Generic return values cause an ICE in type_metadata

[jdm]

fn foo<R>(r: R) -> R {
    r
}

pub fn main() {
    foo(0);
}

yields error: internal compiler error: debuginfo: unexpected type in type_metadata.

I presume this is a ty_infer, so I'm surprised we're seeing this in the debuginfo module while in the trans pass.

[jdm]

#0  0x00007ffff7c95770 in sys::begin_unwind_::_89e154cd0915671::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#1  0x00007ffff7c95d42 in sys::__extensions__::fail_with::anon::anon::expr_fn_24119 () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#2  0x00007ffff7c9560b in c_str::__extensions__::with_ref_24110::_c6798931b183a7::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#3  0x00007ffff7c95cd2 in sys::__extensions__::fail_with::anon::expr_fn_24117 () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#4  0x00007ffff7c9560b in c_str::__extensions__::with_ref_24110::_c6798931b183a7::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#5  0x00007ffff7c1b37a in sys::__extensions__::meth_13517::fail_with::_db4c44d01ce4116::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#6  0x00007ffff75a90f4 in diagnostic::__extensions__::meth_10771::fatal::_e0de3d9f29108f64::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libsyntax-64629f7f0c6a9bc-0.8-pre.so
#7  0x00007ffff75a9af0 in diagnostic::__extensions__::meth_10822::bug::_e0de3d9f29108f64::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libsyntax-64629f7f0c6a9bc-0.8-pre.so
#8  0x00007ffff6bbf3de in driver::session::__extensions__::meth_23342::bug::_e3e78dc632d9282::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#9  0x00007ffff6d35314 in middle::trans::debuginfo::type_metadata::_6ffb86cc508941a::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#10 0x00007ffff6d3d863 in middle::trans::debuginfo::bare_fn_metadata::_2fbe295907ee1ff::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#11 0x00007ffff6d35571 in middle::trans::debuginfo::type_metadata::_6ffb86cc508941a::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#12 0x00007ffff6cdafd9 in middle::trans::debuginfo::create_function_metadata::_ba12118115211059::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#13 0x00007ffff6cd8f7b in middle::trans::debuginfo::create_argument_metadata::_c292eb766c954f::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#14 0x00007ffff6cd81b8 in middle::trans::base::copy_args_to_allocas::_e6196fe18c51660::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#15 0x00007ffff6cd9e64 in middle::trans::base::trans_closure::_11deb1928c3d8d9d::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#16 0x00007ffff6bc2cdd in middle::trans::base::trans_fn::_352dbe505ddb98b8::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#17 0x00007ffff6bc47f8 in middle::trans::monomorphize::monomorphic_fn::_9e41f990d8b797bd::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#18 0x00007ffff6c2a04a in middle::trans::callee::trans_fn_ref_with_vtables::_c4a4eb27f7bbd1a8::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#19 0x00007ffff6c252ef in middle::trans::callee::trans_fn_ref::_c2b41162b567659f::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#20 0x00007ffff6c24036 in middle::trans::callee::trans::trans_def::_53fac45e2b5d1c87::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#21 0x00007ffff6c23d44 in middle::trans::callee::trans::_2df2ee3233c3dd::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#22 0x00007ffff6c2f021 in middle::trans::callee::trans_call::anon::expr_fn_27957 () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#23 0x00007ffff6c43bb6 in middle::trans::callee::trans_call_inner::anon::expr_fn_29191 () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#24 0x00007ffff6bfc4e2 in middle::trans::base::with_scope_result::_ba12aa31770c7c9::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#25 0x00007ffff6c2ef52 in middle::trans::callee::trans_call_inner::_99f2464f619e42b1::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#26 0x00007ffff6c2ec3e in middle::trans::callee::trans_call::_c0cfc1ae4f31f055::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#27 0x00007ffff6c4e2be in middle::trans::expr::trans_rvalue_dps_unadjusted::_2cc3af99a6f8c50::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#28 0x00007ffff6bf342b in middle::trans::expr::trans_into::_2cc3af99a6f8c50::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#29 0x00007ffff6bf28b4 in middle::trans::base::trans_stmt::_93f2ec235871e7b::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#30 0x00007ffff6bf129f in middle::trans::controlflow::trans_block::_6c0716e413df49f::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#31 0x00007ffff6cd9f38 in middle::trans::base::trans_closure::_11deb1928c3d8d9d::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#32 0x00007ffff6bc2cdd in middle::trans::base::trans_fn::_352dbe505ddb98b8::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#33 0x00007ffff6bbe453 in middle::trans::base::trans_item::_b386373bd87f2f56::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#34 0x00007ffff6cde93f in middle::trans::base::trans_mod::_ba7f4876c827d39e::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#35 0x00007ffff6cec601 in middle::trans::base::trans_crate::_6c399ecc10c33d5b::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#36 0x00007ffff724e83a in driver::driver::phase_4_translate_to_llvm::_c579329d3620dfe::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#37 0x00007ffff724f225 in driver::driver::compile_input::_cf621e14707056ca::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#38 0x00007ffff7272506 in run_compiler::_1134abcf278cbd77::_0$x2e8$x2dpre () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#39 0x00007ffff728019e in main::anon::expr_fn_97609 () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#40 0x00007ffff727e715 in monitor::anon::expr_fn_97488 () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#41 0x00007ffff727c1de in task::__extensions__::try_96970::anon::expr_fn_97170 () from /usr/local/bin/../lib/librustc-d3cb8c2ccd84a7a7-0.8-pre.so
#42 0x00007ffff7c697c0 in task::spawn::spawn_raw_newsched::anon::expr_fn_20471 () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#43 0x00007ffff7cafd5e in rt::task::__extensions__::build_start_wrapper::anon::anon::expr_fn_27353 () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#44 0x00007ffff7cae4dd in rt::task::__extensions__::run::anon::expr_fn_27272 () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#45 0x00007ffff7cb007d in rt::task::__extensions__::try_fn::_4ea42b53e45c4d37::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#46 0x00007ffff50fe2d3 in rust_try (f=<optimized out>, fptr=<optimized out>, env=<optimized out>) at /home/jdm/sdb/rust/src/rt/rust_builtin.cpp:552
#47 0x00007ffff7cae394 in rt::task::__extensions__::meth_27270::try::_199ab8d6eb226980::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#48 0x00007ffff7cae26a in rt::task::__extensions__::meth_27267::run::_199ab8d6eb226980::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#49 0x00007ffff7cafa3c in rt::task::__extensions__::build_start_wrapper::anon::expr_fn_27337 () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so
#50 0x00007ffff7ce6b89 in rt::context::__extensions__::task_start_wrapper::_d625afdc49afb93::_0$x2e8$x2dpre () from /usr/local/bin/../lib/libstd-6c65cf4b443341b1-0.8-pre.so

[jdm]

@michaelwoerister This may relate to monomorphization somehow.

[jdm]

trans_fn uses ty::ty_fn_ret(ty::node_id_to_type(ccx.tcx, id)) to refer to the output type of a known function rather than the type in the BareFnSig that debuginfo uses.

[jdm]

Then again, ty_fn_ret appears to do the exact same thing, but perhaps it's using the id of the unique monomorphized function.

[jdm]

trans_closure calls new_fn_ctxt_with_id which performs type substitution on the output type but doesn't store the result anywhere - it just uses it to create an LLVM type from the result.

[michaelwoerister]

Yes, I stumbled upon this while starting to implement generic function support. In my WIP, I just duplicated the behavior from new_fn_ctxt_with_id to get the current type (see michaelwoerister@ceff3f6#L1R381). It works but it doesn't feel quite right. The monomorphization handling could use some cleanup refactoring.