src/librustdoc/html/render/print_item.rs

   1 use clean::AttributesExt;
   2
   3 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
   4 use rustc_hir as hir;
   5 use rustc_hir::def::CtorKind;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_middle::middle::stability;
   8 use rustc_middle::span_bug;
   9 use rustc_middle::ty::layout::LayoutError;
  10 use rustc_middle::ty::{Adt, TyCtxt};
  11 use rustc_span::hygiene::MacroKind;
  12 use rustc_span::symbol::{kw, sym, Symbol};
  13 use rustc_target::abi::{Layout, Primitive, TagEncoding, Variants};
  14 use std::cmp::Ordering;
  15 use std::fmt;
  16 use std::rc::Rc;
  17
  18 use super::{
  19     collect_paths_for_type, document, ensure_trailing_slash, item_ty_to_section,
  20     notable_traits_decl, render_assoc_item, render_assoc_items, render_attributes_in_code,
  21     render_attributes_in_pre, render_impl, render_stability_since_raw, write_srclink,
  22     AssocItemLink, Context, ImplRenderingParameters,
  23 };
  24 use crate::clean;
  25 use crate::config::ModuleSorting;
  26 use crate::formats::item_type::ItemType;
  27 use crate::formats::{AssocItemRender, Impl, RenderMode};
  28 use crate::html::escape::Escape;
  29 use crate::html::format::{
  30     join_with_double_colon, print_abi_with_space, print_constness_with_space, print_where_clause,
  31     Buffer, Ending, PrintWithSpace,
  32 };
  33 use crate::html::highlight;
  34 use crate::html::layout::Page;
  35 use crate::html::markdown::{HeadingOffset, MarkdownSummaryLine};
  36 use crate::html::url_parts_builder::UrlPartsBuilder;
  37
  38 use askama::Template;
  39 use itertools::Itertools;
  40
  41 const ITEM_TABLE_OPEN: &str = "<div class=\"item-table\">";
  42 const ITEM_TABLE_CLOSE: &str = "</div>";
  43 const ITEM_TABLE_ROW_OPEN: &str = "<div class=\"item-row\">";
  44 const ITEM_TABLE_ROW_CLOSE: &str = "</div>";
  45
  46 // A component in a `use` path, like `string` in std::string::ToString
  47 struct PathComponent {
  48     path: String,
  49     name: Symbol,
  50 }
  51
  52 #[derive(Template)]
  53 #[template(path = "print_item.html")]
  54 struct ItemVars<'a> {
  55     page: &'a Page<'a>,
  56     static_root_path: &'a str,
  57     typ: &'a str,
  58     name: &'a str,
  59     item_type: &'a str,
  60     path_components: Vec<PathComponent>,
  61     stability_since_raw: &'a str,
  62     src_href: Option<&'a str>,
  63 }
  64
  65 /// Calls `print_where_clause` and returns `true` if a `where` clause was generated.
  66 fn print_where_clause_and_check<'a, 'tcx: 'a>(
  67     buffer: &mut Buffer,
  68     gens: &'a clean::Generics,
  69     cx: &'a Context<'tcx>,
  70 ) -> bool {
  71     let len_before = buffer.len();
  72     write!(buffer, "{}", print_where_clause(gens, cx, 0, Ending::Newline));
  73     len_before != buffer.len()
  74 }
  75
  76 pub(super) fn print_item(
  77     cx: &mut Context<'_>,
  78     item: &clean::Item,
  79     buf: &mut Buffer,
  80     page: &Page<'_>,
  81 ) {
  82     debug_assert!(!item.is_stripped());
  83     let typ = match *item.kind {
  84         clean::ModuleItem(_) => {
  85             if item.is_crate() {
  86                 "Crate "
  87             } else {
  88                 "Module "
  89             }
  90         }
  91         clean::FunctionItem(..) | clean::ForeignFunctionItem(..) => "Function ",
  92         clean::TraitItem(..) => "Trait ",
  93         clean::StructItem(..) => "Struct ",
  94         clean::UnionItem(..) => "Union ",
  95         clean::EnumItem(..) => "Enum ",
  96         clean::TypedefItem(..) => "Type Definition ",
  97         clean::MacroItem(..) => "Macro ",
  98         clean::ProcMacroItem(ref mac) => match mac.kind {
  99             MacroKind::Bang => "Macro ",
 100             MacroKind::Attr => "Attribute Macro ",
 101             MacroKind::Derive => "Derive Macro ",
 102         },
 103         clean::PrimitiveItem(..) => "Primitive Type ",
 104         clean::StaticItem(..) | clean::ForeignStaticItem(..) => "Static ",
 105         clean::ConstantItem(..) => "Constant ",
 106         clean::ForeignTypeItem => "Foreign Type ",
 107         clean::KeywordItem => "Keyword ",
 108         clean::OpaqueTyItem(..) => "Opaque Type ",
 109         clean::TraitAliasItem(..) => "Trait Alias ",
 110         _ => {
 111             // We don't generate pages for any other type.
 112             unreachable!();
 113         }
 114     };
 115     let mut stability_since_raw = Buffer::new();
 116     render_stability_since_raw(
 117         &mut stability_since_raw,
 118         item.stable_since(cx.tcx()),
 119         item.const_stability(cx.tcx()),
 120         None,
 121         None,
 122     );
 123     let stability_since_raw: String = stability_since_raw.into_inner();
 124
 125     // Write source tag
 126     //
 127     // When this item is part of a `crate use` in a downstream crate, the
 128     // source link in the downstream documentation will actually come back to
 129     // this page, and this link will be auto-clicked. The `id` attribute is
 130     // used to find the link to auto-click.
 131     let src_href =
 132         if cx.include_sources && !item.is_primitive() { cx.src_href(item) } else { None };
 133
 134     let path_components = if item.is_primitive() || item.is_keyword() {
 135         vec![]
 136     } else {
 137         let cur = &cx.current;
 138         let amt = if item.is_mod() { cur.len() - 1 } else { cur.len() };
 139         cur.iter()
 140             .enumerate()
 141             .take(amt)
 142             .map(|(i, component)| PathComponent {
 143                 path: "../".repeat(cur.len() - i - 1),
 144                 name: *component,
 145             })
 146             .collect()
 147     };
 148
 149     let item_vars = ItemVars {
 150         page,
 151         static_root_path: page.get_static_root_path(),
 152         typ,
 153         name: item.name.as_ref().unwrap().as_str(),
 154         item_type: &item.type_().to_string(),
 155         path_components,
 156         stability_since_raw: &stability_since_raw,
 157         src_href: src_href.as_deref(),
 158     };
 159
 160     item_vars.render_into(buf).unwrap();
 161
 162     match &*item.kind {
 163         clean::ModuleItem(ref m) => item_module(buf, cx, item, &m.items),
 164         clean::FunctionItem(ref f) | clean::ForeignFunctionItem(ref f) => {
 165             item_function(buf, cx, item, f)
 166         }
 167         clean::TraitItem(ref t) => item_trait(buf, cx, item, t),
 168         clean::StructItem(ref s) => item_struct(buf, cx, item, s),
 169         clean::UnionItem(ref s) => item_union(buf, cx, item, s),
 170         clean::EnumItem(ref e) => item_enum(buf, cx, item, e),
 171         clean::TypedefItem(ref t) => item_typedef(buf, cx, item, t),
 172         clean::MacroItem(ref m) => item_macro(buf, cx, item, m),
 173         clean::ProcMacroItem(ref m) => item_proc_macro(buf, cx, item, m),
 174         clean::PrimitiveItem(_) => item_primitive(buf, cx, item),
 175         clean::StaticItem(ref i) | clean::ForeignStaticItem(ref i) => item_static(buf, cx, item, i),
 176         clean::ConstantItem(ref c) => item_constant(buf, cx, item, c),
 177         clean::ForeignTypeItem => item_foreign_type(buf, cx, item),
 178         clean::KeywordItem => item_keyword(buf, cx, item),
 179         clean::OpaqueTyItem(ref e) => item_opaque_ty(buf, cx, item, e),
 180         clean::TraitAliasItem(ref ta) => item_trait_alias(buf, cx, item, ta),
 181         _ => {
 182             // We don't generate pages for any other type.
 183             unreachable!();
 184         }
 185     }
 186 }
 187
 188 /// For large structs, enums, unions, etc, determine whether to hide their fields
 189 fn should_hide_fields(n_fields: usize) -> bool {
 190     n_fields > 12
 191 }
 192
 193 fn toggle_open(w: &mut Buffer, text: impl fmt::Display) {
 194     write!(
 195         w,
 196         "<details class=\"rustdoc-toggle type-contents-toggle\">\
 197             <summary class=\"hideme\">\
 198                 <span>Show {}</span>\
 199             </summary>",
 200         text
 201     );
 202 }
 203
 204 fn toggle_close(w: &mut Buffer) {
 205     w.write_str("</details>");
 206 }
 207
 208 fn item_module(w: &mut Buffer, cx: &mut Context<'_>, item: &clean::Item, items: &[clean::Item]) {
 209     document(w, cx, item, None, HeadingOffset::H2);
 210
 211     let mut indices = (0..items.len()).filter(|i| !items[*i].is_stripped()).collect::<Vec<usize>>();
 212
 213     // the order of item types in the listing
 214     fn reorder(ty: ItemType) -> u8 {
 215         match ty {
 216             ItemType::ExternCrate => 0,
 217             ItemType::Import => 1,
 218             ItemType::Primitive => 2,
 219             ItemType::Module => 3,
 220             ItemType::Macro => 4,
 221             ItemType::Struct => 5,
 222             ItemType::Enum => 6,
 223             ItemType::Constant => 7,
 224             ItemType::Static => 8,
 225             ItemType::Trait => 9,
 226             ItemType::Function => 10,
 227             ItemType::Typedef => 12,
 228             ItemType::Union => 13,
 229             _ => 14 + ty as u8,
 230         }
 231     }
 232
 233     fn cmp(
 234         i1: &clean::Item,
 235         i2: &clean::Item,
 236         idx1: usize,
 237         idx2: usize,
 238         tcx: TyCtxt<'_>,
 239     ) -> Ordering {
 240         let ty1 = i1.type_();
 241         let ty2 = i2.type_();
 242         if item_ty_to_section(ty1) != item_ty_to_section(ty2)
 243             || (ty1 != ty2 && (ty1 == ItemType::ExternCrate || ty2 == ItemType::ExternCrate))
 244         {
 245             return (reorder(ty1), idx1).cmp(&(reorder(ty2), idx2));
 246         }
 247         let s1 = i1.stability(tcx).as_ref().map(|s| s.level);
 248         let s2 = i2.stability(tcx).as_ref().map(|s| s.level);
 249         if let (Some(a), Some(b)) = (s1, s2) {
 250             match (a.is_stable(), b.is_stable()) {
 251                 (true, true) | (false, false) => {}
 252                 (false, true) => return Ordering::Less,
 253                 (true, false) => return Ordering::Greater,
 254             }
 255         }
 256         let lhs = i1.name.unwrap_or(kw::Empty);
 257         let rhs = i2.name.unwrap_or(kw::Empty);
 258         compare_names(lhs.as_str(), rhs.as_str())
 259     }
 260
 261     match cx.shared.module_sorting {
 262         ModuleSorting::Alphabetical => {
 263             indices.sort_by(|&i1, &i2| cmp(&items[i1], &items[i2], i1, i2, cx.tcx()));
 264         }
 265         ModuleSorting::DeclarationOrder => {}
 266     }
 267     // This call is to remove re-export duplicates in cases such as:
 268     //
 269     // ```
 270     // pub(crate) mod foo {
 271     //     pub(crate) mod bar {
 272     //         pub(crate) trait Double { fn foo(); }
 273     //     }
 274     // }
 275     //
 276     // pub(crate) use foo::bar::*;
 277     // pub(crate) use foo::*;
 278     // ```
 279     //
 280     // `Double` will appear twice in the generated docs.
 281     //
 282     // FIXME: This code is quite ugly and could be improved. Small issue: DefId
 283     // can be identical even if the elements are different (mostly in imports).
 284     // So in case this is an import, we keep everything by adding a "unique id"
 285     // (which is the position in the vector).
 286     indices.dedup_by_key(|i| {
 287         (
 288             items[*i].item_id,
 289             if items[*i].name.is_some() { Some(full_path(cx, &items[*i])) } else { None },
 290             items[*i].type_(),
 291             if items[*i].is_import() { *i } else { 0 },
 292         )
 293     });
 294
 295     debug!("{:?}", indices);
 296     let mut last_section = None;
 297
 298     for &idx in &indices {
 299         let myitem = &items[idx];
 300         if myitem.is_stripped() {
 301             continue;
 302         }
 303
 304         let my_section = item_ty_to_section(myitem.type_());
 305         if Some(my_section) != last_section {
 306             if last_section.is_some() {
 307                 w.write_str(ITEM_TABLE_CLOSE);
 308             }
 309             last_section = Some(my_section);
 310             write!(
 311                 w,
 312                 "<h2 id=\"{id}\" class=\"small-section-header\">\
 313                     <a href=\"#{id}\">{name}</a>\
 314                  </h2>{}",
 315                 ITEM_TABLE_OPEN,
 316                 id = cx.derive_id(my_section.id().to_owned()),
 317                 name = my_section.name(),
 318             );
 319         }
 320
 321         match *myitem.kind {
 322             clean::ExternCrateItem { ref src } => {
 323                 use crate::html::format::anchor;
 324
 325                 w.write_str(ITEM_TABLE_ROW_OPEN);
 326                 match *src {
 327                     Some(src) => write!(
 328                         w,
 329                         "<div class=\"item-left\"><code>{}extern crate {} as {};",
 330                         myitem.visibility.print_with_space(myitem.item_id, cx),
 331                         anchor(myitem.item_id.expect_def_id(), src, cx),
 332                         myitem.name.unwrap(),
 333                     ),
 334                     None => write!(
 335                         w,
 336                         "<div class=\"item-left\"><code>{}extern crate {};",
 337                         myitem.visibility.print_with_space(myitem.item_id, cx),
 338                         anchor(myitem.item_id.expect_def_id(), myitem.name.unwrap(), cx),
 339                     ),
 340                 }
 341                 w.write_str("</code></div>");
 342                 w.write_str(ITEM_TABLE_ROW_CLOSE);
 343             }
 344
 345             clean::ImportItem(ref import) => {
 346                 let (stab, stab_tags) = if let Some(import_def_id) = import.source.did {
 347                     let ast_attrs = cx.tcx().get_attrs_unchecked(import_def_id);
 348                     let import_attrs = Box::new(clean::Attributes::from_ast(ast_attrs));
 349
 350                     // Just need an item with the correct def_id and attrs
 351                     let import_item = clean::Item {
 352                         item_id: import_def_id.into(),
 353                         attrs: import_attrs,
 354                         cfg: ast_attrs.cfg(cx.tcx(), &cx.cache().hidden_cfg),
 355                         ..myitem.clone()
 356                     };
 357
 358                     let stab = import_item.stability_class(cx.tcx());
 359                     let stab_tags = Some(extra_info_tags(&import_item, item, cx.tcx()));
 360                     (stab, stab_tags)
 361                 } else {
 362                     (None, None)
 363                 };
 364
 365                 let add = if stab.is_some() { " " } else { "" };
 366
 367                 w.write_str(ITEM_TABLE_ROW_OPEN);
 368                 let id = match import.kind {
 369                     clean::ImportKind::Simple(s) => {
 370                         format!(" id=\"{}\"", cx.derive_id(format!("reexport.{}", s)))
 371                     }
 372                     clean::ImportKind::Glob => String::new(),
 373                 };
 374                 write!(
 375                     w,
 376                     "<div class=\"item-left {stab}{add}import-item\"{id}>\
 377                          <code>{vis}{imp}</code>\
 378                      </div>\
 379                      <div class=\"item-right docblock-short\">{stab_tags}</div>",
 380                     stab = stab.unwrap_or_default(),
 381                     vis = myitem.visibility.print_with_space(myitem.item_id, cx),
 382                     imp = import.print(cx),
 383                     stab_tags = stab_tags.unwrap_or_default(),
 384                 );
 385                 w.write_str(ITEM_TABLE_ROW_CLOSE);
 386             }
 387
 388             _ => {
 389                 if myitem.name.is_none() {
 390                     continue;
 391                 }
 392
 393                 let unsafety_flag = match *myitem.kind {
 394                     clean::FunctionItem(_) | clean::ForeignFunctionItem(_)
 395                         if myitem.fn_header(cx.tcx()).unwrap().unsafety
 396                             == hir::Unsafety::Unsafe =>
 397                     {
 398                         "<a title=\"unsafe function\" href=\"#\"><sup>⚠</sup></a>"
 399                     }
 400                     _ => "",
 401                 };
 402
 403                 let stab = myitem.stability_class(cx.tcx());
 404                 let add = if stab.is_some() { " " } else { "" };
 405
 406                 let visibility_emoji = match myitem.visibility {
 407                     clean::Visibility::Restricted(_) => {
 408                         "<span title=\"Restricted Visibility\">&nbsp;🔒</span> "
 409                     }
 410                     _ => "",
 411                 };
 412
 413                 let doc_value = myitem.doc_value().unwrap_or_default();
 414                 w.write_str(ITEM_TABLE_ROW_OPEN);
 415                 write!(
 416                     w,
 417                     "<div class=\"item-left {stab}{add}module-item\">\
 418                         <a class=\"{class}\" href=\"{href}\" title=\"{title}\">{name}</a>\
 419                         {visibility_emoji}\
 420                         {unsafety_flag}\
 421                         {stab_tags}\
 422                      </div>\
 423                      <div class=\"item-right docblock-short\">{docs}</div>",
 424                     name = myitem.name.unwrap(),
 425                     visibility_emoji = visibility_emoji,
 426                     stab_tags = extra_info_tags(myitem, item, cx.tcx()),
 427                     docs = MarkdownSummaryLine(&doc_value, &myitem.links(cx)).into_string(),
 428                     class = myitem.type_(),
 429                     add = add,
 430                     stab = stab.unwrap_or_default(),
 431                     unsafety_flag = unsafety_flag,
 432                     href = item_path(myitem.type_(), myitem.name.unwrap().as_str()),
 433                     title = [full_path(cx, myitem), myitem.type_().to_string()]
 434                         .iter()
 435                         .filter_map(|s| if !s.is_empty() { Some(s.as_str()) } else { None })
 436                         .collect::<Vec<_>>()
 437                         .join(" "),
 438                 );
 439                 w.write_str(ITEM_TABLE_ROW_CLOSE);
 440             }
 441         }
 442     }
 443
 444     if last_section.is_some() {
 445         w.write_str(ITEM_TABLE_CLOSE);
 446     }
 447 }
 448
 449 /// Render the stability, deprecation and portability tags that are displayed in the item's summary
 450 /// at the module level.
 451 fn extra_info_tags(item: &clean::Item, parent: &clean::Item, tcx: TyCtxt<'_>) -> String {
 452     let mut tags = String::new();
 453
 454     fn tag_html(class: &str, title: &str, contents: &str) -> String {
 455         format!(r#"<span class="stab {}" title="{}">{}</span>"#, class, Escape(title), contents)
 456     }
 457
 458     // The trailing space after each tag is to space it properly against the rest of the docs.
 459     if let Some(depr) = &item.deprecation(tcx) {
 460         let mut message = "Deprecated";
 461         if !stability::deprecation_in_effect(depr) {
 462             message = "Deprecation planned";
 463         }
 464         tags += &tag_html("deprecated", "", message);
 465     }
 466
 467     // The "rustc_private" crates are permanently unstable so it makes no sense
 468     // to render "unstable" everywhere.
 469     if item.stability(tcx).as_ref().map(|s| s.is_unstable() && s.feature != sym::rustc_private)
 470         == Some(true)
 471     {
 472         tags += &tag_html("unstable", "", "Experimental");
 473     }
 474
 475     let cfg = match (&item.cfg, parent.cfg.as_ref()) {
 476         (Some(cfg), Some(parent_cfg)) => cfg.simplify_with(parent_cfg),
 477         (cfg, _) => cfg.as_deref().cloned(),
 478     };
 479
 480     debug!("Portability {:?} - {:?} = {:?}", item.cfg, parent.cfg, cfg);
 481     if let Some(ref cfg) = cfg {
 482         tags += &tag_html("portability", &cfg.render_long_plain(), &cfg.render_short_html());
 483     }
 484
 485     tags
 486 }
 487
 488 fn item_function(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, f: &clean::Function) {
 489     let header = it.fn_header(cx.tcx()).expect("printing a function which isn't a function");
 490     let constness = print_constness_with_space(&header.constness, it.const_stability(cx.tcx()));
 491     let unsafety = header.unsafety.print_with_space();
 492     let abi = print_abi_with_space(header.abi).to_string();
 493     let asyncness = header.asyncness.print_with_space();
 494     let visibility = it.visibility.print_with_space(it.item_id, cx).to_string();
 495     let name = it.name.unwrap();
 496
 497     let generics_len = format!("{:#}", f.generics.print(cx)).len();
 498     let header_len = "fn ".len()
 499         + visibility.len()
 500         + constness.len()
 501         + asyncness.len()
 502         + unsafety.len()
 503         + abi.len()
 504         + name.as_str().len()
 505         + generics_len;
 506
 507     wrap_into_docblock(w, |w| {
 508         wrap_item(w, "fn", |w| {
 509             render_attributes_in_pre(w, it, "");
 510             w.reserve(header_len);
 511             write!(
 512                 w,
 513                 "{vis}{constness}{asyncness}{unsafety}{abi}fn \
 514                  {name}{generics}{decl}{notable_traits}{where_clause}",
 515                 vis = visibility,
 516                 constness = constness,
 517                 asyncness = asyncness,
 518                 unsafety = unsafety,
 519                 abi = abi,
 520                 name = name,
 521                 generics = f.generics.print(cx),
 522                 where_clause = print_where_clause(&f.generics, cx, 0, Ending::Newline),
 523                 decl = f.decl.full_print(header_len, 0, header.asyncness, cx),
 524                 notable_traits = notable_traits_decl(&f.decl, cx),
 525             );
 526         });
 527     });
 528     document(w, cx, it, None, HeadingOffset::H2)
 529 }
 530
 531 fn item_trait(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean::Trait) {
 532     let bounds = bounds(&t.bounds, false, cx);
 533     let required_types = t.items.iter().filter(|m| m.is_ty_associated_type()).collect::<Vec<_>>();
 534     let provided_types = t.items.iter().filter(|m| m.is_associated_type()).collect::<Vec<_>>();
 535     let required_consts = t.items.iter().filter(|m| m.is_ty_associated_const()).collect::<Vec<_>>();
 536     let provided_consts = t.items.iter().filter(|m| m.is_associated_const()).collect::<Vec<_>>();
 537     let required_methods = t.items.iter().filter(|m| m.is_ty_method()).collect::<Vec<_>>();
 538     let provided_methods = t.items.iter().filter(|m| m.is_method()).collect::<Vec<_>>();
 539     let count_types = required_types.len() + provided_types.len();
 540     let count_consts = required_consts.len() + provided_consts.len();
 541     let count_methods = required_methods.len() + provided_methods.len();
 542     let must_implement_one_of_functions =
 543         cx.tcx().trait_def(t.def_id).must_implement_one_of.clone();
 544
 545     // Output the trait definition
 546     wrap_into_docblock(w, |w| {
 547         wrap_item(w, "trait", |w| {
 548             render_attributes_in_pre(w, it, "");
 549             write!(
 550                 w,
 551                 "{}{}{}trait {}{}{}",
 552                 it.visibility.print_with_space(it.item_id, cx),
 553                 t.unsafety(cx.tcx()).print_with_space(),
 554                 if t.is_auto(cx.tcx()) { "auto " } else { "" },
 555                 it.name.unwrap(),
 556                 t.generics.print(cx),
 557                 bounds
 558             );
 559
 560             if !t.generics.where_predicates.is_empty() {
 561                 write!(w, "{}", print_where_clause(&t.generics, cx, 0, Ending::Newline));
 562             } else {
 563                 w.write_str(" ");
 564             }
 565
 566             if t.items.is_empty() {
 567                 w.write_str("{ }");
 568             } else {
 569                 // FIXME: we should be using a derived_id for the Anchors here
 570                 w.write_str("{\n");
 571                 let mut toggle = false;
 572
 573                 // If there are too many associated types, hide _everything_
 574                 if should_hide_fields(count_types) {
 575                     toggle = true;
 576                     toggle_open(
 577                         w,
 578                         format_args!(
 579                             "{} associated items",
 580                             count_types + count_consts + count_methods
 581                         ),
 582                     );
 583                 }
 584                 for types in [&required_types, &provided_types] {
 585                     for t in types {
 586                         render_assoc_item(
 587                             w,
 588                             t,
 589                             AssocItemLink::Anchor(None),
 590                             ItemType::Trait,
 591                             cx,
 592                             RenderMode::Normal,
 593                         );
 594                         w.write_str(";\n");
 595                     }
 596                 }
 597                 // If there are too many associated constants, hide everything after them
 598                 // We also do this if the types + consts is large because otherwise we could
 599                 // render a bunch of types and _then_ a bunch of consts just because both were
 600                 // _just_ under the limit
 601                 if !toggle && should_hide_fields(count_types + count_consts) {
 602                     toggle = true;
 603                     toggle_open(
 604                         w,
 605                         format_args!(
 606                             "{} associated constant{} and {} method{}",
 607                             count_consts,
 608                             pluralize(count_consts),
 609                             count_methods,
 610                             pluralize(count_methods),
 611                         ),
 612                     );
 613                 }
 614                 if count_types != 0 && (count_consts != 0 || count_methods != 0) {
 615                     w.write_str("\n");
 616                 }
 617                 for consts in [&required_consts, &provided_consts] {
 618                     for c in consts {
 619                         render_assoc_item(
 620                             w,
 621                             c,
 622                             AssocItemLink::Anchor(None),
 623                             ItemType::Trait,
 624                             cx,
 625                             RenderMode::Normal,
 626                         );
 627                         w.write_str(";\n");
 628                     }
 629                 }
 630                 if !toggle && should_hide_fields(count_methods) {
 631                     toggle = true;
 632                     toggle_open(w, format_args!("{} methods", count_methods));
 633                 }
 634                 if count_consts != 0 && count_methods != 0 {
 635                     w.write_str("\n");
 636                 }
 637                 for (pos, m) in required_methods.iter().enumerate() {
 638                     render_assoc_item(
 639                         w,
 640                         m,
 641                         AssocItemLink::Anchor(None),
 642                         ItemType::Trait,
 643                         cx,
 644                         RenderMode::Normal,
 645                     );
 646                     w.write_str(";\n");
 647
 648                     if pos < required_methods.len() - 1 {
 649                         w.write_str("<span class=\"item-spacer\"></span>");
 650                     }
 651                 }
 652                 if !required_methods.is_empty() && !provided_methods.is_empty() {
 653                     w.write_str("\n");
 654                 }
 655                 for (pos, m) in provided_methods.iter().enumerate() {
 656                     render_assoc_item(
 657                         w,
 658                         m,
 659                         AssocItemLink::Anchor(None),
 660                         ItemType::Trait,
 661                         cx,
 662                         RenderMode::Normal,
 663                     );
 664                     match *m.kind {
 665                         clean::MethodItem(ref inner, _)
 666                             if !inner.generics.where_predicates.is_empty() =>
 667                         {
 668                             w.write_str(",\n    { ... }\n");
 669                         }
 670                         _ => {
 671                             w.write_str(" { ... }\n");
 672                         }
 673                     }
 674
 675                     if pos < provided_methods.len() - 1 {
 676                         w.write_str("<span class=\"item-spacer\"></span>");
 677                     }
 678                 }
 679                 if toggle {
 680                     toggle_close(w);
 681                 }
 682                 w.write_str("}");
 683             }
 684         });
 685     });
 686
 687     // Trait documentation
 688     document(w, cx, it, None, HeadingOffset::H2);
 689
 690     fn write_small_section_header(w: &mut Buffer, id: &str, title: &str, extra_content: &str) {
 691         write!(
 692             w,
 693             "<h2 id=\"{0}\" class=\"small-section-header\">\
 694                 {1}<a href=\"#{0}\" class=\"anchor\"></a>\
 695              </h2>{2}",
 696             id, title, extra_content
 697         )
 698     }
 699
 700     fn trait_item(w: &mut Buffer, cx: &mut Context<'_>, m: &clean::Item, t: &clean::Item) {
 701         let name = m.name.unwrap();
 702         info!("Documenting {} on {:?}", name, t.name);
 703         let item_type = m.type_();
 704         let id = cx.derive_id(format!("{}.{}", item_type, name));
 705         let mut content = Buffer::empty_from(w);
 706         document(&mut content, cx, m, Some(t), HeadingOffset::H5);
 707         let toggled = !content.is_empty();
 708         if toggled {
 709             write!(w, "<details class=\"rustdoc-toggle\" open><summary>");
 710         }
 711         write!(w, "<div id=\"{}\" class=\"method has-srclink\">", id);
 712         write!(w, "<div class=\"rightside\">");
 713
 714         let has_stability = render_stability_since(w, m, t, cx.tcx());
 715         if has_stability {
 716             w.write_str(" · ");
 717         }
 718         write_srclink(cx, m, w);
 719         write!(w, "</div>");
 720         write!(w, "<h4 class=\"code-header\">");
 721         render_assoc_item(
 722             w,
 723             m,
 724             AssocItemLink::Anchor(Some(&id)),
 725             ItemType::Impl,
 726             cx,
 727             RenderMode::Normal,
 728         );
 729         w.write_str("</h4>");
 730         w.write_str("</div>");
 731         if toggled {
 732             write!(w, "</summary>");
 733             w.push_buffer(content);
 734             write!(w, "</details>");
 735         }
 736     }
 737
 738     if !required_types.is_empty() {
 739         write_small_section_header(
 740             w,
 741             "required-associated-types",
 742             "Required Associated Types",
 743             "<div class=\"methods\">",
 744         );
 745         for t in required_types {
 746             trait_item(w, cx, t, it);
 747         }
 748         w.write_str("</div>");
 749     }
 750     if !provided_types.is_empty() {
 751         write_small_section_header(
 752             w,
 753             "provided-associated-types",
 754             "Provided Associated Types",
 755             "<div class=\"methods\">",
 756         );
 757         for t in provided_types {
 758             trait_item(w, cx, t, it);
 759         }
 760         w.write_str("</div>");
 761     }
 762
 763     if !required_consts.is_empty() {
 764         write_small_section_header(
 765             w,
 766             "required-associated-consts",
 767             "Required Associated Constants",
 768             "<div class=\"methods\">",
 769         );
 770         for t in required_consts {
 771             trait_item(w, cx, t, it);
 772         }
 773         w.write_str("</div>");
 774     }
 775     if !provided_consts.is_empty() {
 776         write_small_section_header(
 777             w,
 778             "provided-associated-consts",
 779             "Provided Associated Constants",
 780             "<div class=\"methods\">",
 781         );
 782         for t in provided_consts {
 783             trait_item(w, cx, t, it);
 784         }
 785         w.write_str("</div>");
 786     }
 787
 788     // Output the documentation for each function individually
 789     if !required_methods.is_empty() || must_implement_one_of_functions.is_some() {
 790         write_small_section_header(
 791             w,
 792             "required-methods",
 793             "Required Methods",
 794             "<div class=\"methods\">",
 795         );
 796
 797         if let Some(list) = must_implement_one_of_functions.as_deref() {
 798             write!(
 799                 w,
 800                 "<div class=\"stab must_implement\">At least one of the `{}` methods is required.</div>",
 801                 list.iter().join("`, `")
 802             );
 803         }
 804
 805         for m in required_methods {
 806             trait_item(w, cx, m, it);
 807         }
 808         w.write_str("</div>");
 809     }
 810     if !provided_methods.is_empty() {
 811         write_small_section_header(
 812             w,
 813             "provided-methods",
 814             "Provided Methods",
 815             "<div class=\"methods\">",
 816         );
 817         for m in provided_methods {
 818             trait_item(w, cx, m, it);
 819         }
 820         w.write_str("</div>");
 821     }
 822
 823     // If there are methods directly on this trait object, render them here.
 824     render_assoc_items(w, cx, it, it.item_id.expect_def_id(), AssocItemRender::All);
 825
 826     let cloned_shared = Rc::clone(&cx.shared);
 827     let cache = &cloned_shared.cache;
 828     let mut extern_crates = FxHashSet::default();
 829     if let Some(implementors) = cache.implementors.get(&it.item_id.expect_def_id()) {
 830         // The DefId is for the first Type found with that name. The bool is
 831         // if any Types with the same name but different DefId have been found.
 832         let mut implementor_dups: FxHashMap<Symbol, (DefId, bool)> = FxHashMap::default();
 833         for implementor in implementors {
 834             if let Some(did) = implementor.inner_impl().for_.without_borrowed_ref().def_id(cache) &&
 835                 !did.is_local() {
 836                 extern_crates.insert(did.krate);
 837             }
 838             match implementor.inner_impl().for_.without_borrowed_ref() {
 839                 clean::Type::Path { ref path } if !path.is_assoc_ty() => {
 840                     let did = path.def_id();
 841                     let &mut (prev_did, ref mut has_duplicates) =
 842                         implementor_dups.entry(path.last()).or_insert((did, false));
 843                     if prev_did != did {
 844                         *has_duplicates = true;
 845                     }
 846                 }
 847                 _ => {}
 848             }
 849         }
 850
 851         let (local, foreign) =
 852             implementors.iter().partition::<Vec<_>, _>(|i| i.is_on_local_type(cx));
 853
 854         let (mut synthetic, mut concrete): (Vec<&&Impl>, Vec<&&Impl>) =
 855             local.iter().partition(|i| i.inner_impl().kind.is_auto());
 856
 857         synthetic.sort_by(|a, b| compare_impl(a, b, cx));
 858         concrete.sort_by(|a, b| compare_impl(a, b, cx));
 859
 860         if !foreign.is_empty() {
 861             write_small_section_header(w, "foreign-impls", "Implementations on Foreign Types", "");
 862
 863             for implementor in foreign {
 864                 let provided_methods = implementor.inner_impl().provided_trait_methods(cx.tcx());
 865                 let assoc_link =
 866                     AssocItemLink::GotoSource(implementor.impl_item.item_id, &provided_methods);
 867                 render_impl(
 868                     w,
 869                     cx,
 870                     implementor,
 871                     it,
 872                     assoc_link,
 873                     RenderMode::Normal,
 874                     None,
 875                     &[],
 876                     ImplRenderingParameters {
 877                         show_def_docs: false,
 878                         show_default_items: false,
 879                         show_non_assoc_items: true,
 880                         toggle_open_by_default: false,
 881                     },
 882                 );
 883             }
 884         }
 885
 886         write_small_section_header(
 887             w,
 888             "implementors",
 889             "Implementors",
 890             "<div class=\"item-list\" id=\"implementors-list\">",
 891         );
 892         for implementor in concrete {
 893             render_implementor(cx, implementor, it, w, &implementor_dups, &[]);
 894         }
 895         w.write_str("</div>");
 896
 897         if t.is_auto(cx.tcx()) {
 898             write_small_section_header(
 899                 w,
 900                 "synthetic-implementors",
 901                 "Auto implementors",
 902                 "<div class=\"item-list\" id=\"synthetic-implementors-list\">",
 903             );
 904             for implementor in synthetic {
 905                 render_implementor(
 906                     cx,
 907                     implementor,
 908                     it,
 909                     w,
 910                     &implementor_dups,
 911                     &collect_paths_for_type(implementor.inner_impl().for_.clone(), cache),
 912                 );
 913             }
 914             w.write_str("</div>");
 915         }
 916     } else {
 917         // even without any implementations to write in, we still want the heading and list, so the
 918         // implementors javascript file pulled in below has somewhere to write the impls into
 919         write_small_section_header(
 920             w,
 921             "implementors",
 922             "Implementors",
 923             "<div class=\"item-list\" id=\"implementors-list\"></div>",
 924         );
 925
 926         if t.is_auto(cx.tcx()) {
 927             write_small_section_header(
 928                 w,
 929                 "synthetic-implementors",
 930                 "Auto implementors",
 931                 "<div class=\"item-list\" id=\"synthetic-implementors-list\"></div>",
 932             );
 933         }
 934     }
 935
 936     // Include implementors in crates that depend on the current crate.
 937     //
 938     // This is complicated by the way rustdoc is invoked, which is basically
 939     // the same way rustc is invoked: it gets called, one at a time, for each
 940     // crate. When building the rustdocs for the current crate, rustdoc can
 941     // see crate metadata for its dependencies, but cannot see metadata for its
 942     // dependents.
 943     //
 944     // To make this work, we generate a "hook" at this stage, and our
 945     // dependents can "plug in" to it when they build. For simplicity's sake,
 946     // it's [JSONP]: a JavaScript file with the data we need (and can parse),
 947     // surrounded by a tiny wrapper that the Rust side ignores, but allows the
 948     // JavaScript side to include without having to worry about Same Origin
 949     // Policy. The code for *that* is in `write_shared.rs`.
 950     //
 951     // This is further complicated by `#[doc(inline)]`. We want all copies
 952     // of an inlined trait to reference the same JS file, to address complex
 953     // dependency graphs like this one (lower crates depend on higher crates):
 954     //
 955     // ```text
 956     //  --------------------------------------------
 957     //  |            crate A: trait Foo            |
 958     //  --------------------------------------------
 959     //      |                               |
 960     //  --------------------------------    |
 961     //  | crate B: impl A::Foo for Bar |    |
 962     //  --------------------------------    |
 963     //      |                               |
 964     //  ---------------------------------------------
 965     //  | crate C: #[doc(inline)] use A::Foo as Baz |
 966     //  |          impl Baz for Quux                |
 967     //  ---------------------------------------------
 968     // ```
 969     //
 970     // Basically, we want `C::Baz` and `A::Foo` to show the same set of
 971     // impls, which is easier if they both treat `/implementors/A/trait.Foo.js`
 972     // as the Single Source of Truth.
 973     //
 974     // We also want the `impl Baz for Quux` to be written to
 975     // `trait.Foo.js`. However, when we generate plain HTML for `C::Baz`,
 976     // we're going to want to generate plain HTML for `impl Baz for Quux` too,
 977     // because that'll load faster, and it's better for SEO. And we don't want
 978     // the same impl to show up twice on the same page.
 979     //
 980     // To make this work, the implementors JS file has a structure kinda
 981     // like this:
 982     //
 983     // ```js
 984     // JSONP({
 985     // "B": {"impl A::Foo for Bar"},
 986     // "C": {"impl Baz for Quux"},
 987     // });
 988     // ```
 989     //
 990     // First of all, this means we can rebuild a crate, and it'll replace its own
 991     // data if something changes. That is, `rustdoc` is idempotent. The other
 992     // advantage is that we can list the crates that get included in the HTML,
 993     // and ignore them when doing the JavaScript-based part of rendering.
 994     // So C's HTML will have something like this:
 995     //
 996     // ```html
 997     // <script type="text/javascript" src="/implementors/A/trait.Foo.js"
 998     //     data-ignore-extern-crates="A,B" async></script>
 999     // ```
1000     //
1001     // And, when the JS runs, anything in data-ignore-extern-crates is known
1002     // to already be in the HTML, and will be ignored.
1003     //
1004     // [JSONP]: https://en.wikipedia.org/wiki/JSONP
1005     let mut js_src_path: UrlPartsBuilder = std::iter::repeat("..")
1006         .take(cx.current.len())
1007         .chain(std::iter::once("implementors"))
1008         .collect();
1009     if let Some(did) = it.item_id.as_def_id() &&
1010         let get_extern = { || cache.external_paths.get(&did).map(|s| s.0.clone()) } &&
1011         let Some(fqp) = cache.exact_paths.get(&did).cloned().or_else(get_extern) {
1012         js_src_path.extend(fqp[..fqp.len() - 1].iter().copied());
1013         js_src_path.push_fmt(format_args!("{}.{}.js", it.type_(), fqp.last().unwrap()));
1014     } else {
1015         js_src_path.extend(cx.current.iter().copied());
1016         js_src_path.push_fmt(format_args!("{}.{}.js", it.type_(), it.name.unwrap()));
1017     }
1018     let extern_crates = extern_crates
1019         .into_iter()
1020         .map(|cnum| cx.shared.tcx.crate_name(cnum).to_string())
1021         .collect::<Vec<_>>()
1022         .join(",");
1023     write!(
1024         w,
1025         "<script type=\"text/javascript\" src=\"{src}\" data-ignore-extern-crates=\"{extern_crates}\" async></script>",
1026         src = js_src_path.finish(),
1027     );
1028 }
1029
1030 fn item_trait_alias(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean::TraitAlias) {
1031     wrap_into_docblock(w, |w| {
1032         wrap_item(w, "trait-alias", |w| {
1033             render_attributes_in_pre(w, it, "");
1034             write!(
1035                 w,
1036                 "trait {}{}{} = {};",
1037                 it.name.unwrap(),
1038                 t.generics.print(cx),
1039                 print_where_clause(&t.generics, cx, 0, Ending::Newline),
1040                 bounds(&t.bounds, true, cx)
1041             );
1042         });
1043     });
1044
1045     document(w, cx, it, None, HeadingOffset::H2);
1046
1047     // Render any items associated directly to this alias, as otherwise they
1048     // won't be visible anywhere in the docs. It would be nice to also show
1049     // associated items from the aliased type (see discussion in #32077), but
1050     // we need #14072 to make sense of the generics.
1051     render_assoc_items(w, cx, it, it.item_id.expect_def_id(), AssocItemRender::All)
1052 }
1053
1054 fn item_opaque_ty(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean::OpaqueTy) {
1055     wrap_into_docblock(w, |w| {
1056         wrap_item(w, "opaque", |w| {
1057             render_attributes_in_pre(w, it, "");
1058             write!(
1059                 w,
1060                 "type {}{}{where_clause} = impl {bounds};",
1061                 it.name.unwrap(),
1062                 t.generics.print(cx),
1063                 where_clause = print_where_clause(&t.generics, cx, 0, Ending::Newline),
1064                 bounds = bounds(&t.bounds, false, cx),
1065             );
1066         });
1067     });
1068
1069     document(w, cx, it, None, HeadingOffset::H2);
1070
1071     // Render any items associated directly to this alias, as otherwise they
1072     // won't be visible anywhere in the docs. It would be nice to also show
1073     // associated items from the aliased type (see discussion in #32077), but
1074     // we need #14072 to make sense of the generics.
1075     render_assoc_items(w, cx, it, it.item_id.expect_def_id(), AssocItemRender::All)
1076 }
1077
1078 fn item_typedef(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean::Typedef) {
1079     fn write_content(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Typedef) {
1080         wrap_item(w, "typedef", |w| {
1081             render_attributes_in_pre(w, it, "");
1082             write!(w, "{}", it.visibility.print_with_space(it.item_id, cx));
1083             write!(
1084                 w,
1085                 "type {}{}{where_clause} = {type_};",
1086                 it.name.unwrap(),
1087                 t.generics.print(cx),
1088                 where_clause = print_where_clause(&t.generics, cx, 0, Ending::Newline),
1089                 type_ = t.type_.print(cx),
1090             );
1091         });
1092     }
1093
1094     wrap_into_docblock(w, |w| write_content(w, cx, it, t));
1095
1096     document(w, cx, it, None, HeadingOffset::H2);
1097
1098     let def_id = it.item_id.expect_def_id();
1099     // Render any items associated directly to this alias, as otherwise they
1100     // won't be visible anywhere in the docs. It would be nice to also show
1101     // associated items from the aliased type (see discussion in #32077), but
1102     // we need #14072 to make sense of the generics.
1103     render_assoc_items(w, cx, it, def_id, AssocItemRender::All);
1104     document_type_layout(w, cx, def_id);
1105 }
1106
1107 fn item_union(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, s: &clean::Union) {
1108     wrap_into_docblock(w, |w| {
1109         wrap_item(w, "union", |w| {
1110             render_attributes_in_pre(w, it, "");
1111             render_union(w, it, Some(&s.generics), &s.fields, "", cx);
1112         });
1113     });
1114
1115     document(w, cx, it, None, HeadingOffset::H2);
1116
1117     let mut fields = s
1118         .fields
1119         .iter()
1120         .filter_map(|f| match *f.kind {
1121             clean::StructFieldItem(ref ty) => Some((f, ty)),
1122             _ => None,
1123         })
1124         .peekable();
1125     if fields.peek().is_some() {
1126         write!(
1127             w,
1128             "<h2 id=\"fields\" class=\"fields small-section-header\">\
1129                 Fields<a href=\"#fields\" class=\"anchor\"></a>\
1130             </h2>"
1131         );
1132         for (field, ty) in fields {
1133             let name = field.name.expect("union field name");
1134             let id = format!("{}.{}", ItemType::StructField, name);
1135             write!(
1136                 w,
1137                 "<span id=\"{id}\" class=\"{shortty} small-section-header\">\
1138                      <a href=\"#{id}\" class=\"anchor field\"></a>\
1139                      <code>{name}: {ty}</code>\
1140                  </span>",
1141                 id = id,
1142                 name = name,
1143                 shortty = ItemType::StructField,
1144                 ty = ty.print(cx),
1145             );
1146             if let Some(stability_class) = field.stability_class(cx.tcx()) {
1147                 write!(w, "<span class=\"stab {stab}\"></span>", stab = stability_class);
1148             }
1149             document(w, cx, field, Some(it), HeadingOffset::H3);
1150         }
1151     }
1152     let def_id = it.item_id.expect_def_id();
1153     render_assoc_items(w, cx, it, def_id, AssocItemRender::All);
1154     document_type_layout(w, cx, def_id);
1155 }
1156
1157 fn print_tuple_struct_fields(w: &mut Buffer, cx: &Context<'_>, s: &[clean::Item]) {
1158     for (i, ty) in s.iter().enumerate() {
1159         if i > 0 {
1160             w.write_str(",&nbsp;");
1161         }
1162         match *ty.kind {
1163             clean::StrippedItem(box clean::StructFieldItem(_)) => w.write_str("_"),
1164             clean::StructFieldItem(ref ty) => write!(w, "{}", ty.print(cx)),
1165             _ => unreachable!(),
1166         }
1167     }
1168 }
1169
1170 fn item_enum(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, e: &clean::Enum) {
1171     let count_variants = e.variants().count();
1172     wrap_into_docblock(w, |w| {
1173         wrap_item(w, "enum", |w| {
1174             render_attributes_in_pre(w, it, "");
1175             write!(
1176                 w,
1177                 "{}enum {}{}",
1178                 it.visibility.print_with_space(it.item_id, cx),
1179                 it.name.unwrap(),
1180                 e.generics.print(cx),
1181             );
1182             if !print_where_clause_and_check(w, &e.generics, cx) {
1183                 // If there wasn't a `where` clause, we add a whitespace.
1184                 w.write_str(" ");
1185             }
1186
1187             let variants_stripped = e.has_stripped_entries();
1188             if count_variants == 0 && !variants_stripped {
1189                 w.write_str("{}");
1190             } else {
1191                 w.write_str("{\n");
1192                 let toggle = should_hide_fields(count_variants);
1193                 if toggle {
1194                     toggle_open(w, format_args!("{} variants", count_variants));
1195                 }
1196                 for v in e.variants() {
1197                     w.write_str("    ");
1198                     let name = v.name.unwrap();
1199                     match *v.kind {
1200                         clean::VariantItem(ref var) => match var {
1201                             clean::Variant::CLike => write!(w, "{}", name),
1202                             clean::Variant::Tuple(ref s) => {
1203                                 write!(w, "{}(", name);
1204                                 print_tuple_struct_fields(w, cx, s);
1205                                 w.write_str(")");
1206                             }
1207                             clean::Variant::Struct(ref s) => {
1208                                 render_struct(
1209                                     w,
1210                                     v,
1211                                     None,
1212                                     s.struct_type,
1213                                     &s.fields,
1214                                     "    ",
1215                                     false,
1216                                     cx,
1217                                 );
1218                             }
1219                         },
1220                         _ => unreachable!(),
1221                     }
1222                     w.write_str(",\n");
1223                 }
1224
1225                 if variants_stripped {
1226                     w.write_str("    // some variants omitted\n");
1227                 }
1228                 if toggle {
1229                     toggle_close(w);
1230                 }
1231                 w.write_str("}");
1232             }
1233         });
1234     });
1235
1236     document(w, cx, it, None, HeadingOffset::H2);
1237
1238     if count_variants != 0 {
1239         write!(
1240             w,
1241             "<h2 id=\"variants\" class=\"variants small-section-header\">\
1242                 Variants{}<a href=\"#variants\" class=\"anchor\"></a>\
1243             </h2>",
1244             document_non_exhaustive_header(it)
1245         );
1246         document_non_exhaustive(w, it);
1247         for variant in e.variants() {
1248             let id = cx.derive_id(format!("{}.{}", ItemType::Variant, variant.name.unwrap()));
1249             write!(
1250                 w,
1251                 "<h3 id=\"{id}\" class=\"variant small-section-header\">\
1252                     <a href=\"#{id}\" class=\"anchor field\"></a>\
1253                     <code>{name}",
1254                 id = id,
1255                 name = variant.name.unwrap()
1256             );
1257             if let clean::VariantItem(clean::Variant::Tuple(ref s)) = *variant.kind {
1258                 w.write_str("(");
1259                 print_tuple_struct_fields(w, cx, s);
1260                 w.write_str(")");
1261             }
1262             w.write_str("</code>");
1263             render_stability_since(w, variant, it, cx.tcx());
1264             w.write_str("</h3>");
1265
1266             use crate::clean::Variant;
1267
1268             let heading_and_fields = match &*variant.kind {
1269                 clean::VariantItem(Variant::Struct(s)) => Some(("Fields", &s.fields)),
1270                 // Documentation on tuple variant fields is rare, so to reduce noise we only emit
1271                 // the section if at least one field is documented.
1272                 clean::VariantItem(Variant::Tuple(fields))
1273                     if fields.iter().any(|f| f.doc_value().is_some()) =>
1274                 {
1275                     Some(("Tuple Fields", fields))
1276                 }
1277                 _ => None,
1278             };
1279
1280             if let Some((heading, fields)) = heading_and_fields {
1281                 let variant_id =
1282                     cx.derive_id(format!("{}.{}.fields", ItemType::Variant, variant.name.unwrap()));
1283                 write!(w, "<div class=\"sub-variant\" id=\"{id}\">", id = variant_id);
1284                 write!(w, "<h4>{heading}</h4>", heading = heading);
1285                 document_non_exhaustive(w, variant);
1286                 for field in fields {
1287                     match *field.kind {
1288                         clean::StrippedItem(box clean::StructFieldItem(_)) => {}
1289                         clean::StructFieldItem(ref ty) => {
1290                             let id = cx.derive_id(format!(
1291                                 "variant.{}.field.{}",
1292                                 variant.name.unwrap(),
1293                                 field.name.unwrap()
1294                             ));
1295                             write!(
1296                                 w,
1297                                 "<div class=\"sub-variant-field\">\
1298                                  <span id=\"{id}\" class=\"variant small-section-header\">\
1299                                      <a href=\"#{id}\" class=\"anchor field\"></a>\
1300                                      <code>{f}:&nbsp;{t}</code>\
1301                                  </span>",
1302                                 id = id,
1303                                 f = field.name.unwrap(),
1304                                 t = ty.print(cx)
1305                             );
1306                             document(w, cx, field, Some(variant), HeadingOffset::H5);
1307                             write!(w, "</div>");
1308                         }
1309                         _ => unreachable!(),
1310                     }
1311                 }
1312                 w.write_str("</div>");
1313             }
1314
1315             document(w, cx, variant, Some(it), HeadingOffset::H4);
1316         }
1317     }
1318     let def_id = it.item_id.expect_def_id();
1319     render_assoc_items(w, cx, it, def_id, AssocItemRender::All);
1320     document_type_layout(w, cx, def_id);
1321 }
1322
1323 fn item_macro(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean::Macro) {
1324     wrap_into_docblock(w, |w| {
1325         highlight::render_macro_with_highlighting(&t.source, w);
1326     });
1327     document(w, cx, it, None, HeadingOffset::H2)
1328 }
1329
1330 fn item_proc_macro(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, m: &clean::ProcMacro) {
1331     wrap_into_docblock(w, |w| {
1332         let name = it.name.expect("proc-macros always have names");
1333         match m.kind {
1334             MacroKind::Bang => {
1335                 wrap_item(w, "macro", |w| {
1336                     write!(w, "{}!() {{ /* proc-macro */ }}", name);
1337                 });
1338             }
1339             MacroKind::Attr => {
1340                 wrap_item(w, "attr", |w| {
1341                     write!(w, "#[{}]", name);
1342                 });
1343             }
1344             MacroKind::Derive => {
1345                 wrap_item(w, "derive", |w| {
1346                     write!(w, "#[derive({})]", name);
1347                     if !m.helpers.is_empty() {
1348                         w.push_str("\n{\n");
1349                         w.push_str("    // Attributes available to this derive:\n");
1350                         for attr in &m.helpers {
1351                             writeln!(w, "    #[{}]", attr);
1352                         }
1353                         w.push_str("}\n");
1354                     }
1355                 });
1356             }
1357         }
1358     });
1359     document(w, cx, it, None, HeadingOffset::H2)
1360 }
1361
1362 fn item_primitive(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item) {
1363     document(w, cx, it, None, HeadingOffset::H2);
1364     render_assoc_items(w, cx, it, it.item_id.expect_def_id(), AssocItemRender::All)
1365 }
1366
1367 fn item_constant(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, c: &clean::Constant) {
1368     wrap_into_docblock(w, |w| {
1369         wrap_item(w, "const", |w| {
1370             render_attributes_in_code(w, it);
1371
1372             write!(
1373                 w,
1374                 "{vis}const {name}: {typ}",
1375                 vis = it.visibility.print_with_space(it.item_id, cx),
1376                 name = it.name.unwrap(),
1377                 typ = c.type_.print(cx),
1378             );
1379
1380             // FIXME: The code below now prints
1381             //            ` = _; // 100i32`
1382             //        if the expression is
1383             //            `50 + 50`
1384             //        which looks just wrong.
1385             //        Should we print
1386             //            ` = 100i32;`
1387             //        instead?
1388
1389             let value = c.value(cx.tcx());
1390             let is_literal = c.is_literal(cx.tcx());
1391             let expr = c.expr(cx.tcx());
1392             if value.is_some() || is_literal {
1393                 write!(w, " = {expr};", expr = Escape(&expr));
1394             } else {
1395                 w.write_str(";");
1396             }
1397
1398             if !is_literal {
1399                 if let Some(value) = &value {
1400                     let value_lowercase = value.to_lowercase();
1401                     let expr_lowercase = expr.to_lowercase();
1402
1403                     if value_lowercase != expr_lowercase
1404                         && value_lowercase.trim_end_matches("i32") != expr_lowercase
1405                     {
1406                         write!(w, " // {value}", value = Escape(value));
1407                     }
1408                 }
1409             }
1410         });
1411     });
1412
1413     document(w, cx, it, None, HeadingOffset::H2)
1414 }
1415
1416 fn item_struct(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, s: &clean::Struct) {
1417     wrap_into_docblock(w, |w| {
1418         wrap_item(w, "struct", |w| {
1419             render_attributes_in_code(w, it);
1420             render_struct(w, it, Some(&s.generics), s.struct_type, &s.fields, "", true, cx);
1421         });
1422     });
1423
1424     document(w, cx, it, None, HeadingOffset::H2);
1425
1426     let mut fields = s
1427         .fields
1428         .iter()
1429         .filter_map(|f| match *f.kind {
1430             clean::StructFieldItem(ref ty) => Some((f, ty)),
1431             _ => None,
1432         })
1433         .peekable();
1434     if let CtorKind::Fictive | CtorKind::Fn = s.struct_type {
1435         if fields.peek().is_some() {
1436             write!(
1437                 w,
1438                 "<h2 id=\"fields\" class=\"fields small-section-header\">\
1439                      {}{}<a href=\"#fields\" class=\"anchor\"></a>\
1440                  </h2>",
1441                 if let CtorKind::Fictive = s.struct_type { "Fields" } else { "Tuple Fields" },
1442                 document_non_exhaustive_header(it)
1443             );
1444             document_non_exhaustive(w, it);
1445             for (index, (field, ty)) in fields.enumerate() {
1446                 let field_name =
1447                     field.name.map_or_else(|| index.to_string(), |sym| sym.as_str().to_string());
1448                 let id = cx.derive_id(format!("{}.{}", ItemType::StructField, field_name));
1449                 write!(
1450                     w,
1451                     "<span id=\"{id}\" class=\"{item_type} small-section-header\">\
1452                          <a href=\"#{id}\" class=\"anchor field\"></a>\
1453                          <code>{name}: {ty}</code>\
1454                      </span>",
1455                     item_type = ItemType::StructField,
1456                     id = id,
1457                     name = field_name,
1458                     ty = ty.print(cx)
1459                 );
1460                 document(w, cx, field, Some(it), HeadingOffset::H3);
1461             }
1462         }
1463     }
1464     let def_id = it.item_id.expect_def_id();
1465     render_assoc_items(w, cx, it, def_id, AssocItemRender::All);
1466     document_type_layout(w, cx, def_id);
1467 }
1468
1469 fn item_static(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, s: &clean::Static) {
1470     wrap_into_docblock(w, |w| {
1471         wrap_item(w, "static", |w| {
1472             render_attributes_in_code(w, it);
1473             write!(
1474                 w,
1475                 "{vis}static {mutability}{name}: {typ}",
1476                 vis = it.visibility.print_with_space(it.item_id, cx),
1477                 mutability = s.mutability.print_with_space(),
1478                 name = it.name.unwrap(),
1479                 typ = s.type_.print(cx)
1480             );
1481         });
1482     });
1483     document(w, cx, it, None, HeadingOffset::H2)
1484 }
1485
1486 fn item_foreign_type(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item) {
1487     wrap_into_docblock(w, |w| {
1488         wrap_item(w, "foreigntype", |w| {
1489             w.write_str("extern {\n");
1490             render_attributes_in_code(w, it);
1491             write!(
1492                 w,
1493                 "    {}type {};\n}}",
1494                 it.visibility.print_with_space(it.item_id, cx),
1495                 it.name.unwrap(),
1496             );
1497         });
1498     });
1499
1500     document(w, cx, it, None, HeadingOffset::H2);
1501
1502     render_assoc_items(w, cx, it, it.item_id.expect_def_id(), AssocItemRender::All)
1503 }
1504
1505 fn item_keyword(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item) {
1506     document(w, cx, it, None, HeadingOffset::H2)
1507 }
1508
1509 /// Compare two strings treating multi-digit numbers as single units (i.e. natural sort order).
1510 pub(crate) fn compare_names(mut lhs: &str, mut rhs: &str) -> Ordering {
1511     /// Takes a non-numeric and a numeric part from the given &str.
1512     fn take_parts<'a>(s: &mut &'a str) -> (&'a str, &'a str) {
1513         let i = s.find(|c: char| c.is_ascii_digit());
1514         let (a, b) = s.split_at(i.unwrap_or(s.len()));
1515         let i = b.find(|c: char| !c.is_ascii_digit());
1516         let (b, c) = b.split_at(i.unwrap_or(b.len()));
1517         *s = c;
1518         (a, b)
1519     }
1520
1521     while !lhs.is_empty() || !rhs.is_empty() {
1522         let (la, lb) = take_parts(&mut lhs);
1523         let (ra, rb) = take_parts(&mut rhs);
1524         // First process the non-numeric part.
1525         match la.cmp(ra) {
1526             Ordering::Equal => (),
1527             x => return x,
1528         }
1529         // Then process the numeric part, if both sides have one (and they fit in a u64).
1530         if let (Ok(ln), Ok(rn)) = (lb.parse::<u64>(), rb.parse::<u64>()) {
1531             match ln.cmp(&rn) {
1532                 Ordering::Equal => (),
1533                 x => return x,
1534             }
1535         }
1536         // Then process the numeric part again, but this time as strings.
1537         match lb.cmp(rb) {
1538             Ordering::Equal => (),
1539             x => return x,
1540         }
1541     }
1542
1543     Ordering::Equal
1544 }
1545
1546 pub(super) fn full_path(cx: &Context<'_>, item: &clean::Item) -> String {
1547     let mut s = join_with_double_colon(&cx.current);
1548     s.push_str("::");
1549     s.push_str(item.name.unwrap().as_str());
1550     s
1551 }
1552
1553 pub(super) fn item_path(ty: ItemType, name: &str) -> String {
1554     match ty {
1555         ItemType::Module => format!("{}index.html", ensure_trailing_slash(name)),
1556         _ => format!("{}.{}.html", ty, name),
1557     }
1558 }
1559
1560 fn bounds(t_bounds: &[clean::GenericBound], trait_alias: bool, cx: &Context<'_>) -> String {
1561     let mut bounds = String::new();
1562     if !t_bounds.is_empty() {
1563         if !trait_alias {
1564             bounds.push_str(": ");
1565         }
1566         for (i, p) in t_bounds.iter().enumerate() {
1567             if i > 0 {
1568                 bounds.push_str(" + ");
1569             }
1570             bounds.push_str(&p.print(cx).to_string());
1571         }
1572     }
1573     bounds
1574 }
1575
1576 fn wrap_into_docblock<F>(w: &mut Buffer, f: F)
1577 where
1578     F: FnOnce(&mut Buffer),
1579 {
1580     w.write_str("<div class=\"docblock item-decl\">");
1581     f(w);
1582     w.write_str("</div>")
1583 }
1584
1585 fn wrap_item<F>(w: &mut Buffer, item_name: &str, f: F)
1586 where
1587     F: FnOnce(&mut Buffer),
1588 {
1589     w.write_fmt(format_args!("<pre class=\"rust {}\"><code>", item_name));
1590     f(w);
1591     w.write_str("</code></pre>");
1592 }
1593
1594 fn render_stability_since(
1595     w: &mut Buffer,
1596     item: &clean::Item,
1597     containing_item: &clean::Item,
1598     tcx: TyCtxt<'_>,
1599 ) -> bool {
1600     render_stability_since_raw(
1601         w,
1602         item.stable_since(tcx),
1603         item.const_stability(tcx),
1604         containing_item.stable_since(tcx),
1605         containing_item.const_stable_since(tcx),
1606     )
1607 }
1608
1609 fn compare_impl<'a, 'b>(lhs: &'a &&Impl, rhs: &'b &&Impl, cx: &Context<'_>) -> Ordering {
1610     let lhss = format!("{}", lhs.inner_impl().print(false, cx));
1611     let rhss = format!("{}", rhs.inner_impl().print(false, cx));
1612
1613     // lhs and rhs are formatted as HTML, which may be unnecessary
1614     compare_names(&lhss, &rhss)
1615 }
1616
1617 fn render_implementor(
1618     cx: &mut Context<'_>,
1619     implementor: &Impl,
1620     trait_: &clean::Item,
1621     w: &mut Buffer,
1622     implementor_dups: &FxHashMap<Symbol, (DefId, bool)>,
1623     aliases: &[String],
1624 ) {
1625     // If there's already another implementor that has the same abridged name, use the
1626     // full path, for example in `std::iter::ExactSizeIterator`
1627     let use_absolute = match implementor.inner_impl().for_ {
1628         clean::Type::Path { ref path, .. }
1629         | clean::BorrowedRef { type_: box clean::Type::Path { ref path, .. }, .. }
1630             if !path.is_assoc_ty() =>
1631         {
1632             implementor_dups[&path.last()].1
1633         }
1634         _ => false,
1635     };
1636     render_impl(
1637         w,
1638         cx,
1639         implementor,
1640         trait_,
1641         AssocItemLink::Anchor(None),
1642         RenderMode::Normal,
1643         Some(use_absolute),
1644         aliases,
1645         ImplRenderingParameters {
1646             show_def_docs: false,
1647             show_default_items: false,
1648             show_non_assoc_items: false,
1649             toggle_open_by_default: false,
1650         },
1651     );
1652 }
1653
1654 fn render_union(
1655     w: &mut Buffer,
1656     it: &clean::Item,
1657     g: Option<&clean::Generics>,
1658     fields: &[clean::Item],
1659     tab: &str,
1660     cx: &Context<'_>,
1661 ) {
1662     write!(w, "{}union {}", it.visibility.print_with_space(it.item_id, cx), it.name.unwrap(),);
1663
1664     let where_displayed = g
1665         .map(|g| {
1666             write!(w, "{}", g.print(cx));
1667             print_where_clause_and_check(w, g, cx)
1668         })
1669         .unwrap_or(false);
1670
1671     // If there wasn't a `where` clause, we add a whitespace.
1672     if !where_displayed {
1673         w.write_str(" ");
1674     }
1675
1676     write!(w, "{{\n{}", tab);
1677     let count_fields =
1678         fields.iter().filter(|f| matches!(*f.kind, clean::StructFieldItem(..))).count();
1679     let toggle = should_hide_fields(count_fields);
1680     if toggle {
1681         toggle_open(w, format_args!("{} fields", count_fields));
1682     }
1683
1684     for field in fields {
1685         if let clean::StructFieldItem(ref ty) = *field.kind {
1686             write!(
1687                 w,
1688                 "    {}{}: {},\n{}",
1689                 field.visibility.print_with_space(field.item_id, cx),
1690                 field.name.unwrap(),
1691                 ty.print(cx),
1692                 tab
1693             );
1694         }
1695     }
1696
1697     if it.has_stripped_entries().unwrap() {
1698         write!(w, "    /* private fields */\n{}", tab);
1699     }
1700     if toggle {
1701         toggle_close(w);
1702     }
1703     w.write_str("}");
1704 }
1705
1706 fn render_struct(
1707     w: &mut Buffer,
1708     it: &clean::Item,
1709     g: Option<&clean::Generics>,
1710     ty: CtorKind,
1711     fields: &[clean::Item],
1712     tab: &str,
1713     structhead: bool,
1714     cx: &Context<'_>,
1715 ) {
1716     write!(
1717         w,
1718         "{}{}{}",
1719         it.visibility.print_with_space(it.item_id, cx),
1720         if structhead { "struct " } else { "" },
1721         it.name.unwrap()
1722     );
1723     if let Some(g) = g {
1724         write!(w, "{}", g.print(cx))
1725     }
1726     match ty {
1727         CtorKind::Fictive => {
1728             let where_diplayed = g.map(|g| print_where_clause_and_check(w, g, cx)).unwrap_or(false);
1729
1730             // If there wasn't a `where` clause, we add a whitespace.
1731             if !where_diplayed {
1732                 w.write_str(" {");
1733             } else {
1734                 w.write_str("{");
1735             }
1736             let count_fields =
1737                 fields.iter().filter(|f| matches!(*f.kind, clean::StructFieldItem(..))).count();
1738             let has_visible_fields = count_fields > 0;
1739             let toggle = should_hide_fields(count_fields);
1740             if toggle {
1741                 toggle_open(w, format_args!("{} fields", count_fields));
1742             }
1743             for field in fields {
1744                 if let clean::StructFieldItem(ref ty) = *field.kind {
1745                     write!(
1746                         w,
1747                         "\n{}    {}{}: {},",
1748                         tab,
1749                         field.visibility.print_with_space(field.item_id, cx),
1750                         field.name.unwrap(),
1751                         ty.print(cx),
1752                     );
1753                 }
1754             }
1755
1756             if has_visible_fields {
1757                 if it.has_stripped_entries().unwrap() {
1758                     write!(w, "\n{}    /* private fields */", tab);
1759                 }
1760                 write!(w, "\n{}", tab);
1761             } else if it.has_stripped_entries().unwrap() {
1762                 write!(w, " /* private fields */ ");
1763             }
1764             if toggle {
1765                 toggle_close(w);
1766             }
1767             w.write_str("}");
1768         }
1769         CtorKind::Fn => {
1770             w.write_str("(");
1771             for (i, field) in fields.iter().enumerate() {
1772                 if i > 0 {
1773                     w.write_str(", ");
1774                 }
1775                 match *field.kind {
1776                     clean::StrippedItem(box clean::StructFieldItem(..)) => write!(w, "_"),
1777                     clean::StructFieldItem(ref ty) => {
1778                         write!(
1779                             w,
1780                             "{}{}",
1781                             field.visibility.print_with_space(field.item_id, cx),
1782                             ty.print(cx),
1783                         )
1784                     }
1785                     _ => unreachable!(),
1786                 }
1787             }
1788             w.write_str(")");
1789             if let Some(g) = g {
1790                 write!(w, "{}", print_where_clause(g, cx, 0, Ending::NoNewline));
1791             }
1792             // We only want a ";" when we are displaying a tuple struct, not a variant tuple struct.
1793             if structhead {
1794                 w.write_str(";");
1795             }
1796         }
1797         CtorKind::Const => {
1798             // Needed for PhantomData.
1799             if let Some(g) = g {
1800                 write!(w, "{}", print_where_clause(g, cx, 0, Ending::NoNewline));
1801             }
1802             w.write_str(";");
1803         }
1804     }
1805 }
1806
1807 fn document_non_exhaustive_header(item: &clean::Item) -> &str {
1808     if item.is_non_exhaustive() { " (Non-exhaustive)" } else { "" }
1809 }
1810
1811 fn document_non_exhaustive(w: &mut Buffer, item: &clean::Item) {
1812     if item.is_non_exhaustive() {
1813         write!(
1814             w,
1815             "<details class=\"rustdoc-toggle non-exhaustive\">\
1816                  <summary class=\"hideme\"><span>{}</span></summary>\
1817                  <div class=\"docblock\">",
1818             {
1819                 if item.is_struct() {
1820                     "This struct is marked as non-exhaustive"
1821                 } else if item.is_enum() {
1822                     "This enum is marked as non-exhaustive"
1823                 } else if item.is_variant() {
1824                     "This variant is marked as non-exhaustive"
1825                 } else {
1826                     "This type is marked as non-exhaustive"
1827                 }
1828             }
1829         );
1830
1831         if item.is_struct() {
1832             w.write_str(
1833                 "Non-exhaustive structs could have additional fields added in future. \
1834                  Therefore, non-exhaustive structs cannot be constructed in external crates \
1835                  using the traditional <code>Struct { .. }</code> syntax; cannot be \
1836                  matched against without a wildcard <code>..</code>; and \
1837                  struct update syntax will not work.",
1838             );
1839         } else if item.is_enum() {
1840             w.write_str(
1841                 "Non-exhaustive enums could have additional variants added in future. \
1842                  Therefore, when matching against variants of non-exhaustive enums, an \
1843                  extra wildcard arm must be added to account for any future variants.",
1844             );
1845         } else if item.is_variant() {
1846             w.write_str(
1847                 "Non-exhaustive enum variants could have additional fields added in future. \
1848                  Therefore, non-exhaustive enum variants cannot be constructed in external \
1849                  crates and cannot be matched against.",
1850             );
1851         } else {
1852             w.write_str(
1853                 "This type will require a wildcard arm in any match statements or constructors.",
1854             );
1855         }
1856
1857         w.write_str("</div></details>");
1858     }
1859 }
1860
1861 fn document_type_layout(w: &mut Buffer, cx: &Context<'_>, ty_def_id: DefId) {
1862     fn write_size_of_layout(w: &mut Buffer, layout: Layout<'_>, tag_size: u64) {
1863         if layout.abi().is_unsized() {
1864             write!(w, "(unsized)");
1865         } else {
1866             let bytes = layout.size().bytes() - tag_size;
1867             write!(w, "{size} byte{pl}", size = bytes, pl = if bytes == 1 { "" } else { "s" },);
1868         }
1869     }
1870
1871     if !cx.shared.show_type_layout {
1872         return;
1873     }
1874
1875     writeln!(
1876         w,
1877         "<h2 id=\"layout\" class=\"small-section-header\"> \
1878         Layout<a href=\"#layout\" class=\"anchor\"></a></h2>"
1879     );
1880     writeln!(w, "<div class=\"docblock\">");
1881
1882     let tcx = cx.tcx();
1883     let param_env = tcx.param_env(ty_def_id);
1884     let ty = tcx.type_of(ty_def_id);
1885     match tcx.layout_of(param_env.and(ty)) {
1886         Ok(ty_layout) => {
1887             writeln!(
1888                 w,
1889                 "<div class=\"warning\"><p><strong>Note:</strong> Most layout information is \
1890                  <strong>completely unstable</strong> and may even differ between compilations. \
1891                  The only exception is types with certain <code>repr(...)</code> attributes. \
1892                  Please see the Rust Reference’s \
1893                  <a href=\"https://doc.rust-lang.org/reference/type-layout.html\">“Type Layout”</a> \
1894                  chapter for details on type layout guarantees.</p></div>"
1895             );
1896             w.write_str("<p><strong>Size:</strong> ");
1897             write_size_of_layout(w, ty_layout.layout, 0);
1898             writeln!(w, "</p>");
1899             if let Variants::Multiple { variants, tag, tag_encoding, .. } =
1900                 &ty_layout.layout.variants()
1901             {
1902                 if !variants.is_empty() {
1903                     w.write_str(
1904                         "<p><strong>Size for each variant:</strong></p>\
1905                             <ul>",
1906                     );
1907
1908                     let Adt(adt, _) = ty_layout.ty.kind() else {
1909                         span_bug!(tcx.def_span(ty_def_id), "not an adt")
1910                     };
1911
1912                     let tag_size = if let TagEncoding::Niche { .. } = tag_encoding {
1913                         0
1914                     } else if let Primitive::Int(i, _) = tag.primitive() {
1915                         i.size().bytes()
1916                     } else {
1917                         span_bug!(tcx.def_span(ty_def_id), "tag is neither niche nor int")
1918                     };
1919
1920                     for (index, layout) in variants.iter_enumerated() {
1921                         let name = adt.variant(index).name;
1922                         write!(w, "<li><code>{name}</code>: ", name = name);
1923                         write_size_of_layout(w, *layout, tag_size);
1924                         writeln!(w, "</li>");
1925                     }
1926                     w.write_str("</ul>");
1927                 }
1928             }
1929         }
1930         // This kind of layout error can occur with valid code, e.g. if you try to
1931         // get the layout of a generic type such as `Vec<T>`.
1932         Err(LayoutError::Unknown(_)) => {
1933             writeln!(
1934                 w,
1935                 "<p><strong>Note:</strong> Unable to compute type layout, \
1936                  possibly due to this type having generic parameters. \
1937                  Layout can only be computed for concrete, fully-instantiated types.</p>"
1938             );
1939         }
1940         // This kind of error probably can't happen with valid code, but we don't
1941         // want to panic and prevent the docs from building, so we just let the
1942         // user know that we couldn't compute the layout.
1943         Err(LayoutError::SizeOverflow(_)) => {
1944             writeln!(
1945                 w,
1946                 "<p><strong>Note:</strong> Encountered an error during type layout; \
1947                  the type was too big.</p>"
1948             );
1949         }
1950         Err(LayoutError::NormalizationFailure(_, _)) => {
1951             writeln!(
1952                 w,
1953                 "<p><strong>Note:</strong> Encountered an error during type layout; \
1954                 the type failed to be normalized.</p>"
1955             )
1956         }
1957     }
1958
1959     writeln!(w, "</div>");
1960 }
1961
1962 fn pluralize(count: usize) -> &'static str {
1963     if count > 1 { "s" } else { "" }
1964 }