ICE: Syntax error in if-let and Cell methods cause rustc panic at Box<Any>

[justanotherdot]

Code

use std::cell::Cell;

fn main() {
    let xs: Cell<Option<()>> = Cell::new(None);
    // ditto get_mut, et. al.
    // NB. `if Some` rather than `if let Some`
    if Some(xs) = xs.take() { }
}

Meta

Hi! 👋 First issue; sorry if anything is missing/off.

By the minimal example, it looks like the missing let in the if let seems to cause a syntax error, but the usual diagnostic isn't reported and an ICE occurs, instead.

This does not happen on stable, but I can reproduce on the following versions:

; rustc --version --verbose
rustc 1.48.0-nightly (bbc677480 2020-09-18)
binary: rustc
commit-hash: bbc677480db8da85ea302e1e89d3df1f00e435bf
commit-date: 2020-09-18
host: x86_64-apple-darwin
release: 1.48.0-nightly
LLVM version: 11.0

; cargo +beta rustc -- --version --verbose
   Compiling rustc-ice-2020-10-23 v0.1.0 (/Users/rjs/tmp/rustc-ice-2020-10-23)
rustc 1.48.0-beta.5 (4c78178b1 2020-10-21)
binary: rustc
commit-hash: 4c78178b1c6ee26e493edb58cefaa77ca44e3991
commit-date: 2020-10-21
host: x86_64-apple-darwin
release: 1.48.0-beta.5
LLVM version: 11.0

; cargo +nightly rustc -- --version --verbose
   Compiling rustc-ice-2020-10-23 v0.1.0 (/Users/rjs/tmp/rustc-ice-2020-10-23)
rustc 1.49.0-nightly (1eaadebb3 2020-10-21)
binary: rustc
commit-hash: 1eaadebb3dee31669c7649b32747381d11614fae
commit-date: 2020-10-21
host: x86_64-apple-darwin
release: 1.49.0-nightly
LLVM version: 11.0

Error output

; cargo check
    Checking rustc-ice-2020-10-23 v0.1.0 (/Users/rjs/tmp/rustc-ice-2020-10-23)
error: internal compiler error: compiler/rustc_typeck/src/check/mod.rs:3396:25: while adjusting Expr { hir_id: HirId { owner: DefId(0:4 ~ rustc_ice_2020_10_23[ee17]::main[0])
, local_id: 29 }, kind: Path(Resolved(None, Path { span: src/main.rs:5:19: 5:21 (#0), res: Local(HirId { owner: DefId(0:4 ~ rustc_ice_2020_10_23[ee17]::main[0]), local_id: 1
}), segments: [PathSegment { ident: xs#0, hir_id: Some(HirId { owner: DefId(0:4 ~ rustc_ice_2020_10_23[ee17]::main[0]), local_id: 28 }), res: Some(Local(HirId { owner: DefId(
0:4 ~ rustc_ice_2020_10_23[ee17]::main[0]), local_id: 1 })), args: None, infer_args: true }] })), attrs: ThinVec(None), span: src/main.rs:5:19: 5:21 (#0) }, can't compose [Bo
rrow(Ref('_#0r, Not)) -> &Cell<Option<()>>] and [Borrow(Ref('_#2r, Not)) -> &Cell<Option<()>>]

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:945:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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 1.48.0-nightly (bbc677480 2020-09-18) running on x86_64-apple-darwin

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

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

error: aborting due to previous error

error: could not compile `rustc-ice-2020-10-23`

To learn more, run the command again with --verbose.

Backtrace

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:945:9
stack backtrace:
   0: std::panicking::begin_panic
   1: rustc_errors::HandlerInner::bug
   2: rustc_errors::Handler::bug
   3: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
   4: rustc_middle::ty::context::tls::with_opt::{{closure}}
   5: rustc_middle::ty::context::tls::with_opt
   6: rustc_middle::util::bug::opt_span_bug_fmt
   7: rustc_middle::util::bug::bug_fmt
   8: rustc_typeck::check::FnCtxt::apply_adjustments
   9: rustc_typeck::check::method::confirm::ConfirmContext::confirm
  10: rustc_typeck::check::method::<impl rustc_typeck::check::FnCtxt>::lookup_method
  11: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  12: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation
  13: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_coercable_to_type
  14: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  15: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation
  16: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  17: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation
  18: rustc_typeck::check::_match::<impl rustc_typeck::check::FnCtxt>::check_match
  19: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  20: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation
  21: rustc_typeck::check::FnCtxt::check_block_with_expected
  22: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  23: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation
  24: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_return_expr
  25: rustc_typeck::check::check_fn
  26: rustc_infer::infer::InferCtxtBuilder::enter
  27: rustc_typeck::check::typeck
  28: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::typeck>::compu
te
  29: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  30: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  31: rustc_data_structures::stack::ensure_sufficient_stack
  32: rustc_query_system::query::plumbing::get_query_impl
  33: rustc_query_system::query::plumbing::ensure_query_impl
  34: rustc_typeck::check::typeck_item_bodies
  35: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::typeck_item_bo
dies>::compute
  36: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  37: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  38: rustc_data_structures::stack::ensure_sufficient_stack
  39: rustc_query_system::query::plumbing::get_query_impl
  40: rustc_typeck::check_crate
  41: rustc_interface::passes::analysis
  42: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::com
pute
  43: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  44: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  45: rustc_data_structures::stack::ensure_sufficient_stack
  46: rustc_query_system::query::plumbing::get_query_impl
  47: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  48: rustc_span::with_source_map
  49: rustc_interface::interface::create_compiler_and_run
  50: rustc_span::with_session_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[jonas-schievink]

Duplicate of #77218