rustc_builtin_macros/
alloc_error_handler.rs

1use rustc_ast::expand::allocator::{ALLOC_ERROR_HANDLER, global_fn_name};
2use rustc_ast::{self as ast, FnHeader, FnSig, Generics, ItemKind, Safety, Stmt, StmtKind, TyKind};
3use rustc_expand::base::{Annotatable, ExtCtxt};
4use rustc_span::{Ident, Span, sym};
5use thin_vec::thin_vec;
6
7use crate::diagnostics;
8use crate::util::check_builtin_macro_attribute;
9
10pub(crate) fn expand(
11    ecx: &mut ExtCtxt<'_>,
12    _span: Span,
13    meta_item: &ast::MetaItem,
14    item: Annotatable,
15) -> Vec<Annotatable> {
16    check_builtin_macro_attribute(ecx, meta_item, sym::alloc_error_handler);
17
18    let orig_item = item.clone();
19
20    // Allow using `#[alloc_error_handler]` on an item statement
21    // FIXME - if we get deref patterns, use them to reduce duplication here
22    let (item, ident, is_stmt, sig_span) = if let Annotatable::Item(item) = &item
23        && let ItemKind::Fn(fn_kind) = &item.kind
24    {
25        (item, fn_kind.ident, false, ecx.with_def_site_ctxt(fn_kind.sig.span))
26    } else if let Annotatable::Stmt(stmt) = &item
27        && let StmtKind::Item(item) = &stmt.kind
28        && let ItemKind::Fn(fn_kind) = &item.kind
29    {
30        (item, fn_kind.ident, true, ecx.with_def_site_ctxt(fn_kind.sig.span))
31    } else {
32        ecx.dcx().emit_err(diagnostics::AllocErrorMustBeFn { span: item.span() });
33        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];
34    };
35
36    // Generate a bunch of new items using the AllocFnFactory
37    let span = ecx.with_def_site_ctxt(item.span);
38
39    // Generate item statements for the allocator methods.
40    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)];
41
42    // Generate anonymous constant serving as container for the allocator methods.
43    let const_item = ecx.item_const_underscore(span, ecx.block(span, stmts));
44    let const_item = if is_stmt {
45        Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))
46    } else {
47        Annotatable::Item(const_item)
48    };
49
50    // Return the original item and the new methods.
51    ::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]
52}
53
54// #[rustc_std_internal_symbol]
55// unsafe fn __rust_alloc_error_handler(size: usize, align: usize) -> ! {
56//     handler(core::alloc::Layout::from_size_align_unchecked(size, align))
57// }
58fn generate_handler(cx: &ExtCtxt<'_>, handler: Ident, span: Span, sig_span: Span) -> Stmt {
59    let ty_usize = cx.ty_name(span, sym::usize);
60
61    let layout_new = cx.std_path(span, &[sym::alloc, sym::Layout, sym::from_size_align_unchecked]);
62    let layout_new = cx.expr_path(layout_new);
63    let layout = cx.expr_call(
64        span,
65        layout_new,
66        {
    let len = [(), ()].len();
    let mut vec = ::thin_vec::ThinVec::with_capacity(len);
    vec.push(cx.expr_name(span, sym::size));
    vec.push(cx.expr_name(span, sym::align));
    vec
}thin_vec![cx.expr_name(span, sym::size), cx.expr_name(span, sym::align)],
67    );
68
69    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]);
70
71    let never = ast::FnRetTy::Ty(cx.ty(span, TyKind::Never));
72    let params = {
    let len = [(), ()].len();
    let mut vec = ::thin_vec::ThinVec::with_capacity(len);
    vec.push(cx.param(span, sym::size, ty_usize.clone()));
    vec.push(cx.param(span, sym::align, ty_usize));
    vec
}thin_vec![
73        cx.param(span, sym::size, ty_usize.clone()),
74        cx.param(span, sym::align, ty_usize)
75    ];
76    let decl = cx.fn_decl(params, never);
77    let header = FnHeader { safety: Safety::Unsafe(span), ..FnHeader::default() };
78    let sig = FnSig { decl, header, span };
79
80    let body = Some(cx.block_expr(call));
81    let kind = ItemKind::Fn(cx.item_fn(
82        sig,
83        Ident::from_str_and_span(&global_fn_name(ALLOC_ERROR_HANDLER), span),
84        Generics::default(),
85        body,
86    ));
87
88    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)];
89
90    let item = cx.item(span, attrs, kind);
91    cx.stmt_item(sig_span, item)
92}
rustc_builtin_macros/alloc_error_handler.rs

rustc_builtin_macros/
alloc_error_handler.rs
