avoid suggesting traits from private dependencies

Author: Qelxiros

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -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_private_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));

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"
@@ -12,4 +14,6 @@ path = "lib.rs"
 
 [dependencies]
 core = { path = "../core" }
-compiler_builtins = { path = "../compiler-builtins/compiler-builtins", features = ["compiler-builtins"] }
+compiler_builtins = { path = "../compiler-builtins/compiler-builtins", features = [
+  "compiler-builtins",
+] }

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

@@ -0,0 +1,15 @@
+// Don't suggest importing a function from a private dependency.
+
+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>`
+    }
+}
+
+fn main() {
+    let _ = u8::cast_from_lossy(9);
+    //~^ ERROR no function or associated item named `cast_from_lossy` found for type `u8`
+}

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

@@ -0,0 +1,20 @@
+error[E0599]: no method named `read` found for struct `Vec<u8>` in the current scope
+  --> $DIR/dont-suggest-private-dependencies.rs:7:16
+   |
+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:13:17
+   |
+LL |     let _ = u8::cast_from_lossy(9);
+   |                 ^^^^^^^^^^^^^^^ function or associated item not found in `u8`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0599`.