Auto merge of #123377 - oli-obk:private_projection, r=compiler-errors

Only inspect user-written predicates for privacy concerns

fixes #123288

Previously we looked at the elaborated predicates, which, due to adding various bounds on fields, end up requiring trivially true bounds. But these bounds can contain private types, which the privacy visitor then found and errored about.

Author: bors

compiler/rustc_ty_utils/src/sig_types.rs

@@ -13,6 +13,7 @@ pub trait SpannedTypeVisitor<'tcx> {
     fn visit(&mut self, span: Span, value: impl TypeVisitable<TyCtxt<'tcx>>) -> Self::Result;
 }
 
+#[instrument(level = "trace", skip(tcx, visitor))]
 pub fn walk_types<'tcx, V: SpannedTypeVisitor<'tcx>>(
     tcx: TyCtxt<'tcx>,
     item: LocalDefId,
@@ -36,7 +37,7 @@ pub fn walk_types<'tcx, V: SpannedTypeVisitor<'tcx>>(
             for (hir, ty) in hir_sig.inputs.iter().zip(ty_sig.inputs().iter()) {
                 try_visit!(visitor.visit(hir.span, ty.map_bound(|x| *x)));
             }
-            for (pred, span) in tcx.predicates_of(item).instantiate_identity(tcx) {
+            for (pred, span) in tcx.explicit_predicates_of(item).instantiate_identity(tcx) {
                 try_visit!(visitor.visit(span, pred));
             }
         }
@@ -54,7 +55,7 @@ pub fn walk_types<'tcx, V: SpannedTypeVisitor<'tcx>>(
                 // Associated types in traits don't necessarily have a type that we can visit
                 try_visit!(visitor.visit(ty.span, tcx.type_of(item).instantiate_identity()));
             }
-            for (pred, span) in tcx.predicates_of(item).instantiate_identity(tcx) {
+            for (pred, span) in tcx.explicit_predicates_of(item).instantiate_identity(tcx) {
                 try_visit!(visitor.visit(span, pred));
             }
         }
@@ -76,7 +77,7 @@ pub fn walk_types<'tcx, V: SpannedTypeVisitor<'tcx>>(
                 let ty = field.ty(tcx, args);
                 try_visit!(visitor.visit(span, ty));
             }
-            for (pred, span) in tcx.predicates_of(item).instantiate_identity(tcx) {
+            for (pred, span) in tcx.explicit_predicates_of(item).instantiate_identity(tcx) {
                 try_visit!(visitor.visit(span, pred));
             }
         }
@@ -95,12 +96,12 @@ pub fn walk_types<'tcx, V: SpannedTypeVisitor<'tcx>>(
                 _ => tcx.def_span(item),
             };
             try_visit!(visitor.visit(span, tcx.type_of(item).instantiate_identity()));
-            for (pred, span) in tcx.predicates_of(item).instantiate_identity(tcx) {
+            for (pred, span) in tcx.explicit_predicates_of(item).instantiate_identity(tcx) {
                 try_visit!(visitor.visit(span, pred));
             }
         }
         DefKind::TraitAlias | DefKind::Trait => {
-            for (pred, span) in tcx.predicates_of(item).instantiate_identity(tcx) {
+            for (pred, span) in tcx.explicit_predicates_of(item).instantiate_identity(tcx) {
                 try_visit!(visitor.visit(span, pred));
             }
         }

tests/ui/privacy/generic_struct_field_projection.rs

@@ -0,0 +1,38 @@
+//! To determine all the types that need to be private when looking at `Struct`, we
+//! used to invoke `predicates_of` to also look at types in `where` bounds.
+//! Unfortunately this also computes the inferred outlives bounds, which means for
+//! every field we check that if it is of type `&'a T` then `T: 'a` and if it is of
+//! struct type, we check that the struct satisfies its lifetime parameters by looking
+//! at its inferred outlives bounds. This means we end up with a `<Foo as Trait>::Assoc: 'a`
+//! in the outlives bounds of `Struct`. While this is trivially provable, privacy
+//! only sees `Foo` and `Trait` and determines that `Foo` is private and then errors.
+//! So now we invoke `explicit_predicates_of` to make sure we only care about user-written
+//! predicates.
+
+//@ check-pass
+
+mod baz {
+    struct Foo;
+
+    pub trait Trait {
+        type Assoc;
+    }
+
+    impl Trait for Foo {
+        type Assoc = ();
+    }
+
+    pub struct Bar<'a, T: Trait> {
+        source: &'a T::Assoc,
+    }
+
+    pub struct Baz<'a> {
+        mode: Bar<'a, Foo>,
+    }
+}
+
+pub struct Struct<'a> {
+    lexer: baz::Baz<'a>,
+}
+
+fn main() {}