Prefer visibility map parents that are not doc(hidden) first

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

@@ -375,9 +375,13 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
             use std::collections::vec_deque::VecDeque;
 
             let mut visible_parent_map: DefIdMap<DefId> = Default::default();
-            // This is a secondary visible_parent_map, storing the DefId of parents that re-export
-            // the child as `_`. Since we prefer parents that don't do this, merge this map at the
-            // end, only if we're missing any keys from the former.
+            // This is a secondary visible_parent_map, storing the DefId of
+            // parents that re-export the child as `_` or module parents
+            // which are `#[doc(hidden)]`. Since we prefer paths that don't
+            // do this, merge this map at the end, only if we're missing
+            // keys from the former.
+            // This is a rudimentary check that does not catch all cases,
+            // just the easiest.
             let mut fallback_map: DefIdMap<DefId> = Default::default();
 
             // Issue 46112: We want the map to prefer the shortest
@@ -412,6 +416,11 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
                         return;
                     }
 
+                    if ty::util::is_doc_hidden(tcx, parent) {
+                        fallback_map.insert(def_id, parent);
+                        return;
+                    }
+
                     match visible_parent_map.entry(def_id) {
                         Entry::Occupied(mut entry) => {
                             // If `child` is defined in crate `cnum`, ensure
@@ -439,8 +448,9 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
                 }
             }
 
-            // Fill in any missing entries with the (less preferable) path ending in `::_`.
-            // We still use this path in a diagnostic that suggests importing `::*`.
+            // Fill in any missing entries with the less preferable path.
+            // If this path re-exports the child as `_`, we still use this
+            // path in a diagnostic that suggests importing `::*`.
             for (child, parent) in fallback_map {
                 visible_parent_map.entry(child).or_insert(parent);
             }

src/test/ui/suggestions/dont-suggest-doc-hidden-variant-for-enum/auxiliary/hidden-child.rs

@@ -0,0 +1,8 @@
+#![crate_type = "lib"]
+
+extern crate core;
+
+pub mod __private {
+    #[doc(hidden)]
+    pub use core::option::Option::{self, None, Some};
+}

src/test/ui/suggestions/dont-suggest-doc-hidden-variant-for-enum/auxiliary/hidden-parent.rs

@@ -0,0 +1,8 @@
+#![crate_type = "lib"]
+
+extern crate core;
+
+#[doc(hidden)]
+pub mod __private {
+    pub use core::option::Option::{self, None, Some};
+}

src/test/ui/suggestions/dont-suggest-doc-hidden-variant-for-enum/hidden-child.rs

@@ -0,0 +1,10 @@
+// aux-build:hidden-child.rs
+
+// FIXME(compiler-errors): This currently suggests the wrong thing.
+// UI test exists to track the problem.
+
+extern crate hidden_child;
+
+fn main() {
+    let x: Option<i32> = 1i32; //~ ERROR mismatched types
+}

src/test/ui/suggestions/dont-suggest-doc-hidden-variant-for-enum/hidden-child.stderr

@@ -0,0 +1,18 @@
+error[E0308]: mismatched types
+  --> $DIR/hidden-child.rs:9:26
+   |
+LL |     let x: Option<i32> = 1i32;
+   |            -----------   ^^^^ expected enum `Option`, found `i32`
+   |            |
+   |            expected due to this
+   |
+   = note: expected enum `Option<i32>`
+              found type `i32`
+help: try wrapping the expression in `hidden_child::__private::Some`
+   |
+LL |     let x: Option<i32> = hidden_child::__private::Some(1i32);
+   |                          ++++++++++++++++++++++++++++++    +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/suggestions/dont-suggest-doc-hidden-variant-for-enum/hidden-parent.rs

@@ -0,0 +1,7 @@
+// aux-build:hidden-parent.rs
+
+extern crate hidden_parent;
+
+fn main() {
+    let x: Option<i32> = 1i32; //~ ERROR mismatched types
+}

src/test/ui/suggestions/dont-suggest-doc-hidden-variant-for-enum/hidden-parent.stderr

@@ -0,0 +1,18 @@
+error[E0308]: mismatched types
+  --> $DIR/hidden-parent.rs:6:26
+   |
+LL |     let x: Option<i32> = 1i32;
+   |            -----------   ^^^^ expected enum `Option`, found `i32`
+   |            |
+   |            expected due to this
+   |
+   = note: expected enum `Option<i32>`
+              found type `i32`
+help: try wrapping the expression in `Some`
+   |
+LL |     let x: Option<i32> = Some(1i32);
+   |                          +++++    +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.