Get repr information through AdtDef for foreign items

src/librustdoc/html/render/mod.rs

@@ -849,10 +849,10 @@ fn assoc_method(
     let (indent, indent_str, end_newline) = if parent == ItemType::Trait {
         header_len += 4;
         let indent_str = "    ";
-        write!(w, "{}", render_attributes_in_pre(meth, indent_str));
+        write!(w, "{}", render_attributes_in_pre(meth, indent_str, tcx));
         (4, indent_str, Ending::NoNewline)
     } else {
-        render_attributes_in_code(w, meth);
+        render_attributes_in_code(w, meth, tcx);
         (0, "", Ending::Newline)
     };
     w.reserve(header_len + "<a href=\"\" class=\"fn\">{".len() + "</a>".len());
@@ -1024,8 +1024,12 @@ fn render_assoc_item(
 const ALLOWED_ATTRIBUTES: &[Symbol] =
     &[sym::export_name, sym::link_section, sym::no_mangle, sym::repr, sym::non_exhaustive];
 
-fn attributes(it: &clean::Item) -> Vec<String> {
+fn attributes(it: &clean::Item, tcx: TyCtxt<'_>) -> Vec<String> {
-    it.attrs
+    use rustc_abi::IntegerType;
+    use rustc_middle::ty::ReprFlags;
+
+    let mut attrs: Vec<String> = it
+        .attrs
         .other_attrs
         .iter()
         .filter_map(|attr| {
@@ -1040,17 +1044,62 @@ fn attributes(it: &clean::Item) -> Vec<String> {
                 None
             }
         })
-        .collect()
+        .collect();
+    if let Some(def_id) = it.item_id.as_def_id() &&
+        !def_id.is_local() &&
+        // This check is needed because `adt_def` will panic if not a compatible type otherwise...
+        matches!(it.type_(), ItemType::Struct | ItemType::Enum | ItemType::Union)
+    {
+        let repr = tcx.adt_def(def_id).repr();
+        let mut out = Vec::new();
+        if repr.flags.contains(ReprFlags::IS_C) {
+            out.push("C");
+        }
+        if repr.flags.contains(ReprFlags::IS_TRANSPARENT) {
+            out.push("transparent");
+        }
+        if repr.flags.contains(ReprFlags::IS_SIMD) {
+            out.push("simd");
+        }
+        let pack_s;
+        if let Some(pack) = repr.pack {
+            pack_s = format!("packed({})", pack.bytes());
+            out.push(&pack_s);
+        }
+        let align_s;
+        if let Some(align) = repr.align {
+            align_s = format!("align({})", align.bytes());
+            out.push(&align_s);
+        }
+        let int_s;
+        if let Some(int) = repr.int {
+            int_s = match int {
+                IntegerType::Pointer(is_signed) => {
+                    format!("{}size", if is_signed { 'i' } else { 'u' })
+                }
+                IntegerType::Fixed(size, is_signed) => {
+                    format!("{}{}", if is_signed { 'i' } else { 'u' }, size.size().bytes() * 8)
+                }
+            };
+            out.push(&int_s);
+        }
+        if out.is_empty() {
+            return Vec::new();
+        }
+        attrs.push(format!("#[repr({})]", out.join(", ")));
+    }
+    attrs
 }
 
 // When an attribute is rendered inside a `<pre>` tag, it is formatted using
 // a whitespace prefix and newline.
-fn render_attributes_in_pre<'a>(
+fn render_attributes_in_pre<'a, 'b: 'a>(
     it: &'a clean::Item,
     prefix: &'a str,
-) -> impl fmt::Display + Captures<'a> {
+    tcx: TyCtxt<'b>,
+) -> impl fmt::Display + Captures<'a> + Captures<'b> {
     crate::html::format::display_fn(move |f| {
-        for a in attributes(it) {
+        for a in attributes(it, tcx) {
             writeln!(f, "{}{}", prefix, a)?;
         }
         Ok(())
@@ -1059,8 +1108,8 @@ fn render_attributes_in_pre<'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) {
+fn render_attributes_in_code(w: &mut Buffer, it: &clean::Item, tcx: TyCtxt<'_>) {
-    for a in attributes(it) {
+    for a in attributes(it, tcx) {
         write!(w, "<div class=\"code-attribute\">{}</div>", a);
     }
 }

src/librustdoc/html/render/print_item.rs

@@ -548,7 +548,7 @@ fn item_function(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, f: &cle
             w,
             "{attrs}{vis}{constness}{asyncness}{unsafety}{abi}fn \
                 {name}{generics}{decl}{notable_traits}{where_clause}",
-            attrs = render_attributes_in_pre(it, ""),
+            attrs = render_attributes_in_pre(it, "", tcx),
             vis = visibility,
             constness = constness,
             asyncness = asyncness,
@@ -589,7 +589,7 @@ fn item_trait(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean:
             it.name.unwrap(),
             t.generics.print(cx),
             bounds,
-            attrs = render_attributes_in_pre(it, ""),
+            attrs = render_attributes_in_pre(it, "", tcx),
         );
 
         if !t.generics.where_predicates.is_empty() {
@@ -1063,7 +1063,7 @@ fn item_trait_alias(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &
             t.generics.print(cx),
             print_where_clause(&t.generics, cx, 0, Ending::Newline),
             bounds(&t.bounds, true, cx),
-            attrs = render_attributes_in_pre(it, ""),
+            attrs = render_attributes_in_pre(it, "", cx.tcx()),
         );
     });
 
@@ -1085,7 +1085,7 @@ fn item_opaque_ty(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &cl
             t.generics.print(cx),
             where_clause = print_where_clause(&t.generics, cx, 0, Ending::Newline),
             bounds = bounds(&t.bounds, false, cx),
-            attrs = render_attributes_in_pre(it, ""),
+            attrs = render_attributes_in_pre(it, "", cx.tcx()),
         );
     });
 
@@ -1109,7 +1109,7 @@ fn item_typedef(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clea
                 t.generics.print(cx),
                 where_clause = print_where_clause(&t.generics, cx, 0, Ending::Newline),
                 type_ = t.type_.print(cx),
-                attrs = render_attributes_in_pre(it, ""),
+                attrs = render_attributes_in_pre(it, "", cx.tcx()),
             );
         });
     }
@@ -1168,7 +1168,8 @@ fn item_union(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, s: &clean:
             &'b self,
         ) -> impl fmt::Display + Captures<'a> + 'b + Captures<'cx> {
             display_fn(move |f| {
-                let v = render_attributes_in_pre(self.it, "");
+                let tcx = self.cx.borrow().tcx();
+                let v = render_attributes_in_pre(self.it, "", tcx);
                 write!(f, "{v}")
             })
         }
@@ -1250,7 +1251,7 @@ fn item_enum(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, e: &clean::
             visibility_print_with_space(it.visibility(tcx), it.item_id, cx),
             it.name.unwrap(),
             e.generics.print(cx),
-            attrs = render_attributes_in_pre(it, ""),
+            attrs = render_attributes_in_pre(it, "", tcx),
         );
         if !print_where_clause_and_check(w, &e.generics, cx) {
             // If there wasn't a `where` clause, we add a whitespace.
@@ -1445,7 +1446,7 @@ fn item_primitive(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item) {
 fn item_constant(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, c: &clean::Constant) {
     wrap_item(w, |w| {
         let tcx = cx.tcx();
-        render_attributes_in_code(w, it);
+        render_attributes_in_code(w, it, tcx);
 
         write!(
             w,
@@ -1492,7 +1493,7 @@ fn item_constant(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, c: &cle
 
 fn item_struct(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, s: &clean::Struct) {
     wrap_item(w, |w| {
-        render_attributes_in_code(w, it);
+        render_attributes_in_code(w, it, cx.tcx());
         render_struct(w, it, Some(&s.generics), s.ctor_kind, &s.fields, "", true, cx);
     });
 
@@ -1542,7 +1543,7 @@ fn item_struct(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, s: &clean
 
 fn item_static(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, s: &clean::Static) {
     wrap_item(w, |w| {
-        render_attributes_in_code(w, it);
+        render_attributes_in_code(w, it, cx.tcx());
         write!(
             w,
             "{vis}static {mutability}{name}: {typ}",
@@ -1558,7 +1559,7 @@ fn item_static(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, s: &clean
 fn item_foreign_type(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item) {
     wrap_item(w, |w| {
         w.write_str("extern {\n");
-        render_attributes_in_code(w, it);
+        render_attributes_in_code(w, it, cx.tcx());
         write!(
             w,
             "    {}type {};\n}}",

src/librustdoc/lib.rs

@@ -33,6 +33,7 @@ extern crate tracing;
 // Dependencies listed in Cargo.toml do not need `extern crate`.
 
 extern crate pulldown_cmark;
+extern crate rustc_abi;
 extern crate rustc_ast;
 extern crate rustc_ast_pretty;
 extern crate rustc_attr;