Rollup merge of #83337 - Manishearth:item-hide, r=GuillaumeGomez

rustdoc: Hide item contents, not items

This tweaks rustdoc to hide item contents instead of items, and only when there are too many of them.

This means that users will _always_ see the type parameters, and will _often_ see fields/etc as long as they are small. Traits have some heuristics for hiding only the methods or only the methods and the consts, since the associated types are super important.

I'm happy to play around with the heuristics here; we could potentially make it so that structs/enums/etc are always hidden but traits will try really hard to show type aliases.

This needs a test, but you can see it rendered at https://manishearth.net/sand/doc_render/bar/

<details>

<summary> Code example </summary>

```rust
pub struct PubStruct {
    pub a: usize,
    pub b: usize,
}

pub struct BigPubStruct {
    pub a: usize,
    pub b: usize,
    pub c: usize,
    pub d: usize,
    pub e: usize,
    pub f: usize,
}

pub union BigUnion {
    pub a: usize,
    pub b: usize,
    pub c: usize,
    pub d: usize,
    pub e: usize,
    pub f: usize,
}

pub union Union {
    pub a: usize,
    pub b: usize,
    pub c: usize,
}

pub struct PrivStruct {
    a: usize,
    b: usize,
}

pub enum Enum {
    A, B, C,
    D {
        a: u8,
        b: u8
    }
}

pub enum LargeEnum {
    A, B, C, D, E, F, G, H, I, J
}

pub trait Trait {
    type A;
    #[must_use]
    fn foo();
    fn bar();
}

pub trait GinormousTrait {
    type A;
    type B;
    type C;
    type D;
    type E;
    type F;
    const N: usize = 1;
    #[must_use]
    fn foo();
    fn bar();
}

pub trait HugeTrait {
    type A;
    const M: usize = 1;
    const N: usize = 1;
    const O: usize = 1;
    const P: usize = 1;
    const Q: usize = 1;
    #[must_use]
    fn foo();
    fn bar();
}

pub trait BigTrait {
    type A;
    #[must_use]
    fn foo();
    fn bar();
    fn baz();
    fn quux();
    fn frob();
    fn greeble();
}

#[macro_export]
macro_rules! foo {
    (a) => {a};
}
```

</details>

Fixes https://github.com/rust-lang/rust/issues/82114

11 files changed, 347 insertions, 154 deletions

diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index efd453f96b8..9886b5ceeed 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -43,7 +43,6 @@ use std::path::PathBuf;
 use std::str;
 use std::string::ToString;
 
-use itertools::Itertools;
 use rustc_ast_pretty::pprust;
 use rustc_attr::{Deprecation, StabilityLevel};
 use rustc_data_structures::fx::FxHashSet;
@@ -486,18 +485,7 @@ fn settings(root_path: &str, suffix: &str, themes: &[StylePath]) -> Result<Strin
             ],
         )
             .into(),
-        (
-            "Auto-hide item declarations",
-            vec![
-                ("auto-hide-struct", "Auto-hide structs declaration", true),
-                ("auto-hide-enum", "Auto-hide enums declaration", false),
-                ("auto-hide-union", "Auto-hide unions declaration", true),
-                ("auto-hide-trait", "Auto-hide traits declaration", true),
-                ("auto-hide-macro", "Auto-hide macros declaration", false),
-            ],
-        )
-            .into(),
-        ("auto-hide-attributes", "Auto-hide item attributes.", true).into(),
+        ("auto-hide-large-items", "Auto-hide item contents for large items.", true).into(),
         ("auto-hide-method-docs", "Auto-hide item methods' documentation", false).into(),
         ("auto-hide-trait-implementations", "Auto-hide trait implementation documentation", true)
             .into(),
@@ -947,19 +935,21 @@ fn render_assoc_item(
             + name.as_str().len()
             + generics_len;
 
-        let (indent, end_newline) = if parent == ItemType::Trait {
+        let (indent, indent_str, end_newline) = if parent == ItemType::Trait {
             header_len += 4;
-            (4, false)
+            let indent_str = "    ";
+            render_attributes_in_pre(w, meth, indent_str);
+            (4, indent_str, false)
         } else {
-            (0, true)
+            render_attributes_in_code(w, meth);
+            (0, "", true)
         };
-        render_attributes(w, meth, false);
         w.reserve(header_len + "<a href=\"\" class=\"fnname\">{".len() + "</a>".len());
         write!(
             w,
             "{}{}{}{}{}{}{}fn <a href=\"{href}\" class=\"fnname\">{name}</a>\
              {generics}{decl}{notable_traits}{where_clause}",
-            if parent == ItemType::Trait { "    " } else { "" },
+            indent_str,
             vis,
             constness,
             asyncness,
@@ -1015,35 +1005,33 @@ const ALLOWED_ATTRIBUTES: &[Symbol] = &[
     sym::non_exhaustive,
 ];
 
-// The `top` parameter is used when generating the item declaration to ensure it doesn't have a
-// left padding. For example:
-//
-// #[foo] <----- "top" attribute
-// struct Foo {
-//     #[bar] <---- not "top" attribute
-//     bar: usize,
-// }
-fn render_attributes(w: &mut Buffer, it: &clean::Item, top: bool) {
-    let attrs = it
-        .attrs
+fn attributes(it: &clean::Item) -> Vec<String> {
+    it.attrs
         .other_attrs
         .iter()
         .filter_map(|attr| {
             if ALLOWED_ATTRIBUTES.contains(&attr.name_or_empty()) {
-                Some(pprust::attribute_to_string(&attr))
+                Some(pprust::attribute_to_string(&attr).replace("\n", "").replace("  ", " "))
             } else {
                 None
             }
         })
-        .join("\n");
+        .collect()
+}
 
-    if !attrs.is_empty() {
-        write!(
-            w,
-            "<span class=\"docblock attributes{}\">{}</span>",
-            if top { " top-attr" } else { "" },
-            &attrs
-        );
+// When an attribute is rendered inside a `<pre>` tag, it is formatted using
+// a whitespace prefix and newline.
+fn render_attributes_in_pre(w: &mut Buffer, it: &clean::Item, prefix: &str) {
+    for a in attributes(it) {
+        write!(w, "{}{}\n", prefix, a);
+    }
+}
+
+// When an attribute is rendered inside a <code> tag, it is formatted using
+// a div to produce a newline after it.
+fn render_attributes_in_code(w: &mut Buffer, it: &clean::Item) {
+    for a in attributes(it) {
+        write!(w, "<div class=\"code-attribute\">{}</div>", a);
     }
 }
 
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index 0cdfe435b9c..ff9e4d031da 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -11,8 +11,8 @@ use rustc_span::symbol::{kw, sym, Symbol};
 
 use super::{
     collect_paths_for_type, document, ensure_trailing_slash, item_ty_to_strs, notable_traits_decl,
-    render_assoc_item, render_assoc_items, render_attributes, render_impl,
-    render_stability_since_raw, write_srclink, AssocItemLink, Context,
+    render_assoc_item, render_assoc_items, render_attributes_in_code, render_attributes_in_pre,
+    render_impl, render_stability_since_raw, write_srclink, AssocItemLink, Context,
 };
 use crate::clean::{self, GetDefId};
 use crate::formats::cache::Cache;
@@ -131,6 +131,26 @@ pub(super) fn print_item(cx: &Context<'_>, item: &clean::Item, buf: &mut Buffer)
     }
 }
 
+/// For large structs, enums, unions, etc, determine whether to hide their fields
+fn should_hide_fields(n_fields: usize) -> bool {
+    n_fields > 12
+}
+
+fn toggle_open(w: &mut Buffer, text: &str) {
+    write!(
+        w,
+        "<details class=\"rustdoc-toggle type-contents-toggle\">\
+            <summary class=\"hideme\">\
+                <span>Show {}</span>\
+            </summary>",
+        text
+    );
+}
+
+fn toggle_close(w: &mut Buffer) {
+    w.write_str("</details>");
+}
+
 fn item_module(w: &mut Buffer, cx: &Context<'_>, item: &clean::Item, items: &[clean::Item]) {
     document(w, cx, item, None);
 
@@ -377,7 +397,7 @@ fn item_function(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, f: &clean::
     )
     .len();
     w.write_str("<pre class=\"rust fn\">");
-    render_attributes(w, it, false);
+    render_attributes_in_pre(w, it, "");
     write!(
         w,
         "{vis}{constness}{asyncness}{unsafety}{abi}fn \
@@ -406,7 +426,7 @@ fn item_trait(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
     // Output the trait definition
     wrap_into_docblock(w, |w| {
         w.write_str("<pre class=\"rust trait\">");
-        render_attributes(w, it, true);
+        render_attributes_in_pre(w, it, "");
         write!(
             w,
             "{}{}{}trait {}{}{}",
@@ -429,10 +449,25 @@ fn item_trait(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
         } else {
             // FIXME: we should be using a derived_id for the Anchors here
             w.write_str("{\n");
+            let mut toggle = false;
+
+            // If there are too many associated types, hide _everything_
+            if should_hide_fields(types.len()) {
+                toggle = true;
+                toggle_open(w, "associated items");
+            }
             for t in &types {
                 render_assoc_item(w, t, AssocItemLink::Anchor(None), ItemType::Trait, cx);
                 w.write_str(";\n");
             }
+            // If there are too many associated constants, hide everything after them
+            // We also do this if the types + consts is large because otherwise we could
+            // render a bunch of types and _then_ a bunch of consts just because both were
+            // _just_ under the limit
+            if !toggle && should_hide_fields(types.len() + consts.len()) {
+                toggle = true;
+                toggle_open(w, "associated constants and methods");
+            }
             if !types.is_empty() && !consts.is_empty() {
                 w.write_str("\n");
             }
@@ -440,6 +475,10 @@ fn item_trait(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
                 render_assoc_item(w, t, AssocItemLink::Anchor(None), ItemType::Trait, cx);
                 w.write_str(";\n");
             }
+            if !toggle && should_hide_fields(required.len() + provided.len()) {
+                toggle = true;
+                toggle_open(w, "methods");
+            }
             if !consts.is_empty() && !required.is_empty() {
                 w.write_str("\n");
             }
@@ -470,6 +509,9 @@ fn item_trait(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
                     w.write_str("<div class=\"item-spacer\"></div>");
                 }
             }
+            if toggle {
+                toggle_close(w);
+            }
             w.write_str("}");
         }
         w.write_str("</pre>")
@@ -693,7 +735,7 @@ fn item_trait(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
 
 fn item_trait_alias(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::TraitAlias) {
     w.write_str("<pre class=\"rust trait-alias\">");
-    render_attributes(w, it, false);
+    render_attributes_in_pre(w, it, "");
     write!(
         w,
         "trait {}{}{} = {};</pre>",
@@ -714,7 +756,7 @@ fn item_trait_alias(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clea
 
 fn item_opaque_ty(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::OpaqueTy) {
     w.write_str("<pre class=\"rust opaque\">");
-    render_attributes(w, it, false);
+    render_attributes_in_pre(w, it, "");
     write!(
         w,
         "type {}{}{where_clause} = impl {bounds};</pre>",
@@ -735,7 +777,7 @@ fn item_opaque_ty(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean:
 
 fn item_typedef(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Typedef) {
     w.write_str("<pre class=\"rust typedef\">");
-    render_attributes(w, it, false);
+    render_attributes_in_pre(w, it, "");
     write!(
         w,
         "type {}{}{where_clause} = {type_};</pre>",
@@ -757,7 +799,7 @@ fn item_typedef(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::T
 fn item_union(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::Union) {
     wrap_into_docblock(w, |w| {
         w.write_str("<pre class=\"rust union\">");
-        render_attributes(w, it, true);
+        render_attributes_in_pre(w, it, "");
         render_union(w, it, Some(&s.generics), &s.fields, "", true, cx);
         w.write_str("</pre>")
     });
@@ -803,7 +845,7 @@ fn item_union(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::Uni
 fn item_enum(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, e: &clean::Enum) {
     wrap_into_docblock(w, |w| {
         w.write_str("<pre class=\"rust enum\">");
-        render_attributes(w, it, true);
+        render_attributes_in_pre(w, it, "");
         write!(
             w,
             "{}enum {}{}{}",
@@ -816,6 +858,10 @@ fn item_enum(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, e: &clean::Enum
             w.write_str(" {}");
         } else {
             w.write_str(" {\n");
+            let toggle = should_hide_fields(e.variants.len());
+            if toggle {
+                toggle_open(w, "variants");
+            }
             for v in &e.variants {
                 w.write_str("    ");
                 let name = v.name.as_ref().unwrap();
@@ -844,6 +890,9 @@ fn item_enum(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, e: &clean::Enum
             if e.variants_stripped {
                 w.write_str("    // some variants omitted\n");
             }
+            if toggle {
+                toggle_close(w);
+            }
             w.write_str("}");
         }
         w.write_str("</pre>")
@@ -976,7 +1025,7 @@ fn item_primitive(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item) {
 
 fn item_constant(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, c: &clean::Constant) {
     w.write_str("<pre class=\"rust const\">");
-    render_attributes(w, it, false);
+    render_attributes_in_code(w, it);
 
     write!(
         w,
@@ -1015,7 +1064,7 @@ fn item_constant(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, c: &clean::
 fn item_struct(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::Struct) {
     wrap_into_docblock(w, |w| {
         w.write_str("<pre class=\"rust struct\">");
-        render_attributes(w, it, true);
+        render_attributes_in_code(w, it);
         render_struct(w, it, Some(&s.generics), s.struct_type, &s.fields, "", true, cx);
         w.write_str("</pre>")
     });
@@ -1064,7 +1113,7 @@ fn item_struct(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::St
 
 fn item_static(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::Static) {
     w.write_str("<pre class=\"rust static\">");
-    render_attributes(w, it, false);
+    render_attributes_in_code(w, it);
     write!(
         w,
         "{vis}static {mutability}{name}: {typ}</pre>",
@@ -1078,7 +1127,7 @@ fn item_static(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::St
 
 fn item_foreign_type(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item) {
     w.write_str("<pre class=\"rust foreigntype\">extern {\n");
-    render_attributes(w, it, false);
+    render_attributes_in_code(w, it);
     write!(
         w,
         "    {}type {};\n}}</pre>",
@@ -1171,7 +1220,7 @@ fn wrap_into_docblock<F>(w: &mut Buffer, f: F)
 where
     F: FnOnce(&mut Buffer),
 {
-    w.write_str("<div class=\"docblock type-decl hidden-by-usual-hider\">");
+    w.write_str("<div class=\"docblock type-decl\">");
     f(w);
     w.write_str("</div>")
 }
@@ -1261,6 +1310,13 @@ fn render_union(
     }
 
     write!(w, " {{\n{}", tab);
+    let count_fields =
+        fields.iter().filter(|f| matches!(*f.kind, clean::StructFieldItem(..))).count();
+    let toggle = should_hide_fields(count_fields);
+    if toggle {
+        toggle_open(w, "fields");
+    }
+
     for field in fields {
         if let clean::StructFieldItem(ref ty) = *field.kind {
             write!(
@@ -1277,6 +1333,9 @@ fn render_union(
     if it.has_stripped_fields().unwrap() {
         write!(w, "    // some fields omitted\n{}", tab);
     }
+    if toggle {
+        toggle_close(w);
+    }
     w.write_str("}");
 }
 
@@ -1305,8 +1364,14 @@ fn render_struct(
             if let Some(g) = g {
                 write!(w, "{}", print_where_clause(g, cx.cache(), cx.tcx(), 0, true),)
             }
-            let mut has_visible_fields = false;
             w.write_str(" {");
+            let count_fields =
+                fields.iter().filter(|f| matches!(*f.kind, clean::StructFieldItem(..))).count();
+            let has_visible_fields = count_fields > 0;
+            let toggle = should_hide_fields(count_fields);
+            if toggle {
+                toggle_open(w, "fields");
+            }
             for field in fields {
                 if let clean::StructFieldItem(ref ty) = *field.kind {
                     write!(
@@ -1317,7 +1382,6 @@ fn render_struct(
                         field.name.as_ref().unwrap(),
                         ty.print(cx.cache(), cx.tcx()),
                     );
-                    has_visible_fields = true;
                 }
             }
 
@@ -1331,6 +1395,9 @@ fn render_struct(
                 // `{ /* fields omitted */ }` to save space.
                 write!(w, " /* fields omitted */ ");
             }
+            if toggle {
+                toggle_close(w);
+            }
             w.write_str("}");
         }
         CtorKind::Fn => {
diff --git a/src/librustdoc/html/static/main.js b/src/librustdoc/html/static/main.js
index 80dc6b923f6..d71cc15a457 100644
--- a/src/librustdoc/html/static/main.js
+++ b/src/librustdoc/html/static/main.js
@@ -2316,6 +2316,9 @@ function hideThemeButtonState() {
         if (hasClass(innerToggle, "will-expand")) {
             updateLocalStorage("rustdoc-collapse", "false");
             removeClass(innerToggle, "will-expand");
+            onEachLazy(document.getElementsByTagName("details"), function(e) {
+                e.open = true;
+            });
             onEveryMatchingChild(innerToggle, "inner", function(e) {
                 e.innerHTML = labelForToggleButton(false);
             });
@@ -2328,6 +2331,9 @@ function hideThemeButtonState() {
         } else {
             updateLocalStorage("rustdoc-collapse", "true");
             addClass(innerToggle, "will-expand");
+            onEachLazy(document.getElementsByTagName("details"), function(e) {
+                e.open = false;
+            });
             onEveryMatchingChild(innerToggle, "inner", function(e) {
                 var parent = e.parentNode;
                 var superParent = null;
@@ -2569,6 +2575,7 @@ function hideThemeButtonState() {
         var toggle = createSimpleToggle(false);
         var hideMethodDocs = getSettingValue("auto-hide-method-docs") === "true";
         var hideImplementors = getSettingValue("auto-collapse-implementors") !== "false";
+        var hideLargeItemContents = getSettingValue("auto-hide-large-items") !== "false";
 
         var func = function(e) {
             var next = e.nextElementSibling;
@@ -2615,6 +2622,14 @@ function hideThemeButtonState() {
         onEachLazy(document.getElementsByClassName("associatedconstant"), func);
         onEachLazy(document.getElementsByClassName("impl"), funcImpl);
         var impl_call = function() {};
+        // Large items are hidden by default in the HTML. If the setting overrides that, show 'em.
+        if (!hideLargeItemContents) {
+            onEachLazy(document.getElementsByTagName("details"), function (e) {
+                if (hasClass(e, "type-contents-toggle")) {
+                    e.open = true;
+                }
+            });
+        }
         if (hideMethodDocs === true) {
             impl_call = function(e, newToggle) {
                 if (e.id.match(/^impl(?:-\d+)?$/) === null) {
@@ -2683,18 +2698,7 @@ function hideThemeButtonState() {
                 });
             }
         }
-        var showItemDeclarations = getSettingValue("auto-hide-" + className);
-        if (showItemDeclarations === null) {
-            if (className === "enum" || className === "macro") {
-                showItemDeclarations = "false";
-            } else if (className === "struct" || className === "union" || className === "trait") {
-                showItemDeclarations = "true";
-            } else {
-                // In case we found an unknown type, we just use the "parent" value.
-                showItemDeclarations = getSettingValue("auto-hide-declarations");
-            }
-        }
-        showItemDeclarations = showItemDeclarations === "false";
+
         function buildToggleWrapper(e) {
             if (hasClass(e, "autohide")) {
                 var wrap = e.previousElementSibling;
@@ -2721,11 +2725,8 @@ function hideThemeButtonState() {
                 var extraClass;
 
                 if (hasClass(e, "type-decl")) {
-                    fontSize = "20px";
-                    otherMessage = "&nbsp;Show&nbsp;declaration";
-                    if (showItemDeclarations === false) {
-                        extraClass = "collapsed";
-                    }
+                    // We do something special for these
+                    return;
                 } else if (hasClass(e, "sub-variant")) {
                     otherMessage = "&nbsp;Show&nbsp;fields";
                 } else if (hasClass(e, "non-exhaustive")) {
@@ -2750,11 +2751,8 @@ function hideThemeButtonState() {
                         otherMessage,
                         fontSize,
                         extraClass,
-                        hasClass(e, "type-decl") === false || showItemDeclarations === true),
+                        true),
                     e);
-                if (hasClass(e, "type-decl") === true && showItemDeclarations === true) {
-                    collapseDocs(e.previousSibling.childNodes[0], "toggle");
-                }
                 if (hasClass(e, "non-exhaustive") === true) {
                     collapseDocs(e.previousSibling.childNodes[0], "toggle");
                 }
@@ -2772,38 +2770,6 @@ function hideThemeButtonState() {
         }
     }());
 
-    function createToggleWrapper(tog) {
-        var span = document.createElement("span");
-        span.className = "toggle-label";
-        span.style.display = "none";
-        span.innerHTML = "&nbsp;Expand&nbsp;attributes";
-        tog.appendChild(span);
-
-        var wrapper = document.createElement("div");
-        wrapper.className = "toggle-wrapper toggle-attributes";
-        wrapper.appendChild(tog);
-        return wrapper;
-    }
-
-    (function() {
-        // To avoid checking on "rustdoc-item-attributes" value on every loop...
-        var itemAttributesFunc = function() {};
-        if (getSettingValue("auto-hide-attributes") !== "false") {
-            itemAttributesFunc = function(x) {
-                collapseDocs(x.previousSibling.childNodes[0], "toggle");
-            };
-        }
-        var attributesToggle = createToggleWrapper(createSimpleToggle(false));
-        onEachLazy(main.getElementsByClassName("attributes"), function(i_e) {
-            var attr_tog = attributesToggle.cloneNode(true);
-            if (hasClass(i_e, "top-attr") === true) {
-                addClass(attr_tog, "top-attr");
-            }
-            i_e.parentNode.insertBefore(attr_tog, i_e);
-            itemAttributesFunc(i_e);
-        });
-    }());
-
     (function() {
         // To avoid checking on "rustdoc-line-numbers" value on every loop...
         var lineNumbersFunc = function() {};
diff --git a/src/librustdoc/html/static/rustdoc.css b/src/librustdoc/html/static/rustdoc.css
index 705ae17f3eb..427564cd779 100644
--- a/src/librustdoc/html/static/rustdoc.css
+++ b/src/librustdoc/html/static/rustdoc.css
@@ -1056,12 +1056,6 @@ h3 > .collapse-toggle, h4 > .collapse-toggle {
 	margin-top: 3px;
 }
 
-.enum > .toggle-wrapper + .docblock, .struct > .toggle-wrapper + .docblock {
-	margin-left: 30px;
-	margin-bottom: 20px;
-	margin-top: 5px;
-}
-
 .docblock > .section-header:first-child {
 	margin-left: 15px;
 	margin-top: 0;
@@ -1071,30 +1065,10 @@ h3 > .collapse-toggle, h4 > .collapse-toggle {
 	left: -10px;
 }
 
-.enum > .collapsed, .struct > .collapsed {
-	margin-bottom: 25px;
-}
-
 #main > .variant, #main > .structfield {
 	display: block;
 }
 
-.attributes {
-	display: block;
-	margin-top: 0px !important;
-	margin-right: 0px;
-	margin-bottom: 0px !important;
-	margin-left: 30px;
-}
-.toggle-attributes.collapsed {
-	margin-bottom: 0;
-}
-.impl-items > .toggle-attributes {
-	margin-left: 20px;
-}
-.impl-items .attributes {
-	font-weight: 500;
-}
 
 :target > code {
 	opacity: 1;
@@ -1781,16 +1755,54 @@ div.name.expand::before {
 	top: 2px;
 }
 
-/* This part is to fix the "Expand attributes" part in the type declaration. */
-.type-decl > pre > .toggle-wrapper.toggle-attributes.top-attr {
-	margin-left: 0 !important;
+/* The hideme class is used on summary tags that contain a span with
+	placeholder text shown only when the toggle is closed. For instance,
+	"Expand description" or "Show methods". */
+details.rustdoc-toggle > summary.hideme {
+	cursor: pointer;
+}
+
+details.rustdoc-toggle > summary::-webkit-details-marker {
+	display: none;
+}
+
+details.rustdoc-toggle > summary.hideme > span {
+	margin-left: 9px;
 }
-.type-decl > pre > .docblock.attributes.top-attr {
-	margin-left: 1.8em !important;
+
+details.rustdoc-toggle > summary::before {
+	content: "[+]";
+	font-weight: 300;
+	font-size: 0.8em;
+	letter-spacing: 1px;
+}
+
+details.rustdoc-toggle > summary.hideme::before {
+	position: relative;
 }
-.type-decl > pre > .toggle-attributes {
-	margin-left: 2.2em;
+
+details.rustdoc-toggle > summary:not(.hideme)::before {
+	float: left;
 }
-.type-decl > pre > .docblock.attributes {
-	margin-left: 4em;
+
+/* When a "hideme" summary is open and the "Expand description" or "Show
+	methods" text is hidden, we want the [-] toggle that remains to not
+	affect the layout of the items to its right. To do that, we use
+	absolute positioning. Note that we also set position: relative
+	on the parent <details> to make this work properly. */
+details.rustdoc-toggle[open] > summary.hideme {
+	position: absolute;
+}
+
+details.rustdoc-toggle[open] {
+	position: relative;
+}
+
+details.rustdoc-toggle[open] > summary.hideme > span {
+	display: none;
+}
+
+details.rustdoc-toggle[open] > summary::before {
+	content: "[−]";
+	display: inline;
 }
diff --git a/src/librustdoc/html/static/storage.js b/src/librustdoc/html/static/storage.js
index c68128516d2..2ed87fdedae 100644
--- a/src/librustdoc/html/static/storage.js
+++ b/src/librustdoc/html/static/storage.js
@@ -1,6 +1,5 @@
 // From rust:
 /* global resourcesSuffix */
-
 var darkThemes = ["dark", "ayu"];
 window.currentTheme = document.getElementById("themeStyle");
 window.mainTheme = document.getElementById("mainThemeStyle");
diff --git a/src/librustdoc/html/static/themes/ayu.css b/src/librustdoc/html/static/themes/ayu.css
index b24f4035ca8..5f6f3d66e57 100644
--- a/src/librustdoc/html/static/themes/ayu.css
+++ b/src/librustdoc/html/static/themes/ayu.css
@@ -224,7 +224,9 @@ a {
 	color: #39AFD7;
 }
 
-.collapse-toggle {
+.collapse-toggle,
+details.rustdoc-toggle > summary.hideme > span,
+details.rustdoc-toggle > summary::before {
 	color: #999;
 }
 
diff --git a/src/librustdoc/html/static/themes/dark.css b/src/librustdoc/html/static/themes/dark.css
index e863ed03f51..2ce6cf4cc45 100644
--- a/src/librustdoc/html/static/themes/dark.css
+++ b/src/librustdoc/html/static/themes/dark.css
@@ -186,7 +186,9 @@ a.test-arrow {
 	color: #dedede;
 }
 
-.collapse-toggle {
+.collapse-toggle,
+details.rustdoc-toggle > summary.hideme > span,
+details.rustdoc-toggle > summary::before {
 	color: #999;
 }
 
diff --git a/src/librustdoc/html/static/themes/light.css b/src/librustdoc/html/static/themes/light.css
index 9335dd96d29..31b3562cfcb 100644
--- a/src/librustdoc/html/static/themes/light.css
+++ b/src/librustdoc/html/static/themes/light.css
@@ -184,7 +184,9 @@ a.test-arrow {
 	color: #f5f5f5;
 }
 
-.collapse-toggle {
+.collapse-toggle,
+details.rustdoc-toggle > summary.hideme > span,
+details.rustdoc-toggle > summary::before {
 	color: #999;
 }
 
diff --git a/src/test/rustdoc/attributes.rs b/src/test/rustdoc/attributes.rs
index 54c5939f908..51cd4a6cbfd 100644
--- a/src/test/rustdoc/attributes.rs
+++ b/src/test/rustdoc/attributes.rs
@@ -1,21 +1,21 @@
 #![crate_name = "foo"]
 
-// @has foo/fn.f.html '//*[@class="docblock attributes"]' '#[no_mangle]'
+// @has foo/fn.f.html '//*[@class="rust fn"]' '#[no_mangle]'
 #[no_mangle]
 pub extern "C" fn f() {}
 
-// @has foo/fn.g.html '//*[@class="docblock attributes"]' '#[export_name = "bar"]'
+// @has foo/fn.g.html '//*[@class="rust fn"]' '#[export_name = "bar"]'
 #[export_name = "bar"]
 pub extern "C" fn g() {}
 
-// @matches foo/enum.Foo.html '//*[@class="docblock attributes top-attr"]' \
-//      '(?m)\A#\[repr\(i64\)\]\n#\[must_use\]\Z'
+// @matches foo/enum.Foo.html '//*[@class="rust enum"]' \
+//      '#\[repr\(i64\)\]\n#\[must_use\]'
 #[repr(i64)]
 #[must_use]
 pub enum Foo {
     Bar,
 }
 
-// @has foo/struct.Repr.html '//*[@class="docblock attributes top-attr"]' '#[repr(C, align(8))]'
+// @has foo/struct.Repr.html '//*[@class="docblock type-decl"]' '#[repr(C, align(8))]'
 #[repr(C, align(8))]
 pub struct Repr;
diff --git a/src/test/rustdoc/item-hide-threshold.rs b/src/test/rustdoc/item-hide-threshold.rs
new file mode 100644
index 00000000000..616eef95662
--- /dev/null
+++ b/src/test/rustdoc/item-hide-threshold.rs
@@ -0,0 +1,155 @@
+#![allow(unused)]
+
+// @has 'item_hide_threshold/struct.PubStruct.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 0
+pub struct PubStruct {
+    pub a: usize,
+    pub b: usize,
+}
+
+// @has 'item_hide_threshold/struct.BigPubStruct.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 1
+// @has - '//details[@class="rustdoc-toggle type-contents-toggle"]' 'Show fields'
+pub struct BigPubStruct {
+    pub a: usize,
+    pub b: usize,
+    pub c: usize,
+    pub d: usize,
+    pub e: usize,
+    pub f: usize,
+    pub g: usize,
+    pub h: usize,
+    pub i: usize,
+    pub j: usize,
+    pub k: usize,
+    pub l: usize,
+    pub m: usize,
+}
+
+// @has 'item_hide_threshold/union.BigUnion.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 1
+// @has - '//details[@class="rustdoc-toggle type-contents-toggle"]' 'Show fields'
+pub union BigUnion {
+    pub a: usize,
+    pub b: usize,
+    pub c: usize,
+    pub d: usize,
+    pub e: usize,
+    pub f: usize,
+    pub g: usize,
+    pub h: usize,
+    pub i: usize,
+    pub j: usize,
+    pub k: usize,
+    pub l: usize,
+    pub m: usize,
+}
+
+// @has 'item_hide_threshold/union.Union.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 0
+pub union Union {
+    pub a: usize,
+    pub b: usize,
+    pub c: usize,
+}
+
+// @has 'item_hide_threshold/struct.PrivStruct.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 0
+// @has - '//div[@class="docblock type-decl"]' 'fields omitted'
+pub struct PrivStruct {
+    a: usize,
+    b: usize,
+}
+
+// @has 'item_hide_threshold/enum.Enum.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 0
+pub enum Enum {
+    A, B, C,
+    D {
+        a: u8,
+        b: u8
+    }
+}
+
+// @has 'item_hide_threshold/enum.LargeEnum.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 1
+// @has - '//details[@class="rustdoc-toggle type-contents-toggle"]' 'Show variants'
+pub enum LargeEnum {
+    A, B, C, D, E, F(u8), G, H, I, J, K, L, M
+}
+
+// @has 'item_hide_threshold/trait.Trait.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 0
+pub trait Trait {
+    type A;
+    #[must_use]
+    fn foo();
+    fn bar();
+}
+
+// @has 'item_hide_threshold/trait.GinormousTrait.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 1
+// @has - '//details[@class="rustdoc-toggle type-contents-toggle"]' 'Show associated items'
+pub trait GinormousTrait {
+    type A;
+    type B;
+    type C;
+    type D;
+    type E;
+    type F;
+    type G;
+    type H;
+    type I;
+    type J;
+    type K;
+    type L;
+    type M;
+    const N: usize = 1;
+    #[must_use]
+    fn foo();
+    fn bar();
+}
+
+// @has 'item_hide_threshold/trait.HugeTrait.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 1
+// @has - '//details[@class="rustdoc-toggle type-contents-toggle"]' 'Show associated constants and methods'
+pub trait HugeTrait {
+    type A;
+    const M: usize = 1;
+    const N: usize = 1;
+    const O: usize = 1;
+    const P: usize = 1;
+    const Q: usize = 1;
+    const R: usize = 1;
+    const S: usize = 1;
+    const T: usize = 1;
+    const U: usize = 1;
+    const V: usize = 1;
+    const W: usize = 1;
+    const X: usize = 1;
+    #[must_use]
+    fn foo();
+    fn bar();
+}
+
+// @has 'item_hide_threshold/trait.BigTrait.html'
+// @count - '//details[@class="rustdoc-toggle type-contents-toggle"]' 1
+// @has - '//details[@class="rustdoc-toggle type-contents-toggle"]' 'Show methods'
+pub trait BigTrait {
+    type A;
+    #[must_use]
+    fn foo();
+    fn bar();
+    fn baz();
+    fn quux();
+    fn frob();
+    fn greeble();
+    fn blap();
+    fn whoop();
+    fn pow();
+    fn bang();
+    fn oomph();
+    fn argh();
+    fn wap();
+    fn ouch();
+}
diff --git a/src/test/rustdoc/trait-attributes.rs b/src/test/rustdoc/trait-attributes.rs
index 2a103509ae1..2bb24a82193 100644
--- a/src/test/rustdoc/trait-attributes.rs
+++ b/src/test/rustdoc/trait-attributes.rs
@@ -2,7 +2,7 @@
 
 
 pub trait Foo {
-    // @has foo/trait.Foo.html '//h3[@id="tymethod.foo"]//span[@class="docblock attributes"]' '#[must_use]'
+    // @has foo/trait.Foo.html '//h3[@id="tymethod.foo"]//div[@class="code-attribute"]' '#[must_use]'
     #[must_use]
     fn foo();
 }
@@ -11,11 +11,11 @@ pub trait Foo {
 pub struct Bar;
 
 impl Bar {
-    // @has foo/struct.Bar.html '//h4[@id="method.bar"]//span[@class="docblock attributes"]' '#[must_use]'
+    // @has foo/struct.Bar.html '//h4[@id="method.bar"]//div[@class="code-attribute"]' '#[must_use]'
     #[must_use]
     pub fn bar() {}
 
-    // @has foo/struct.Bar.html '//h4[@id="method.bar2"]//span[@class="docblock attributes"]' '#[must_use]'
+    // @has foo/struct.Bar.html '//h4[@id="method.bar2"]//div[@class="code-attribute"]' '#[must_use]'
     #[must_use]
     pub fn bar2() {}
 }