diff options
Diffstat (limited to 'compiler/rustc_ast_lowering/src/format.rs')
| -rw-r--r-- | compiler/rustc_ast_lowering/src/format.rs | 25 |
1 files changed, 24 insertions, 1 deletions
diff --git a/compiler/rustc_ast_lowering/src/format.rs b/compiler/rustc_ast_lowering/src/format.rs index 9b295339d94..afcf8b15cd8 100644 --- a/compiler/rustc_ast_lowering/src/format.rs +++ b/compiler/rustc_ast_lowering/src/format.rs @@ -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), |