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)]enumMyError{NotFound{key:Vec<u8>},Err41,}impl std::error::ErrorforMyError{}impl std::fmt::DisplayforMyError{fnfmt(&self,f:&mut std::fmt::Formatter) -> std::fmt::Result{matchself{MyError::NotFound{ key } => write!(
f,"unknown error with code {}.",String::from_utf8(*key).unwrap()),MyError::Err41 => write!(f,"Sit by a lake"),}}}fnmain(){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/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::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)

Details

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:881:backtrace::backtrace::trace_unsynchronized
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:662:std::sys_common::backtrace::_print_fmt
at src/libstd/sys_common/backtrace.rs:763: <std::sys_common::backtrace::_print::DisplayBacktraceas core::fmt::Display>::fmt
at src/libstd/sys_common/backtrace.rs:604:core::fmt::write
at src/libcore/fmt/mod.rs:10285:std::io::Write::write_fmt
at src/libstd/io/mod.rs:14126:std::sys_common::backtrace::_print
at src/libstd/sys_common/backtrace.rs:647:std::sys_common::backtrace::print
at src/libstd/sys_common/backtrace.rs:498:std::panicking::default_hook::{{closure}}
at src/libstd/panicking.rs:1969:std::panicking::default_hook
at src/libstd/panicking.rs:21010:rustc_driver::report_ice
11: std::panicking::rust_panic_with_hook
at src/libstd/panicking.rs:47712: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::QueryAccessorsfor 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