calculate `Arguments::estimated_capacity()` at compile-time - #162052

joboet · 2026-08-31T10:20:10Z

Arguments::estimated_capacity() iterates over the entire formatting template to calculate its estimate, but there's nothing in the heuristic that couldn't be computed at compile-time. Thus, let's try just that. This has the unfortunate side-effect of making Arguments bigger – but there might be ways of reducing the impact of that.

Draft until I've had a chance to look at the performance of this.

joboet · 2026-08-31T10:20:24Z

@bors try @rust-timer queue

calculate `Arguments::estimated_capacity()` at compile-time

rust-bors · 2026-08-31T11:19:13Z

☀️ Try build successful (CI)
Build commit: 6976f97 (6976f97b830ebc168504a5b24b3267315de2b7e5)
Base parent: be4b6a9 (be4b6a99a3c605d27786c7d48772fec5bd2df76c)

rust-timer · 2026-08-31T15:23:42Z

Finished benchmarking commit (6976f97): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.3%, 1.3%]	18
Regressions ❌ (secondary)	4.4%	[0.1%, 36.5%]	23
Improvements ✅ (primary)	-0.9%	[-5.8%, -0.2%]	9
Improvements ✅ (secondary)	-0.6%	[-0.8%, -0.5%]	2
All ❌✅ (primary)	0.1%	[-5.8%, 1.3%]	27

Max RSS (memory usage)

Results (primary 1.3%, secondary 4.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.3%	[1.3%, 1.3%]	1
Regressions ❌ (secondary)	6.6%	[4.4%, 8.8%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.5%	[-0.5%, -0.5%]	1
All ❌✅ (primary)	1.3%	[1.3%, 1.3%]	1

Cycles

Results (primary -4.4%, secondary 15.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	18.0%	[3.2%, 36.7%]	6
Improvements ✅ (primary)	-4.4%	[-6.3%, -2.5%]	2
Improvements ✅ (secondary)	-1.8%	[-1.8%, -1.8%]	1
All ❌✅ (primary)	-4.4%	[-6.3%, -2.5%]	2

Binary size

Results (primary 1.1%, secondary 1.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.2%	[0.1%, 5.7%]	79
Regressions ❌ (secondary)	1.0%	[0.0%, 4.9%]	97
Improvements ✅ (primary)	-0.2%	[-0.4%, -0.0%]	5
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.1%	[-0.4%, 5.7%]	84

Bootstrap: 474.007s -> 478.148s (0.87%)
Artifact size: 307.41 MiB -> 403.42 MiB (31.23%)

joboet · 2026-09-01T08:59:25Z

I had an idea...
@bors try @rust-timer queue

calculate `Arguments::estimated_capacity()` at compile-time

rust-log-analyzer · 2026-09-01T09:36:44Z

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [ui] tests/ui/unpretty/flattened-format-args.rs stdout ----
Saved the actual stdout to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/unpretty/flattened-format-args/flattened-format-args.stdout`
diff of stdout:

14                 super let args = [format_argument::new_display(args.0)];
15                 unsafe {
16                     format_arguments::new(b"\x08a 123 b \xc0\x05 xyz\n\x00",
-                         &args)
+                         &args, 26usize)
18                 }
19             });
20     };


The actual stdout differed from the expected stdout
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args unpretty/flattened-format-args.rs`

error: 1 errors occurred comparing output.
status: exit status: 0
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/unpretty/flattened-format-args.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/unpretty/flattened-format-args" "-Znext-solver=coherence" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "--edition=2015" "-Zunpretty=hir" "-Zflatten-format-args=yes"
--- stdout -------------------------------
extern crate std;
#[attr = PreludeImport]
use ::std::prelude::rust_2015::*;
//@ compile-flags: -Zunpretty=hir -Zflatten-format-args=yes
//@ check-pass
//@ edition: 2015

fn main() {
    let x = 1;
    // Should flatten to println!("a 123 b {x} xyz\n"):
    {
        ::std::io::_print({
                super let args = (&x,);
                super let args = [format_argument::new_display(args.0)];
                unsafe {
                    format_arguments::new(b"\x08a 123 b \xc0\x05 xyz\n\x00",
                        &args, 26usize)
                }
            });
    };
}
------------------------------------------
stderr: none

---- [ui] tests/ui/unpretty/flattened-format-args.rs stdout end ----
---- [ui] tests/ui/unpretty/exhaustive.rs#hir stdout ----
Saved the actual stdout to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/unpretty/exhaustive.hir/exhaustive.hir.stdout`
diff of stdout:

390         {
391             super let args = (&expr,);
392             super let args = [format_argument::new_display(args.0)];
-             unsafe { format_arguments::new(b"\xc0\x00", &args) }
+             unsafe { format_arguments::new(b"\xc0\x00", &args, 0usize) }
394         };
395     }
396 }


The actual stdout differed from the expected stdout
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args unpretty/exhaustive.rs`

error in revision `hir`: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/unpretty/exhaustive.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--cfg" "hir" "--check-cfg" "cfg(test,FALSE,expanded,hir)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/unpretty/exhaustive.hir" "-Znext-solver=coherence" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "--edition=2024" "-Zunpretty=hir"
--- stdout -------------------------------
//@ revisions: expanded hir
//@[expanded]compile-flags: -Zunpretty=expanded
//@[expanded]check-pass
//@[hir]compile-flags: -Zunpretty=hir
//@[hir]check-fail
//@ edition:2024

// Note: the HIR revision includes a `.stderr` file because there are some
// errors that only occur once we get past the AST.

#![allow(incomplete_features)]
#![attr = Feature([auto_traits#0, builtin_syntax#0, const_trait_impl#0,
coroutines#0, decl_macro#0, deref_patterns#0, explicit_tail_calls#0,
gen_blocks#0, more_qualified_paths#0, never_patterns#0, pattern_types#0,
pattern_type_macro#0, prelude_import#0, specialization#0, trace_macros#0,
trait_alias#0, try_blocks#0, try_blocks_heterogeneous#0, yeet_expr#0])]
extern crate std;
#[attr = PreludeImport]
use std::prelude::rust_2024::*;

mod prelude {
    use std::prelude::rust_2024::*;

---

    /// outer single-line doc comment
    /**
     * outer multi-line doc comment
     */
    #[doc = "outer doc attribute"]
    #[doc = "macro"]
    #[allow()]
    #[attr = Repr {reprs: [ReprC]}]
    struct Struct;
}

mod expressions {
    /// ExprKind::Array
    fn expr_array() {
        [];
        [true];
        [true];
        [true, true];
        ["long........................................................................"];
        ["long............................................................",
                true];
    }

    /// ExprKind::ConstBlock
    fn expr_const_block() {
---
                };
    }

    /// ExprKind::Call
    fn expr_call() {
        let f;
        f();
        f::<u8>();
        f::<1>();
        f::<'static, u8, 1>();
        f(true);
        f(true);
        ()();
    }

    /// ExprKind::MethodCall
    fn expr_method_call() {
        let x;
        x.f();
        x.f::<u8>();
        x.collect::<Vec<_>>();
    }

    /// ExprKind::Tup
    fn expr_tup() { (); (true,); (true, false); (true, false); }

    /// ExprKind::Binary
    fn expr_binary() {
        let (a, b, c, d, x, y);
        true || false;
        true || false && false;
        a < 1 && 2 < b && c > 3 && 4 > d;
        a & b & !c;
        a + b * c - d + -1 * -2 - -3;
        x = !y;
    }

    /// ExprKind::Unary
    fn expr_unary() { let expr; *expr; !expr; -expr; }

    /// ExprKind::Lit
    fn expr_lit() { 'x'; 1000i8; 1.00000000000000000000001; }

    /// ExprKind::Cast
    fn expr_cast() { let expr; expr as T; expr as T<u8>; }

    /// ExprKind::Type
    fn expr_type() { let expr; type_ascribe!(expr, T); }

    /// ExprKind::Let
    fn expr_let() {
        let b;
        if let Some(a) = b { }
        if let _ = true && false { }
        if let _ = (true && false) { }
    }

    /// ExprKind::If
    fn expr_if() {
        if true { }
        if !true { }
        if let true = true { } else { }
        if true { } else if false { }
        if true { } else if false { } else { }
        if true { return; } else if false { 0 } else { 0 }
    }

    /// ExprKind::While
    fn expr_while() {
        loop { if false { } else { break; } }
        'a: loop { if false { } else { break; } }
        loop { if let true = true { } else { break; } }
    }

    /// ExprKind::ForLoop
    fn expr_for_loop() {
        let x;
        {
            let _t =
                match into_iter(x) {
                    mut iter =>
                        loop {
                            match next(&mut iter) {
                                None {} => break,
                                Some {  0: _ } => { }
                            }
                        },
                };
            _t
        };
        {
            let _t =
                match into_iter(x) {
                    mut iter =>
                        'a: loop {
                            match next(&mut iter) {
                                None {} => break,
                                Some {  0: _ } => { }
                            }
                        },
                };
            _t
        }
    }

    /// ExprKind::Loop
    fn expr_loop() { loop { } 'a: loop { } }

    /// ExprKind::Match
    fn expr_match() {
        let value;
        match value { }
        match value { ok => 1, }
        match value { ok => 1, err => 0, }
    }

    /// ExprKind::Closure
    fn expr_closure() {
        let value;
        || { };
        |x| { };
        |x: u8| { };
        || ();
        move || value;
        || |mut _task_context: ResumeTy| { { let _t = value; _t } };
        move || |mut _task_context: ResumeTy| { { let _t = value; _t } };
        || value; //[hir]~ ERROR closures cannot be static
        move || value; //[hir]~ ERROR closures cannot be static
        || |mut _task_context: ResumeTy| { { let _t = value; _t } };
        move || |mut _task_context: ResumeTy| { { let _t = value; _t } };
        || -> u8 { value };
        1 + (|| { });
    }

    /// ExprKind::Block
    fn expr_block() {
        { }
---
        { }
    }

    /// ExprKind::Gen
    fn expr_gen() {
        |mut _task_context: ResumeTy| { };
        move |mut _task_context: ResumeTy| { };
        || { };
        move || { };
        |mut _task_context: ResumeTy| { };
        move |mut _task_context: ResumeTy| { };
    }

    /// ExprKind::Await
    fn expr_await() {
        let fut;
        {
            fut; //[hir]~ ERROR `await` is only allowed
            (/*ERROR*/)
        };
    }

    /// ExprKind::TryBlock
    fn expr_try_block() {
        { from_output(()) }
        { return; from_output(()) }
        type_ascribe!({ from_output(()) }, Option<_>);
        type_ascribe!({
                from_output(match branch(None) {
                        Break {  0: residual } => #[allow(unreachable_code)]
                            break from_residual(residual),
                        Continue {  0: val } => #[allow(unreachable_code)]
                            val,
                    })
            }, Option<String>)
    }

    /// ExprKind::Assign
    fn expr_assign() { let expr; expr = true; }

    /// ExprKind::AssignOp
    fn expr_assign_op() { let expr; expr += true; }

    /// ExprKind::Field
    fn expr_field() { let expr; expr.field; expr.0; }

    /// ExprKind::Index
    fn expr_index() { let expr; expr[true]; }

    /// ExprKind::Range
    fn expr_range() {
        let (lo, hi);
        RangeFull {  };
        RangeTo { end: hi };
        RangeFrom { start: lo };
        Range { start: lo, end: hi };
        Range { start: lo, end: hi };
        RangeToInclusive { end: hi };
        range_inclusive_new(lo, hi);
        range_inclusive_new(-2, -1);
    }

    /// ExprKind::Underscore
    fn expr_underscore() {
        (/*ERROR*/); //[hir]~ ERROR in expressions, `_` can only
    }

    /// ExprKind::Path
    fn expr_path() {
        let x;
        crate::expressions::expr_path;
        crate::expressions::expr_path::<'static>;
        <T as Default>::default;
        <T as ::core::default::Default>::default;
        x; //[hir]~ ERROR parenthesized type parameters
        x::<T, T>; //[hir]~ ERROR parenthesized type parameters
        crate::expressions::expr_path;
        //[hir]~^ ERROR parenthesized type parameters
        //[hir]~| ERROR parenthesized type parameters
        core::marker::PhantomData;
        //[hir]~^ ERROR parenthesized type parameters
        //[hir]~| ERROR parenthesized type parameters
    }

    /// ExprKind::AddrOf
    fn expr_addr_of() {
        let expr;
        &expr;
        &mut expr;
        &raw const expr;
        &raw mut expr;
    }

    /// ExprKind::Break
    fn expr_break() { 'a: { break; break 'a; break true; break 'a true; } }

    /// ExprKind::Continue
    fn expr_continue() { 'a: { continue; continue 'a; } }

    /// ExprKind::Ret
    fn expr_ret() { return; return true; }


---




        //[hir]~ ERROR `yield` can only be used





---


        // ...

        //[hir]~ ERROR invalid ABI





---




        //[hir]~ ERROR `..` patterns are not allowed here





---




        //[hir]~ ERROR parenthesized type parameters


        //[hir]~ ERROR `impl Trait` is not allowed
        //[hir]~ ERROR `impl Trait` is not allowed
        //[hir]~ ERROR `impl Trait` is not allowed
        //[hir]~ ERROR `impl Trait` is not allowed
        //[hir]~ ERROR `impl Trait` is not allowed
        //[hir]~ ERROR `impl Trait` is not allowed









        const { offset_of!(T, field) };
    }
    /// ExprKind::MacCall
    fn expr_mac_call() { "..."; "..."; "..."; }
    /// ExprKind::Struct
    fn expr_struct() {
        struct Struct {
        }
        let (x, base);
        Struct {  };
        <Struct as ToOwned>::Owned {  };
        Struct { .. };
        Struct { ..base };
        Struct { x };
        Struct { x, ..base };
        Struct { x: true };
        Struct { x: true, .. };
        Struct { x: true, ..base };
        Struct { 0: true, ..base };
    }
    /// ExprKind::Repeat
    fn expr_repeat() { [(); 0]; }
    /// ExprKind::Paren
    fn expr_paren() { let expr; expr; }
    /// ExprKind::Try
    fn expr_try() {
        let expr;
        match branch(expr) {
            Break {  0: residual } => #[allow(unreachable_code)]
                return from_residual(residual),
            Continue {  0: val } => #[allow(unreachable_code)]
                val,
        };
    }
    /// ExprKind::Yield
    fn expr_yield() { yield (); yield true; }
    /// ExprKind::Yeet
    fn expr_yeet() { return from_yeet(()); return from_yeet(0); }
    /// ExprKind::Become
    fn expr_become() { become true; }
    /// ExprKind::IncludedBytes
    fn expr_include_bytes() {
        b"data for include_bytes in ../expanded-exhaustive.rs\n";
    }
    /// ExprKind::FormatArgs
    fn expr_format_args() {
        let expr;
        format_arguments::from_str("");
        {
            super let args = (&expr,);
            super let args = [format_argument::new_display(args.0)];
            unsafe { format_arguments::new(b"\xc0\x00", &args, 0usize) }
        };
    }
}
mod items {
    /// ItemKind::ExternCrate
    mod item_extern_crate {
        extern crate core;
        extern crate self as unpretty;
        extern crate core as _;
    }
    /// ItemKind::Use
    mod item_use {
        use ::{};
        use crate::expressions;
        use crate::items::item_use;
        use core::*;
    }
    /// ItemKind::Static
    mod item_static {
        static A: () = { };
        static mut B: () = { };
    }
    /// ItemKind::Const
    mod item_const {
        const A: () = { };
        trait TraitItems {
            const
            B:
            ();
            const
            C:
---
    mod item_fn {
        const unsafe extern "C" fn f() { }
        async unsafe extern "C" fn g()
            ->
                /*impl Trait*/ |mut _task_context: ResumeTy|
            { { let _t = { }; _t } }
        fn h<'a, T>() where T: 'a { }
        trait TraitItems {
            unsafe extern "C" fn f();
        }
        impl TraitItems for _ {
            unsafe extern "C" fn f() { }
        }
    }
---
            Tuple(),
            Struct {
                },
        }
        enum Generic<'a, T> where T: 'a {
            Tuple(T),
            Struct {
                    t: T,
                },
        }
    }
---
    /// ItemKind::TraitAlias
    mod item_trait_alias {
        trait Trait<T> = Sized where for<'a> T: 'a;
    }
    /// ItemKind::Impl
    mod item_impl {
        impl () { }
        impl <T> () { }
        impl Default for () { }
        impl <T> const Default for () { }
    }
    /// ItemKind::MacCall
    mod item_mac_call { }
    /// ItemKind::MacroDef
    mod item_macro_def {
        macro_rules! mac { () => {...}; }
        macro stringify { () => {} }
    }
    /// ItemKind::Delegation
    /** FIXME: todo */
    mod item_delegation { }
    /// ItemKind::DelegationMac
    /** FIXME: todo */
    mod item_delegation_mac { }
}
mod patterns {
    /// PatKind::Missing
    fn pat_missing() { let _: for fn(u32, T, &'_ str); }
    /// PatKind::Wild
    fn pat_wild() { let _; }
    /// PatKind::Ident
    fn pat_ident() {
        let x;
        let ref x;
        let mut x;
        let ref mut x;
        let ref mut x@_;
    }
    /// PatKind::Struct
    fn pat_struct() {
        let T {};
        let T::<T> {};
        let T::<'static> {};
        let T {  x };
        let T {  x: _x };
        let T { .. };
        let T {  x, .. };
        let T {  x: _x, .. };
        let T {  0: _x, .. };
        let <T as ToOwned>::Owned {};
    }
    /// PatKind::TupleStruct
    fn pat_tuple_struct() {
        struct Tuple();
        let Tuple();
        let Tuple::<T>();
        let Tuple::<'static>();
        let Tuple(x);
        let Tuple(..);
        let Tuple(x, ..);
    }
    /// PatKind::Or
    fn pat_or() { let true | false; let true; let true | false; }
    /// PatKind::Path
    fn pat_path() {
        let core::marker::PhantomData;
        let core::marker::PhantomData::<T>;
        let core::marker::PhantomData::<'static>;
        let <T as Trait>::CONST;
    }
    /// PatKind::Tuple
    fn pat_tuple() { let (); let (true,); let (true, false); }
    /// PatKind::Deref
    fn pat_deref() { let deref!(pat); }
    /// PatKind::Ref
    fn pat_ref() { let &pat; let &mut pat; }
    /// PatKind::Expr
    fn pat_expr() { let 1000i8; let -""; }
    /// PatKind::Range
    fn pat_range() { let ..1; let 0...; let 0..1; let 0...1; let -2...-1; }
    /// PatKind::Slice
    fn pat_slice() { let []; let [true]; let [true]; let [true, false]; }
    /// PatKind::Rest
    fn pat_rest() { let _; }
    /// PatKind::Never
    fn pat_never() { let !; let Some(!); }
    /// PatKind::Paren
    fn pat_paren() { let pat; }
    /// PatKind::MacCall
    fn pat_mac_call() { let ""; let ""; let ""; }
}
mod statements {
    /// StmtKind::Let
    fn stmt_let() {
        let _;
---
        struct Struct {
        }
        struct Unit;
    }
    /// StmtKind::Expr
    fn stmt_expr() { () }
    /// StmtKind::Semi
    fn stmt_semi() { 1 + 1; }
    /// StmtKind::Empty
    fn stmt_empty() { }
    /// StmtKind::MacCall
    fn stmt_mac_call() { "..."; "..."; "..."; }
}
mod types {
    /// TyKind::Slice
    fn ty_slice() { let _: [T]; }
    /// TyKind::Array
    fn ty_array() { let _: [T; 0]; }
    /// TyKind::Ptr
    fn ty_ptr() { let _: *const T; let _: *mut T; }
    /// TyKind::Ref
    fn ty_ref() {
        let _: &T;
        let _: &mut T;
        let _: &'static T;
        let _: &'static mut [T];
        let _: &T<T<T<T<T>>>>;
        let _: &T<T<T<T<T>>>>;
    }
    /// TyKind::BareFn
    fn ty_bare_fn() {
        let _: fn();
        let _: fn() -> ();
        let _: fn(T);
        let _: fn(t: T);
        let _: fn();
        let _: for<'a> fn();
    }
    /// TyKind::Never
    fn ty_never() { let _: !; }
    /// TyKind::Tup
    fn ty_tup() { let _: (); let _: (T,); let _: (T, T); }
    /// TyKind::Path
    fn ty_path() {
        let _: T;
        let _: T<'static>;
        let _: T<T>;
        let _: T<T>;
        let _: T;
        let _: <T as ToOwned>::Owned;
    }
    /// TyKind::TraitObject
    fn ty_trait_object() {
        let _: dyn Send;
        let _: dyn Send + 'static;
        let _: dyn Send + 'static;
        let _: dyn for<'a> Send;
    }
    /// TyKind::ImplTrait
    const fn ty_impl_trait() {
        let _: (/*ERROR*/);
        let _: (/*ERROR*/);
        let _: (/*ERROR*/);
        let _: (/*ERROR*/);
        let _: (/*ERROR*/);
        let _: (/*ERROR*/);
    }
    /// TyKind::Paren
    fn ty_paren() { let _: T; }
    /// TyKind::Typeof
    /** unused for now */
    fn ty_typeof() { }
    /// TyKind::Infer
    fn ty_infer() { let _: _; }
    /// TyKind::ImplicitSelf
    /** there is no syntax for this */
    fn ty_implicit_self() { }
    /// TyKind::MacCall
    fn ty_mac_call() {
        macro_rules! ty { ($ty:ty) => { $ty } }
        let _: T;
        let _: T;
        let _: T;
    }
    /// TyKind::CVarArgs
    /** FIXME: todo */
    fn ty_c_var_args() { }
    /// TyKind::Pat
    fn ty_pat() { let _: u32 is 1..=RangeMax; }
}
mod visibilities {
    /// VisibilityKind::Public
    mod visibility_public {
        struct Pub;
---
--- stderr -------------------------------
error[E0697]: closures cannot be static
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:209:9
   |
LL |         static || value;            //[hir]~ ERROR closures cannot be static
   |         ^^^^^^^^^

error[E0697]: closures cannot be static
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:210:9
   |
LL |         static move || value;       //[hir]~ ERROR closures cannot be static
   |         ^^^^^^^^^^^^^^

error[E0728]: `await` is only allowed inside `async` functions and blocks
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:239:13
   |
LL |     fn expr_await() {
   |     --------------- this is not `async`
LL |         let fut;
LL |         fut.await;  //[hir]~ ERROR `await` is only allowed
   |             ^^^^^ only allowed inside `async` functions and blocks

error: in expressions, `_` can only be used on the left-hand side of an assignment
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:290:9
   |
LL |         _;      //[hir]~ ERROR in expressions, `_` can only
   |         ^ `_` not allowed here

error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:300:9
   |
LL |         x::();            //[hir]~ ERROR parenthesized type parameters
   |         ^^^^^ only `Fn` traits may use parentheses

error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:301:9
   |
LL |         x::(T, T) -> T;   //[hir]~ ERROR parenthesized type parameters
   |         ^^^^^^^^^^^^^^ only `Fn` traits may use parentheses
   |
help: use angle brackets instead
   |
LL -         x::(T, T) -> T;   //[hir]~ ERROR parenthesized type parameters
LL +         x::<T, T> -> T;   //[hir]~ ERROR parenthesized type parameters
   |

error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:302:9
   |
LL |         crate::() -> ()::expressions::() -> ()::expr_path;
   |         ^^^^^^^^^^^^^^^ only `Fn` traits may use parentheses

error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:302:26
   |
LL |         crate::() -> ()::expressions::() -> ()::expr_path;
   |                          ^^^^^^^^^^^^^^^^^^^^^ only `Fn` traits may use parentheses

error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:305:9
   |
LL |         core::()::marker::()::PhantomData;
   |         ^^^^^^^^ only `Fn` traits may use parentheses

error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:305:19
   |
LL |         core::()::marker::()::PhantomData;
   |                   ^^^^^^^^^^ only `Fn` traits may use parentheses

error: `yield` can only be used in `#[coroutine]` closures, or `gen` blocks
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:392:9
   |
LL |         yield;          //[hir]~ ERROR `yield` can only be used
   |         ^^^^^
   |
help: use `#[coroutine]` to make this closure a coroutine
   |
LL |     #[coroutine] fn expr_yield() {
   |     ++++++++++++

error[E0703]: invalid ABI: found `C++`
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:472:23
   |
LL |         unsafe extern "C++" {}  //[hir]~ ERROR invalid ABI
   |                       ^^^^^ invalid ABI
   |
   = note: invoke `rustc --print=calling-conventions` for a full list of supported calling conventions

error: `..` patterns are not allowed here
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:674:13
   |
LL |         let ..;     //[hir]~ ERROR `..` patterns are not allowed here
   |             ^^
   |
   = note: only allowed in tuple, tuple struct, and slice patterns

error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:789:16
   |
LL |         let _: T() -> !;    //[hir]~ ERROR parenthesized type parameters
   |                ^^^^^^^^ only `Fn` traits may use parentheses

error[E0562]: `impl Trait` is not allowed in the type of variable bindings
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:803:16
   |
LL |         let _: impl Send;               //[hir]~ ERROR `impl Trait` is not allowed
   |                ^^^^^^^^^
   |
   = note: `impl Trait` is only allowed in arguments and return types of functions and methods
   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
   = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0562]: `impl Trait` is not allowed in the type of variable bindings
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:804:16
   |
LL |         let _: impl Send + 'static;     //[hir]~ ERROR `impl Trait` is not allowed
   |                ^^^^^^^^^^^^^^^^^^^
   |
   = note: `impl Trait` is only allowed in arguments and return types of functions and methods
   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
   = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0562]: `impl Trait` is not allowed in the type of variable bindings
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:805:16
   |
LL |         let _: impl 'static + Send;     //[hir]~ ERROR `impl Trait` is not allowed
   |                ^^^^^^^^^^^^^^^^^^^
   |
   = note: `impl Trait` is only allowed in arguments and return types of functions and methods
   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
   = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0562]: `impl Trait` is not allowed in the type of variable bindings
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:806:16
   |
LL |         let _: impl ?Sized;             //[hir]~ ERROR `impl Trait` is not allowed
   |                ^^^^^^^^^^^
   |
   = note: `impl Trait` is only allowed in arguments and return types of functions and methods
   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
   = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0562]: `impl Trait` is not allowed in the type of variable bindings
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:807:16
   |
LL |         let _: impl [const] Clone;       //[hir]~ ERROR `impl Trait` is not allowed
   |                ^^^^^^^^^^^^^^^^^^
   |
   = note: `impl Trait` is only allowed in arguments and return types of functions and methods
   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
   = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0562]: `impl Trait` is not allowed in the type of variable bindings
##[error]  --> /checkout/tests/ui/unpretty/exhaustive.rs:808:16
   |
LL |         let _: impl for<'a> Send;       //[hir]~ ERROR `impl Trait` is not allowed
   |                ^^^^^^^^^^^^^^^^^
   |
   = note: `impl Trait` is only allowed in arguments and return types of functions and methods
   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
   = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error: aborting due to 20 previous errors

Some errors have detailed explanations: E0214, E0562, E0697, E0703, E0728.
For more information about an error, try `rustc --explain E0214`.

rust-bors · 2026-09-01T09:59:28Z

☀️ Try build successful (CI)
Build commit: 0022abb (0022abbf7156a1442b78f632b74f639d7f5cb467)
Base parent: 7022271 (70222712809cd5cc1718ed8995914a1cbacb6b92)

rust-timer · 2026-09-01T10:42:17Z

Finished benchmarking commit (0022abb): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.1%, 2.1%]	22
Regressions ❌ (secondary)	4.7%	[0.1%, 36.2%]	22
Improvements ✅ (primary)	-0.7%	[-5.7%, -0.1%]	14
Improvements ✅ (secondary)	-0.4%	[-0.8%, -0.1%]	6
All ❌✅ (primary)	0.1%	[-5.7%, 2.1%]	36

Max RSS (memory usage)

Results (primary 3.7%, secondary 1.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	5.1%	[1.6%, 12.6%]	4
Regressions ❌ (secondary)	5.2%	[3.8%, 9.0%]	8
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-4.0%	[-7.9%, -2.2%]	6
All ❌✅ (primary)	3.7%	[-2.0%, 12.6%]	5

Cycles

Results (primary -7.0%, secondary 7.8%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	15.8%	[2.6%, 37.0%]	7
Improvements ✅ (primary)	-7.0%	[-7.0%, -7.0%]	1
Improvements ✅ (secondary)	-6.2%	[-7.8%, -3.8%]	4
All ❌✅ (primary)	-7.0%	[-7.0%, -7.0%]	1

Binary size

Results (primary 1.3%, secondary 1.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.5%	[0.2%, 5.7%]	58
Regressions ❌ (secondary)	1.1%	[0.0%, 4.9%]	87
Improvements ✅ (primary)	-0.2%	[-1.1%, -0.0%]	9
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	1
All ❌✅ (primary)	1.3%	[-1.1%, 5.7%]	67

Bootstrap: 475.539s -> 475.55s (0.00%)
Artifact size: 400.59 MiB -> 403.80 MiB (0.80%)

calculate Arguments::estimated_capacity() at compile-time

a35359e