Point out implicit deref coercions in borrow

Clean up code

src/test/ui/borrowck/issue-81365-2.rs

@@ -0,0 +1,30 @@
+use std::ops::Deref;
+
+struct DerefTarget {
+    target_field: bool,
+}
+struct Container {
+    target: DerefTarget,
+    container_field: bool,
+}
+
+impl Deref for Container {
+    type Target = DerefTarget;
+    fn deref(&self) -> &Self::Target {
+        &self.target
+    }
+}
+
+struct Outer {
+    container: Container,
+}
+
+impl Outer {
+    fn bad_borrow(&mut self) {
+        let first = &self.container.target_field;
+        self.container.container_field = true; //~ ERROR E0506
+        first;
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/issue-81365-2.stderr

@@ -0,0 +1,15 @@
+error[E0506]: cannot assign to `self.container.container_field` because it is borrowed
+  --> $DIR/issue-81365-2.rs:25:9
+   |
+LL |         let first = &self.container.target_field;
+   |                      -------------- borrow of `self.container.container_field` occurs here
+LL |         self.container.container_field = true;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `self.container.container_field` occurs here
+LL |         first;
+   |         ----- borrow later used here
+   |
+   = note: borrow occurs due to deref coercion to `DerefTarget`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0506`.

src/test/ui/borrowck/issue-81365-3.rs

@@ -0,0 +1,37 @@
+use std::ops::Deref;
+
+struct DerefTarget {
+    target_field: bool,
+}
+struct Container {
+    target: DerefTarget,
+    container_field: bool,
+}
+
+impl Deref for Container {
+    type Target = DerefTarget;
+    fn deref(&self) -> &Self::Target {
+        &self.target
+    }
+}
+
+struct Outer {
+    container: Container,
+}
+
+impl Deref for Outer {
+    type Target = Container;
+    fn deref(&self) -> &Self::Target {
+        &self.container
+    }
+}
+
+impl Outer {
+    fn bad_borrow(&mut self) {
+        let first = &self.target_field;
+        self.container.container_field = true; //~ ERROR E0506
+        first;
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/issue-81365-3.stderr

@@ -0,0 +1,15 @@
+error[E0506]: cannot assign to `self.container.container_field` because it is borrowed
+  --> $DIR/issue-81365-3.rs:32:9
+   |
+LL |         let first = &self.target_field;
+   |                      ---- borrow of `self.container.container_field` occurs here
+LL |         self.container.container_field = true;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `self.container.container_field` occurs here
+LL |         first;
+   |         ----- borrow later used here
+   |
+   = note: borrow occurs due to deref coercion to `Container`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0506`.

src/test/ui/borrowck/issue-81365-4.rs

@@ -0,0 +1,38 @@
+use std::ops::Deref;
+
+struct DerefTarget {
+    target_field: bool,
+}
+struct Container {
+    target: DerefTarget,
+    container_field: bool,
+}
+
+impl Deref for Container {
+    type Target = DerefTarget;
+    fn deref(&self) -> &Self::Target {
+        &self.target
+    }
+}
+
+struct Outer {
+    container: Container,
+    outer_field: bool,
+}
+
+impl Deref for Outer {
+    type Target = Container;
+    fn deref(&self) -> &Self::Target {
+        &self.container
+    }
+}
+
+impl Outer {
+    fn bad_borrow(&mut self) {
+        let first = &self.target_field;
+        self.outer_field = true; //~ ERROR E0506
+        first;
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/issue-81365-4.stderr

@@ -0,0 +1,15 @@
+error[E0506]: cannot assign to `self.outer_field` because it is borrowed
+  --> $DIR/issue-81365-4.rs:33:9
+   |
+LL |         let first = &self.target_field;
+   |                      ---- borrow of `self.outer_field` occurs here
+LL |         self.outer_field = true;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `self.outer_field` occurs here
+LL |         first;
+   |         ----- borrow later used here
+   |
+   = note: borrow occurs due to deref coercion to `Container`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0506`.

src/test/ui/borrowck/issue-81365-5.rs

@@ -0,0 +1,33 @@
+use std::ops::Deref;
+
+struct DerefTarget {
+    target_field: bool,
+}
+
+impl DerefTarget {
+    fn get(&self) -> &bool {
+        &self.target_field
+    }
+}
+
+struct Container {
+    target: DerefTarget,
+    container_field: bool,
+}
+
+impl Deref for Container {
+    type Target = DerefTarget;
+    fn deref(&self) -> &Self::Target {
+        &self.target
+    }
+}
+
+impl Container {
+    fn bad_borrow(&mut self) {
+        let first = self.get();
+        self.container_field = true; //~ ERROR E0506
+        first;
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/issue-81365-5.stderr

@@ -0,0 +1,15 @@
+error[E0506]: cannot assign to `self.container_field` because it is borrowed
+  --> $DIR/issue-81365-5.rs:28:9
+   |
+LL |         let first = self.get();
+   |                     ---- borrow of `self.container_field` occurs here
+LL |         self.container_field = true;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `self.container_field` occurs here
+LL |         first;
+   |         ----- borrow later used here
+   |
+   = note: borrow occurs due to deref coercion to `DerefTarget`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0506`.

src/test/ui/borrowck/issue-81365-6.rs

@@ -0,0 +1,23 @@
+use std::ops::Deref;
+
+struct Container {
+    target: Vec<()>,
+    container_field: bool,
+}
+
+impl Deref for Container {
+    type Target = [()];
+    fn deref(&self) -> &Self::Target {
+        &self.target
+    }
+}
+
+impl Container {
+    fn bad_borrow(&mut self) {
+        let first = &self[0];
+        self.container_field = true; //~ ERROR E0506
+        first;
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/issue-81365-6.stderr

@@ -0,0 +1,15 @@
+error[E0506]: cannot assign to `self.container_field` because it is borrowed
+  --> $DIR/issue-81365-6.rs:18:9
+   |
+LL |         let first = &self[0];
+   |                      ---- borrow of `self.container_field` occurs here
+LL |         self.container_field = true;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `self.container_field` occurs here
+LL |         first;
+   |         ----- borrow later used here
+   |
+   = note: borrow occurs due to deref coercion to `[()]`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0506`.

src/test/ui/borrowck/issue-81365-7.rs

@@ -0,0 +1,24 @@
+use std::ops::Deref;
+
+struct DerefTarget {
+    target_field: bool,
+}
+struct Container {
+    target: DerefTarget,
+    container_field: bool,
+}
+
+impl Deref for Container {
+    type Target = DerefTarget;
+    fn deref(&self) -> &Self::Target {
+        &self.target
+    }
+}
+
+fn bad_borrow(c: &mut Container) {
+    let first = &c.target_field;
+    c.container_field = true; //~ ERROR E0506
+    first;
+}
+
+fn main() {}

src/test/ui/borrowck/issue-81365-7.stderr

@@ -0,0 +1,15 @@
+error[E0506]: cannot assign to `c.container_field` because it is borrowed
+  --> $DIR/issue-81365-7.rs:20:5
+   |
+LL |     let first = &c.target_field;
+   |                  - borrow of `c.container_field` occurs here
+LL |     c.container_field = true;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `c.container_field` occurs here
+LL |     first;
+   |     ----- borrow later used here
+   |
+   = note: borrow occurs due to deref coercion to `DerefTarget`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0506`.

src/test/ui/borrowck/issue-81365-8.rs

@@ -0,0 +1,26 @@
+use std::ops::Deref;
+
+struct DerefTarget {
+    target_field: bool,
+}
+struct Container {
+    target: DerefTarget,
+    container_field: bool,
+}
+
+impl Deref for Container {
+    type Target = DerefTarget;
+    fn deref(&self) -> &Self::Target {
+        &self.target
+    }
+}
+
+impl Container {
+    fn bad_borrow(&mut self) {
+        let first = &(*self).target_field;
+        self.container_field = true; //~ ERROR E0506
+        first;
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/issue-81365.rs

@@ -0,0 +1,26 @@
+use std::ops::Deref;
+
+struct DerefTarget {
+    target_field: bool,
+}
+struct Container {
+    target: DerefTarget,
+    container_field: bool,
+}
+
+impl Deref for Container {
+    type Target = DerefTarget;
+    fn deref(&self) -> &Self::Target {
+        &self.target
+    }
+}
+
+impl Container {
+    fn bad_borrow(&mut self) {
+        let first = &self.target_field;
+        self.container_field = true; //~ ERROR E0506
+        first;
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/issue-81365.stderr

@@ -0,0 +1,15 @@
+error[E0506]: cannot assign to `self.container_field` because it is borrowed
+  --> $DIR/issue-81365.rs:21:9
+   |
+LL |         let first = &self.target_field;
+   |                      ---- borrow of `self.container_field` occurs here
+LL |         self.container_field = true;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `self.container_field` occurs here
+LL |         first;
+   |         ----- borrow later used here
+   |
+   = note: borrow occurs due to deref coercion to `DerefTarget`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0506`.