avoid suggesting traits from private dependencies

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -1588,7 +1588,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             &infcx_
         };
 
-        tcx.all_traits()
+        tcx.all_traits_including_private()
             .filter(|trait_def_id| {
                 // Consider only traits with the associated type
                 tcx.associated_items(*trait_def_id)

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1725,7 +1725,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             if unsatisfied_predicates.is_empty()
                 // ...or if we already suggested that name because of `rustc_confusable` annotation
                 && Some(similar_candidate.name()) != confusable_suggested
-                // and if the we aren't in an expansion.
+                // and if we aren't in an expansion.
                 && !span.from_expansion()
             {
                 self.find_likely_intended_associated_item(
@@ -3477,9 +3477,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         err: &mut Diag<'_>,
         item_name: Ident,
-        valid_out_of_scope_traits: Vec<DefId>,
+        mut valid_out_of_scope_traits: Vec<DefId>,
         explain: bool,
     ) -> bool {
+        valid_out_of_scope_traits.retain(|id| self.tcx.is_user_visible_dep(id.krate));
         if !valid_out_of_scope_traits.is_empty() {
             let mut candidates = valid_out_of_scope_traits;
             candidates.sort_by_key(|id| self.tcx.def_path_str(id));
@@ -4384,7 +4385,7 @@ pub(crate) struct TraitInfo {
 /// Retrieves all traits in this crate and any dependent crates,
 /// and wraps them into `TraitInfo` for custom sorting.
 pub(crate) fn all_traits(tcx: TyCtxt<'_>) -> Vec<TraitInfo> {
-    tcx.all_traits().map(|def_id| TraitInfo { def_id }).collect()
+    tcx.all_traits_including_private().map(|def_id| TraitInfo { def_id }).collect()
 }
 
 fn print_disambiguation_help<'tcx>(

compiler/rustc_middle/src/ty/context.rs

@@ -2318,7 +2318,7 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     /// All traits in the crate graph, including those not visible to the user.
-    pub fn all_traits(self) -> impl Iterator<Item = DefId> {
+    pub fn all_traits_including_private(self) -> impl Iterator<Item = DefId> {
         iter::once(LOCAL_CRATE)
             .chain(self.crates(()).iter().copied())
             .flat_map(move |cnum| self.traits(cnum).iter().copied())

compiler/rustc_smir/src/rustc_smir/context.rs

@@ -130,7 +130,11 @@ impl<'tcx> SmirCtxt<'tcx> {
 
     pub fn all_trait_decls(&self) -> stable_mir::TraitDecls {
         let mut tables = self.0.borrow_mut();
-        tables.tcx.all_traits().map(|trait_def_id| tables.trait_def(trait_def_id)).collect()
+        tables
+            .tcx
+            .all_traits_including_private()
+            .map(|trait_def_id| tables.trait_def(trait_def_id))
+            .collect()
     }
 
     pub fn trait_decls(&self, crate_num: CrateNum) -> stable_mir::TraitDecls {

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -1850,7 +1850,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         let trait_def_id = trait_pred.def_id();
         let trait_name = self.tcx.item_name(trait_def_id);
         let crate_name = self.tcx.crate_name(trait_def_id.krate);
-        if let Some(other_trait_def_id) = self.tcx.all_traits().find(|def_id| {
+        if let Some(other_trait_def_id) = self.tcx.all_traits_including_private().find(|def_id| {
             trait_name == self.tcx.item_name(trait_def_id)
                 && trait_def_id.krate != def_id.krate
                 && crate_name == self.tcx.crate_name(def_id.krate)

library/rustc-std-workspace-core/Cargo.toml

@@ -1,3 +1,5 @@
+cargo-features = ["public-dependency"]
+
 [package]
 name = "rustc-std-workspace-core"
 version = "1.99.0"

src/librustdoc/clean/blanket_impl.rs

@@ -23,7 +23,7 @@ pub(crate) fn synthesize_blanket_impls(
     let ty = tcx.type_of(item_def_id);
 
     let mut blanket_impls = Vec::new();
-    for trait_def_id in tcx.all_traits() {
+    for trait_def_id in tcx.visible_traits() {
         if !cx.cache.effective_visibilities.is_reachable(tcx, trait_def_id)
             || cx.generated_synthetics.contains(&(ty.skip_binder(), trait_def_id))
         {

src/librustdoc/core.rs

@@ -353,7 +353,7 @@ pub(crate) fn run_global_ctxt(
     rustc_passes::stability::check_unused_or_stable_features(tcx);
 
     let auto_traits =
-        tcx.all_traits().filter(|&trait_def_id| tcx.trait_is_auto(trait_def_id)).collect();
+        tcx.visible_traits().filter(|&trait_def_id| tcx.trait_is_auto(trait_def_id)).collect();
 
     let mut ctxt = DocContext {
         tcx,

tests/ui/typeck/auxiliary/private-dep.rs

@@ -0,0 +1,3 @@
+pub trait A {
+    fn foo() {}
+}

tests/ui/typeck/auxiliary/public-dep.rs

@@ -0,0 +1,11 @@
+//@ aux-crate:priv:private_dep=private-dep.rs
+//@ compile-flags: -Zunstable-options
+
+extern crate private_dep;
+use private_dep::A;
+
+pub struct B;
+
+impl A for B {
+    fn foo() {}
+}

tests/ui/typeck/dont-suggest-private-dependencies.rs

@@ -0,0 +1,30 @@
+// Don't suggest importing a function from a private dependency.
+// Issues: #138191, #142676
+
+// Avoid suggesting traits from std-private deps
+//@ forbid-output: compiler_builtins
+//@ forbid-output: object
+
+// Check a custom trait to withstand changes in above crates
+//@ aux-crate:public_dep=public-dep.rs
+//@ compile-flags: -Zunstable-options
+//@ forbid-output: private_dep
+
+struct VecReader(Vec<u8>);
+
+impl std::io::Read for VecReader {
+    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+        self.0.read(buf)
+        //~^ ERROR no method named `read` found for struct `Vec<u8>`
+    }
+}
+
+extern crate public_dep;
+use public_dep::B;
+
+fn main() {
+    let _ = u8::cast_from_lossy(9);
+    //~^ ERROR no function or associated item named `cast_from_lossy` found for type `u8`
+    let _ = B::foo();
+    //~^ ERROR no function or associated item named `foo` found for struct `B`
+}

tests/ui/typeck/dont-suggest-private-dependencies.stderr

@@ -0,0 +1,26 @@
+error[E0599]: no method named `read` found for struct `Vec<u8>` in the current scope
+  --> $DIR/dont-suggest-private-dependencies.rs:17:16
+   |
+LL |         self.0.read(buf)
+   |                ^^^^
+   |
+help: there is a method `read_at` with a similar name
+   |
+LL |         self.0.read_at(buf)
+   |                    +++
+
+error[E0599]: no function or associated item named `cast_from_lossy` found for type `u8` in the current scope
+  --> $DIR/dont-suggest-private-dependencies.rs:26:17
+   |
+LL |     let _ = u8::cast_from_lossy(9);
+   |                 ^^^^^^^^^^^^^^^ function or associated item not found in `u8`
+
+error[E0599]: no function or associated item named `foo` found for struct `B` in the current scope
+  --> $DIR/dont-suggest-private-dependencies.rs:28:16
+   |
+LL |     let _ = B::foo();
+   |                ^^^ function or associated item not found in `B`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0599`.