rustc_builtin_macros/
alloc_error_handler.rs

1use rustc_ast::expand::allocator::{ALLOC_ERROR_HANDLER, global_fn_name};
2use rustc_ast::{
3    self as ast, Fn, FnHeader, FnSig, Generics, ItemKind, Safety, Stmt, StmtKind, TyKind,
4};
5use rustc_expand::base::{Annotatable, ExtCtxt};
6use rustc_span::{Ident, Span, kw, sym};
7use thin_vec::{ThinVec, thin_vec};
8
9use crate::diagnostics;
10use crate::util::check_builtin_macro_attribute;
11
12pub(crate) fn expand(
13    ecx: &mut ExtCtxt<'_>,
14    _span: Span,
15    meta_item: &ast::MetaItem,
16    item: Annotatable,
17) -> Vec<Annotatable> {
18    check_builtin_macro_attribute(ecx, meta_item, sym::alloc_error_handler);
19
20    let orig_item = item.clone();
21
22    // Allow using `#[alloc_error_handler]` on an item statement
23    // FIXME - if we get deref patterns, use them to reduce duplication here
24    let (item, ident, is_stmt, sig_span) = if let Annotatable::Item(item) = &item
25        && let ItemKind::Fn(fn_kind) = &item.kind
26    {
27        (item, fn_kind.ident, false, ecx.with_def_site_ctxt(fn_kind.sig.span))
28    } else if let Annotatable::Stmt(stmt) = &item
29        && let StmtKind::Item(item) = &stmt.kind
30        && let ItemKind::Fn(fn_kind) = &item.kind
31    {
32        (item, fn_kind.ident, true, ecx.with_def_site_ctxt(fn_kind.sig.span))
33    } else {
34        ecx.dcx().emit_err(diagnostics::AllocErrorMustBeFn { span: item.span() });
35        return ::alloc::boxed::box_assume_init_into_vec_unsafe(::alloc::intrinsics::write_box_via_move(::alloc::boxed::Box::new_uninit(),
        [orig_item]))vec![orig_item];
36    };
37
38    // Generate a bunch of new items using the AllocFnFactory
39    let span = ecx.with_def_site_ctxt(item.span);
40
41    // Generate item statements for the allocator methods.
42    let stmts = {
    let len = [()].len();
    let mut vec = ::thin_vec::ThinVec::with_capacity(len);
    vec.push(generate_handler(ecx, ident, span, sig_span));
    vec
}thin_vec![generate_handler(ecx, ident, span, sig_span)];
43
44    // Generate anonymous constant serving as container for the allocator methods.
45    let const_ty = ecx.ty(sig_span, TyKind::Tup(ThinVec::new()));
46    let const_body = ecx.expr_block(ecx.block(span, stmts));
47    let const_item =
48        ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, Some(const_body));
49    let const_item = if is_stmt {
50        Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))
51    } else {
52        Annotatable::Item(const_item)
53    };
54
55    // Return the original item and the new methods.
56    ::alloc::boxed::box_assume_init_into_vec_unsafe(::alloc::intrinsics::write_box_via_move(::alloc::boxed::Box::new_uninit(),
        [orig_item, const_item]))vec![orig_item, const_item]
57}
58
59// #[rustc_std_internal_symbol]
60// unsafe fn __rust_alloc_error_handler(size: usize, align: usize) -> ! {
61//     handler(core::alloc::Layout::from_size_align_unchecked(size, align))
62// }
63fn generate_handler(cx: &ExtCtxt<'_>, handler: Ident, span: Span, sig_span: Span) -> Stmt {
64    let usize = cx.path_ident(span, Ident::new(sym::usize, span));
65    let ty_usize = cx.ty_path(usize);
66    let size = Ident::new(sym::size, span);
67    let align = Ident::new(sym::align, span);
68
69    let layout_new = cx.std_path(&[sym::alloc, sym::Layout, sym::from_size_align_unchecked]);
70    let layout_new = cx.expr_path(cx.path(span, layout_new));
71    let layout = cx.expr_call(
72        span,
73        layout_new,
74        {
    let len = [(), ()].len();
    let mut vec = ::thin_vec::ThinVec::with_capacity(len);
    vec.push(cx.expr_ident(span, size));
    vec.push(cx.expr_ident(span, align));
    vec
}thin_vec![cx.expr_ident(span, size), cx.expr_ident(span, align)],
75    );
76
77    let call = cx.expr_call_ident(sig_span, handler, {
    let len = [()].len();
    let mut vec = ::thin_vec::ThinVec::with_capacity(len);
    vec.push(layout);
    vec
}thin_vec![layout]);
78
79    let never = ast::FnRetTy::Ty(cx.ty(span, TyKind::Never));
80    let params = {
    let len = [(), ()].len();
    let mut vec = ::thin_vec::ThinVec::with_capacity(len);
    vec.push(cx.param(span, size, ty_usize.clone()));
    vec.push(cx.param(span, align, ty_usize));
    vec
}thin_vec![cx.param(span, size, ty_usize.clone()), cx.param(span, align, ty_usize)];
81    let decl = cx.fn_decl(params, never);
82    let header = FnHeader { safety: Safety::Unsafe(span), ..FnHeader::default() };
83    let sig = FnSig { decl, header, span };
84
85    let body = Some(cx.block_expr(call));
86    let kind = ItemKind::Fn(Box::new(Fn {
87        defaultness: ast::Defaultness::Implicit,
88        sig,
89        ident: Ident::from_str_and_span(&global_fn_name(ALLOC_ERROR_HANDLER), span),
90        generics: Generics::default(),
91        contract: None,
92        body,
93        define_opaque: None,
94        eii_impl: None,
95    }));
96
97    let attrs = {
    let len = [()].len();
    let mut vec = ::thin_vec::ThinVec::with_capacity(len);
    vec.push(cx.attr_word(sym::rustc_std_internal_symbol, span));
    vec
}thin_vec![cx.attr_word(sym::rustc_std_internal_symbol, span)];
98
99    let item = cx.item(span, attrs, kind);
100    cx.stmt_item(sig_span, item)
101}
rustc_builtin_macros/alloc_error_handler.rs

rustc_builtin_macros/
alloc_error_handler.rs
