Rustdoc-Json: Retain Stripped Modules when they are imported, not when they have items.

Fixes #101103
Fixes #100973

3 files changed, 51 insertions, 3 deletions

diff --git a/src/librustdoc/json/conversions.rs b/src/librustdoc/json/conversions.rs
index c4e8b6f5f84..20b9eb1c27e 100644
--- a/src/librustdoc/json/conversions.rs
+++ b/src/librustdoc/json/conversions.rs
@@ -46,10 +46,14 @@ impl JsonRenderer<'_> {
             clean::KeywordItem => return None,
             clean::StrippedItem(ref inner) => {
                 match &**inner {
-                    // We document non-empty stripped modules as with `Module::is_stripped` set to
+                    // We document stripped modules as with `Module::is_stripped` set to
                     // `true`, to prevent contained items from being orphaned for downstream users,
                     // as JSON does no inlining.
-                    clean::ModuleItem(m) if !m.items.is_empty() => from_clean_item(item, self.tcx),
+                    clean::ModuleItem(_)
+                        if self.imported_items.contains(&item_id.expect_def_id()) =>
+                    {
+                        from_clean_item(item, self.tcx)
+                    }
                     _ => return None,
                 }
             }
diff --git a/src/librustdoc/json/import_finder.rs b/src/librustdoc/json/import_finder.rs
new file mode 100644
index 00000000000..c5c687df74f
--- /dev/null
+++ b/src/librustdoc/json/import_finder.rs
@@ -0,0 +1,38 @@
+use rustc_data_structures::fx::FxHashSet;
+use rustc_hir::def_id::DefId;
+
+use crate::{
+    clean::{self, Import, ImportSource, Item},
+    fold::DocFolder,
+};
+
+/// Get the id's of all items that are `pub use`d in the crate.
+///
+/// We need this to know if a stripped module is `pub use mod::*`, to decide
+/// if it needs to be kept in the index, despite being stripped.
+///
+/// See [#100973](https://github.com/rust-lang/rust/issues/100973) and
+/// [#101103](https://github.com/rust-lang/rust/issues/101103) for times when
+/// this information is needed.
+pub(crate) fn get_imports(krate: clean::Crate) -> (clean::Crate, FxHashSet<DefId>) {
+    let mut finder = ImportFinder { imported: FxHashSet::default() };
+    let krate = finder.fold_crate(krate);
+    (krate, finder.imported)
+}
+
+struct ImportFinder {
+    imported: FxHashSet<DefId>,
+}
+
+impl DocFolder for ImportFinder {
+    fn fold_item(&mut self, i: Item) -> Option<Item> {
+        match *i.kind {
+            clean::ImportItem(Import { source: ImportSource { did: Some(did), .. }, .. }) => {
+                self.imported.insert(did);
+                Some(i)
+            }
+
+            _ => Some(self.fold_item_recur(i)),
+        }
+    }
+}
diff --git a/src/librustdoc/json/mod.rs b/src/librustdoc/json/mod.rs
index 7b1b059e14d..577aad8f3bb 100644
--- a/src/librustdoc/json/mod.rs
+++ b/src/librustdoc/json/mod.rs
@@ -5,6 +5,7 @@
 //! docs for usage and details.
 
 mod conversions;
+mod import_finder;
 
 use std::cell::RefCell;
 use std::fs::{create_dir_all, File};
@@ -12,7 +13,7 @@ use std::io::{BufWriter, Write};
 use std::path::PathBuf;
 use std::rc::Rc;
 
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
@@ -39,6 +40,7 @@ pub(crate) struct JsonRenderer<'tcx> {
     /// The directory where the blob will be written to.
     out_path: PathBuf,
     cache: Rc<Cache>,
+    imported_items: FxHashSet<DefId>,
 }
 
 impl<'tcx> JsonRenderer<'tcx> {
@@ -157,12 +159,16 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
         tcx: TyCtxt<'tcx>,
     ) -> Result<(Self, clean::Crate), Error> {
         debug!("Initializing json renderer");
+
+        let (krate, imported_items) = import_finder::get_imports(krate);
+
         Ok((
             JsonRenderer {
                 tcx,
                 index: Rc::new(RefCell::new(FxHashMap::default())),
                 out_path: options.output,
                 cache: Rc::new(cache),
+                imported_items,
             },
             krate,
         ))