Rustc panic when assigning a dereferenced box as the condition in an if statement

[Arc-blroth]

Code

Note that this code is invalid in terms of expected behavior: line 5 should test for equality rather than perform assignment.

use std::ops::Deref;

fn main() {
    println!("Do urchins dream of gophers?");
    if "Rust" = Box::new("Go").deref() {
        println!("Definitely!");
    }
    println!("Maybe!");
}

Meta

rustc --version --verbose:

rustc 1.49.0-nightly (ffa2e7ae8 2020-10-24)
binary: rustc
commit-hash: ffa2e7ae8fbf9badc035740db949b9dae271c29f
commit-date: 2020-10-24
host: x86_64-pc-windows-msvc
release: 1.49.0-nightly
LLVM version: 11.0

Error output

error: internal compiler error: compiler\rustc_typeck\src\check\fn_ctxt\_impl.rs:308:25: while adjusting Expr { hir_id: HirId { owner: DefId(0:4 ~ panicc[d4b8]::main), local_id: 67 }, kind: Call(Expr { hir_id: HirId { owner: DefId(0:4 ~ panicc[d4b8]::main), local_id: 65 }, kind: Path(TypeRelative(Ty { hir_id: HirId { owner: DefId(0:4 ~ panicc[d4b8]::main), local_id: 63 }, kind: Path(Resolved(None, Path { span: src\main.rs:5:17: 5:25 (#0), res: Def(Struct, DefId(5:91 ~ alloc[730d]::boxed::Box)), segments: [PathSegment { ident: Box#0, hir_id: Some(HirId { owner: DefId(0:4 ~ panicc[d4b8]::main), local_id: 62 }), res: Some(Err), args: None, infer_args: true }] })), span: src\main.rs:5:17: 5:25 (#0) }, PathSegment { ident: new#0, hir_id: Some(HirId { owner: DefId(0:4 ~ panicc[d4b8]::main), local_id: 64 }), res: Some(Err), args: None, infer_args: true })), attrs: ThinVec(None), span: src\main.rs:5:17: 5:25 (#0) }, [Expr { hir_id: HirId { owner: DefId(0:4 ~ panicc[d4b8]::main), local_id: 66 }, kind: Lit(Spanned { node: Str("Go", Cooked), span: src\main.rs:5:26: 5:30 (#0) }), attrs: ThinVec(None), span: src\main.rs:5:26: 5:30 (#0) }]), attrs: ThinVec(None), span: src\main.rs:5:17: 5:31 (#0) }, can't compose [Borrow(Ref('_#19r, Not)) -> &Box<&str>] and [Borrow(Ref('_#24r, Not)) -> &Box<&str>]

thread 'rustc' panicked at 'Box<Any>', compiler\rustc_errors\src\lib.rs:945:9

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 1.49.0-nightly (ffa2e7ae8 2020-10-24) running on x86_64-pc-windows-msvc

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [typeck] type-checking `main`
#1 [typeck_item_bodies] type-checking all item bodies
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

Backtrace

   0:     0x7ff95db39b7e - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hbb7524420f9ae79f
   1:     0x7ff95db67adb - core::fmt::write::h435be716304d26a1
   2:     0x7ff95db2b508 - <std::io::IoSliceMut as core::fmt::Debug>::fmt::h89e6d3fd1c80838c
   3:     0x7ff95db3f0bd - std::panicking::take_hook::h1b5ffd09c3541ec0
   4:     0x7ff95db3ec98 - std::panicking::take_hook::h1b5ffd09c3541ec0
   5:     0x7ff954422587 - rustc_driver::report_ice::h0a6a09ce1a074efd
   6:     0x7ff95db3fb10 - std::panicking::rust_panic_with_hook::he9661a82982eed74
   7:     0x7ff958a8b3d0 - <rustc_errors::registry::InvalidErrorCode as core::fmt::Debug>::fmt::haa47007281d8d69d
   8:     0x7ff958a8b379 - <rustc_errors::registry::InvalidErrorCode as core::fmt::Debug>::fmt::haa47007281d8d69d
   9:     0x7ff958a93661 - <rustc_errors::diagnostic::StringPart as core::fmt::Debug>::fmt::h0e74c1792db6aa41
  10:     0x7ff958ac5d6f - rustc_errors::HandlerInner::err_count::h3797b647eeace099
  11:     0x7ff958ac4422 - rustc_errors::Handler::bug::h0a174d32ca88e813
  12:     0x7ff9586f65df - rustc_middle::util::bug::bug_fmt::h42bac936f78c8dfd
  13:     0x7ff9586f13c0 - rustc_middle::ty::walk::<impl rustc_middle::ty::subst::GenericArg>::walk_shallow::h0d56592a32eb5063
  14:     0x7ff9586f1363 - rustc_middle::ty::walk::<impl rustc_middle::ty::subst::GenericArg>::walk_shallow::h0d56592a32eb5063
  15:     0x7ff9586f650c - rustc_middle::util::bug::bug_fmt::h42bac936f78c8dfd
  16:     0x7ff9586f6470 - rustc_middle::util::bug::bug_fmt::h42bac936f78c8dfd
  17:     0x7ff956a64906 - rustc_typeck::check::fn_ctxt::_impl::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::apply_adjustments::hf110cdba23a2cd0e
  18:     0x7ff956ce8d27 - <rustc_typeck::check::dropck::SimpleEqRelation as rustc_middle::ty::relate::TypeRelation>::consts::h457188dbba040b2c
  19:     0x7ff956a83b41 - rustc_typeck::check::method::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::lookup_method::h7243b08e064ce505
  20:     0x7ff956a536af - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  21:     0x7ff956a53016 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  22:     0x7ff956a52e41 - rustc_typeck::check::demand::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_for_cast::hb500583c43a84416
  23:     0x7ff956a560d7 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  24:     0x7ff956a53016 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  25:     0x7ff956a5363d - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  26:     0x7ff956a53016 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  27:     0x7ff956a39b70 - rustc_typeck::check::_match::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_match::h6d42c08016f9a803
  28:     0x7ff956a53e20 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  29:     0x7ff956a53016 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  30:     0x7ff956a70445 - rustc_typeck::check::fn_ctxt::checks::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_stmt::h017d3e5d2e493fca
  31:     0x7ff956a70ea6 - rustc_typeck::check::fn_ctxt::checks::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_block_no_value::h665bf96a03f6498e
  32:     0x7ff956a53b5f - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  33:     0x7ff956a53016 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  34:     0x7ff956a5dba8 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::hdb5f692ff025cdbe
  35:     0x7ff956b82b81 - rustc_typeck::check::check::check_wf_new::h19e270445413f329
  36:     0x7ff956cbfbb0 - <rustc_typeck::astconv::PathSeg as core::fmt::Debug>::fmt::hfd86fd5c2458e7e2
  37:     0x7ff956d54e1a - <rustc_typeck::check::fixup_opaque_types::FixupFolder as rustc_middle::ty::fold::TypeFolder>::fold_ty::hcdc6c08b5c1ca355
  38:     0x7ff956c5f40e - <rustc_typeck::bounds::Bounds as core::fmt::Debug>::fmt::ha3a532628cf583e4
  39:     0x7ff956b70966 - <rustc_typeck::outlives::implicit_infer::InferVisitor as rustc_hir::itemlikevisit::ItemLikeVisitor>::visit_item::h8baf1728e76b3c64
  40:     0x7ff956c35d54 - <<rustc_typeck::collect::const_evaluatable_predicates_of::ConstCollector as rustc_hir::intravisit::Visitor>::visit_ty::TyAliasVisitor as rustc_middle::ty::fold::TypeVisitor>::visit_const::hf3927083f687e271
  41:     0x7ff956bd158d - <rustc_typeck::outlives::explicit::ExplicitPredicatesMap as core::fmt::Debug>::fmt::hd3d7c0c50e41d57c
  42:     0x7ff956abcd4e - rustc_typeck::check::writeback::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::resolve_type_vars_in_body::h4c9e8bc9efe88ee2
  43:     0x7ff956b44c72 - rustc_typeck::check::writeback::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::resolve_type_vars_in_body::h4c9e8bc9efe88ee2
  44:     0x7ff956d5a5a4 - <rustc_typeck::check::CheckItemTypesVisitor as rustc_hir::itemlikevisit::ItemLikeVisitor>::visit_item::h42a56a7a7b0b6e7b
  45:     0x7ff956c2418d - <<rustc_typeck::collect::const_evaluatable_predicates_of::ConstCollector as rustc_hir::intravisit::Visitor>::visit_ty::TyAliasVisitor as rustc_middle::ty::fold::TypeVisitor>::visit_const::hf3927083f687e271
  46:     0x7ff956b71466 - <rustc_typeck::outlives::implicit_infer::InferVisitor as rustc_hir::itemlikevisit::ItemLikeVisitor>::visit_item::h8baf1728e76b3c64
  47:     0x7ff956c37f7f - <<rustc_typeck::collect::const_evaluatable_predicates_of::ConstCollector as rustc_hir::intravisit::Visitor>::visit_ty::TyAliasVisitor as rustc_middle::ty::fold::TypeVisitor>::visit_const::hf3927083f687e271
  48:     0x7ff956bd2789 - <rustc_typeck::outlives::explicit::ExplicitPredicatesMap as core::fmt::Debug>::fmt::hd3d7c0c50e41d57c
  49:     0x7ff956adedeb - rustc_typeck::check::writeback::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::resolve_type_vars_in_body::h4c9e8bc9efe88ee2
  50:     0x7ff956c78bba - rustc_typeck::check_crate::he8b36c3222a01778
  51:     0x7ff954639b83 - rustc_interface::passes::QueryContext::print_stats::h83316569f356654e
  52:     0x7ff9543a90ab - <[i64] as rand::AsByteSliceMut>::to_le::he7bd17e5835d34e6
  53:     0x7ff9543aa7b6 - <[i64] as rand::AsByteSliceMut>::to_le::he7bd17e5835d34e6
  54:     0x7ff95443f8af - rustc_ast::util::parser::prec_let_scrutinee_needs_par::h67b9ec40d4cf07ae
  55:     0x7ff9544399be - <rustc_driver::Compilation as core::fmt::Debug>::fmt::h514b7a76f78a44e9
  56:     0x7ff9543cc912 - <rustc_span::symbol::SymbolStr as core::fmt::Display>::fmt::h58939e9964733da9
  57:     0x7ff9543ab44c - <[i64] as rand::AsByteSliceMut>::to_le::he7bd17e5835d34e6
  58:     0x7ff95443b308 - rustc_ast::util::parser::prec_let_scrutinee_needs_par::h67b9ec40d4cf07ae
  59:     0x7ff954402d66 - <rustc_ast::ast::Item<rustc_ast::ast::AssocItemKind> as rustc_ast::attr::HasAttrs>::attrs::hd867a83e3b0f360d
  60:     0x7ff95443e5c8 - rustc_ast::util::parser::prec_let_scrutinee_needs_par::h67b9ec40d4cf07ae
  61:     0x7ff954426f00 - <rustc_driver::Compilation as core::fmt::Debug>::fmt::h514b7a76f78a44e9
  62:     0x7ff9544429cb - rustc_ast::util::parser::prec_let_scrutinee_needs_par::h67b9ec40d4cf07ae
  63:     0x7ff9543c4723 - <rustc_span::symbol::SymbolStr as core::fmt::Display>::fmt::h58939e9964733da9
  64:     0x7ff95db4fb37 - std::sys::windows::thread::Thread::new::hdbe5c1228d1cf93a
  65:     0x7ff9b7e17034 - BaseThreadInitThunk
  66:     0x7ff9b99dcec1 - RtlUserThreadStart

[SNCPlay42]

This is probably a duplicate of #77218, which just got fixed and the fix hasn't made it to nightly yet.