ICE when accessing an associated constant of a generic impl

[jebrosen]

(minimized test case provided by @tmandry )

This is triggered by accessing an associated constant of a generic impl. Here's a minimized testcase that ICEs on nightly (playground link):

pub struct Foo<T>(T);

impl<T> Foo<T> {
    const HASH_LEN: usize = 20;

    fn stuff() {
        let _ = Self::HASH_LEN;
    }
}

If a lifetime parameter is used instead of a type parameter, no ICE occurs.

Original bug report follows

---

Compiling mysql_common fails on rustc 1.31.0-nightly (78ff609d7 2018-10-19), but works on the previous nightly rustc 1.31.0-nightly (e7f5d4805 2018-10-18).

   Compiling mysql_common v0.10.0 (/home/mee/code/rust_mysql_common)                                                                                                                           
thread 'main' panicked at 'assertion failed: !impl_self_ty.has_infer_types()', librustc_mir/borrow_check/nll/type_check/mod.rs:1033:21                                                         
stack backtrace:                                                                                                                                                                               
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace                                                                                                                                
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49                                                                                                                                  
   1: std::sys_common::backtrace::print                                                                                                                                                        
             at libstd/sys_common/backtrace.rs:71                                                                                                                                              
             at libstd/sys_common/backtrace.rs:59                                                                                                                                              
   2: std::panicking::default_hook::{{closure}}                                                                                                                                                
             at libstd/panicking.rs:211                                                                                                                                                        
   3: std::panicking::default_hook                                                                                                                                                             
             at libstd/panicking.rs:227                                                                                                                                                        
   4: rustc::util::common::panic_hook                                                                                                                                                          
   5: std::panicking::rust_panic_with_hook                                                                                                                                                     
             at libstd/panicking.rs:480                                                                                                                                                        
   6: std::panicking::begin_panic                                                                                                                                                              
   7: rustc_mir::borrow_check::nll::type_check::TypeChecker::relate_type_and_user_type                                                                                                         
   8: <rustc_mir::borrow_check::nll::type_check::TypeVerifier<'a, 'b, 'gcx, 'tcx> as rustc::mir::visit::Visitor<'tcx>>::visit_constant                                                         
   9: <rustc_mir::borrow_check::nll::type_check::TypeVerifier<'a, 'b, 'gcx, 'tcx> as rustc::mir::visit::Visitor<'tcx>>::visit_rvalue                                                           
  10: <rustc_mir::borrow_check::nll::type_check::TypeVerifier<'a, 'b, 'gcx, 'tcx> as rustc::mir::visit::Visitor<'tcx>>::visit_mir                                                              
  11: rustc_mir::borrow_check::nll::type_check::type_check_internal                                                                                                                            
  12: rustc::ty::context::tls::with_related_context                                                                                                                                            
  13: rustc::infer::InferCtxtBuilder::enter                                                                                                                                                    
  14: <rustc_mir::borrow_check::nll::type_check::TypeckMir as rustc_mir::transform::MirPass>::run_pass                                                                                         
  15: rustc_mir::transform::mir_const::{{closure}}                                                                                                                                             
  16: rustc_mir::transform::mir_const                                                                                                                                                          
  17: rustc::ty::query::__query_compute::mir_const                                                                                                                                             
  18: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::mir_const<'tcx>>::compute                                                          
  19: rustc::ty::context::tls::with_context                                                                                                                                                    
  20: rustc::dep_graph::graph::DepGraph::with_task_impl                                                                                                                                        
  21: rustc::ty::context::tls::with_related_context                                                                                                                                            
  22: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job                                                                                      
  23: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query                                                                                                 
  24: rustc::ty::query::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_const                                                                                                           
  25: rustc_mir::transform::mir_validated                                                                                                                                                      
  26: rustc::ty::query::__query_compute::mir_validated                                                                                                                                         
  27: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::mir_validated<'tcx>>::compute                                                      
  28: rustc::ty::context::tls::with_context                                                                                                                                                    
  29: rustc::dep_graph::graph::DepGraph::with_task_impl                                                                                                                                        
  30: rustc::ty::context::tls::with_related_context                                                                                                                                            
  31: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job                                                                                      
  32: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query                                                                                                 
  33: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::ensure_query                                                                                              
  34: rustc_borrowck::borrowck::borrowck                                                                                                                                                       
  35: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::borrowck<'tcx>>::compute                                                           
  36: rustc::ty::context::tls::with_context                                                                                                                                                    
  37: rustc::dep_graph::graph::DepGraph::with_task_impl                                                                                                                                        
  38: rustc::ty::context::tls::with_related_context                                                                                                                                            
  39: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job                                                                                      
  40: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query                                                                                                 
  41: rustc::ty::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::par_body_owners                                                                                                            
  42: rustc_borrowck::borrowck::check_crate                                                                                                                                                    
  43: rustc::util::common::time                                                                                                                                                                
  44: rustc::ty::context::tls::enter_context                                                                                                                                                   
  45: <std::thread::local::LocalKey<T>>::with                                                                                                                                                  
  46: rustc::ty::context::TyCtxt::create_and_enter                                                                                                                                             
  47: rustc_driver::driver::compile_input                                                                                                                                                      
  48: rustc_driver::run_compiler_with_pool                                                                                                                                                     
  49: rustc_driver::driver::spawn_thread_pool                                                                                                                                                  
  50: rustc_driver::run_compiler                                                                                                                                                               
  51: <scoped_tls::ScopedKey<T>>::set                                                                                                                                                          
  52: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once                                                                                                          
  53: __rust_maybe_catch_panic                                                                                                                                                                 
             at libpanic_unwind/lib.rs:102                                                                                                                                                     
  54: rustc_driver::run                                                                                                                                                                        
  55: rustc_driver::main                                                                                                                                                                       
  56: std::rt::lang_start::{{closure}}                                                                                                                                                         
  57: std::panicking::try::do_call                                                                                                                                                             
             at libstd/rt.rs:59                                                                                                                                                                
             at libstd/panicking.rs:310                                                                                                                                                        
  58: __rust_maybe_catch_panic                                                                                                                                                                 
             at libpanic_unwind/lib.rs:102                                                                                                                                                     
  59: std::rt::lang_start_internal                                                                                                                                                             
             at libstd/panicking.rs:289                                                                                                                                                        
             at libstd/panic.rs:392                                                                                                                                                            
             at libstd/rt.rs:58                                                                                                                                                                
  60: main                                                                                                                                                                                     
  61: __libc_start_main                                                                                                                                                                        
  62: <unknown>                                                                                                                                                                                
query stack during panic:                                                                                                                                                                      
#0 [mir_const] processing `<crypto::rsa::Pkcs1OaepPadding<T>>::mgf1`                                                                                                                           
#1 [mir_validated] processing `<crypto::rsa::Pkcs1OaepPadding<T>>::mgf1`                                                                                                                       
#2 [borrowck] processing `<crypto::rsa::Pkcs1OaepPadding<T>>::mgf1`                                                                                                                            
end of query stack                                                                                                                                                                             
                                                                                                                                                                                               
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 1.31.0-nightly (78ff609d7 2018-10-19) running on x86_64-unknown-linux-gnu                                                                                                          
                                                                                                                                                                                               
note: compiler flags: -C debuginfo=2 -C incremental --crate-type lib                                                                                                                           
                                                                                                                                                                                               
note: some of the compiler flags provided by cargo are hidden                                                                                                                                  
                                                                                                                                                                                               
error: Could not compile `mysql_common`.                                                                                                                                                       

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

thread 'main' panicked at 'assertion failed: !impl_self_ty.has_infer_types()', librustc_mir/borrow_check/nll/type_check/mod.rs:1033:21

Some additional detail with RUST_LOG=debug before and after the stack trace:

 INFO 2018-10-20T04:27:03Z: rustc_mir::build: fn_id DefId(0/0:65 ~ mysql_common[73d2]::crypto[0]::rsa[0]::{{impl}}[2]::mgf1[0]) has attrs Borrowed([Attribute { id: AttrId(52), style: Outer, path: path(doc), tokens: TokenStream { kind: Stream([TokenStream { kind: Tree(Token(src/crypto/rsa.rs:70:5: 70:56, Eq)) }, TokenStream { kind: Tree(Token(src/crypto/rsa.rs:70:5: 70:56, Literal(Str_(/// Mask Generation Function as defined in rfc2437.), None))) }]) }, is_sugared_doc: true, span: src/crypto/rsa.rs:70:5: 70:56 }, Attribute { id: AttrId(53), style: Outer, path: path(doc), tokens: TokenStream { kind: Stream([TokenStream { kind: Tree(Token(src/crypto/rsa.rs:71:5: 71:8, Eq)) }, TokenStream { kind: Tree(Token(src/crypto/rsa.rs:71:5: 71:8, Literal(Str_(///), None))) }]) }, is_sugared_doc: true, span: src/crypto/rsa.rs:71:5: 71:8 }, Attribute { id: AttrId(54), style: Outer, path: path(doc), tokens: TokenStream { kind: Stream([TokenStream { kind: Tree(Token(src/crypto/rsa.rs:72:5: 72:46, Eq)) }, TokenStream { kind: Tree(Token(src/crypto/rsa.rs:72:5: 72:46, Literal(Str_(/// It will use SHA-1 as a hash function.), None))) }]) }, is_sugared_doc: true, span: src/crypto/rsa.rs:72:5: 72:46 }])
 INFO 2018-10-20T04:27:03Z: rustc_mir::build: fn_id DefId(0/1:18 ~ mysql_common[73d2]::crypto[0]::rsa[0]::{{impl}}[2]::mgf1[0]::{{closure}}[0]) has attrs Borrowed([])                         
thread 'main' panicked at 'assertion failed: !impl_self_ty.has_infer_types()', librustc_mir/borrow_check/nll/type_check/mod.rs:1033:21
[stack backtrace]

The problematic code appears to be https://github.com/blackbeam/rust_mysql_common/blob/master/src/crypto/rsa.rs#L88

PR #55152 looks like a likely cause as it touched the failing assert! and nearby code, cc @nikomatsakis

EDIT: typo in PR number.

[jebrosen]

I tried bisecting this but quite a few commits in that PR throw out errors starting with:

error: internal compiler error: broken MIR in DefId(

Bisect log:

# bad: [78ff609d7375ee2a2c6d0222776ac612eb1b75be] Auto merge of #55152 - nikomatsakis:nll-issue-54571-type-annot-in-constants, r=pnkfelix
# good: [e7f5d48059aa14cc2808473564deadd72d1e818d] Auto merge of #54976 - davidtwco:issue-52663-special-case-closures, r=nikomatsakis
git bisect start '78ff609d7' 'e7f5d4805'
# good: [0724efd9a1aac9cf4620795786fb8e896fbb17b3] Rollup merge of #55013 - matthewjasper:propagate-generator-bounds, r=nikomatsakis
git bisect good 0724efd9a1aac9cf4620795786fb8e896fbb17b3
# skip: [e94959b9369d611aed86a4c179406a96e983278a] propagate user-type annotation for constants in expressions
git bisect skip e94959b9369d611aed86a4c179406a96e983278a
# skip: [a0a3b4c0585129405c09a9be46a1a3f8d3411b3b] replace `UserTypeAnnotation::AdtDef` with `TypeOf`
git bisect skip a0a3b4c0585129405c09a9be46a1a3f8d3411b3b
# bad: [9a7bb0ef249258aacf144d04f5d437ba70533128] normalize the self-type that we extract from impl
git bisect bad 9a7bb0ef249258aacf144d04f5d437ba70533128
# bad: [2d98e9e0aa6a990ec12f476c495be6720ad81f51] create type ascription for any cast
git bisect bad 2d98e9e0aa6a990ec12f476c495be6720ad81f51
# good: [dbab381da1a46a18e46a04a61156aec40c59a4f6] Auto merge of #55040 - scalexm:param-env, r=nikomatsakis
git bisect good dbab381da1a46a18e46a04a61156aec40c59a4f6
# skip: [e7ab33e7a61ff046f1736f1b027c16d9494e20b8] type_check/mod.rs: rustfmt
git bisect skip e7ab33e7a61ff046f1736f1b027c16d9494e20b8
# good: [ebdfda64f893f30675320e15349b2948b2194ea9] convert `FnDef` to `TypeOf`, which is more general
git bisect good ebdfda64f893f30675320e15349b2948b2194ea9
# bad: [121f3c8d19c3549ab0b51a14034ffb8b097faf42] normalize after substitution
git bisect bad 121f3c8d19c3549ab0b51a14034ffb8b097faf42
# skip: [f99300fcbdfec2908aeb93c823fc37f92a4d2d30] pull `relate_type_and_user_type` code into `type_check` module
git bisect skip f99300fcbdfec2908aeb93c823fc37f92a4d2d30
# only skipped commits left to test
# possible first bad commit: [121f3c8d19c3549ab0b51a14034ffb8b097faf42] normalize after substitution
# possible first bad commit: [f99300fcbdfec2908aeb93c823fc37f92a4d2d30] pull `relate_type_and_user_type` code into `type_check` module
# possible first bad commit: [e7ab33e7a61ff046f1736f1b027c16d9494e20b8] type_check/mod.rs: rustfmt
# possible first bad commit: [a0a3b4c0585129405c09a9be46a1a3f8d3411b3b] replace `UserTypeAnnotation::AdtDef` with `TypeOf`
# possible first bad commit: [e94959b9369d611aed86a4c179406a96e983278a] propagate user-type annotation for constants in expressions

[tmandry]

Just confirmed that this was triggered by #55152. The merge commit fails; its first parent does not.

@jebrosen Thanks for your detailed reports, btw!

[tmandry]

This is triggered by accessing an associated constant of a generic impl. Here's a minimized testcase that ICEs on nightly (playground link):

pub struct Foo<T>(T);

impl<T> Foo<T> {
    const HASH_LEN: usize = 20;

    fn stuff() {
        let _ = Self::HASH_LEN;
    }
}

If a lifetime parameter is used instead of a type parameter, no ICE occurs.

This is all I know, someone else will have to figure out what it means. :)

[jebrosen]

@tmandry Aha! That does happen in mysql_common as well, a few lines above the location I pointed out before:

https://github.com/blackbeam/rust_mysql_common/blob/e4e80124c3c711cfc9e0f22de2784113914ef4c6/src/crypto/rsa.rs#L86

[tmandry]

@jebrosen Indeed, I used that code as my starting point for the minimized testcase. Thanks for pointing to it :)

#55273 had another case; that code also makes use of Self::CONST.

[jebrosen]

I reverted only commit e94959b locally, and both mysql_common and the minimized test case above compile again.

[pnkfelix]

it looks to me like #55261 and #55219 are duplicates of each other.

[pnkfelix]

(Well except that #55261 only fails on 2015 edition. So I'll close that in favor of #55219, which has a more general test case that exhibits failure on both 2015 and 2018 editions.)

[pnkfelix]

an NLL PR injected this so it seems fair that someone from WG-compiler-nll should have to fix it.

Tagging with NLL-complete. Note that migration does not mitigate this because it is an ICE.