Turn format arguments types into lang items.

compiler/rustc_hir/src/lang_items.rs

@@ -244,6 +244,14 @@ language_item_table! {
     /// libstd panic entry point. Necessary for const eval to be able to catch it
     BeginPanic,              sym::begin_panic,         begin_panic_fn,             Target::Fn,             GenericRequirement::None;
 
+    // Lang items needed for `format_args!()`.
+    FormatAlignment,         sym::format_alignment,    format_alignment,           Target::Enum,           GenericRequirement::None;
+    FormatArgument,          sym::format_argument,     format_argument,            Target::Struct,         GenericRequirement::None;
+    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;
     BoxFree,                 sym::box_free,            box_free_fn,                Target::Fn,             GenericRequirement::Minimum(1);
     DropInPlace,             sym::drop_in_place,       drop_in_place_fn,           Target::Fn,             GenericRequirement::Minimum(1);

compiler/rustc_span/src/symbol.rs

@@ -721,11 +721,17 @@ symbols! {
         forbid,
         forget,
         format,
+        format_alignment,
         format_args,
         format_args_capture,
         format_args_macro,
         format_args_nl,
+        format_argument,
+        format_arguments,
+        format_count,
         format_macro,
+        format_placeholder,
+        format_unsafe_arg,
         freeze,
         freg,
         frem_fast,

library/core/src/fmt/mod.rs

@@ -262,6 +262,7 @@ extern "C" {
 /// family of functions. It contains a function to format the given value. At
 /// compile time it is ensured that the function and the value have the correct
 /// types, and then this struct is used to canonicalize arguments to one type.
+#[cfg_attr(not(bootstrap), lang = "format_argument")]
 #[derive(Copy, Clone)]
 #[allow(missing_debug_implementations)]
 #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
@@ -274,6 +275,7 @@ pub struct ArgumentV1<'a> {
 /// 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.
+#[cfg_attr(not(bootstrap), lang = "format_unsafe_arg")]
 #[allow(missing_debug_implementations)]
 #[doc(hidden)]
 #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
@@ -468,8 +470,8 @@ impl<'a> Arguments<'a> {
 /// ```
 ///
 /// [`format()`]: ../../std/fmt/fn.format.html
+#[cfg_attr(not(bootstrap), lang = "format_arguments")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[cfg_attr(not(test), rustc_diagnostic_item = "Arguments")]
 #[derive(Copy, Clone)]
 pub struct Arguments<'a> {
     // Format string pieces to print.

library/core/src/fmt/rt/v1.rs

@@ -5,7 +5,9 @@
 //! these can be statically allocated and are slightly optimized for the runtime
 #![allow(missing_debug_implementations)]
 
+#[cfg_attr(not(bootstrap), lang = "format_placeholder")]
 #[derive(Copy, Clone)]
+// FIXME: Rename this to Placeholder
 pub struct Argument {
     pub position: usize,
     pub format: FormatSpec,
@@ -21,6 +23,7 @@ pub struct FormatSpec {
 }
 
 /// Possible alignments that can be requested as part of a formatting directive.
+#[cfg_attr(not(bootstrap), lang = "format_alignment")]
 #[derive(Copy, Clone, PartialEq, Eq)]
 pub enum Alignment {
     /// Indication that contents should be left-aligned.
@@ -34,6 +37,7 @@ pub enum Alignment {
 }
 
 /// Used by [width](https://doc.rust-lang.org/std/fmt/#width) and [precision](https://doc.rust-lang.org/std/fmt/#precision) specifiers.
+#[cfg_attr(not(bootstrap), lang = "format_count")]
 #[derive(Copy, Clone)]
 pub enum Count {
     /// Specified with a literal number, stores the value