better lvalue errors for things implementing DerefMut

8 files changed, 132 insertions, 6 deletions

diff --git a/src/test/ui/suggestions/mut-ref-reassignment.stderr b/src/test/ui/suggestions/mut-ref-reassignment.stderr
index 3bd98c76307..b3cb6dd0614 100644
--- a/src/test/ui/suggestions/mut-ref-reassignment.stderr
+++ b/src/test/ui/suggestions/mut-ref-reassignment.stderr
@@ -8,7 +8,7 @@ LL |     opt = None;
    |
    = note: expected mutable reference `&mut Option<String>`
                            found enum `Option<_>`
-help: consider dereferencing here to assign to the mutable borrowed piece of memory
+help: consider dereferencing here to assign to the mutably borrowed value
    |
 LL |     *opt = None;
    |     +
@@ -34,7 +34,7 @@ LL |     opt = Some(String::new())
    |
    = note: expected mutable reference `&mut Option<String>`
                            found enum `Option<String>`
-help: consider dereferencing here to assign to the mutable borrowed piece of memory
+help: consider dereferencing here to assign to the mutably borrowed value
    |
 LL |     *opt = Some(String::new())
    |     +
diff --git a/src/test/ui/typeck/assign-non-lval-derefmut.fixed b/src/test/ui/typeck/assign-non-lval-derefmut.fixed
new file mode 100644
index 00000000000..0c23199af22
--- /dev/null
+++ b/src/test/ui/typeck/assign-non-lval-derefmut.fixed
@@ -0,0 +1,15 @@
+// run-rustfix
+
+fn main() {
+    let x = std::sync::Mutex::new(1usize);
+    *x.lock().unwrap() = 2;
+    //~^ ERROR invalid left-hand side of assignment
+    *x.lock().unwrap() += 1;
+    //~^ ERROR binary assignment operation `+=` cannot be applied to type `MutexGuard<'_, usize>`
+
+    let mut y = x.lock().unwrap();
+    *y = 2;
+    //~^ ERROR mismatched types
+    *y += 1;
+    //~^ ERROR binary assignment operation `+=` cannot be applied to type `MutexGuard<'_, usize>`
+}
diff --git a/src/test/ui/typeck/assign-non-lval-derefmut.rs b/src/test/ui/typeck/assign-non-lval-derefmut.rs
new file mode 100644
index 00000000000..ec1882f5271
--- /dev/null
+++ b/src/test/ui/typeck/assign-non-lval-derefmut.rs
@@ -0,0 +1,15 @@
+// run-rustfix
+
+fn main() {
+    let x = std::sync::Mutex::new(1usize);
+    x.lock().unwrap() = 2;
+    //~^ ERROR invalid left-hand side of assignment
+    x.lock().unwrap() += 1;
+    //~^ ERROR binary assignment operation `+=` cannot be applied to type `MutexGuard<'_, usize>`
+
+    let mut y = x.lock().unwrap();
+    y = 2;
+    //~^ ERROR mismatched types
+    y += 1;
+    //~^ ERROR binary assignment operation `+=` cannot be applied to type `MutexGuard<'_, usize>`
+}
diff --git a/src/test/ui/typeck/assign-non-lval-derefmut.stderr b/src/test/ui/typeck/assign-non-lval-derefmut.stderr
new file mode 100644
index 00000000000..a6fcdfe21f4
--- /dev/null
+++ b/src/test/ui/typeck/assign-non-lval-derefmut.stderr
@@ -0,0 +1,58 @@
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/assign-non-lval-derefmut.rs:5:23
+   |
+LL |     x.lock().unwrap() = 2;
+   |     ----------------- ^
+   |     |
+   |     cannot assign to this expression
+   |
+help: consider dereferencing here to assign to the mutably borrowed value
+   |
+LL |     *x.lock().unwrap() = 2;
+   |     +
+
+error[E0368]: binary assignment operation `+=` cannot be applied to type `MutexGuard<'_, usize>`
+  --> $DIR/assign-non-lval-derefmut.rs:7:5
+   |
+LL |     x.lock().unwrap() += 1;
+   |     -----------------^^^^^
+   |     |
+   |     cannot use `+=` on type `MutexGuard<'_, usize>`
+   |
+help: `+=` can be used on `usize`, you can dereference `x.lock().unwrap()`
+   |
+LL |     *x.lock().unwrap() += 1;
+   |     +
+
+error[E0308]: mismatched types
+  --> $DIR/assign-non-lval-derefmut.rs:11:9
+   |
+LL |     let mut y = x.lock().unwrap();
+   |                 ----------------- expected due to this value
+LL |     y = 2;
+   |         ^ expected struct `MutexGuard`, found integer
+   |
+   = note: expected struct `MutexGuard<'_, usize>`
+                found type `{integer}`
+help: consider dereferencing here to assign to the mutably borrowed value
+   |
+LL |     *y = 2;
+   |     +
+
+error[E0368]: binary assignment operation `+=` cannot be applied to type `MutexGuard<'_, usize>`
+  --> $DIR/assign-non-lval-derefmut.rs:13:5
+   |
+LL |     y += 1;
+   |     -^^^^^
+   |     |
+   |     cannot use `+=` on type `MutexGuard<'_, usize>`
+   |
+help: `+=` can be used on `usize`, you can dereference `y`
+   |
+LL |     *y += 1;
+   |     +
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0070, E0308, E0368.
+For more information about an error, try `rustc --explain E0070`.
diff --git a/src/test/ui/typeck/assign-non-lval-mut-ref.fixed b/src/test/ui/typeck/assign-non-lval-mut-ref.fixed
index c4dadfbdfce..10c7b9dbfb3 100644
--- a/src/test/ui/typeck/assign-non-lval-mut-ref.fixed
+++ b/src/test/ui/typeck/assign-non-lval-mut-ref.fixed
@@ -6,4 +6,10 @@ fn main() {
     //~^ ERROR invalid left-hand side of assignment
     *x.last_mut().unwrap() += 1;
     //~^ ERROR binary assignment operation `+=` cannot be applied to type `&mut usize`
+
+    let y = x.last_mut().unwrap();
+    *y = 2;
+    //~^ ERROR mismatched types
+    *y += 1;
+    //~^ ERROR binary assignment operation `+=` cannot be applied to type `&mut usize`
 }
diff --git a/src/test/ui/typeck/assign-non-lval-mut-ref.rs b/src/test/ui/typeck/assign-non-lval-mut-ref.rs
index 39573ddb6d0..bceff0ef09d 100644
--- a/src/test/ui/typeck/assign-non-lval-mut-ref.rs
+++ b/src/test/ui/typeck/assign-non-lval-mut-ref.rs
@@ -6,4 +6,10 @@ fn main() {
     //~^ ERROR invalid left-hand side of assignment
     x.last_mut().unwrap() += 1;
     //~^ ERROR binary assignment operation `+=` cannot be applied to type `&mut usize`
+
+    let y = x.last_mut().unwrap();
+    y = 2;
+    //~^ ERROR mismatched types
+    y += 1;
+    //~^ ERROR binary assignment operation `+=` cannot be applied to type `&mut usize`
 }
diff --git a/src/test/ui/typeck/assign-non-lval-mut-ref.stderr b/src/test/ui/typeck/assign-non-lval-mut-ref.stderr
index b0ca089b709..be2e9fe95e8 100644
--- a/src/test/ui/typeck/assign-non-lval-mut-ref.stderr
+++ b/src/test/ui/typeck/assign-non-lval-mut-ref.stderr
@@ -6,7 +6,7 @@ LL |     x.last_mut().unwrap() = 2;
    |     |
    |     cannot assign to this expression
    |
-help: consider dereferencing here to assign to the mutable borrowed piece of memory
+help: consider dereferencing here to assign to the mutably borrowed value
    |
 LL |     *x.last_mut().unwrap() = 2;
    |     +
@@ -24,7 +24,33 @@ help: `+=` can be used on `usize`, you can dereference `x.last_mut().unwrap()`
 LL |     *x.last_mut().unwrap() += 1;
    |     +
 
-error: aborting due to 2 previous errors
+error[E0308]: mismatched types
+  --> $DIR/assign-non-lval-mut-ref.rs:11:9
+   |
+LL |     let y = x.last_mut().unwrap();
+   |             --------------------- expected due to this value
+LL |     y = 2;
+   |         ^ expected `&mut usize`, found integer
+   |
+help: consider dereferencing here to assign to the mutably borrowed value
+   |
+LL |     *y = 2;
+   |     +
+
+error[E0368]: binary assignment operation `+=` cannot be applied to type `&mut usize`
+  --> $DIR/assign-non-lval-mut-ref.rs:13:5
+   |
+LL |     y += 1;
+   |     -^^^^^
+   |     |
+   |     cannot use `+=` on type `&mut usize`
+   |
+help: `+=` can be used on `usize`, you can dereference `y`
+   |
+LL |     *y += 1;
+   |     +
+
+error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0070, E0368.
+Some errors have detailed explanations: E0070, E0308, E0368.
 For more information about an error, try `rustc --explain E0070`.
diff --git a/src/test/ui/typeck/issue-93486.stderr b/src/test/ui/typeck/issue-93486.stderr
index 95eb021965f..167edc8942a 100644
--- a/src/test/ui/typeck/issue-93486.stderr
+++ b/src/test/ui/typeck/issue-93486.stderr
@@ -6,7 +6,7 @@ LL |         vec![].last_mut().unwrap() = 3_u8;
    |         |
    |         cannot assign to this expression
    |
-help: consider dereferencing here to assign to the mutable borrowed piece of memory
+help: consider dereferencing here to assign to the mutably borrowed value
    |
 LL |         *vec![].last_mut().unwrap() = 3_u8;
    |         +