Test that opaque types can't have themselves as a hidden type with incompatible lifetimes

Author: oli-obk

tests/ui/type-alias-impl-trait/different_args_considered_equal.rs

@@ -0,0 +1,15 @@
+#![feature(type_alias_impl_trait)]
+
+pub type Opaque<'a> = impl Sized;
+
+fn get_one<'a>(a: *mut &'a str) -> Opaque<'a> {
+    a
+}
+
+fn get_iter<'a>() -> Option<Opaque<'a>> {
+    //~^ ERROR:  item does not constrain
+    None::<Opaque<'static>>
+    //~^ ERROR lifetime may not live long enough
+}
+
+fn main() {}

tests/ui/type-alias-impl-trait/different_args_considered_equal.stderr

@@ -0,0 +1,24 @@
+error: item does not constrain `Opaque::{opaque#0}`, but has it in its signature
+  --> $DIR/different_args_considered_equal.rs:9:4
+   |
+LL | fn get_iter<'a>() -> Option<Opaque<'a>> {
+   |    ^^^^^^^^
+   |
+   = note: consider moving the opaque type's declaration and defining uses into a separate module
+note: this opaque type is in the signature
+  --> $DIR/different_args_considered_equal.rs:3:23
+   |
+LL | pub type Opaque<'a> = impl Sized;
+   |                       ^^^^^^^^^^
+
+error: lifetime may not live long enough
+  --> $DIR/different_args_considered_equal.rs:11:5
+   |
+LL | fn get_iter<'a>() -> Option<Opaque<'a>> {
+   |             -- lifetime `'a` defined here
+LL |
+LL |     None::<Opaque<'static>>
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
+
+error: aborting due to 2 previous errors
+

tests/ui/type-alias-impl-trait/different_args_considered_equal2.rs

@@ -0,0 +1,14 @@
+#![feature(type_alias_impl_trait)]
+
+pub type Opaque<'a> = impl Sized;
+
+fn get_one<'a>(a: *mut &'a str) -> Option<Opaque<'a>> {
+    if a.is_null() {
+        Some(a)
+    } else {
+        None::<Opaque<'static>>
+        //~^ ERROR lifetime may not live long enough
+    }
+}
+
+fn main() {}

tests/ui/type-alias-impl-trait/different_args_considered_equal2.stderr

@@ -0,0 +1,11 @@
+error: lifetime may not live long enough
+  --> $DIR/different_args_considered_equal2.rs:9:9
+   |
+LL | fn get_one<'a>(a: *mut &'a str) -> Option<Opaque<'a>> {
+   |            -- lifetime `'a` defined here
+...
+LL |         None::<Opaque<'static>>
+   |         ^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
+
+error: aborting due to 1 previous error
+

tests/ui/type-alias-impl-trait/different_args_considered_equal3.rs

@@ -0,0 +1,22 @@
+//! Test that we don't allow coercing an opaque type with a static
+//! lifetime to a free version of itself. While this kind of
+//! conversion is fine for rigid types, the hidden type behind an opaque
+//! type may
+
+#![feature(type_alias_impl_trait)]
+
+mod defining_scope {
+    pub type Opaque<'a> = impl Sized;
+
+    fn get_one<'a>(a: *mut &'a str) -> Opaque<'a> {
+        a
+    }
+}
+use defining_scope::Opaque;
+
+fn get_iter<'a>() -> Option<Opaque<'a>> {
+    None::<Opaque<'static>>
+    //~^ ERROR lifetime may not live long enough
+}
+
+fn main() {}

tests/ui/type-alias-impl-trait/different_args_considered_equal3.stderr

@@ -0,0 +1,10 @@
+error: lifetime may not live long enough
+  --> $DIR/different_args_considered_equal3.rs:18:5
+   |
+LL | fn get_iter<'a>() -> Option<Opaque<'a>> {
+   |             -- lifetime `'a` defined here
+LL |     None::<Opaque<'static>>
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
+
+error: aborting due to 1 previous error
+