Introduce a query for visible crates

Add a query for crates that are visible and shoule appear in
diagnostics. This excludes stdlib-private crates unless the
`rustc_private` feature is set, in which case there is no difference
from the existing `.crates(())` query.

Author: tgross35

compiler/rustc_metadata/src/creader.rs

@@ -390,10 +390,12 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         None
     }
 
-    // The `dependency` type is determined by the command line arguments(`--extern`) and
-    // `private_dep`. However, sometimes the directly dependent crate is not specified by
-    // `--extern`, in this case, `private-dep` is none during loading. This is equivalent to the
-    // scenario where the command parameter is set to `public-dependency`
+    /// The `dependency` type is determined by the command line arguments(`--extern`) and
+    /// `private_dep`.
+    ///
+    /// Sometimes the directly dependent crate is not specified by `--extern`, in this case,
+    /// `private-dep` is none during loading. This is equivalent to the scenario where the
+    /// command parameter is set to `public-dependency`
     fn is_private_dep(&self, name: &str, private_dep: Option<bool>) -> bool {
         self.sess.opts.externs.get(name).map_or(private_dep.unwrap_or(false), |e| e.is_private_dep)
             && private_dep.unwrap_or(true)

compiler/rustc_metadata/src/locator.rs

@@ -262,7 +262,7 @@ pub(crate) struct CrateLocator<'a> {
 
 #[derive(Clone)]
 pub(crate) struct CratePaths {
-    name: Symbol,
+    pub(crate) name: Symbol,
     source: CrateSource,
 }
 

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -18,7 +18,7 @@ use rustc_middle::util::Providers;
 use rustc_session::cstore::{CrateStore, ExternCrate};
 use rustc_session::{Session, StableCrateId};
 use rustc_span::hygiene::ExpnId;
-use rustc_span::{Span, Symbol, kw};
+use rustc_span::{Span, Symbol, kw, sym};
 
 use super::{Decodable, DecodeContext, DecodeIterator};
 use crate::creader::{CStore, LoadedMacro};
@@ -561,6 +561,23 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
             tcx.untracked().cstore.freeze();
             tcx.arena.alloc_from_iter(CStore::from_tcx(tcx).iter_crate_data().map(|(cnum, _)| cnum))
         },
+        visible_crates: |tcx, ()| {
+            // The list of loaded crates is now frozen in query cache,
+            // so make sure cstore is not mutably accessed from here on.
+            tcx.untracked().cstore.freeze();
+
+            // if `#![feature(rustc_private)]` is enabled in the current crate, include private
+            // dependencies (e.g. of `std`.)
+            if tcx.features().enabled(sym::rustc_private) {
+                tcx.crates(())
+            } else {
+                tcx.arena.alloc_from_iter(
+                    CStore::from_tcx(tcx)
+                        .iter_crate_data()
+                        .filter_map(|(cnum, meta)| (!meta.private_dep).then_some(cnum)),
+                )
+            }
+        },
         used_crates: |tcx, ()| {
             // The list of loaded crates is now frozen in query cache,
             // so make sure cstore is not mutably accessed from here on.

compiler/rustc_middle/src/query/mod.rs

@@ -2128,10 +2128,21 @@ rustc_queries! {
         eval_always
         desc { "calculating the stability index for the local crate" }
     }
+    /// All available crates in the graph. Use `.visible_crates(())` instead if results should only
+    /// include user-visible crates (such as for diagnostics).
     query crates(_: ()) -> &'tcx [CrateNum] {
         eval_always
         desc { "fetching all foreign CrateNum instances" }
     }
+    /// Crates that are meant to be accessible by the user. Use `.crates(())` if the entire crate
+    /// graph is required.
+    ///
+    /// This excludes e.g. private dependencies of the standard library, unless `rustc_private` is
+    /// enabled.
+    query visible_crates(_: ()) -> &'tcx [CrateNum] {
+        eval_always
+        desc { "fetching all user-reachable CrateNum instances" }
+    }
     // Crates that are loaded non-speculatively (not for diagnostics or doc links).
     // FIXME: This is currently only used for collecting lang items, but should be used instead of
     // `crates` in most other cases too.