Fix missing trait impls for type in rustc docs

src/librustdoc/clean/inline.rs

@@ -443,11 +443,13 @@ pub(crate) fn build_impl(
             return;
         }
 
-        if let Some(stab) = tcx.lookup_stability(did)
-            && stab.is_unstable()
-            && stab.feature == sym::rustc_private
-        {
-            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
+            {
+                return;
+            }
         }
     }
 
@@ -477,8 +479,11 @@ pub(crate) fn build_impl(
                 return;
             }
 
-            if let Some(stab) = tcx.lookup_stability(did) {
-                if stab.is_unstable() && stab.feature == sym::rustc_private {
+            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
+                {
                     return;
                 }
             }

src/librustdoc/config.rs

@@ -281,6 +281,8 @@ 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)]
@@ -347,6 +349,7 @@ impl Options {
 
         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);
 
@@ -760,6 +763,7 @@ impl Options {
             call_locations,
             no_emit_shared: false,
             html_no_source,
+            force_unstable_if_unmarked,
         };
         Some((options, render_options))
     }

tests/rustdoc/inline_cross/auxiliary/issue-76736-1.rs

@@ -0,0 +1,6 @@
+#![feature(staged_api)]
+#![unstable(feature = "rustc_private", issue = "none")]
+
+pub trait MaybeResult<T> {}
+
+impl<T> MaybeResult<T> for T {}

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

@@ -0,0 +1,5 @@
+#![feature(rustc_private)]
+
+extern crate issue_76736_1;
+
+pub struct Bar;

tests/rustdoc/inline_cross/issue-76736-1.rs

@@ -0,0 +1,15 @@
+// aux-build:issue-76736-1.rs
+// aux-build:issue-76736-2.rs
+
+#![crate_name = "foo"]
+
+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;

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

@@ -0,0 +1,16 @@
+// aux-build:issue-76736-1.rs
+// aux-build:issue-76736-2.rs
+
+#![crate_name = "foo"]
+#![feature(rustc_private)]
+
+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;

tests/rustdoc/inline_cross/issue-76736-3.rs

@@ -0,0 +1,16 @@
+// compile-flags: -Zforce-unstable-if-unmarked
+// aux-build:issue-76736-1.rs
+// aux-build:issue-76736-2.rs
+
+#![crate_name = "foo"]
+
+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;