Rollup merge of #73257 - davidtwco:issue-73249-improper-ctypes-projection, r=lcnr,varkor

ty: projections in `transparent_newtype_field`

Fixes #73249.

This PR modifies `transparent_newtype_field` so that it handles
projections with generic parameters, where `normalize_erasing_regions`
would ICE.

src/test/ui/lint/lint-ctypes-73249-1.rs

@@ -0,0 +1,21 @@
+// check-pass
+#![deny(improper_ctypes)]
+
+pub trait Foo {
+    type Assoc: 'static;
+}
+
+impl Foo for () {
+    type Assoc = u32;
+}
+
+extern "C" {
+    pub fn lint_me(x: Bar<()>);
+}
+
+#[repr(transparent)]
+pub struct Bar<T: Foo> {
+    value: &'static <T as Foo>::Assoc,
+}
+
+fn main() {}

src/test/ui/lint/lint-ctypes-73249-2.rs

@@ -0,0 +1,29 @@
+#![feature(type_alias_impl_trait)]
+#![deny(improper_ctypes)]
+
+pub trait Baz { }
+
+impl Baz for () { }
+
+type Qux = impl Baz;
+
+fn assign() -> Qux {}
+
+pub trait Foo {
+    type Assoc: 'static;
+}
+
+impl Foo for () {
+    type Assoc = Qux;
+}
+
+#[repr(transparent)]
+pub struct A<T: Foo> {
+    x: &'static <T as Foo>::Assoc,
+}
+
+extern "C" {
+    pub fn lint_me() -> A<()>; //~ ERROR: uses type `impl Baz`
+}
+
+fn main() {}

src/test/ui/lint/lint-ctypes-73249-2.stderr

@@ -0,0 +1,15 @@
+error: `extern` block uses type `impl Baz`, which is not FFI-safe
+  --> $DIR/lint-ctypes-73249-2.rs:26:25
+   |
+LL |     pub fn lint_me() -> A<()>;
+   |                         ^^^^^ not FFI-safe
+   |
+note: the lint level is defined here
+  --> $DIR/lint-ctypes-73249-2.rs:2:9
+   |
+LL | #![deny(improper_ctypes)]
+   |         ^^^^^^^^^^^^^^^
+   = note: opaque types have no C equivalent
+
+error: aborting due to previous error
+

src/test/ui/lint/lint-ctypes-73249-3.rs

@@ -0,0 +1,21 @@
+#![feature(type_alias_impl_trait)]
+#![deny(improper_ctypes)]
+
+pub trait Baz { }
+
+impl Baz for u32 { }
+
+type Qux = impl Baz;
+
+fn assign() -> Qux { 3 }
+
+#[repr(C)]
+pub struct A {
+    x: Qux,
+}
+
+extern "C" {
+    pub fn lint_me() -> A; //~ ERROR: uses type `impl Baz`
+}
+
+fn main() {}

src/test/ui/lint/lint-ctypes-73249-3.stderr

@@ -0,0 +1,15 @@
+error: `extern` block uses type `impl Baz`, which is not FFI-safe
+  --> $DIR/lint-ctypes-73249-3.rs:18:25
+   |
+LL |     pub fn lint_me() -> A;
+   |                         ^ not FFI-safe
+   |
+note: the lint level is defined here
+  --> $DIR/lint-ctypes-73249-3.rs:2:9
+   |
+LL | #![deny(improper_ctypes)]
+   |         ^^^^^^^^^^^^^^^
+   = note: opaque types have no C equivalent
+
+error: aborting due to previous error
+

src/test/ui/lint/lint-ctypes-73249-4.rs

@@ -0,0 +1,24 @@
+// check-pass
+#![deny(improper_ctypes)]
+
+use std::marker::PhantomData;
+
+trait Foo {
+    type Assoc;
+}
+
+impl Foo for () {
+    type Assoc = PhantomData<()>;
+}
+
+#[repr(transparent)]
+struct Wow<T> where T: Foo<Assoc = PhantomData<T>> {
+    x: <T as Foo>::Assoc,
+    v: u32,
+}
+
+extern "C" {
+    fn test(v: Wow<()>);
+}
+
+fn main() {}

src/test/ui/lint/lint-ctypes-73249-5.rs

@@ -0,0 +1,21 @@
+#![feature(type_alias_impl_trait)]
+#![deny(improper_ctypes)]
+
+pub trait Baz { }
+
+impl Baz for u32 { }
+
+type Qux = impl Baz;
+
+fn assign() -> Qux { 3 }
+
+#[repr(transparent)]
+pub struct A {
+    x: Qux,
+}
+
+extern "C" {
+    pub fn lint_me() -> A; //~ ERROR: uses type `impl Baz`
+}
+
+fn main() {}

src/test/ui/lint/lint-ctypes-73249-5.stderr

@@ -0,0 +1,15 @@
+error: `extern` block uses type `impl Baz`, which is not FFI-safe
+  --> $DIR/lint-ctypes-73249-5.rs:18:25
+   |
+LL |     pub fn lint_me() -> A;
+   |                         ^ not FFI-safe
+   |
+note: the lint level is defined here
+  --> $DIR/lint-ctypes-73249-5.rs:2:9
+   |
+LL | #![deny(improper_ctypes)]
+   |         ^^^^^^^^^^^^^^^
+   = note: opaque types have no C equivalent
+
+error: aborting due to previous error
+

src/test/ui/lint/lint-ctypes-73249.rs

@@ -0,0 +1,21 @@
+// check-pass
+#![deny(improper_ctypes)]
+
+pub trait Foo {
+    type Assoc;
+}
+
+impl Foo for () {
+    type Assoc = u32;
+}
+
+extern "C" {
+    pub fn lint_me(x: Bar<()>);
+}
+
+#[repr(transparent)]
+pub struct Bar<T: Foo> {
+    value: <T as Foo>::Assoc,
+}
+
+fn main() {}