2 files changed, 106 insertions, 0 deletions
diff --git a/compiler/rustc_builtin_macros/src/alloc_error_handler.rs b/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
new file mode 100644
index 00000000000..eaf1b1167cf
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
@@ -0,0 +1,104 @@
+use crate::util::check_builtin_macro_attribute;
+
+use rustc_ast::ptr::P;
+use rustc_ast::{self as ast, FnHeader, FnSig, Generics, StmtKind};
+use rustc_ast::{Fn, ItemKind, Stmt, TyKind, Unsafe};
+use rustc_expand::base::{Annotatable, ExtCtxt};
+use rustc_span::symbol::{kw, sym, Ident};
+use rustc_span::Span;
+use thin_vec::thin_vec;
+
+pub fn expand(
+    ecx: &mut ExtCtxt<'_>,
+    _span: Span,
+    meta_item: &ast::MetaItem,
+    item: Annotatable,
+) -> Vec<Annotatable> {
+    check_builtin_macro_attribute(ecx, meta_item, sym::alloc_error_handler);
+
+    let orig_item = item.clone();
+    let not_function = || {
+        ecx.sess
+            .parse_sess
+            .span_diagnostic
+            .span_err(item.span(), "alloc_error_handler must be a function");
+        vec![orig_item.clone()]
+    };
+
+    // Allow using `#[alloc_error_handler]` on an item statement
+    // FIXME - if we get deref patterns, use them to reduce duplication here
+    let (item, is_stmt, sig_span) = match &item {
+        Annotatable::Item(item) => match item.kind {
+            ItemKind::Fn(ref fn_kind) => (item, false, ecx.with_def_site_ctxt(fn_kind.sig.span)),
+            _ => return not_function(),
+        },
+        Annotatable::Stmt(stmt) => match &stmt.kind {
+            StmtKind::Item(item_) => match item_.kind {
+                ItemKind::Fn(ref fn_kind) => {
+                    (item_, true, ecx.with_def_site_ctxt(fn_kind.sig.span))
+                }
+                _ => return not_function(),
+            },
+            _ => return not_function(),
+        },
+        _ => return not_function(),
+    };
+
+    // Generate a bunch of new items using the AllocFnFactory
+    let span = ecx.with_def_site_ctxt(item.span);
+
+    // Generate item statements for the allocator methods.
+    let stmts = vec![generate_handler(ecx, item.ident, span, sig_span)];
+
+    // Generate anonymous constant serving as container for the allocator methods.
+    let const_ty = ecx.ty(sig_span, TyKind::Tup(Vec::new()));
+    let const_body = ecx.expr_block(ecx.block(span, stmts));
+    let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
+    let const_item = if is_stmt {
+        Annotatable::Stmt(P(ecx.stmt_item(span, const_item)))
+    } else {
+        Annotatable::Item(const_item)
+    };
+
+    // Return the original item and the new methods.
+    vec![orig_item, const_item]
+}
+
+// #[rustc_std_internal_symbol]
+// unsafe fn __rg_oom(size: usize, align: usize) -> ! {
+//     handler(core::alloc::Layout::from_size_align_unchecked(size, align))
+// }
+fn generate_handler(cx: &ExtCtxt<'_>, handler: Ident, span: Span, sig_span: Span) -> Stmt {
+    let usize = cx.path_ident(span, Ident::new(sym::usize, span));
+    let ty_usize = cx.ty_path(usize);
+    let size = Ident::from_str_and_span("size", span);
+    let align = Ident::from_str_and_span("align", span);
+
+    let layout_new = cx.std_path(&[sym::alloc, sym::Layout, sym::from_size_align_unchecked]);
+    let layout_new = cx.expr_path(cx.path(span, layout_new));
+    let layout =
+        cx.expr_call(span, layout_new, vec![cx.expr_ident(span, size), cx.expr_ident(span, align)]);
+
+    let call = cx.expr_call_ident(sig_span, handler, vec![layout]);
+
+    let never = ast::FnRetTy::Ty(cx.ty(span, TyKind::Never));
+    let params = vec![cx.param(span, size, ty_usize.clone()), cx.param(span, align, ty_usize)];
+    let decl = cx.fn_decl(params, never);
+    let header = FnHeader { unsafety: Unsafe::Yes(span), ..FnHeader::default() };
+    let sig = FnSig { decl, header, span: span };
+
+    let body = Some(cx.block_expr(call));
+    let kind = ItemKind::Fn(Box::new(Fn {
+        defaultness: ast::Defaultness::Final,
+        sig,
+        generics: Generics::default(),
+        body,
+    }));
+
+    let special = sym::rustc_std_internal_symbol;
+    let special = cx.meta_word(span, special);
+    let attrs = thin_vec![cx.attribute(special)];
+
+    let item = cx.item(span, Ident::from_str_and_span("__rg_oom", span), attrs, kind);
+    cx.stmt_item(sig_span, item)
+}
diff --git a/compiler/rustc_builtin_macros/src/lib.rs b/compiler/rustc_builtin_macros/src/lib.rs
index c7ea7de8f4e..bde0102186a 100644
--- a/compiler/rustc_builtin_macros/src/lib.rs
+++ b/compiler/rustc_builtin_macros/src/lib.rs
@@ -25,6 +25,7 @@ use rustc_expand::base::{MacroExpanderFn, ResolverExpand, SyntaxExtensionKind};
 use rustc_expand::proc_macro::BangProcMacro;
 use rustc_span::symbol::sym;
 
+mod alloc_error_handler;
 mod assert;
 mod cfg;
 mod cfg_accessible;
@@ -94,6 +95,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
     }
 
     register_attr! {
+        alloc_error_handler: alloc_error_handler::expand,
         bench: test::expand_bench,
         cfg_accessible: cfg_accessible::Expander,
         cfg_eval: cfg_eval::expand,