ICE: unwrap on an Err `PlaceBuilder`

[ehuss]

Encountered an ICE when building yew 0.18.0 on edition 2021. I have roughly narrowed it down to the following (can probably be reduced further). Seems to be an issue with closure captures.

Code

// Build with edition 2021
use std::rc::Rc;

#[derive(Clone, PartialEq)]
struct Props {
    field_1: u32,
    field_2: u32,
}

#[derive(Clone, Debug, PartialEq)]
struct Node;

#[derive(Clone)]
struct NodeRef(Rc<Node>);

enum VNode {
    VRef(Node),
}

impl VNode {
    fn first_node(&self) -> Node {
        match self {
            VNode::VRef(node) => node.clone(),
        }
    }
}

impl NodeRef {
    fn get(&self) -> Option<Node> {
        Some(self.0.as_ref().clone())
    }
}

struct Properties;

fn main() {
    let test_node = Node;
    let test_node_ref = NodeRef(Rc::new(test_node));
    let check_node_ref = |vnode: VNode| {
        assert_eq!(vnode.first_node(), test_node_ref.get().unwrap());
    };

    let props = Props {
        field_1: 1,
        field_2: 1,
    };
    let props_2 = props.clone();

    check_node_ref(VNode::VRef({
        {
            let _ = |__yew_props: Props| {
                let _: Props = props_2;
            };
            props_2;
        }
        Node
    }));
}

Meta

rustc --version --verbose:

rustc 1.56.0-nightly (ccffcafd5 2021-08-11)
binary: rustc
commit-hash: ccffcafd55e58f769d4b0efc0064bf65e76998e4
commit-date: 2021-08-11
host: x86_64-apple-darwin
release: 1.56.0-nightly
LLVM version: 12.0.1

Error output

thread 'rustc' panicked at 'called Result::unwrap() on an Err value: PlaceBuilder { base: Upvar { var_hir_id: HirId { owner: DefId(0:16 ~ foo[602f]::main), local_id: 106 }, closure_def_id: DefId(0:18 ~ foo[602f]::main::{closure#1}), closure_kind: Fn }, projection: [] }', compiler/rustc_mir_build/src/build/expr/as_place.rs:306:69

Backtrace

stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::result::unwrap_failed
   3: rustc_mir_build::build::expr::as_place::PlaceBuilder::into_place
   4: rustc_mir_build::build::matches::simplify::<impl rustc_mir_build::build::Builder>::simplify_candidate
   5: rustc_mir_build::build::matches::<impl rustc_mir_build::build::Builder>::lower_match_tree
   6: rustc_mir_build::build::matches::<impl rustc_mir_build::build::Builder>::place_into_pattern
   7: rustc_mir_build::build::matches::<impl rustc_mir_build::build::Builder>::expr_into_pattern
   8: rustc_mir_build::build::block::<impl rustc_mir_build::build::Builder>::ast_block_stmts
   9: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  10: rustc_mir_build::build::scope::<impl rustc_mir_build::build::Builder>::in_scope
  11: rustc_data_structures::stack::ensure_sufficient_stack
  12: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  13: rustc_mir_build::build::scope::<impl rustc_mir_build::build::Builder>::in_scope
  14: rustc_data_structures::stack::ensure_sufficient_stack
  15: rustc_mir_build::build::expr::into::<impl rustc_mir_build::build::Builder>::expr_into_dest
  16: rustc_mir_build::build::construct_fn
  17: rustc_infer::infer::InferCtxtBuilder::enter
  18: rustc_mir_build::build::mir_built
  19: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  20: rustc_data_structures::stack::ensure_sufficient_stack
  21: rustc_query_system::query::plumbing::get_query_impl
  22: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_built
  23: rustc_mir::transform::check_unsafety::unsafety_check_result
  24: core::ops::function::FnOnce::call_once
  25: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  26: rustc_data_structures::stack::ensure_sufficient_stack
  27: rustc_query_system::query::plumbing::force_query_with_job
  28: rustc_query_system::query::plumbing::get_query_impl
  29: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  30: <rustc_mir::transform::check_unsafety::UnsafetyChecker as rustc_middle::mir::visit::Visitor>::visit_rvalue
  31: rustc_mir::transform::check_unsafety::unsafety_check_result
  32: core::ops::function::FnOnce::call_once
  33: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  34: rustc_data_structures::stack::ensure_sufficient_stack
  35: rustc_query_system::query::plumbing::force_query_with_job
  36: rustc_query_system::query::plumbing::get_query_impl
  37: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  38: rustc_mir::transform::mir_const
  39: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  40: rustc_data_structures::stack::ensure_sufficient_stack
  41: rustc_query_system::query::plumbing::get_query_impl
  42: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_const
  43: rustc_mir::transform::mir_promoted
  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_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_promoted
  48: rustc_mir::borrow_check::mir_borrowck
  49: core::ops::function::FnOnce::call_once
  50: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  51: rustc_data_structures::stack::ensure_sufficient_stack
  52: rustc_query_system::query::plumbing::force_query_with_job
  53: rustc_query_system::query::plumbing::get_query_impl
  54: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_borrowck
  55: rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::par_body_owners
  56: rustc_interface::passes::analysis
  57: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  58: rustc_data_structures::stack::ensure_sufficient_stack
  59: rustc_query_system::query::plumbing::force_query_with_job
  60: rustc_query_system::query::plumbing::get_query_impl
  61: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
  62: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  63: rustc_span::with_source_map
  64: rustc_interface::interface::create_compiler_and_run
  65: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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 1.56.0-nightly (ccffcafd5 2021-08-11) running on x86_64-apple-darwin

note: compiler flags: -Z unstable-options -C embed-bitcode=no -C split-debuginfo=unpacked -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [mir_built] building MIR for `main::{closure#1}`
#1 [unsafety_check_result] unsafety-checking `main::{closure#1}`
#2 [unsafety_check_result] unsafety-checking `main`
#3 [mir_const] processing MIR for `main`
#4 [mir_promoted] processing `main`
#5 [mir_borrowck] borrow-checking `main`
#6 [analysis] running analysis passes on this crate
end of query stack

cc @rust-lang/wg-rfc-2229

[roxelo]

The code can be further simplified to:

fn main() {
    let props = Props {
        field_1: 1,
        field_2: 1,
    };
    let props_2 = props.clone();

    let _ = |__yew_props: Props| {
        let _: Props = props_2;
    };
}

The issue seems to be around using type annotation. If a type annotation is included, the right hand side of the let statement should always be read.

fn main() {
    let props = Props {
        field_1: 1,
        field_2: 1,
    };
    let props_2 = props.clone();

    let _ = |__yew_props: Props| {
        let _ = props_2; // No ICE when we remove the type annotation
    };
}

[arora-aman]

let _: Props = props_2; Is there a runtime check/ is MIR generated for checking if props_2 as Props is valid?

Because if that's the case then we need props_2 to be caputred.

[roxelo]

@rustbot claim
I should have a fix later tonight

[ehuss]

@roxelo We found another instance of this PlaceBuilder ICE that still fails with #88039 included:

#![feature(capture_disjoint_fields)]

fn foo<MsU>(handler: impl FnOnce() -> MsU + Clone + 'static) {
    Box::new(move |value| {
        (|_| handler.clone()())(value);
        None
    }) as Box<dyn Fn(i32) -> Option<i32>>;
}

fn main() {}

Found trying to migrate seed 0.8.0.

Let me know if you need any more information.