Use visible_crates rather than crates for solving and diagnostics

For places where we don't want stdlib-private crates to be accessible,
use `.visible_crates()` rather than `.crates()`. The current effect is
that items in stdlib-private crates will no longer show up in
diagnostics related to trait selection.

Fixes: rust-lang#135232

compiler/rustc_middle/src/ty/context.rs

@@ -2078,9 +2078,10 @@ impl<'tcx> TyCtxt<'tcx> {
         self.limits(()).move_size_limit
     }
 
+    /// All traits that are visible within the crate graph (i.e. excluding private dependencies).
     pub fn all_traits(self) -> impl Iterator<Item = DefId> + 'tcx {
         iter::once(LOCAL_CRATE)
-            .chain(self.crates(()).iter().copied())
+            .chain(self.visible_crates(()).iter().copied())
             .flat_map(move |cnum| self.traits(cnum).iter().copied())
     }
 

compiler/rustc_passes/src/diagnostic_items.rs

@@ -80,7 +80,7 @@ fn all_diagnostic_items(tcx: TyCtxt<'_>, (): ()) -> DiagnosticItems {
     let mut items = DiagnosticItems::default();
 
     // Collect diagnostic items in other crates.
-    for &cnum in tcx.crates(()).iter().chain(std::iter::once(&LOCAL_CRATE)) {
+    for &cnum in tcx.visible_crates(()).iter().chain(std::iter::once(&LOCAL_CRATE)) {
         for (&name, &def_id) in &tcx.diagnostic_items(cnum).name_to_id {
             collect_item(tcx, &mut items, name, def_id);
         }

tests/ui/std/sysroot-private.default.stderr

@@ -1,11 +1,11 @@
 error[E0405]: cannot find trait `Equivalent` in this scope
-  --> $DIR/sysroot-private.rs:24:18
+  --> $DIR/sysroot-private.rs:25:18
    |
 LL | trait Trait2<K>: Equivalent<K> {}
    |                  ^^^^^^^^^^ not found in this scope
 
 error[E0412]: cannot find type `K` in this scope
-  --> $DIR/sysroot-private.rs:29:35
+  --> $DIR/sysroot-private.rs:30:35
    |
 LL | fn trait_member<T>(val: &T, key: &K) -> bool {
    |                 -                 ^
@@ -22,13 +22,13 @@ LL | fn trait_member<T, K>(val: &T, key: &K) -> bool {
    |                  +++
 
 error[E0220]: associated type `Buf` not found for `Trait`
-  --> $DIR/sysroot-private.rs:19:31
+  --> $DIR/sysroot-private.rs:20:31
    |
 LL | type AssociatedTy = dyn Trait<Buf = i32, Bar = i32>;
-   |                               ^^^ there is an associated type `Buf` in the trait `addr2line::lookup::LookupContinuation`
+   |                               ^^^ help: `Trait` has the following associated type: `Bar`
 
 error[E0425]: cannot find function `memchr2` in this scope
-  --> $DIR/sysroot-private.rs:37:5
+  --> $DIR/sysroot-private.rs:38:5
    |
 LL |     memchr2(b'a', b'b', buf)
    |     ^^^^^^^ not found in this scope

tests/ui/std/sysroot-private.rs

@@ -16,9 +16,10 @@
 trait Trait { type Bar; }
 
 // Attempt to get a suggestion for `addr2line::LookupContinuation`, which has member `Buf`
+// Note that the suggestion only happens when `rustc_private` is enabled.
 type AssociatedTy = dyn Trait<Buf = i32, Bar = i32>;
 //~^ ERROR associated type `Buf` not found
-//~| NOTE there is an associated type `Buf` in the trait `addr2line::lookup::LookupContinuation`
+//[rustc_private_enabled]~| NOTE there is an associated type `Buf` in the trait `addr2line::lookup::LookupContinuation`
 
 // Attempt to get a suggestion for `hashbrown::Equivalent`
 trait Trait2<K>: Equivalent<K> {}

tests/ui/std/sysroot-private.rustc_private_enabled.stderr

@@ -1,11 +1,11 @@
 error[E0405]: cannot find trait `Equivalent` in this scope
-  --> $DIR/sysroot-private.rs:24:18
+  --> $DIR/sysroot-private.rs:25:18
    |
 LL | trait Trait2<K>: Equivalent<K> {}
    |                  ^^^^^^^^^^ not found in this scope
 
 error[E0412]: cannot find type `K` in this scope
-  --> $DIR/sysroot-private.rs:29:35
+  --> $DIR/sysroot-private.rs:30:35
    |
 LL | fn trait_member<T>(val: &T, key: &K) -> bool {
    |                 -                 ^
@@ -22,13 +22,13 @@ LL | fn trait_member<T, K>(val: &T, key: &K) -> bool {
    |                  +++
 
 error[E0220]: associated type `Buf` not found for `Trait`
-  --> $DIR/sysroot-private.rs:19:31
+  --> $DIR/sysroot-private.rs:20:31
    |
 LL | type AssociatedTy = dyn Trait<Buf = i32, Bar = i32>;
    |                               ^^^ there is an associated type `Buf` in the trait `addr2line::lookup::LookupContinuation`
 
 error[E0425]: cannot find function `memchr2` in this scope
-  --> $DIR/sysroot-private.rs:37:5
+  --> $DIR/sysroot-private.rs:38:5
    |
 LL |     memchr2(b'a', b'b', buf)
    |     ^^^^^^^ not found in this scope