bjoernager/rust
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Auto merge of #139131 - m-ou-se:format-args-struct-expr, r=Mark-Simulacrum

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Simplify expansion for format_args!().

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

Before:

```rust
        Placeholder::new(…, …, …, …)
```

After:

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

(I originally avoided the struct expression, because `Placeholder` had a lot of fields. But now that https://github.com/rust-lang/rust/pull/136974 is merged, it only has four fields left.)

This will make the `fmt` argument to `fmt::Arguments::new_v1_formatted()` a candidate for const promotion, which is important if we ever hope to tackle https://github.com/rust-lang/rust/issues/92698 (It doesn't change anything yet though, because the `args` argument to `fmt::Arguments::new_v1_formatted()` is not const-promotable.)
This commit is contained in:
bors 2025-03-30 21:59:02 +00:00
commit 2ea33b5910
3 changed files with 18 additions and 22 deletions
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28
compiler/rustc_ast_lowering/src/format.rs
View file

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

4
compiler/rustc_span/src/symbol.rs
View file

@ -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,