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Limit lifetime of format_args!() with inlined args.

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This commit is contained in:
Mara Bos 2023-04-24 17:31:32 +02:00
parent ecd3dbab4e
commit d5843ddaf1
3 changed files with 40 additions and 1 deletions
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25
compiler/rustc_ast_lowering/src/format.rs
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@ -446,7 +446,30 @@ fn expand_format_args<'hir>(
&& argmap.iter().enumerate().all(|(i, (&(j, _), _))| i == j)
&& arguments.iter().skip(1).all(|arg| !may_contain_yield_point(&arg.expr));
let args = if use_simple_array {
let args = if arguments.is_empty() {
// Generate:
// &<core::fmt::Argument>::none()
//
// Note:
// `none()` just returns `[]`. We use `none()` rather than `[]` to limit the lifetime.
//
// This makes sure that this still fails to compile, even when the argument is inlined:
//
// ```
// let f = format_args!("{}", "a");
// println!("{f}"); // error E0716
// ```
//
// Cases where keeping the object around is allowed, such as `format_args!("a")`,
// are handled above by the `allow_const` case.
let none_fn = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
macsp,
hir::LangItem::FormatArgument,
sym::none,
));
let none = ctx.expr_call(macsp, none_fn, &[]);
ctx.expr(macsp, hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, none))
} else if use_simple_array {
// Generate:
// &[
// <core::fmt::Argument>::new_display(&arg0),