min_const_generics infers the wrong type depending on trait bounds in scope

[fee1-dead]

I tried this code: play

pub struct Optional<const IS_PRESENT: usize, T> where (): UsizeBool<IS_PRESENT> {
    inner: [T; IS_PRESENT]
}

pub trait UsizeBool<const X: usize> {}

impl UsizeBool<0> for () {}
impl UsizeBool<1> for () {}

impl<T> Optional<1, T> {
    pub fn some(x: T) -> Self {
        Self { inner: [x] } 
    }
}

pub struct Main<const A: usize, const B: usize> where (): UsizeBool<A> + UsizeBool<B> {
    // A is used as a field in the actual code, but irrelevant to this error
    value: Optional<B, u32>,
}

impl<const A: usize> Main<A, 0> where (): UsizeBool<A> /* + UsizeBool<1> */ {
    pub fn foo(mut self, x: u32) -> Main<A, 1> {
        Main {
            value: Optional::some(x),
        }
    }
}

I expected to see this happen: successfully compiles

Instead, this happened: compiler errors

error[E0308]: mismatched types
  --> src/lib.rs:25:20
   |
25 |             value: Optional::some(x),
   |                    ^^^^^^^^^^^^^^^^^ expected `A`, found `1`
   |
   = note: expected struct `Optional<_, A>`
              found struct `Optional<_, 1>`

error[E0308]: mismatched types
  --> src/lib.rs:24:9
   |
23 |       pub fn foo(mut self, x: u32) -> Main<A, 1> {
   |                                       ---------- expected `Main<A, 1>` because of return type
24 | /         Main {
25 | |             value: Optional::some(x),
26 | |         }
   | |_________^ expected `1`, found `A`
   |
   = note: expected struct `Main<_, 1>`
              found struct `Main<_, A>`

For more information about this error, try `rustc --explain E0308`.
error: could not compile `playground` due to 2 previous errors

If I uncomment the + UsizeBool<1> bound, it would compile successfully.

Meta

rustc --version --verbose:

rustc 1.66.0-nightly (4b8f43199 2022-10-19)
binary: rustc
commit-hash: 4b8f4319954ff2642690b9e5cbe4af352d095bf6
commit-date: 2022-10-19
host: x86_64-unknown-linux-gnu
release: 1.66.0-nightly
LLVM version: 15.0.2

Backtrace

rustc a.rs --crate-type lib -Z treat-err-as-bug
error: internal compiler error: `InferCtxt` incorrectly tainted by errors

thread 'rustc' panicked at 'aborting due to `-Z treat-err-as-bug=1`', compiler/rustc_errors/src/lib.rs:1575:30
stack backtrace:
   0:     0x7f6fdae3b6e0 - std::backtrace_rs::backtrace::libunwind::trace::h2119464896b45b57
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   1:     0x7f6fdae3b6e0 - std::backtrace_rs::backtrace::trace_unsynchronized::h99b1d9b13310118f
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f6fdae3b6e0 - std::sys_common::backtrace::_print_fmt::hbe6d08ff752ef116
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f6fdae3b6e0 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h6dd4a5ce328f2e15
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f6fdae975fe - core::fmt::write::h4593006cca976c9b
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/core/src/fmt/mod.rs:1209:17
   5:     0x7f6fdae2b855 - std::io::Write::write_fmt::h75d064e88170c1b4
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/io/mod.rs:1682:15
   6:     0x7f6fdae3b4a5 - std::sys_common::backtrace::_print::hfe138f63dad5fb4c
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f6fdae3b4a5 - std::sys_common::backtrace::print::he836ff7168a1f810
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f6fdae3e2af - std::panicking::default_hook::{{closure}}::h4a0ff709ff17404d
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/panicking.rs:267:22
   9:     0x7f6fdae3dfea - std::panicking::default_hook::h45465b3e5f51d8d9
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/panicking.rs:286:9
  10:     0x7f6fdd7bd811 - <rustc_driver[2feadf6a045f69f8]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[b141a5f448cbfdbc]::ops::function::FnOnce<(&core[b141a5f448cbfdbc]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f6fdae3ead9 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h2f9ca2b8279bca39
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/alloc/src/boxed.rs:2001:9
  12:     0x7f6fdae3ead9 - std::panicking::rust_panic_with_hook::he67ffd9c867b0e23
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/panicking.rs:692:13
  13:     0x7f6fdae3e811 - std::panicking::begin_panic_handler::{{closure}}::hd5726cc546d97607
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/panicking.rs:577:13
  14:     0x7f6fdae3bb8c - std::sys_common::backtrace::__rust_end_short_backtrace::h1ec30e3932d3b5f1
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/sys_common/backtrace.rs:137:18
  15:     0x7f6fdae3e572 - rust_begin_unwind
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/panicking.rs:575:5
  16:     0x7f6fdae93fe3 - core::panicking::panic_fmt::h64e692afa97ebc63
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/core/src/panicking.rs:65:14
  17:     0x7f6fdc24ae93 - <rustc_errors[3c325fb77ff98e3b]::HandlerInner>::panic_if_treat_err_as_bug
  18:     0x7f6fdc248fbe - <rustc_errors[3c325fb77ff98e3b]::HandlerInner>::emit_diagnostic
  19:     0x7f6fde713141 - <rustc_errors[3c325fb77ff98e3b]::HandlerInner>::emit_diag_at_span::<rustc_span[f76be64242de1050]::span_encoding::Span>
  20:     0x7f6fde713265 - <rustc_errors[3c325fb77ff98e3b]::HandlerInner>::span_bug::<rustc_span[f76be64242de1050]::span_encoding::Span, &str>
  21:     0x7f6fde712ed3 - <rustc_errors[3c325fb77ff98e3b]::Handler>::delay_span_bug::<rustc_span[f76be64242de1050]::span_encoding::Span, &str>
  22:     0x7f6fde74e32d - <rustc_infer[d3358ef915d99f18]::infer::InferCtxt>::set_tainted_by_errors
  23:     0x7f6fdc477334 - <rustc_hir_analysis[4ff8e3b274fef4a]::check::fn_ctxt::FnCtxt>::demand_coerce_diag
  24:     0x7f6fdc4725ec - <rustc_hir_analysis[4ff8e3b274fef4a]::check::fn_ctxt::FnCtxt>::check_expr_struct_fields
  25:     0x7f6fdc3a8b45 - <rustc_hir_analysis[4ff8e3b274fef4a]::check::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  26:     0x7f6fdc3d1e1f - <rustc_hir_analysis[4ff8e3b274fef4a]::check::fn_ctxt::FnCtxt>::check_block_with_expected
  27:     0x7f6fdc3a6711 - <rustc_hir_analysis[4ff8e3b274fef4a]::check::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  28:     0x7f6fdcd43636 - <rustc_hir_analysis[4ff8e3b274fef4a]::check::fn_ctxt::FnCtxt>::check_return_expr
  29:     0x7f6fdcd39c9c - rustc_hir_analysis[4ff8e3b274fef4a]::check::check::check_fn
  30:     0x7f6fdcd2a0f4 - <rustc_hir_analysis[4ff8e3b274fef4a]::check::inherited::InheritedBuilder>::enter::<rustc_hir_analysis[4ff8e3b274fef4a]::check::typeck_with_fallback<rustc_hir_analysis[4ff8e3b274fef4a]::check::typeck::{closure#0}>::{closure#1}, &rustc_middle[d605453e4543da8c]::ty::context::TypeckResults>
  31:     0x7f6fdcd28fbc - rustc_hir_analysis[4ff8e3b274fef4a]::check::typeck
  32:     0x7f6fdcfbc495 - rustc_query_system[e96ca7e2da71ed3f]::query::plumbing::try_execute_query::<rustc_query_impl[cd5064426dba224b]::plumbing::QueryCtxt, rustc_query_system[e96ca7e2da71ed3f]::query::caches::DefaultCache<rustc_span[f76be64242de1050]::def_id::LocalDefId, &rustc_middle[d605453e4543da8c]::ty::context::TypeckResults>>
  33:     0x7f6fdcfbc19e - <rustc_query_impl[cd5064426dba224b]::Queries as rustc_middle[d605453e4543da8c]::ty::query::QueryEngine>::typeck
  34:     0x7f6fdd4f7507 - rustc_data_structures[1cc047c6d78b3c56]::sync::par_for_each_in::<&[rustc_span[f76be64242de1050]::def_id::LocalDefId], <rustc_middle[d605453e4543da8c]::hir::map::Map>::par_body_owners<rustc_hir_analysis[4ff8e3b274fef4a]::check::typeck_item_bodies::{closure#0}>::{closure#0}>
  35:     0x7f6fdd4f72c3 - rustc_hir_analysis[4ff8e3b274fef4a]::check::typeck_item_bodies
  36:     0x7f6fdd4057ca - rustc_query_system[e96ca7e2da71ed3f]::query::plumbing::try_execute_query::<rustc_query_impl[cd5064426dba224b]::plumbing::QueryCtxt, rustc_query_system[e96ca7e2da71ed3f]::query::caches::DefaultCache<(), ()>>
  37:     0x7f6fdd4054f7 - rustc_query_system[e96ca7e2da71ed3f]::query::plumbing::get_query::<rustc_query_impl[cd5064426dba224b]::queries::typeck_item_bodies, rustc_query_impl[cd5064426dba224b]::plumbing::QueryCtxt>
  38:     0x7f6fdd1a8eff - <rustc_session[407507c50234e03]::session::Session>::time::<(), rustc_hir_analysis[4ff8e3b274fef4a]::check_crate::{closure#7}>
  39:     0x7f6fdd1a8acf - rustc_hir_analysis[4ff8e3b274fef4a]::check_crate
  40:     0x7f6fdd1a85d7 - rustc_interface[a32f49e72690e02b]::passes::analysis
  41:     0x7f6fdd549354 - rustc_query_system[e96ca7e2da71ed3f]::query::plumbing::try_execute_query::<rustc_query_impl[cd5064426dba224b]::plumbing::QueryCtxt, rustc_query_system[e96ca7e2da71ed3f]::query::caches::DefaultCache<(), core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>>>
  42:     0x7f6fdd549087 - rustc_query_system[e96ca7e2da71ed3f]::query::plumbing::get_query::<rustc_query_impl[cd5064426dba224b]::queries::analysis, rustc_query_impl[cd5064426dba224b]::plumbing::QueryCtxt>
  43:     0x7f6fdc5038e3 - <rustc_interface[a32f49e72690e02b]::passes::QueryContext>::enter::<rustc_driver[2feadf6a045f69f8]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>>
  44:     0x7f6fdc4ff826 - <rustc_interface[a32f49e72690e02b]::interface::Compiler>::enter::<rustc_driver[2feadf6a045f69f8]::run_compiler::{closure#1}::{closure#2}, core[b141a5f448cbfdbc]::result::Result<core[b141a5f448cbfdbc]::option::Option<rustc_interface[a32f49e72690e02b]::queries::Linker>, rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>>
  45:     0x7f6fdc4f6edc - rustc_span[f76be64242de1050]::with_source_map::<core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>, rustc_interface[a32f49e72690e02b]::interface::run_compiler<core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>, rustc_driver[2feadf6a045f69f8]::run_compiler::{closure#1}>::{closure#0}::{closure#1}>
  46:     0x7f6fdc4f68a2 - <scoped_tls[98436e20d4fee4d6]::ScopedKey<rustc_span[f76be64242de1050]::SessionGlobals>>::set::<rustc_interface[a32f49e72690e02b]::interface::run_compiler<core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>, rustc_driver[2feadf6a045f69f8]::run_compiler::{closure#1}>::{closure#0}, core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>>
  47:     0x7f6fdc4f4fcf - std[5adef4932411bbc2]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[a32f49e72690e02b]::util::run_in_thread_pool_with_globals<rustc_interface[a32f49e72690e02b]::interface::run_compiler<core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>, rustc_driver[2feadf6a045f69f8]::run_compiler::{closure#1}>::{closure#0}, core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>>
  48:     0x7f6fdc4f4e3f - <<std[5adef4932411bbc2]::thread::Builder>::spawn_unchecked_<rustc_interface[a32f49e72690e02b]::util::run_in_thread_pool_with_globals<rustc_interface[a32f49e72690e02b]::interface::run_compiler<core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>, rustc_driver[2feadf6a045f69f8]::run_compiler::{closure#1}>::{closure#0}, core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[b141a5f448cbfdbc]::result::Result<(), rustc_errors[3c325fb77ff98e3b]::ErrorGuaranteed>>::{closure#1} as core[b141a5f448cbfdbc]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  49:     0x7f6fdae485f3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hecb24e4d2d235ab4
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/alloc/src/boxed.rs:1987:9
  50:     0x7f6fdae485f3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h05e0c493dc58e461
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/alloc/src/boxed.rs:1987:9
  51:     0x7f6fdae485f3 - std::sys::unix::thread::Thread::new::thread_start::h6913f7fb82d0a425
                               at /rustc/4b8f4319954ff2642690b9e5cbe4af352d095bf6/library/std/src/sys/unix/thread.rs:108:17
  52:     0x7f6fdabb6e86 - start_thread
  53:     0x7f6fdac3dc60 - __clone3
  54:                0x0 - <unknown>

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.66.0-nightly (4b8f43199 2022-10-19) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -Z treat-err-as-bug

query stack during panic:
#0 [typeck] type-checking `<impl at a.rs:22:1: 22:32>::foo`
#1 [typeck_item_bodies] type-checking all item bodies
#2 [analysis] running analysis passes on this crate
end of query stack

[compiler-errors]

Possibly/probably related: #103741

[fmease]

Closing as a duplicate of #24066. If you feel it's worth keeping this open anyway, I can of course reopen it.