rustdoc: use stability, instead of features, to decide what to show

To decide if internal items should be inlined in a doc page,
check if the crate is itself internal, rather than if it has
the rustc_private feature flag. The standard library uses
internal items, but is not itself internal and should not show
internal items on its docs pages.

src/librustdoc/clean/inline.rs

@@ -14,6 +14,7 @@
 use rustc_metadata::creader::{CStore, LoadedMacro};
 use rustc_middle::ty::fast_reject::SimplifiedType;
 use rustc_middle::ty::{self, TyCtxt};
+use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{kw, sym, Symbol};
 
@@ -444,25 +445,25 @@ pub(crate) fn build_impl(
 
     let associated_trait = tcx.impl_trait_ref(did).map(ty::EarlyBinder::skip_binder);
 
+    // Do not inline compiler-internal items unless we're a compiler-internal crate.
+    let is_compiler_internal = |did| {
+        tcx.lookup_stability(did)
+            .is_some_and(|stab| stab.is_unstable() && stab.feature == sym::rustc_private)
+    };
+    let document_compiler_internal = is_compiler_internal(LOCAL_CRATE.as_def_id());
+    let is_directly_public = |cx: &mut DocContext<'_>, did| {
+        cx.cache.effective_visibilities.is_directly_public(tcx, did)
+            && (document_compiler_internal || !is_compiler_internal(did))
+    };
+
     // Only inline impl if the implemented trait is
     // reachable in rustdoc generated documentation
     if !did.is_local()
         && let Some(traitref) = associated_trait
-    {
-        let did = traitref.def_id;
-        if !cx.cache.effective_visibilities.is_directly_public(tcx, did) {
-            return;
-        }
-
-        if !tcx.features().rustc_private && !cx.render_options.force_unstable_if_unmarked {
-            if let Some(stab) = tcx.lookup_stability(did)
-                && stab.is_unstable()
-                && stab.feature == sym::rustc_private
+        && !is_directly_public(cx, traitref.def_id)
     {
         return;
     }
-        }
-    }
 
     let impl_item = match did.as_local() {
         Some(did) => match &tcx.hir().expect_item(did).kind {
@@ -484,22 +485,12 @@ pub(crate) fn build_impl(
 
     // Only inline impl if the implementing type is
     // reachable in rustdoc generated documentation
-    if !did.is_local() {
-        if let Some(did) = for_.def_id(&cx.cache) {
-            if !cx.cache.effective_visibilities.is_directly_public(tcx, did) {
-                return;
-            }
-
-            if !tcx.features().rustc_private && !cx.render_options.force_unstable_if_unmarked {
-                if let Some(stab) = tcx.lookup_stability(did)
-                    && stab.is_unstable()
-                    && stab.feature == sym::rustc_private
+    if !did.is_local()
+        && let Some(did) = for_.def_id(&cx.cache)
+        && !is_directly_public(cx, did)
     {
         return;
     }
-            }
-        }
-    }
 
     let document_hidden = cx.render_options.document_hidden;
     let predicates = tcx.explicit_predicates_of(did);

src/librustdoc/config.rs

@@ -285,8 +285,6 @@ pub(crate) struct RenderOptions {
     pub(crate) no_emit_shared: bool,
     /// If `true`, HTML source code pages won't be generated.
     pub(crate) html_no_source: bool,
-    /// Whether `-Zforce-unstable-if-unmarked` unstable option is set
-    pub(crate) force_unstable_if_unmarked: bool,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -353,7 +351,6 @@ pub(crate) fn from_matches(
 
         let codegen_options = CodegenOptions::build(early_dcx, matches);
         let unstable_opts = UnstableOptions::build(early_dcx, matches);
-        let force_unstable_if_unmarked = unstable_opts.force_unstable_if_unmarked;
 
         let dcx = new_dcx(error_format, None, diagnostic_width, &unstable_opts);
 
@@ -790,7 +787,6 @@ fn println_condition(condition: Condition) {
             call_locations,
             no_emit_shared: false,
             html_no_source,
-            force_unstable_if_unmarked,
         };
         Some((options, render_options))
     }

tests/rustdoc/inline_cross/issue-76736-2.rs

@@ -1,6 +1,8 @@
 //@ aux-build:issue-76736-1.rs
 //@ aux-build:issue-76736-2.rs
 
+// https://github.com/rust-lang/rust/issues/124635
+
 #![crate_name = "foo"]
 #![feature(rustc_private)]
 
@@ -8,9 +10,9 @@
 extern crate issue_76736_2;
 
 // @has foo/struct.Foo.html
-// @has - '//*[@class="impl"]//h3[@class="code-header"]' 'MaybeResult'
+// @!has - '//*[@class="impl"]//h3[@class="code-header"]' 'MaybeResult'
 pub struct Foo;
 
 // @has foo/struct.Bar.html
-// @has - '//*[@class="impl"]//h3[@class="code-header"]' 'MaybeResult'
+// @!has - '//*[@class="impl"]//h3[@class="code-header"]' 'MaybeResult'
 pub use issue_76736_2::Bar;

tests/rustdoc/inline_cross/issue-76736-4.rs

@@ -0,0 +1,19 @@
+//@ aux-build:issue-76736-1.rs
+//@ aux-build:issue-76736-2.rs
+
+// https://github.com/rust-lang/rust/issues/124635
+
+#![crate_name = "foo"]
+#![feature(rustc_private, staged_api)]
+#![unstable(feature = "rustc_private", issue = "none")]
+
+extern crate issue_76736_1;
+extern crate issue_76736_2;
+
+// @has foo/struct.Foo.html
+// @has - '//*[@class="impl"]//h3[@class="code-header"]' 'MaybeResult'
+pub struct Foo;
+
+// @has foo/struct.Bar.html
+// @has - '//*[@class="impl"]//h3[@class="code-header"]' 'MaybeResult'
+pub use issue_76736_2::Bar;