Auto merge of #135278 - tgross35:ignore-std-dep-crates, r=SparrowLii

Exclude dependencies of `std` for diagnostics

Currently crates in the sysroot can show up in diagnostic suggestions, such as in https://github.com/rust-lang/rust/issues/135232. To prevent this, duplicate `all_traits` into `visible_traits` which only shows traits in non-private crates.

Setting `#![feature(rustc_private)]` overrides this and makes items in private crates visible as well, since `rustc_private` enables use of `std`'s private dependencies.

This may be reviewed per-commit.

Fixes: https://github.com/rust-lang/rust/issues/135232

compiler/rustc_middle/src/query/mod.rs

@@ -2129,6 +2129,8 @@ rustc_queries! {
         eval_always
         desc { "calculating the stability index for the local crate" }
     }
+    /// All available crates in the graph, including those that should not be user-facing
+    /// (such as private crates).
     query crates(_: ()) -> &'tcx [CrateNum] {
         eval_always
         desc { "fetching all foreign CrateNum instances" }

compiler/rustc_middle/src/ty/context.rs

@@ -2078,12 +2078,23 @@ impl<'tcx> TyCtxt<'tcx> {
         self.limits(()).move_size_limit
     }
 
+    /// All traits in the crate graph, including those not visible to the user.
     pub fn all_traits(self) -> impl Iterator<Item = DefId> + 'tcx {
         iter::once(LOCAL_CRATE)
             .chain(self.crates(()).iter().copied())
             .flat_map(move |cnum| self.traits(cnum).iter().copied())
     }
 
+    /// All traits that are visible within the crate graph (i.e. excluding private dependencies).
+    pub fn visible_traits(self) -> impl Iterator<Item = DefId> + 'tcx {
+        let visible_crates =
+            self.crates(()).iter().copied().filter(move |cnum| self.is_user_visible_dep(*cnum));
+
+        iter::once(LOCAL_CRATE)
+            .chain(visible_crates)
+            .flat_map(move |cnum| self.traits(cnum).iter().copied())
+    }
+
     #[inline]
     pub fn local_visibility(self, def_id: LocalDefId) -> Visibility {
         self.visibility(def_id).expect_local()

compiler/rustc_middle/src/ty/util.rs

@@ -876,6 +876,11 @@ impl<'tcx> TyCtxt<'tcx> {
     /// [public]: TyCtxt::is_private_dep
     /// [direct]: rustc_session::cstore::ExternCrate::is_direct
     pub fn is_user_visible_dep(self, key: CrateNum) -> bool {
+        // `#![rustc_private]` overrides defaults to make private dependencies usable.
+        if self.features().enabled(sym::rustc_private) {
+            return true;
+        }
+
         // | Private | Direct | Visible |                    |
         // |---------|--------|---------|--------------------|
         // | Yes     | Yes    | Yes     | !true || true   |