Test for casts removing principal trait

Author: Darksonn

tests/ui/cast/ptr-to-ptr-principalless.rs

@@ -46,4 +46,29 @@ fn unprincipled_wrap2_static<'a>(x: *mut (dyn Send + 'a)) -> *mut Wrapper<dyn Sy
     //~^ ERROR: lifetime may not live long enough
 }
 
+// Cast away principal trait
+trait Trait {}
+
+fn unprincipled3<'a, 'b>(x: *mut (dyn Trait + Send + 'a)) -> *mut (dyn Send + 'b) {
+    x as _
+    //~^ ERROR: lifetime may not live long enough
+}
+
+fn unprincipled3_static<'a>(x: *mut (dyn Trait + Send + 'a)) -> *mut (dyn Send + 'static) {
+    x as _
+    //~^ ERROR: lifetime may not live long enough
+}
+
+fn unprincipled_wrap3<'a, 'b>(x: *mut (dyn Trait + Send + 'a)) -> *mut Wrapper<dyn Send + 'b> {
+    x as _
+    //~^ ERROR: casting `*mut (dyn Trait + Send + 'a)` as `*mut Wrapper<(dyn Send + 'b)>` is invalid
+}
+
+fn unprincipled_wrap3_static<'a>(
+    x: *mut (dyn Trait + Send + 'a)
+) -> *mut Wrapper<dyn Send + 'static> {
+    x as _
+    //~^ ERROR: casting `*mut (dyn Trait + Send + 'a)` as `*mut Wrapper<(dyn Send + 'static)>` is invalid
+}
+
 fn main() {}

tests/ui/cast/ptr-to-ptr-principalless.stderr

@@ -1,3 +1,19 @@
+error[E0606]: casting `*mut (dyn Trait + Send + 'a)` as `*mut Wrapper<(dyn Send + 'b)>` is invalid
+  --> $DIR/ptr-to-ptr-principalless.rs:63:5
+   |
+LL |     x as _
+   |     ^^^^^^
+   |
+   = note: the trait objects may have different vtables
+
+error[E0606]: casting `*mut (dyn Trait + Send + 'a)` as `*mut Wrapper<(dyn Send + 'static)>` is invalid
+  --> $DIR/ptr-to-ptr-principalless.rs:70:5
+   |
+LL |     x as _
+   |     ^^^^^^
+   |
+   = note: the trait objects may have different vtables
+
 error: lifetime may not live long enough
   --> $DIR/ptr-to-ptr-principalless.rs:8:5
    |
@@ -202,5 +218,57 @@ LL - fn unprincipled_wrap2_static<'a>(x: *mut (dyn Send + 'a)) -> *mut Wrapper<d
 LL + fn unprincipled_wrap2_static<'a>(x: *mut (dyn Send + 'static)) -> *mut Wrapper<dyn Sync + 'static> {
    |
 
-error: aborting due to 8 previous errors
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-ptr-principalless.rs:53:5
+   |
+LL | fn unprincipled3<'a, 'b>(x: *mut (dyn Trait + Send + 'a)) -> *mut (dyn Send + 'b) {
+   |                  --  -- lifetime `'b` defined here
+   |                  |
+   |                  lifetime `'a` defined here
+LL |     x as _
+   |     ^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
+   |
+   = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of a mutable pointer to `dyn Send`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+note: raw pointer casts of trait objects do not cast away lifetimes
+  --> $DIR/ptr-to-ptr-principalless.rs:53:5
+   |
+LL |     x as _
+   |     ^^^^^^
+   = note: this was previously accepted by the compiler but was changed recently
+   = help: see <https://github.com/rust-lang/rust/issues/141402> for more information
+
+error: lifetime may not live long enough
+  --> $DIR/ptr-to-ptr-principalless.rs:58:5
+   |
+LL | fn unprincipled3_static<'a>(x: *mut (dyn Trait + Send + 'a)) -> *mut (dyn Send + 'static) {
+   |                         -- lifetime `'a` defined here
+LL |     x as _
+   |     ^^^^^^ returning this value requires that `'a` must outlive `'static`
+   |
+   = note: requirement occurs because of a mutable pointer to `dyn Send`
+   = note: mutable pointers are invariant over their type parameter
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+note: raw pointer casts of trait objects do not cast away lifetimes
+  --> $DIR/ptr-to-ptr-principalless.rs:58:5
+   |
+LL |     x as _
+   |     ^^^^^^
+   = note: this was previously accepted by the compiler but was changed recently
+   = help: see <https://github.com/rust-lang/rust/issues/141402> for more information
+help: consider changing the trait object's explicit `'static` bound to the lifetime of argument `x`
+   |
+LL - fn unprincipled3_static<'a>(x: *mut (dyn Trait + Send + 'a)) -> *mut (dyn Send + 'static) {
+LL + fn unprincipled3_static<'a>(x: *mut (dyn Trait + Send + 'a)) -> *mut (dyn Send + 'a) {
+   |
+help: alternatively, add an explicit `'static` bound to this reference
+   |
+LL - fn unprincipled3_static<'a>(x: *mut (dyn Trait + Send + 'a)) -> *mut (dyn Send + 'static) {
+LL + fn unprincipled3_static<'a>(x: *mut (dyn Trait + Send + 'static)) -> *mut (dyn Send + 'static) {
+   |
+
+error: aborting due to 12 previous errors
 
+For more information about this error, try `rustc --explain E0606`.

tests/ui/cast/ptr-to-trait-obj-ok.rs

@@ -20,6 +20,10 @@ fn unprincipled<'a: 'b, 'b>(x: *mut (dyn Send + 'a)) -> *mut (dyn Sync + 'b) {
     x as _
 }
 
+fn remove_principal<'a: 'b, 'b, 't>(x: *mut (dyn Trait<'t> + Send + 'a)) -> *mut (dyn Send + 'b) {
+    x as _
+}
+
 // If it is possible to coerce from the source to the target type modulo
 // regions, then we skip the HIR checks for ptr-to-ptr casts and possibly
 // insert an unsizing coercion into the MIR before the ptr-to-ptr cast.