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ICE with non-utf8 const generic &str #75763
Description
Code
#![feature(const_generics)]
struct Bug<const S: &'static str>;
fn main() {
let b: Bug::<{
unsafe {
std::mem::transmute::<&[u8], &str>(&[0xC0, 0xC1, 0xF5])
}
}>;
}Meta
rustc --version --verbose:
rustc 1.47.0-nightly (e15510ca3 2020-08-20)
Error output
thread 'rustc' panicked at 'non utf8 str from miri: Utf8Error { valid_up_to: 0, error_len: Some(1) }
Backtrace
stack backtrace:
0: rust_begin_unwind
at /rustc/e15510ca33ea15c893b78710101c962b11459963/library/std/src/panicking.rs:475
1: core::panicking::panic_fmt
at /rustc/e15510ca33ea15c893b78710101c962b11459963/library/core/src/panicking.rs:85
2: core::option::expect_none_failed
at /rustc/e15510ca33ea15c893b78710101c962b11459963/library/core/src/option.rs:1221
3: rustc_middle::ty::print::pretty::PrettyPrinter::pretty_print_const
4: rustc_middle::ty::print::pretty::<impl core::fmt::Display for &rustc_middle::ty::consts::Const>::fmt
5: core::fmt::write
at /rustc/e15510ca33ea15c893b78710101c962b11459963/library/core/src/fmt/mod.rs:1117
6: rustc_middle::ty::print::obsolete::DefPathBasedNames::push_generic_params
7: rustc_codegen_llvm::type_of::uncached_llvm_type
8: <rustc_target::abi::TyAndLayout<&rustc_middle::ty::TyS> as rustc_codegen_llvm::type_of::LayoutLlvmExt>::llvm_type
9: rustc_codegen_ssa::mir::operand::OperandRef<V>::new_zst
10: <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold
11: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
12: rustc_codegen_ssa::mir::codegen_mir
13: rustc_codegen_ssa::base::codegen_instance
14: <rustc_middle::mir::mono::MonoItem as rustc_codegen_ssa::mono_item::MonoItemExt>::define
15: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
16: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
17: rustc_codegen_llvm::base::compile_codegen_unit
18: rustc_codegen_ssa::base::codegen_crate
19: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
20: rustc_interface::passes::QueryContext::enter
21: rustc_interface::queries::Queries::ongoing_codegen
22: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
23: rustc_span::with_source_map
24: rustc_interface::interface::create_compiler_and_run
25: 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
Metadata
Metadata
Assignees
Labels
Area: const generics (parameters and arguments)Category: This is a bug.Call for participation: An issue has been fixed and does not reproduce, but no test has been added.`#![feature(const_generics)]`Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️Relevant to the compiler team, which will review and decide on the PR/issue.
Activity
FedericoPonzi commentedon Sep 2, 2020
It looks like it's correctly complied on rustc 1.48.0-nightly:
https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=3c6f489ca24c8ea66c9759f990a19f5a
DutchGhost commentedon Sep 2, 2020
I dont think this should compile at all. After all, we cause UB, the value of the const generic does not comply with the rules of
&str.lcnr commentedon Sep 3, 2020
A str being valid utf-8 is not a language invariant, so this should not be UB to my knowledge.
cc @RalfJung
I do expect this to be the correct behavior, so marking as
E-needs-testlcnr commentedon Sep 3, 2020
We do have to compare the
strs to check for equality though, which might cause library ub so 🤷RalfJung commentedon Sep 3, 2020
@lcnr I think you are free to decide on your own invariant here -- assuming that two
strare equal if and only if the underlying[u8]are equal, it's your call whether you want to allow non-UTF-8strin types or not.What is the plan for other library types? Like, imagine a user defined a newtype around
u8that must be even. The compiler cannot even know that such an invariant exists so it cannot be enforced. Equality checking anyway happens by comparing the underlying bytes. So if we follow that analogy, the non-UTF-8strshould be fine, but we have to make sure that we use the right notion of equality.lcnr commentedon Sep 3, 2020
👍 yeah, see #72396 for more details here I guess
One concern is that we probably want to print
strs instd::any::type_nameand in encodings, so we need to either deal with invalid utf there or forbid it entirely 🤔 Will have to keep that in mind before stabilizingstrparameters.RalfJung commentedon Sep 3, 2020
Yeah, you could either use
from_utf8_lossy(so any special treatment ofstris confined to the printing code) or makestra very special compiler-understood type even for the type system itself (and reject non-UTF-8 strings early). The former seems more principled to me but that is just a slight preference.lcnr commentedon Sep 3, 2020
from_utf8_lossywon't work for symbol mangling, as otherwise two distinct types can have the same symbol: https://rust.godbolt.org/z/ox7f8W (current ICE is unrelated, as const generics is not yet fully supported there)Printing invalid utf8 as bytes might be simpler there 🤔 I guess cc @eddyb about that
RalfJung commentedon Sep 3, 2020
Oh, this is not just pretty-printing but needs to be injective?
Then I guess some
\i{...}or so (for "invalid") would work.Rollup merge of rust-lang#78388 - camelid:regression-tests, r=lcnr