1 files changed, 86 insertions, 0 deletions
diff --git a/src/librustdoc/html/render/type_layout.rs b/src/librustdoc/html/render/type_layout.rs
new file mode 100644
index 000000000..c9b95b1e6
--- /dev/null
+++ b/src/librustdoc/html/render/type_layout.rs
@@ -0,0 +1,86 @@
+use askama::Template;
+
+use rustc_data_structures::captures::Captures;
+use rustc_hir::def_id::DefId;
+use rustc_middle::span_bug;
+use rustc_middle::ty::layout::LayoutError;
+use rustc_middle::ty::Adt;
+use rustc_span::symbol::Symbol;
+use rustc_target::abi::{Primitive, TagEncoding, Variants};
+
+use std::fmt;
+
+use crate::html::format::display_fn;
+use crate::html::render::Context;
+
+#[derive(Template)]
+#[template(path = "type_layout.html")]
+struct TypeLayout<'cx> {
+    variants: Vec<(Symbol, TypeLayoutSize)>,
+    type_layout_size: Result<TypeLayoutSize, LayoutError<'cx>>,
+}
+
+#[derive(Template)]
+#[template(path = "type_layout_size.html")]
+struct TypeLayoutSize {
+    is_unsized: bool,
+    is_uninhabited: bool,
+    size: u64,
+}
+
+pub(crate) fn document_type_layout<'a, 'cx: 'a>(
+    cx: &'a Context<'cx>,
+    ty_def_id: DefId,
+) -> impl fmt::Display + 'a + Captures<'cx> {
+    display_fn(move |f| {
+        if !cx.shared.show_type_layout {
+            return Ok(());
+        }
+
+        let tcx = cx.tcx();
+        let param_env = tcx.param_env(ty_def_id);
+        let ty = tcx.type_of(ty_def_id).subst_identity();
+        let type_layout = tcx.layout_of(param_env.and(ty));
+
+        let variants =
+            if let Ok(type_layout) = type_layout &&
+                let Variants::Multiple { variants, tag, tag_encoding, .. } =
+                    type_layout.layout.variants() &&
+                !variants.is_empty()
+            {
+                let tag_size =
+                    if let TagEncoding::Niche { .. } = tag_encoding {
+                        0
+                    } else if let Primitive::Int(i, _) = tag.primitive() {
+                        i.size().bytes()
+                    } else {
+                        span_bug!(tcx.def_span(ty_def_id), "tag is neither niche nor int")
+                    };
+                variants
+                    .iter_enumerated()
+                    .map(|(variant_idx, variant_layout)| {
+                        let Adt(adt, _) = type_layout.ty.kind() else {
+                            span_bug!(tcx.def_span(ty_def_id), "not an adt")
+                        };
+                        let name = adt.variant(variant_idx).name;
+                        let is_unsized = variant_layout.abi.is_unsized();
+                        let is_uninhabited = variant_layout.abi.is_uninhabited();
+                        let size = variant_layout.size.bytes() - tag_size;
+                        let type_layout_size = TypeLayoutSize { is_unsized, is_uninhabited, size };
+                        (name, type_layout_size)
+                    })
+                    .collect()
+            } else {
+                Vec::new()
+            };
+
+        let type_layout_size = tcx.layout_of(param_env.and(ty)).map(|layout| {
+            let is_unsized = layout.abi.is_unsized();
+            let is_uninhabited = layout.abi.is_uninhabited();
+            let size = layout.size.bytes();
+            TypeLayoutSize { is_unsized, is_uninhabited, size }
+        });
+
+        Ok(TypeLayout { variants, type_layout_size }.render_into(f).unwrap())
+    })
+}