict)]
-
-    fn reservation_conflict() {
-        let mut v = vec![0, 1, 2];
-        let shared = &v;
-
-        v.push(shared.len());
-        //~^ ERROR cannot borrow `v` as mutable
-        //~| WARNING may become a hard error in the future
-    }
-}
-
-fn main() {}
diff --git a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-future-compat-lint.stderr b/src/test/ui/borrowck/two-phase-reservation-sharing-interference-future-compat-lint.stderr
deleted file mode 100644
index aab21c9e78b..00000000000
--- a/src/test/ui/borrowck/two-phase-reservation-sharing-interference-future-compat-lint.stderr
+++ /dev/null
@@ -1,42 +0,0 @@
-warning: cannot borrow `v` as mutable because it is also borrowed as immutable
-  --> $DIR/two-phase-reservation-sharing-interference-future-compat-lint.rs:24:9
-   |
-LL |         let shared = &v;
-   |                      -- immutable borrow occurs here
-LL | 
-LL |         v.push(shared.len());
-   |         ^^^^^^^------------^
-   |         |      |
-   |         |      immutable borrow later used here
-   |         mutable borrow occurs here
-   |
-note: the lint level is defined here
-  --> $DIR/two-phase-reservation-sharing-interference-future-compat-lint.rs:18:13
-   |
-LL |     #![warn(mutable_borrow_reservation_conflict)]
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = warning: this borrowing pattern was not meant to be accepted, and may become a hard error in the future
-   = note: for more information, see issue #59159 <https://github.com/rust-lang/rust/issues/59159>
-
-error: cannot borrow `v` as mutable because it is also borrowed as immutable
-  --> $DIR/two-phase-reservation-sharing-interference-future-compat-lint.rs:37:9
-   |
-LL |         let shared = &v;
-   |                      -- immutable borrow occurs here
-LL | 
-LL |         v.push(shared.len());
-   |         ^^^^^^^------------^
-   |         |      |
-   |         |      immutable borrow later used here
-   |         mutable borrow occurs here
-   |
-note: the lint level is defined here
-  --> $DIR/two-phase-reservation-sharing-interference-future-compat-lint.rs:31:13
-   |
-LL |     #![deny(mutable_borrow_reservation_conflict)]
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = warning: this borrowing pattern was not meant to be accepted, and may become a hard error in the future
-   = note: for more information, see issue #59159 <https://github.com/rust-lang/rust/issues/59159>
-
-error: aborting due to previous error; 1 warning emitted
-
diff --git a/src/test/ui/error-codes/E0502.nll.stderr b/src/test/ui/error-codes/E0502.nll.stderr
index a3c7ef76189..94cc89754db 100644
--- a/src/test/ui/error-codes/E0502.nll.stderr
+++ b/src/test/ui/error-codes/E0502.nll.stderr
@@ -1,10 +1,10 @@
 error[E0502]: cannot borrow `*a` as mutable because it is also borrowed as immutable
-  --> $DIR/E0502.rs:4:9
+  --> $DIR/E0502.rs:4:5
    |
 LL |     let ref y = a;
    |         ----- immutable borrow occurs here
 LL |     bar(a);
-   |         ^ mutable borrow occurs here
+   |     ^^^^^^ mutable borrow occurs here
 LL |     y.use_ref();
    |     ----------- immutable borrow later used here
 
diff --git a/src/test/ui/issues/issue-61623.rs b/src/test/ui/issues/issue-61623.rs
index e5b8747bd80..82df50d9dc3 100644
--- a/src/test/ui/issues/issue-61623.rs
+++ b/src/test/ui/issues/issue-61623.rs
@@ -5,7 +5,6 @@ fn f2<P>(_: P, _: ()) {}
 fn f3<'a>(x: &'a ((), &'a mut ())) {
     f2(|| x.0, f1(x.1))
 //~^ ERROR cannot borrow `*x.1` as mutable, as it is behind a `&` reference
-//~| ERROR cannot borrow `*x.1` as mutable because it is also borrowed as immutable
 }
 
 fn main() {}
diff --git a/src/test/ui/issues/issue-61623.stderr b/src/test/ui/issues/issue-61623.stderr
index 901c7598176..f6546054233 100644
--- a/src/test/ui/issues/issue-61623.stderr
+++ b/src/test/ui/issues/issue-61623.stderr
@@ -6,17 +6,6 @@ LL | fn f3<'a>(x: &'a ((), &'a mut ())) {
 LL |     f2(|| x.0, f1(x.1))
    |                   ^^^ `x` is a `&` reference, so the data it refers to cannot be borrowed as mutable
 
-error[E0502]: cannot borrow `*x.1` as mutable because it is also borrowed as immutable
-  --> $DIR/issue-61623.rs:6:19
-   |
-LL |     f2(|| x.0, f1(x.1))
-   |     -- -- ---     ^^^ mutable borrow occurs here
-   |     |  |  |
-   |     |  |  first borrow occurs due to use of `x` in closure
-   |     |  immutable borrow occurs here
-   |     immutable borrow later used by call
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0502, E0596.
-For more information about an error, try `rustc --explain E0502`.
+For more information about this error, try `rustc --explain E0596`.
diff --git a/src/test/ui/nll/lint-no-err.rs b/src/test/ui/nll/lint-no-err.rs
index 4b4169faadf..f5f7bf0a758 100644
--- a/src/test/ui/nll/lint-no-err.rs
+++ b/src/test/ui/nll/lint-no-err.rs
@@ -23,6 +23,4 @@ fn main() {
     let mut conflict = Repro;
     let prev = conflict.get();
     conflict.insert(*prev + *x);
-    //~^ WARN cannot borrow `conflict` as mutable because it is also borrowed as immutable
-    //~| WARN this borrowing pattern was not meant to be accepted
 }
diff --git a/src/test/ui/nll/lint-no-err.stderr b/src/test/ui/nll/lint-no-err.stderr
deleted file mode 100644
index 1e7aecfaa64..00000000000
--- a/src/test/ui/nll/lint-no-err.stderr
+++ /dev/null
@@ -1,17 +0,0 @@
-warning: cannot borrow `conflict` as mutable because it is also borrowed as immutable
-  --> $DIR/lint-no-err.rs:25:5
-   |
-LL |     let prev = conflict.get();
-   |                -------------- immutable borrow occurs here
-LL |     conflict.insert(*prev + *x);
-   |     ^^^^^^^^^^^^^^^^-----^^^^^^
-   |     |               |
-   |     |               immutable borrow later used here
-   |     mutable borrow occurs here
-   |
-   = note: `#[warn(mutable_borrow_reservation_conflict)]` on by default
-   = warning: this borrowing pattern was not meant to be accepted, and may become a hard error in the future
-   = note: for more information, see issue #59159 <https://github.com/rust-lang/rust/issues/59159>
-
-warning: 1 warning emitted
-