Rollup merge of #78678 - Nemo157:doc-cfg-w-traits, r=jyn514,GuillaumeGomez

Add tests and improve rendering of cfgs on traits

Shows the additional features required to get the trait implementation, suppressing any already shown on the current page. One interesting effect from this is if you have a cfg-ed type, implementing a cfg-ed trait (so the implementation depends on both cfgs), you will get the inverted pair of cfgs shown on each page:

![image](https://user-images.githubusercontent.com/81079/97904671-207bdc00-1d41-11eb-8144-707e8017d2b6.png)

![image](https://user-images.githubusercontent.com/81079/97904700-27a2ea00-1d41-11eb-8b9f-e925ba339044.png)

The hidden items on the trait implementation also now get the correct cfgs displayed on them.

Tests are blocked on #78673.

fixes #68100
cc #43781

1 files changed, 43 insertions, 29 deletions

diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index eebb07f0476..fc0ce4b1f09 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -2251,6 +2251,22 @@ fn stability_tags(item: &clean::Item, parent: &clean::Item) -> String {
     tags
 }
 
+fn portability(item: &clean::Item, parent: Option<&clean::Item>) -> Option<String> {
+    let cfg = match (&item.attrs.cfg, parent.and_then(|p| p.attrs.cfg.as_ref())) {
+        (Some(cfg), Some(parent_cfg)) => cfg.simplify_with(parent_cfg),
+        (cfg, _) => cfg.as_deref().cloned(),
+    };
+
+    debug!(
+        "Portability {:?} - {:?} = {:?}",
+        item.attrs.cfg,
+        parent.and_then(|p| p.attrs.cfg.as_ref()),
+        cfg
+    );
+
+    Some(format!("<div class=\"stab portability\">{}</div>", cfg?.render_long_html()))
+}
+
 /// Render the stability and/or deprecation warning that is displayed at the top of the item's
 /// documentation.
 fn short_stability(item: &clean::Item, cx: &Context, parent: Option<&clean::Item>) -> Vec<String> {
@@ -2328,19 +2344,8 @@ fn short_stability(item: &clean::Item, cx: &Context, parent: Option<&clean::Item
         stability.push(format!("<div class=\"stab unstable\">{}</div>", message));
     }
 
-    let cfg = match (&item.attrs.cfg, parent.and_then(|p| p.attrs.cfg.as_ref())) {
-        (Some(cfg), Some(parent_cfg)) => cfg.simplify_with(parent_cfg),
-        (cfg, _) => cfg.as_deref().cloned(),
-    };
-
-    debug!(
-        "Portability {:?} - {:?} = {:?}",
-        item.attrs.cfg,
-        parent.and_then(|p| p.attrs.cfg.as_ref()),
-        cfg
-    );
-    if let Some(cfg) = cfg {
-        stability.push(format!("<div class=\"stab portability\">{}</div>", cfg.render_long_html()));
+    if let Some(portability) = portability(item, parent) {
+        stability.push(portability);
     }
 
     stability
@@ -2431,6 +2436,7 @@ fn item_function(w: &mut Buffer, cx: &Context, it: &clean::Item, f: &clean::Func
 fn render_implementor(
     cx: &Context,
     implementor: &Impl,
+    parent: &clean::Item,
     w: &mut Buffer,
     implementor_dups: &FxHashMap<&str, (DefId, bool)>,
     aliases: &[String],
@@ -2450,7 +2456,7 @@ fn render_implementor(
         w,
         cx,
         implementor,
-        None,
+        parent,
         AssocItemLink::Anchor(None),
         RenderMode::Normal,
         implementor.impl_item.stable_since().as_deref(),
@@ -2480,7 +2486,7 @@ fn render_impls(
                 &mut buffer,
                 cx,
                 i,
-                Some(containing_item),
+                containing_item,
                 assoc_link,
                 RenderMode::Normal,
                 containing_item.stable_since().as_deref(),
@@ -2727,7 +2733,7 @@ fn item_trait(w: &mut Buffer, cx: &Context, it: &clean::Item, t: &clean::Trait,
                     w,
                     cx,
                     &implementor,
-                    None,
+                    it,
                     assoc_link,
                     RenderMode::Normal,
                     implementor.impl_item.stable_since().as_deref(),
@@ -2749,7 +2755,7 @@ fn item_trait(w: &mut Buffer, cx: &Context, it: &clean::Item, t: &clean::Trait,
             "<div class=\"item-list\" id=\"implementors-list\">",
         );
         for implementor in concrete {
-            render_implementor(cx, implementor, w, &implementor_dups, &[], cache);
+            render_implementor(cx, implementor, it, w, &implementor_dups, &[], cache);
         }
         write_loading_content(w, "</div>");
 
@@ -2764,6 +2770,7 @@ fn item_trait(w: &mut Buffer, cx: &Context, it: &clean::Item, t: &clean::Trait,
                 render_implementor(
                     cx,
                     implementor,
+                    it,
                     w,
                     &implementor_dups,
                     &collect_paths_for_type(implementor.inner_impl().for_.clone()),
@@ -3430,7 +3437,7 @@ fn render_assoc_items(
                 w,
                 cx,
                 i,
-                Some(containing_item),
+                containing_item,
                 AssocItemLink::Anchor(None),
                 render_mode,
                 containing_item.stable_since().as_deref(),
@@ -3622,7 +3629,7 @@ fn render_impl(
     w: &mut Buffer,
     cx: &Context,
     i: &Impl,
-    parent: Option<&clean::Item>,
+    parent: &clean::Item,
     link: AssocItemLink<'_>,
     render_mode: RenderMode,
     outer_version: Option<&str>,
@@ -3635,6 +3642,9 @@ fn render_impl(
     aliases: &[String],
     cache: &Cache,
 ) {
+    let traits = &cache.traits;
+    let trait_ = i.trait_did().map(|did| &traits[&did]);
+
     if render_mode == RenderMode::Normal {
         let id = cx.derive_id(match i.inner_impl().trait_ {
             Some(ref t) => {
@@ -3687,6 +3697,13 @@ fn render_impl(
             );
         }
         write!(w, "</h3>");
+
+        if trait_.is_some() {
+            if let Some(portability) = portability(&i.impl_item, Some(parent)) {
+                write!(w, "<div class=\"stability\">{}</div>", portability);
+            }
+        }
+
         if let Some(ref dox) = cx.shared.maybe_collapsed_doc_value(&i.impl_item) {
             let mut ids = cx.id_map.borrow_mut();
             write!(
@@ -3709,7 +3726,7 @@ fn render_impl(
         w: &mut Buffer,
         cx: &Context,
         item: &clean::Item,
-        parent: Option<&clean::Item>,
+        parent: &clean::Item,
         link: AssocItemLink<'_>,
         render_mode: RenderMode,
         is_default_item: bool,
@@ -3794,7 +3811,7 @@ fn render_impl(
                     if let Some(it) = t.items.iter().find(|i| i.name == item.name) {
                         // We need the stability of the item from the trait
                         // because impls can't have a stability.
-                        document_stability(w, cx, it, is_hidden, parent);
+                        document_stability(w, cx, it, is_hidden, Some(parent));
                         if item.doc_value().is_some() {
                             document_full(w, item, cx, "", is_hidden);
                         } else if show_def_docs {
@@ -3804,13 +3821,13 @@ fn render_impl(
                         }
                     }
                 } else {
-                    document_stability(w, cx, item, is_hidden, parent);
+                    document_stability(w, cx, item, is_hidden, Some(parent));
                     if show_def_docs {
                         document_full(w, item, cx, "", is_hidden);
                     }
                 }
             } else {
-                document_stability(w, cx, item, is_hidden, parent);
+                document_stability(w, cx, item, is_hidden, Some(parent));
                 if show_def_docs {
                     document_short(w, item, link, "", is_hidden);
                 }
@@ -3818,16 +3835,13 @@ fn render_impl(
         }
     }
 
-    let traits = &cache.traits;
-    let trait_ = i.trait_did().map(|did| &traits[&did]);
-
     write!(w, "<div class=\"impl-items\">");
     for trait_item in &i.inner_impl().items {
         doc_impl_item(
             w,
             cx,
             trait_item,
-            parent,
+            if trait_.is_some() { &i.impl_item } else { parent },
             link,
             render_mode,
             false,
@@ -3843,7 +3857,7 @@ fn render_impl(
         cx: &Context,
         t: &clean::Trait,
         i: &clean::Impl,
-        parent: Option<&clean::Item>,
+        parent: &clean::Item,
         render_mode: RenderMode,
         outer_version: Option<&str>,
         show_def_docs: bool,
@@ -3884,7 +3898,7 @@ fn render_impl(
                 cx,
                 t,
                 &i.inner_impl(),
-                parent,
+                &i.impl_item,
                 render_mode,
                 outer_version,
                 show_def_docs,