Preserve the parent module of DocFragments

- Add `parent_module` to `DocFragment`
- Require the `parent_module` of the item being inlined
- Preserve the hir_id for ExternCrates so rustdoc can find the parent module later
- Take an optional `parent_module` for `build_impl` and `merge_attrs`.
  Preserve the difference between parent modules for each doc-comment.
- Support arbitrarily many re-exports in from_ast. In retrospect this is
  probably not used and could be simplified to a single
  `Option<(Attrs, DefId)>`.
- Don't require the parent_module for all `impl`s, just inlined items

  In particular, this will be `None` whenever the attribute is not on a
  re-export.

- Only store the parent_module, not the HirId

  When re-exporting a re-export, the HirId is not available. Fortunately,
  `collect_intra_doc_links` doesn't actually need all the info from a
  HirId, just the parent module.

src/librustdoc/clean/inline.rs

@@ -15,7 +15,7 @@ use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
 
-use crate::clean::{self, GetDefId, ToSource, TypeKind};
+use crate::clean::{self, Attributes, GetDefId, ToSource, TypeKind};
 use crate::core::DocContext;
 use crate::doctree;
 
@@ -35,8 +35,11 @@ type Attrs<'hir> = rustc_middle::ty::Attributes<'hir>;
 ///
 /// The returned value is `None` if the definition could not be inlined,
 /// and `Some` of a vector of items if it was successfully expanded.
+///
+/// `parent_module` refers to the parent of the *re-export*, not the original item.
 pub fn try_inline(
     cx: &DocContext<'_>,
+    parent_module: DefId,
     res: Res,
     name: Symbol,
     attrs: Option<Attrs<'_>>,
@@ -48,12 +51,13 @@ pub fn try_inline(
     }
     let mut ret = Vec::new();
 
+    debug!("attrs={:?}", attrs);
     let attrs_clone = attrs;
 
     let inner = match res {
         Res::Def(DefKind::Trait, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Trait);
-            ret.extend(build_impls(cx, did, attrs));
+            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
             clean::TraitItem(build_external_trait(cx, did))
         }
         Res::Def(DefKind::Fn, did) => {
@@ -62,27 +66,27 @@ pub fn try_inline(
         }
         Res::Def(DefKind::Struct, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Struct);
-            ret.extend(build_impls(cx, did, attrs));
+            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
             clean::StructItem(build_struct(cx, did))
         }
         Res::Def(DefKind::Union, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Union);
-            ret.extend(build_impls(cx, did, attrs));
+            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
             clean::UnionItem(build_union(cx, did))
         }
         Res::Def(DefKind::TyAlias, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Typedef);
-            ret.extend(build_impls(cx, did, attrs));
+            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
             clean::TypedefItem(build_type_alias(cx, did), false)
         }
         Res::Def(DefKind::Enum, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Enum);
-            ret.extend(build_impls(cx, did, attrs));
+            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
             clean::EnumItem(build_enum(cx, did))
         }
         Res::Def(DefKind::ForeignTy, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Foreign);
-            ret.extend(build_impls(cx, did, attrs));
+            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
             clean::ForeignTypeItem
         }
         // Never inline enum variants but leave them shown as re-exports.
@@ -117,7 +121,7 @@ pub fn try_inline(
     };
 
     let target_attrs = load_attrs(cx, did);
-    let attrs = merge_attrs(cx, target_attrs, attrs_clone);
+    let attrs = merge_attrs(cx, Some(parent_module), target_attrs, attrs_clone);
 
     cx.renderinfo.borrow_mut().inlined.insert(did);
     ret.push(clean::Item {
@@ -291,40 +295,52 @@ pub fn build_ty(cx: &DocContext<'_>, did: DefId) -> Option<clean::Type> {
 }
 
 /// Builds all inherent implementations of an ADT (struct/union/enum) or Trait item/path/reexport.
-pub fn build_impls(cx: &DocContext<'_>, did: DefId, attrs: Option<Attrs<'_>>) -> Vec<clean::Item> {
+pub fn build_impls(
+    cx: &DocContext<'_>,
+    parent_module: Option<DefId>,
+    did: DefId,
+    attrs: Option<Attrs<'_>>,
+) -> Vec<clean::Item> {
     let tcx = cx.tcx;
     let mut impls = Vec::new();
 
     // for each implementation of an item represented by `did`, build the clean::Item for that impl
     for &did in tcx.inherent_impls(did).iter() {
-        build_impl(cx, did, attrs, &mut impls);
+        build_impl(cx, parent_module, did, attrs, &mut impls);
     }
 
     impls
 }
 
+/// `parent_module` refers to the parent of the re-export, not the original item
 fn merge_attrs(
     cx: &DocContext<'_>,
-    attrs: Attrs<'_>,
-    other_attrs: Option<Attrs<'_>>,
+    parent_module: Option<DefId>,
+    old_attrs: Attrs<'_>,
+    new_attrs: Option<Attrs<'_>>,
 ) -> clean::Attributes {
     // NOTE: If we have additional attributes (from a re-export),
     // always insert them first. This ensure that re-export
     // doc comments show up before the original doc comments
     // when we render them.
-    let merged_attrs = if let Some(inner) = other_attrs {
-        let mut both = inner.to_vec();
-        both.extend_from_slice(attrs);
-        both
+    if let Some(inner) = new_attrs {
+        if let Some(new_id) = parent_module {
+            let diag = cx.sess().diagnostic();
+            Attributes::from_ast(diag, old_attrs, Some((inner, new_id)))
+        } else {
+            let mut both = inner.to_vec();
+            both.extend_from_slice(old_attrs);
+            both.clean(cx)
+        }
     } else {
-        attrs.to_vec()
-    };
-    merged_attrs.clean(cx)
+        old_attrs.clean(cx)
+    }
 }
 
 /// Builds a specific implementation of a type. The `did` could be a type method or trait method.
 pub fn build_impl(
     cx: &DocContext<'_>,
+    parent_module: impl Into<Option<DefId>>,
     did: DefId,
     attrs: Option<Attrs<'_>>,
     ret: &mut Vec<clean::Item>,
@@ -333,7 +349,8 @@ pub fn build_impl(
         return;
     }
 
-    let attrs = merge_attrs(cx, load_attrs(cx, did), attrs);
+    let attrs = merge_attrs(cx, parent_module.into(), load_attrs(cx, did), attrs);
+    debug!("merged_attrs={:?}", attrs);
 
     let tcx = cx.tcx;
     let associated_trait = tcx.impl_trait_ref(did);
@@ -499,7 +516,9 @@ fn build_module(cx: &DocContext<'_>, did: DefId, visited: &mut FxHashSet<DefId>)
                             },
                         )),
                     });
-                } else if let Some(i) = try_inline(cx, item.res, item.ident.name, None, visited) {
+                } else if let Some(i) =
+                    try_inline(cx, did, item.res, item.ident.name, None, visited)
+                {
                     items.extend(i)
                 }
             }

src/librustdoc/clean/mod.rs

@@ -284,7 +284,7 @@ impl Clean<Item> for doctree::Module<'_> {
 
 impl Clean<Attributes> for [ast::Attribute] {
     fn clean(&self, cx: &DocContext<'_>) -> Attributes {
-        Attributes::from_ast(cx.sess().diagnostic(), self)
+        Attributes::from_ast(cx.sess().diagnostic(), self, None)
     }
 }
 
@@ -2205,9 +2205,14 @@ impl Clean<Vec<Item>> for doctree::ExternCrate<'_> {
 
             let res = Res::Def(DefKind::Mod, DefId { krate: self.cnum, index: CRATE_DEF_INDEX });
 
-            if let Some(items) =
-                inline::try_inline(cx, res, self.name, Some(self.attrs), &mut visited)
-            {
+            if let Some(items) = inline::try_inline(
+                cx,
+                cx.tcx.parent_module(self.hir_id).to_def_id(),
+                res,
+                self.name,
+                Some(self.attrs),
+                &mut visited,
+            ) {
                 return items;
             }
         }
@@ -2268,9 +2273,14 @@ impl Clean<Vec<Item>> for doctree::Import<'_> {
             }
             if !denied {
                 let mut visited = FxHashSet::default();
-                if let Some(items) =
-                    inline::try_inline(cx, path.res, name, Some(self.attrs), &mut visited)
-                {
+                if let Some(items) = inline::try_inline(
+                    cx,
+                    cx.tcx.parent_module(self.id).to_def_id(),
+                    path.res,
+                    name,
+                    Some(self.attrs),
+                    &mut visited,
+                ) {
                     return items;
                 }
             }

src/librustdoc/clean/types.rs

@@ -373,6 +373,11 @@ impl<I: IntoIterator<Item = ast::NestedMetaItem>> NestedAttributesExt for I {
 pub struct DocFragment {
     pub line: usize,
     pub span: rustc_span::Span,
+    /// The module this doc-comment came from.
+    ///
+    /// This allows distinguishing between the original documentation and a pub re-export.
+    /// If it is `None`, the item was not re-exported.
+    pub parent_module: Option<DefId>,
     pub doc: String,
     pub kind: DocFragmentKind,
 }
@@ -521,16 +526,25 @@ impl Attributes {
         false
     }
 
-    pub fn from_ast(diagnostic: &::rustc_errors::Handler, attrs: &[ast::Attribute]) -> Attributes {
+    pub fn from_ast(
+        diagnostic: &::rustc_errors::Handler,
+        attrs: &[ast::Attribute],
+        additional_attrs: Option<(&[ast::Attribute], DefId)>,
+    ) -> Attributes {
         let mut doc_strings = vec![];
         let mut sp = None;
         let mut cfg = Cfg::True;
         let mut doc_line = 0;
 
-        let other_attrs = attrs
-            .iter()
-            .filter_map(|attr| {
+        // Additional documentation should be shown before the original documentation
+        let other_attrs = additional_attrs
+            .into_iter()
+            .map(|(attrs, id)| attrs.iter().map(move |attr| (attr, Some(id))))
+            .flatten()
+            .chain(attrs.iter().map(|attr| (attr, None)))
+            .filter_map(|(attr, parent_module)| {
                 if let Some(value) = attr.doc_str() {
+                    trace!("got doc_str={:?}", value);
                     let value = beautify_doc_string(value);
                     let kind = if attr.is_doc_comment() {
                         DocFragmentKind::SugaredDoc
@@ -540,7 +554,13 @@ impl Attributes {
 
                     let line = doc_line;
                     doc_line += value.lines().count();
-                    doc_strings.push(DocFragment { line, span: attr.span, doc: value, kind });
+                    doc_strings.push(DocFragment {
+                        line,
+                        span: attr.span,
+                        doc: value,
+                        kind,
+                        parent_module,
+                    });
 
                     if sp.is_none() {
                         sp = Some(attr.span);
@@ -565,6 +585,7 @@ impl Attributes {
                                     span: attr.span,
                                     doc: contents,
                                     kind: DocFragmentKind::Include { filename },
+                                    parent_module: parent_module,
                                 });
                             }
                         }

src/librustdoc/clean/utils.rs

@@ -361,7 +361,7 @@ pub fn build_deref_target_impls(cx: &DocContext<'_>, items: &[Item], ret: &mut V
         let primitive = match *target {
             ResolvedPath { did, .. } if did.is_local() => continue,
             ResolvedPath { did, .. } => {
-                ret.extend(inline::build_impls(cx, did, None));
+                ret.extend(inline::build_impls(cx, None, did, None));
                 continue;
             }
             _ => match target.primitive_type() {
@@ -371,7 +371,7 @@ pub fn build_deref_target_impls(cx: &DocContext<'_>, items: &[Item], ret: &mut V
         };
         for &did in primitive.impls(tcx) {
             if !did.is_local() {
-                inline::build_impl(cx, did, None, ret);
+                inline::build_impl(cx, None, did, None, ret);
             }
         }
     }

src/librustdoc/doctest.rs

@@ -927,7 +927,7 @@ impl<'a, 'hir, 'tcx> HirCollector<'a, 'hir, 'tcx> {
         sp: Span,
         nested: F,
     ) {
-        let mut attrs = Attributes::from_ast(self.sess.diagnostic(), attrs);
+        let mut attrs = Attributes::from_ast(self.sess.diagnostic(), attrs, None);
         if let Some(ref cfg) = attrs.cfg {
             if !cfg.matches(&self.sess.parse_sess, Some(&self.sess.features_untracked())) {
                 return;

src/librustdoc/doctree.rs

@@ -8,6 +8,7 @@ use rustc_span::{self, Span, Symbol};
 
 use rustc_hir as hir;
 use rustc_hir::def_id::CrateNum;
+use rustc_hir::HirId;
 
 pub struct Module<'hir> {
     pub name: Option<Symbol>,
@@ -236,6 +237,7 @@ pub struct Macro<'hir> {
 
 pub struct ExternCrate<'hir> {
     pub name: Symbol,
+    pub hir_id: HirId,
     pub cnum: CrateNum,
     pub path: Option<String>,
     pub vis: &'hir hir::Visibility<'hir>,

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -767,8 +767,16 @@ impl<'a, 'tcx> DocFolder for LinkCollector<'a, 'tcx> {
             self.mod_ids.push(item.def_id);
         }
 
+        #[cfg(debug_assertions)]
+        for attr in &item.attrs.doc_strings {
+            if let Some(id) = attr.parent_module {
+                trace!("docs {:?} came from {:?}", attr.doc, id);
+            } else {
+                debug!("no parent found for {:?}", attr.doc);
+            }
+        }
         let dox = item.attrs.collapsed_doc_value().unwrap_or_else(String::new);
-        trace!("got documentation '{}'", dox);
+        //trace!("got documentation '{}'", dox);
 
         // find item's parent to resolve `Self` in item's docs below
         let parent_name = self.cx.as_local_hir_id(item.def_id).and_then(|item_hir| {

src/librustdoc/passes/collect_trait_impls.rs

@@ -30,15 +30,15 @@ pub fn collect_trait_impls(krate: Crate, cx: &DocContext<'_>) -> Crate {
     for &cnum in cx.tcx.crates().iter() {
         for &(did, _) in cx.tcx.all_trait_implementations(cnum).iter() {
             cx.tcx.sess.time("build_extern_trait_impl", || {
-                inline::build_impl(cx, did, None, &mut new_items);
+                inline::build_impl(cx, None, did, None, &mut new_items);
             });
         }
     }
 
     // Also try to inline primitive impls from other crates.
     for &def_id in PrimitiveType::all_impls(cx.tcx).values().flatten() {
         if !def_id.is_local() {
-            inline::build_impl(cx, def_id, None, &mut new_items);
+            inline::build_impl(cx, None, def_id, None, &mut new_items);
 
             // FIXME(eddyb) is this `doc(hidden)` check needed?
             if !cx.tcx.get_attrs(def_id).lists(sym::doc).has_word(sym::hidden) {
@@ -90,7 +90,7 @@ pub fn collect_trait_impls(krate: Crate, cx: &DocContext<'_>) -> Crate {
         for &impl_node in cx.tcx.hir().trait_impls(trait_did) {
             let impl_did = cx.tcx.hir().local_def_id(impl_node);
             cx.tcx.sess.time("build_local_trait_impl", || {
-                inline::build_impl(cx, impl_did.to_def_id(), None, &mut new_items);
+                inline::build_impl(cx, None, impl_did.to_def_id(), None, &mut new_items);
             });
         }
     }

src/librustdoc/visit_ast.rs

@@ -399,6 +399,7 @@ impl<'a, 'tcx> RustdocVisitor<'a, 'tcx> {
                 om.extern_crates.push(ExternCrate {
                     cnum: self.cx.tcx.extern_mod_stmt_cnum(def_id).unwrap_or(LOCAL_CRATE),
                     name: ident.name,
+                    hir_id: item.hir_id,
                     path: orig_name.map(|x| x.to_string()),
                     vis: &item.vis,
                     attrs: &item.attrs,