Auto merge of rust-lang#73257 - davidtwco:issue-73249-improper-ctypes…

…-projection, r=lcnr,varkor

ty: projections in `transparent_newtype_field`

Fixes rust-lang#73249.

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

src/librustc_middle/ty/mod.rs

@@ -1807,6 +1807,19 @@ impl<'tcx> VariantDef {
     pub fn is_field_list_non_exhaustive(&self) -> bool {
         self.flags.intersects(VariantFlags::IS_FIELD_LIST_NON_EXHAUSTIVE)
     }
+
+    /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
+    /// field.
+    pub fn transparent_newtype_field(&self, tcx: TyCtxt<'tcx>) -> Option<&FieldDef> {
+        for field in &self.fields {
+            let field_ty = field.ty(tcx, InternalSubsts::identity_for_item(tcx, self.def_id));
+            if !field_ty.is_zst(tcx, self.def_id) {
+                return Some(field);
+            }
+        }
+
+        None
+    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
@@ -2376,29 +2389,6 @@ impl<'tcx> AdtDef {
     pub fn sized_constraint(&self, tcx: TyCtxt<'tcx>) -> &'tcx [Ty<'tcx>] {
         tcx.adt_sized_constraint(self.did).0
     }
-
-    /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
-    /// field.
-    pub fn transparent_newtype_field(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        param_env: ParamEnv<'tcx>,
-    ) -> Option<&FieldDef> {
-        assert!(self.is_struct() && self.repr.transparent());
-
-        for field in &self.non_enum_variant().fields {
-            let field_ty = tcx.normalize_erasing_regions(
-                param_env,
-                field.ty(tcx, InternalSubsts::identity_for_item(tcx, self.did)),
-            );
-
-            if !field_ty.is_zst(tcx, self.did) {
-                return Some(field);
-            }
-        }
-
-        None
-    }
 }
 
 impl<'tcx> FieldDef {

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() {}