Remove core::fmt::rt::UnsafeArg.

We can now just make new_v1_formatted an unsafe fn.

Author: m-ou-se

compiler/rustc_ast_lowering/src/format.rs

@@ -536,34 +536,32 @@ fn expand_format_args<'hir>(
 
     let call = if let Some(format_options) = format_options {
         // Generate:
-        //     <core::fmt::Arguments>::new_v1_formatted(
-        //         lit_pieces,
-        //         args,
-        //         format_options,
-        //         unsafe { ::core::fmt::UnsafeArg::new() }
-        //     )
+        //     unsafe {
+        //         <core::fmt::Arguments>::new_v1_formatted(
+        //             lit_pieces,
+        //             args,
+        //             format_options,
+        //         )
+        //     }
         let new_v1_formatted = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
             macsp,
             hir::LangItem::FormatArguments,
             sym::new_v1_formatted,
         ));
-        let unsafe_arg_new = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
-            macsp,
-            hir::LangItem::FormatUnsafeArg,
-            sym::new,
-        ));
-        let unsafe_arg_new_call = ctx.expr_call(macsp, unsafe_arg_new, &[]);
+        let args = ctx.arena.alloc_from_iter([lit_pieces, args, format_options]);
+        let call = ctx.expr_call(macsp, new_v1_formatted, args);
         let hir_id = ctx.next_id();
-        let unsafe_arg = ctx.expr_block(ctx.arena.alloc(hir::Block {
-            stmts: &[],
-            expr: Some(unsafe_arg_new_call),
-            hir_id,
-            rules: hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::CompilerGenerated),
-            span: macsp,
-            targeted_by_break: false,
-        }));
-        let args = ctx.arena.alloc_from_iter([lit_pieces, args, format_options, unsafe_arg]);
-        hir::ExprKind::Call(new_v1_formatted, args)
+        hir::ExprKind::Block(
+            ctx.arena.alloc(hir::Block {
+                stmts: &[],
+                expr: Some(call),
+                hir_id,
+                rules: hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::CompilerGenerated),
+                span: macsp,
+                targeted_by_break: false,
+            }),
+            None,
+        )
     } else {
         // Generate:
         //     <core::fmt::Arguments>::new_v1(

compiler/rustc_hir/src/lang_items.rs

@@ -329,7 +329,6 @@ language_item_table! {
     FormatArguments,         sym::format_arguments,    format_arguments,           Target::Struct,         GenericRequirement::None;
     FormatCount,             sym::format_count,        format_count,               Target::Enum,           GenericRequirement::None;
     FormatPlaceholder,       sym::format_placeholder,  format_placeholder,         Target::Struct,         GenericRequirement::None;
-    FormatUnsafeArg,         sym::format_unsafe_arg,   format_unsafe_arg,          Target::Struct,         GenericRequirement::None;
 
     ExchangeMalloc,          sym::exchange_malloc,     exchange_malloc_fn,         Target::Fn,             GenericRequirement::None;
     DropInPlace,             sym::drop_in_place,       drop_in_place_fn,           Target::Fn,             GenericRequirement::Minimum(1);

compiler/rustc_span/src/symbol.rs

@@ -1038,7 +1038,6 @@ symbols! {
         format_count,
         format_macro,
         format_placeholder,
-        format_unsafe_arg,
         freeze,
         freeze_impls,
         freg,

library/core/src/fmt/mod.rs

@@ -645,8 +645,7 @@ impl<'a> Arguments<'a> {
 
     /// Specifies nonstandard formatting parameters.
     ///
-    /// An `rt::UnsafeArg` is required because the following invariants must be held
-    /// in order for this function to be safe:
+    /// Safety:
     /// 1. The `pieces` slice must be at least as long as `fmt`.
     /// 2. Every `rt::Placeholder::position` value within `fmt` must be a valid index of `args`.
     /// 3. Every `rt::Count::Param` within `fmt` must contain a valid index of `args`.

library/core/src/fmt/rt.rs

@@ -198,17 +198,16 @@ impl Argument<'_> {
     }
 }
 
-/// This struct represents the unsafety of constructing an `Arguments`.
-/// It exists, rather than an unsafe function, in order to simplify the expansion
-/// of `format_args!(..)` and reduce the scope of the `unsafe` block.
+/// Bootstrap only.
+#[cfg(bootstrap)]
 #[lang = "format_unsafe_arg"]
 pub struct UnsafeArg {
     _private: (),
 }
 
+#[cfg(bootstrap)]
 impl UnsafeArg {
-    /// See documentation where `UnsafeArg` is required to know when it is safe to
-    /// create and use `UnsafeArg`.
+    /// Bootstrap only.
     #[inline]
     pub const unsafe fn new() -> Self {
         Self { _private: () }