Do not ICE when dereferencing non-Copy raw pointer

[estebank]

CC #52262. Confirmed to remove the unnecessary ICE, but without a repro case.

[rust-highfive]

r? @zackmdavis

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[estebank]

CC @oli-obk

[ghost]

main.rs:

#[derive(Debug)]
enum MyError {
    NotFound { key: Vec<u8> },
    Err41,
}

impl std::error::Error for MyError {}

impl std::fmt::Display for MyError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {
            MyError::NotFound { key } => write!(
                f,
                "unknown error with code {}.",
                String::from_utf8(*key).unwrap()
            ),
            MyError::Err41 => write!(f, "Sit by a lake"),
        }
    }
}
fn main() {
    println!("Hello, world!");
}

Before:

$ RUST_BACKTRACE=1 /home/user/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc -Z treat-err-as-bug=500 ./main.rs 
error[E0507]: cannot move out of `*key` which is behind a shared reference
  --> ./main.rs:15:35
   |
15 |                 String::from_utf8(*key).unwrap()
   |                                   ^^^^ move occurs because `*key` has type `std::vec::Vec<u8>`, which does not implement the `Copy` trait

error: internal compiler error: src/librustc_mir/borrow_check/mod.rs:1949: Accessing `(*_4)` with the kind `Write(Move)` shouldn't be possible
  --> ./main.rs:15:35
   |
15 |                 String::from_utf8(*key).unwrap()
   |                                   ^^^^

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:871:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:76
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:60
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1028
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:64
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:196
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:477
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::span_bug
  14: rustc_errors::Handler::span_bug
  15: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  16: rustc::ty::context::tls::with_opt::{{closure}}
  17: rustc::ty::context::tls::with_context_opt
  18: rustc::ty::context::tls::with_opt
  19: rustc::util::bug::opt_span_bug_fmt
  20: rustc::util::bug::span_bug_fmt
  21: rustc_mir::borrow_check::MirBorrowckCtxt::access_place
  22: rustc_mir::borrow_check::MirBorrowckCtxt::consume_operand
  23: <rustc_mir::borrow_check::MirBorrowckCtxt as rustc_mir::dataflow::DataflowResultsConsumer>::visit_statement_entry
  24: rustc_mir::borrow_check::do_mir_borrowck
  25: rustc::ty::context::GlobalCtxt::enter_local
  26: rustc_mir::borrow_check::mir_borrowck
  27: rustc::ty::query::__query_compute::mir_borrowck
  28: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::mir_borrowck>::compute
  29: rustc::dep_graph::graph::DepGraph::with_task_impl
  30: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  31: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners
  32: rustc::util::common::time
  33: rustc_interface::passes::analysis
  34: rustc::ty::query::__query_compute::analysis
  35: rustc::dep_graph::graph::DepGraph::with_task_impl
  36: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  37: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  38: rustc_interface::passes::create_global_ctxt::{{closure}}
  39: rustc_interface::interface::run_compiler_in_existing_thread_pool
  40: std::thread::local::LocalKey<T>::with
  41: scoped_tls::ScopedKey<T>::set
  42: syntax::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.40.0-nightly (22bc9e1d9 2019-09-30) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z treat-err-as-bug=500

query stack during panic:
#0 [mir_borrowck] processing `<MyError as std::fmt::Display>::fmt`
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0507`.

before, without backtrace:

$ RUST_BACKTRACE=0 /home/user/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc -Z treat-err-as-bug=500 ./main.rs 
error[E0507]: cannot move out of `*key` which is behind a shared reference
  --> ./main.rs:15:35
   |
15 |                 String::from_utf8(*key).unwrap()
   |                                   ^^^^ move occurs because `*key` has type `std::vec::Vec<u8>`, which does not implement the `Copy` trait

error: internal compiler error: src/librustc_mir/borrow_check/mod.rs:1949: Accessing `(*_4)` with the kind `Write(Move)` shouldn't be possible
  --> ./main.rs:15:35
   |
15 |                 String::from_utf8(*key).unwrap()
   |                                   ^^^^

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:871:9
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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.40.0-nightly (22bc9e1d9 2019-09-30) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z treat-err-as-bug=500

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0507`.

after patch:

$ RUST_BACKTRACE=1 rustc -Z treat-err-as-bug=500 ./main.rs 
!! master-installed (default)
!! Executing '/home/user/.cargo/bin/rustc' in pwd='/tmp/blah/src' with args(3): '-Z treat-err-as-bug=500 ./main.rs'
error[E0507]: cannot move out of `*key` which is behind a shared reference
  --> ./main.rs:15:35
   |
15 |                 String::from_utf8(*key).unwrap()
   |                                   ^^^^ move occurs because `*key` has type `std::vec::Vec<u8>`, which does not implement the `Copy` trait

error: aborting due to previous error

For more information about this error, try `rustc --explain E0507`.

EDIT: looks like this issue happened before and there's a repro. in #54597 (comment) but that version didn't require -Z treat-err-as-bug=500 !!

[ghost]

It would be nice to have a repro case for the legit case when that error should be shown. There might be one inside #46908 ????? I'm trying to find it, but my knowledge is limited, I might fail. (already discarded example one if that was even supposed to show the error, unsure)
EDIT: gave up searching 'cause I don't even know what I'm doing :) need more knowledge, most likely.

[ghost]

Do not ICE when dereferencing non-Copy raw pointer

Note: true only when using -Z treat-err-as-bug=500 (500 is a bit random, it has to be large enough, to not cause the ICE because of the original errors, so at least 2 in that case)

What do I mean by ICE because of the original errors? for example when using -Z treat-err-as-bug=1 aka -Z treat-err-as-bug you get the normally occurring ICE because of using treat-err-as-bug
-Z treat-err-as-bug=val -- treat error numberval that occurs as bug (aka causes ICE)

example of such ICE:

$ RUST_BACKTRACE=1 /home/user/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc -Z treat-err-as-bug=1 ./c.rs 
error[E0507]: cannot move out of `*array` which is behind a shared reference
  --> ./c.rs:16:13
   |
16 |             *array
   |             ^^^^^^
   |             |
   |             move occurs because `*array` has type `std::vec::Vec<Value>`, which does not implement the `Copy` trait
   |             help: consider borrowing here: `&*array`

thread 'rustc' panicked at 'aborting due to `-Z treat-err-as-bug=1`', src/librustc_errors/lib.rs:941:13
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:76
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:60
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1028
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:64
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:196
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:477
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::emit_diagnostic
  14: rustc_errors::diagnostic_builder::DiagnosticBuilder::into_diagnostic
  15: rustc_errors::diagnostic_builder::DiagnosticBuilder::buffer
  16: rustc_mir::borrow_check::move_errors::<impl rustc_mir::borrow_check::MirBorrowckCtxt>::report
  17: rustc_mir::borrow_check::do_mir_borrowck
  18: rustc::ty::context::GlobalCtxt::enter_local
  19: rustc_mir::borrow_check::mir_borrowck
  20: rustc::ty::query::__query_compute::mir_borrowck
  21: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::mir_borrowck>::compute
  22: rustc::dep_graph::graph::DepGraph::with_task_impl
  23: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  24: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners
  25: rustc::util::common::time
  26: rustc_interface::passes::analysis
  27: rustc::ty::query::__query_compute::analysis
  28: rustc::dep_graph::graph::DepGraph::with_task_impl
  29: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  30: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  31: rustc_interface::passes::create_global_ctxt::{{closure}}
  32: rustc_interface::interface::run_compiler_in_existing_thread_pool
  33: std::thread::local::LocalKey<T>::with
  34: scoped_tls::ScopedKey<T>::set
  35: syntax::with_globals
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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.40.0-nightly (22bc9e1d9 2019-09-30) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z treat-err-as-bug=1

query stack during panic:
#0 [mir_borrowck] processing `foo`
#1 [analysis] running analysis passes on this crate
end of query stack

this is normal!

[Centril]

r? @matthewjasper

[zackmdavis]

r? @zackmdavis

@bors r+

[bors]

📌 Commit e8796ca has been approved by zackmdavis