15 files changed, 76 insertions, 53 deletions
diff --git a/tests/ui/union/field_checks.rs b/tests/ui/union/field_checks.rs
index d5d1e44ac..bb4eccb4c 100644
--- a/tests/ui/union/field_checks.rs
+++ b/tests/ui/union/field_checks.rs
@@ -21,15 +21,15 @@ union U24<T> { // OK
 }
 
 union U3 {
-    a: String, //~ ERROR unions cannot contain fields that may need dropping
+    a: String, //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
 }
 
 union U32 { // field that does not drop but is not `Copy`, either
-    a: std::cell::RefCell<i32>, //~ ERROR unions cannot contain fields that may need dropping
+    a: std::cell::RefCell<i32>, //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
 }
 
 union U4<T> {
-    a: T, //~ ERROR unions cannot contain fields that may need dropping
+    a: T, //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
 }
 
 union U5 { // Having a drop impl is OK
@@ -41,11 +41,11 @@ impl Drop for U5 {
 }
 
 union U5Nested { // a nested union that drops is NOT OK
-    nest: U5, //~ ERROR unions cannot contain fields that may need dropping
+    nest: U5, //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
 }
 
 union U5Nested2 { // for now we don't special-case empty arrays
-    nest: [U5; 0], //~ ERROR unions cannot contain fields that may need dropping
+    nest: [U5; 0], //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
 }
 
 union U6 { // OK
diff --git a/tests/ui/union/field_checks.stderr b/tests/ui/union/field_checks.stderr
index 1f97e97ac..32407a749 100644
--- a/tests/ui/union/field_checks.stderr
+++ b/tests/ui/union/field_checks.stderr
@@ -1,59 +1,59 @@
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/field_checks.rs:24:5
    |
 LL |     a: String,
    |     ^^^^^^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<String>,
    |        +++++++++++++++++++++++      +
 
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/field_checks.rs:28:5
    |
 LL |     a: std::cell::RefCell<i32>,
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<std::cell::RefCell<i32>>,
    |        +++++++++++++++++++++++                       +
 
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/field_checks.rs:32:5
    |
 LL |     a: T,
    |     ^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<T>,
    |        +++++++++++++++++++++++ +
 
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/field_checks.rs:44:5
    |
 LL |     nest: U5,
    |     ^^^^^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     nest: std::mem::ManuallyDrop<U5>,
    |           +++++++++++++++++++++++  +
 
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/field_checks.rs:48:5
    |
 LL |     nest: [U5; 0],
    |     ^^^^^^^^^^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     nest: std::mem::ManuallyDrop<[U5; 0]>,
    |           +++++++++++++++++++++++       +
diff --git a/tests/ui/union/issue-41073.rs b/tests/ui/union/issue-41073.rs
index 4dfdc606b..f7a82b4e7 100644
--- a/tests/ui/union/issue-41073.rs
+++ b/tests/ui/union/issue-41073.rs
@@ -1,5 +1,5 @@
 union Test {
-    a: A, //~ ERROR unions cannot contain fields that may need dropping
+    a: A, //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
     b: B
 }
 
diff --git a/tests/ui/union/issue-41073.stderr b/tests/ui/union/issue-41073.stderr
index b3887fa0f..ae1c4dfed 100644
--- a/tests/ui/union/issue-41073.stderr
+++ b/tests/ui/union/issue-41073.stderr
@@ -1,11 +1,11 @@
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/issue-41073.rs:2:5
    |
 LL |     a: A,
    |     ^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<A>,
    |        +++++++++++++++++++++++ +
diff --git a/tests/ui/union/union-copy.rs b/tests/ui/union/union-copy.rs
index 5c3f8d908..7ad0a11c6 100644
--- a/tests/ui/union/union-copy.rs
+++ b/tests/ui/union/union-copy.rs
@@ -9,6 +9,6 @@ union W {
 }
 
 impl Copy for U {} // OK
-impl Copy for W {} //~ ERROR the trait `Copy` may not be implemented for this type
+impl Copy for W {} //~ ERROR the trait `Copy` cannot be implemented for this type
 
 fn main() {}
diff --git a/tests/ui/union/union-copy.stderr b/tests/ui/union/union-copy.stderr
index 53ee4dd2e..ff6fa48db 100644
--- a/tests/ui/union/union-copy.stderr
+++ b/tests/ui/union/union-copy.stderr
@@ -1,4 +1,4 @@
-error[E0204]: the trait `Copy` may not be implemented for this type
+error[E0204]: the trait `Copy` cannot be implemented for this type
   --> $DIR/union-copy.rs:12:15
    |
 LL |     a: std::mem::ManuallyDrop<String>
diff --git a/tests/ui/union/union-derive-clone.mirunsafeck.stderr b/tests/ui/union/union-derive-clone.mirunsafeck.stderr
index b80e8b988..4d23d230f 100644
--- a/tests/ui/union/union-derive-clone.mirunsafeck.stderr
+++ b/tests/ui/union/union-derive-clone.mirunsafeck.stderr
@@ -9,7 +9,8 @@ note: required by a bound in `AssertParamIsCopy`
    = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider annotating `U1` with `#[derive(Copy)]`
    |
-LL | #[derive(Copy)]
+LL + #[derive(Copy)]
+LL | union U1 {
    |
 
 error[E0599]: the method `clone` exists for union `U5<CloneNoCopy>`, but its trait bounds were not satisfied
@@ -34,7 +35,8 @@ LL | #[derive(Clone, Copy)]
    |          ^^^^^ unsatisfied trait bound introduced in this `derive` macro
 help: consider annotating `CloneNoCopy` with `#[derive(Clone, Copy)]`
    |
-LL | #[derive(Clone, Copy)]
+LL + #[derive(Clone, Copy)]
+LL | struct CloneNoCopy;
    |
 
 error: aborting due to 2 previous errors
diff --git a/tests/ui/union/union-derive-clone.thirunsafeck.stderr b/tests/ui/union/union-derive-clone.thirunsafeck.stderr
index b80e8b988..4d23d230f 100644
--- a/tests/ui/union/union-derive-clone.thirunsafeck.stderr
+++ b/tests/ui/union/union-derive-clone.thirunsafeck.stderr
@@ -9,7 +9,8 @@ note: required by a bound in `AssertParamIsCopy`
    = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider annotating `U1` with `#[derive(Copy)]`
    |
-LL | #[derive(Copy)]
+LL + #[derive(Copy)]
+LL | union U1 {
    |
 
 error[E0599]: the method `clone` exists for union `U5<CloneNoCopy>`, but its trait bounds were not satisfied
@@ -34,7 +35,8 @@ LL | #[derive(Clone, Copy)]
    |          ^^^^^ unsatisfied trait bound introduced in this `derive` macro
 help: consider annotating `CloneNoCopy` with `#[derive(Clone, Copy)]`
    |
-LL | #[derive(Clone, Copy)]
+LL + #[derive(Clone, Copy)]
+LL | struct CloneNoCopy;
    |
 
 error: aborting due to 2 previous errors
diff --git a/tests/ui/union/union-derive-eq.mirunsafeck.stderr b/tests/ui/union/union-derive-eq.mirunsafeck.stderr
index 9e55390b5..136cd883e 100644
--- a/tests/ui/union/union-derive-eq.mirunsafeck.stderr
+++ b/tests/ui/union/union-derive-eq.mirunsafeck.stderr
@@ -12,7 +12,8 @@ note: required by a bound in `AssertParamIsEq`
    = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider annotating `PartialEqNotEq` with `#[derive(Eq)]`
    |
-LL | #[derive(Eq)]
+LL + #[derive(Eq)]
+LL | struct PartialEqNotEq;
    |
 
 error: aborting due to previous error
diff --git a/tests/ui/union/union-derive-eq.thirunsafeck.stderr b/tests/ui/union/union-derive-eq.thirunsafeck.stderr
index 9e55390b5..136cd883e 100644
--- a/tests/ui/union/union-derive-eq.thirunsafeck.stderr
+++ b/tests/ui/union/union-derive-eq.thirunsafeck.stderr
@@ -12,7 +12,8 @@ note: required by a bound in `AssertParamIsEq`
    = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider annotating `PartialEqNotEq` with `#[derive(Eq)]`
    |
-LL | #[derive(Eq)]
+LL + #[derive(Eq)]
+LL | struct PartialEqNotEq;
    |
 
 error: aborting due to previous error
diff --git a/tests/ui/union/union-with-drop-fields.mirunsafeck.stderr b/tests/ui/union/union-with-drop-fields.mirunsafeck.stderr
index 93fe996d2..9861a21cb 100644
--- a/tests/ui/union/union-with-drop-fields.mirunsafeck.stderr
+++ b/tests/ui/union/union-with-drop-fields.mirunsafeck.stderr
@@ -1,35 +1,35 @@
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/union-with-drop-fields.rs:11:5
    |
 LL |     a: String,
    |     ^^^^^^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<String>,
    |        +++++++++++++++++++++++      +
 
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/union-with-drop-fields.rs:19:5
    |
 LL |     a: S,
    |     ^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<S>,
    |        +++++++++++++++++++++++ +
 
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/union-with-drop-fields.rs:24:5
    |
 LL |     a: T,
    |     ^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<T>,
    |        +++++++++++++++++++++++ +
diff --git a/tests/ui/union/union-with-drop-fields.rs b/tests/ui/union/union-with-drop-fields.rs
index a7a8b69e7..9720830fb 100644
--- a/tests/ui/union/union-with-drop-fields.rs
+++ b/tests/ui/union/union-with-drop-fields.rs
@@ -8,7 +8,7 @@ union U {
 }
 
 union W {
-    a: String, //~ ERROR unions cannot contain fields that may need dropping
+    a: String, //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
     b: String, // OK, only one field is reported
 }
 
@@ -16,12 +16,12 @@ struct S(String);
 
 // `S` doesn't implement `Drop` trait, but still has non-trivial destructor
 union Y {
-    a: S, //~ ERROR unions cannot contain fields that may need dropping
+    a: S, //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
 }
 
 // We don't know if `T` is trivially-destructable or not until trans
 union J<T> {
-    a: T, //~ ERROR unions cannot contain fields that may need dropping
+    a: T, //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
 }
 
 union H<T: Copy> {
diff --git a/tests/ui/union/union-with-drop-fields.thirunsafeck.stderr b/tests/ui/union/union-with-drop-fields.thirunsafeck.stderr
index 93fe996d2..9861a21cb 100644
--- a/tests/ui/union/union-with-drop-fields.thirunsafeck.stderr
+++ b/tests/ui/union/union-with-drop-fields.thirunsafeck.stderr
@@ -1,35 +1,35 @@
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/union-with-drop-fields.rs:11:5
    |
 LL |     a: String,
    |     ^^^^^^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<String>,
    |        +++++++++++++++++++++++      +
 
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/union-with-drop-fields.rs:19:5
    |
 LL |     a: S,
    |     ^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<S>,
    |        +++++++++++++++++++++++ +
 
-error[E0740]: unions cannot contain fields that may need dropping
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
   --> $DIR/union-with-drop-fields.rs:24:5
    |
 LL |     a: T,
    |     ^^^^
    |
-   = note: a type is guaranteed not to need dropping when it implements `Copy`, or when it is the special `ManuallyDrop<_>` type
-help: when the type does not implement `Copy`, wrap it inside a `ManuallyDrop<_>` and ensure it is manually dropped
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
    |
 LL |     a: std::mem::ManuallyDrop<T>,
    |        +++++++++++++++++++++++ +
diff --git a/tests/ui/union/unresolved-field-isnt-copy.rs b/tests/ui/union/unresolved-field-isnt-copy.rs
new file mode 100644
index 000000000..7a6d79b2f
--- /dev/null
+++ b/tests/ui/union/unresolved-field-isnt-copy.rs
@@ -0,0 +1,8 @@
+// Unresolved fields are not copy, but also shouldn't report an extra E0740.
+
+pub union Foo {
+    x: *const Missing,
+    //~^ ERROR cannot find type `Missing` in this scope
+}
+
+fn main() {}
diff --git a/tests/ui/union/unresolved-field-isnt-copy.stderr b/tests/ui/union/unresolved-field-isnt-copy.stderr
new file mode 100644
index 000000000..22301582e
--- /dev/null
+++ b/tests/ui/union/unresolved-field-isnt-copy.stderr
@@ -0,0 +1,9 @@
+error[E0412]: cannot find type `Missing` in this scope
+  --> $DIR/unresolved-field-isnt-copy.rs:4:15
+   |
+LL |     x: *const Missing,
+   |               ^^^^^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0412`.