If the parent dependency is private, treat dependents as private

Currently, marking a dependency private does not automatically make all
its child dependencies private. Resolve this by making its children
private by default as well.

This also resolves some FIXMEs for tests that are intended to fail but
previously passed.

[1]: https://github.com/rust-lang/rust/pull/135501#issuecomment-2620242419

compiler/rustc_metadata/src/creader.rs

@@ -168,7 +168,10 @@ fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
 enum CrateOrigin<'a> {
     /// This crate was a dependency of another crate.
     IndirectDependency {
+        /// Where this dependency was included from.
         dep_root: &'a CratePaths,
+        /// True if the parent is private, meaning the dependent should also be private.
+        parent_private: bool,
         /// Dependency info about this crate.
         dep: &'a CrateDep,
     },
@@ -194,6 +197,17 @@ fn dep(&self) -> Option<&'a CrateDep> {
             _ => None,
         }
     }
+
+    /// `Some(true)` if the dependency is private or its parent is private, `Some(false)` if the
+    /// dependency is not private, `None` if it could not be determined.
+    fn private_dep(&self) -> Option<bool> {
+        match self {
+            CrateOrigin::IndirectDependency { parent_private, dep, .. } => {
+                Some(dep.is_private || *parent_private)
+            }
+            _ => None,
+        }
+    }
 }
 
 impl CStore {
@@ -585,7 +599,8 @@ fn register_crate(
             &crate_paths
         };
 
-        let cnum_map = self.resolve_crate_deps(dep_root, &crate_root, &metadata, cnum, dep_kind)?;
+        let cnum_map =
+            self.resolve_crate_deps(dep_root, &crate_root, &metadata, cnum, dep_kind, private_dep)?;
 
         let raw_proc_macros = if crate_root.is_proc_macro_crate() {
             let temp_root;
@@ -722,7 +737,7 @@ fn maybe_resolve_crate<'b>(
         let host_hash = dep.map(|d| d.host_hash).flatten();
         let extra_filename = dep.map(|d| &d.extra_filename[..]);
         let path_kind = if dep.is_some() { PathKind::Dependency } else { PathKind::Crate };
-        let private_dep = dep.map(|d| d.is_private);
+        let private_dep = origin.private_dep();
 
         let result = if let Some(cnum) = self.existing_match(name, hash, path_kind) {
             (LoadResult::Previous(cnum), None)
@@ -819,6 +834,7 @@ fn resolve_crate_deps(
         metadata: &MetadataBlob,
         krate: CrateNum,
         dep_kind: CrateDepKind,
+        parent_is_private: bool,
     ) -> Result<CrateNumMap, CrateError> {
         debug!(
             "resolving deps of external crate `{}` with dep root `{}`",
@@ -837,11 +853,12 @@ fn resolve_crate_deps(
         crate_num_map.push(krate);
         for dep in deps {
             info!(
-                "resolving dep `{}`->`{}` hash: `{}` extra filename: `{}`",
+                "resolving dep `{}`->`{}` hash: `{}` extra filename: `{}` private {}",
                 crate_root.name(),
                 dep.name,
                 dep.hash,
-                dep.extra_filename
+                dep.extra_filename,
+                dep.is_private,
             );
             let dep_kind = match dep_kind {
                 CrateDepKind::MacrosOnly => CrateDepKind::MacrosOnly,
@@ -850,7 +867,11 @@ fn resolve_crate_deps(
             let cnum = self.maybe_resolve_crate(
                 dep.name,
                 dep_kind,
-                CrateOrigin::IndirectDependency { dep_root, dep: &dep },
+                CrateOrigin::IndirectDependency {
+                    dep_root,
+                    parent_private: parent_is_private,
+                    dep: &dep,
+                },
             )?;
             crate_num_map.push(cnum);
         }

tests/ui/privacy/pub-priv-dep/reexport_from_priv.rs

@@ -1,6 +1,5 @@
 //@ aux-crate:priv:reexport=reexport.rs
 //@ compile-flags: -Zunstable-options
-//@ check-pass
 
 // Checks the behavior of a reexported item from a private dependency.
 
@@ -9,7 +8,7 @@
 
 extern crate reexport;
 
-// FIXME: This should trigger.
 pub fn leaks_priv() -> reexport::Shared {
+    //~^ ERROR type `Shared` from private dependency 'shared' in public interface
     reexport::Shared
 }

tests/ui/privacy/pub-priv-dep/reexport_from_priv.stderr

@@ -0,0 +1,14 @@
+error: type `Shared` from private dependency 'shared' in public interface
+  --> $DIR/reexport_from_priv.rs:11:1
+   |
+LL | pub fn leaks_priv() -> reexport::Shared {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/reexport_from_priv.rs:7:9
+   |
+LL | #![deny(exported_private_dependencies)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/privacy/pub-priv-dep/shared_indirect.rs

@@ -1,7 +1,6 @@
 //@ aux-crate:priv:shared=shared.rs
 //@ aux-crate:priv:indirect1=indirect1.rs
 //@ compile-flags: -Zunstable-options
-//@ check-pass
 
 // A shared dependency, where it is only indirectly public.
 //
@@ -23,7 +22,7 @@
 extern crate shared;
 extern crate indirect1;
 
-// FIXME: This should trigger.
 pub fn leaks_priv() -> shared::Shared {
+    //~^ ERROR type `Shared` from private dependency 'shared' in public interface
     shared::Shared
 }

tests/ui/privacy/pub-priv-dep/shared_indirect.stderr

@@ -0,0 +1,14 @@
+error: type `Shared` from private dependency 'shared' in public interface
+  --> $DIR/shared_indirect.rs:25:1
+   |
+LL | pub fn leaks_priv() -> shared::Shared {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/shared_indirect.rs:20:9
+   |
+LL | #![deny(exported_private_dependencies)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+