Simplify expansion for format_args!().

Instead of calling new(), we can just use a struct expression directly.

Before:

        Placeholder::new(…, …, …, …)

After:

        Placeholder {
                position: …,
                flags: …,
                width: …,
                precision: …,
        }

compiler/rustc_ast_lowering/src/format.rs

@@ -323,14 +323,12 @@ fn make_count<'hir>(
 /// Generates
 ///
 /// ```text
-///     <core::fmt::rt::Placeholder::new(
+///     <core::fmt::rt::Placeholder {
-///         …usize, // position
+///         position: …usize,
-///         '…', // fill
+///         flags: …u32,
-///         <core::fmt::rt::Alignment>::…, // alignment
+///         precision: <core::fmt::rt::Count::…>,
-///         …u32, // flags
+///         width: <core::fmt::rt::Count::…>,
-///         <core::fmt::rt::Count::…>, // width
+///     }
-///         <core::fmt::rt::Count::…>, // precision
-///     )
 /// ```
 fn make_format_spec<'hir>(
     ctx: &mut LoweringContext<'_, 'hir>,
@@ -384,13 +382,13 @@ fn make_format_spec<'hir>(
     let flags = ctx.expr_u32(sp, flags);
     let precision = make_count(ctx, sp, precision, argmap);
     let width = make_count(ctx, sp, width, argmap);
-    let format_placeholder_new = ctx.arena.alloc(ctx.expr_lang_item_type_relative(
+    let position = ctx.expr_field(Ident::new(sym::position, sp), ctx.arena.alloc(position), sp);
-        sp,
+    let flags = ctx.expr_field(Ident::new(sym::flags, sp), ctx.arena.alloc(flags), sp);
-        hir::LangItem::FormatPlaceholder,
+    let precision = ctx.expr_field(Ident::new(sym::precision, sp), ctx.arena.alloc(precision), sp);
-        sym::new,
+    let width = ctx.expr_field(Ident::new(sym::width, sp), ctx.arena.alloc(width), sp);
-    ));
+    let placeholder = ctx.arena.alloc(hir::QPath::LangItem(hir::LangItem::FormatPlaceholder, sp));
-    let args = ctx.arena.alloc_from_iter([position, flags, precision, width]);
+    let fields = ctx.arena.alloc_from_iter([position, flags, precision, width]);
-    ctx.expr_call_mut(sp, format_placeholder_new, args)
+    ctx.expr(sp, hir::ExprKind::Struct(placeholder, fields, hir::StructTailExpr::None))
 }
 
 fn expand_format_args<'hir>(

compiler/rustc_span/src/symbol.rs

@@ -986,6 +986,7 @@ symbols! {
         field_init_shorthand,
         file,
         file_options,
+        flags,
         float,
         float_to_int_unchecked,
         floorf128,
@@ -1570,6 +1571,7 @@ symbols! {
         pointer_like,
         poll,
         poll_next,
+        position,
         post_dash_lto: "post-lto",
         postfix_match,
         powerpc_target_feature,
@@ -1585,6 +1587,7 @@ symbols! {
         precise_capturing,
         precise_capturing_in_traits,
         precise_pointer_size_matching,
+        precision,
         pref_align_of,
         prefetch_read_data,
         prefetch_read_instruction,
@@ -2274,6 +2277,7 @@ symbols! {
         wasm_target_feature,
         where_clause_attrs,
         while_let,
+        width,
         windows,
         windows_subsystem,
         with_negative_coherence,

library/core/src/fmt/rt.rs

@@ -20,8 +20,8 @@ pub struct Placeholder {
     pub width: Count,
 }
 
+#[cfg(bootstrap)]
 impl Placeholder {
-    #[cfg(bootstrap)]
     #[inline]
     pub const fn new(
         position: usize,
@@ -33,12 +33,6 @@ impl Placeholder {
     ) -> Self {
         Self { position, fill, align, flags, precision, width }
     }
-
-    #[cfg(not(bootstrap))]
-    #[inline]
-    pub const fn new(position: usize, flags: u32, precision: Count, width: Count) -> Self {
-        Self { position, flags, precision, width }
-    }
 }
 
 #[cfg(bootstrap)]