Auto merge of #106745 - m-ou-se:format-args-ast, r=oli-obk

Move format_args!() into AST (and expand it during AST lowering)

Implements rust-lang/compiler-team#541

This moves FormatArgs from rustc_builtin_macros to rustc_ast_lowering. For now, the end result is the same. But this allows for future changes to do smarter things with format_args!(). It also allows Clippy to directly access the ast::FormatArgs, making things a lot easier.

This change turns the format args types into lang items. The builtin macro used to refer to them by their path. After this change, the path is no longer relevant, making it easier to make changes in `core`.

This updates clippy to use the new language items, but this doesn't yet make clippy use the ast::FormatArgs structure that's now available. That should be done after this is merged.

core/src/fmt/mod.rs

@@ -267,6 +267,7 @@ 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")]
@@ -279,6 +280,7 @@ 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")]
@@ -473,8 +475,8 @@ 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.

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,
@@ -20,7 +22,22 @@ pub struct FormatSpec {
     pub width: Count,
 }
 
+impl Argument {
+    #[inline(always)]
+    pub const fn new(
+        position: usize,
+        fill: char,
+        align: Alignment,
+        flags: u32,
+        precision: Count,
+        width: Count,
+    ) -> Self {
+        Self { position, format: FormatSpec { fill, align, flags, precision, width } }
+    }
+}
+
 /// 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 +51,7 @@ 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