ICE with per-type serializer

[nikomatsakis]

@erickt's implementation of #3740 leads to an ICE with this backtrace:

#0  upcall_fail (expr=0x1293624f0 "option::get none", file=0x1016671c0 "/Users/nmatsakis/versioned/rust-green/src/rustc/rustc.rc", line=1) at rust_upcall.cpp:94
#1  0x00000001001120f7 in rt::rustrt::rust_upcall_fail::_74a64c4360d2dcec::_04 ()
#2  0x000000010003c5c7 in rt::rt_fail_::_74a64c4360d2dcec::_04 ()
#3  0x0000000100b8d5a8 in option::get_23338::_29fe71a392a4924::_04 ()
#4  0x0000000100b8d43d in option::__extensions__::get_23335::_f0c217aeadcb2131::_04 ()
#5  0x00000001015012b9 in metadata::decoder::get_impl_method::_783f8d1a39c49ab::_04 ()
#6  0x0000000100d3b393 in metadata::csearch::get_impl_method::_6b7fc67f87eddc92::_04 ()
#7  0x0000000100d38f74 in middle::trans::meth::method_with_name::_ba3c2a2e023f72d::_04 ()
#8  0x0000000100bd2362 in middle::trans::meth::trans_static_method_callee::_f9ec6ca09ccac979::_04 ()
#9  0x0000000100bcb78d in middle::trans::callee::trans::trans_def::_67363582be12cd36::_04 ()
#10 0x0000000100bcb2ce in middle::trans::callee::trans::_f48ed4270a0c3c0::_04 ()
#11 0x0000000100bd6cd8 in middle::trans::callee::trans_call::anon::expr_fn_24271 ()
#12 0x0000000100bef739 in middle::trans::callee::trans_call_inner::anon::expr_fn_25077 ()
#13 0x0000000100b8ca0f in middle::trans::base::with_scope::_996fb23bb7f2845::_04 ()
#14 0x0000000100bd6bdb in middle::trans::callee::trans_call_inner::_ff61dbd7aaf3bd3::_04 ()
#15 0x0000000100bd6983 in middle::trans::callee::trans_call::_64631445544261e3::_04 ()
#16 0x0000000100c06c0c in middle::trans::expr::trans_rvalue_dps_unadjusted::_ead42a4b3d1be38a::_04 ()
#17 0x0000000100bff841 in middle::trans::expr::trans_into_unadjusted::_ead42a4b3d1be38a::_04 ()
#18 0x0000000100b73177 in middle::trans::expr::trans_into::_ead42a4b3d1be38a::_04 ()
#19 0x0000000100c8de0b in middle::trans::base::init_local::_a0ad6e37ca3614::_04 ()
#20 0x0000000100c8f93a in middle::trans::base::trans_stmt::anon::expr_fn_27842 ()
#21 0x0000000100b71492 in vec::each_22729::anon::expr_fn_22735 ()
#22 0x0000000100b713ba in vec::as_imm_buf_22732::_2bccd72f7286ea4a::_04 ()
#23 0x0000000100b71298 in vec::each_22729::_74aecc843b4616d::_04 ()
#24 0x0000000100b72f0a in middle::trans::base::trans_stmt::_cb45203fc1c777f9::_04 ()
#25 0x0000000100b7162b in middle::trans::controlflow::trans_block::anon::expr_fn_22743 ()
#26 0x0000000100b71492 in vec::each_22729::anon::expr_fn_22735 ()
#27 0x0000000100b713ba in vec::as_imm_buf_22732::_2bccd72f7286ea4a::_04 ()
#28 0x0000000100b71298 in vec::each_22729::_74aecc843b4616d::_04 ()
#29 0x0000000100b6fafe in middle::trans::controlflow::trans_block::_2448b950a43ba10::_04 ()
#30 0x0000000100c0e499 in middle::trans::expr::trans_rvalue_dps_unadjusted::anon::expr_fn_25395 ()
#31 0x0000000100b8ca0f in middle::trans::base::with_scope::_996fb23bb7f2845::_04 ()
#32 0x0000000100c0585b in middle::trans::expr::trans_rvalue_dps_unadjusted::_ead42a4b3d1be38a::_04 ()
#33 0x0000000100bff841 in middle::trans::expr::trans_into_unadjusted::_ead42a4b3d1be38a::_04 ()
#34 0x0000000100b73177 in middle::trans::expr::trans_into::_ead42a4b3d1be38a::_04 ()
#35 0x0000000100b6fba2 in middle::trans::controlflow::trans_block::_2448b950a43ba10::_04 ()
#36 0x00000001015b6a3a in __morestack ()
#37 0x0000000100b6f8fc in middle::trans::controlflow::trans_block::_2448b950a43ba10::_04 ()
#38 0x0000000100bdccdb in vec::__extensions__::each_24341::anon::expr_fn_24344 ()
#39 0x0000000100b71492 in vec::each_22729::anon::expr_fn_22735 ()
#40 0x0000000100b713ba in vec::as_imm_buf_22732::_2bccd72f7286ea4a::_04 ()
#41 0x0000000100b71298 in vec::each_22729::_74aecc843b4616d::_04 ()
#42 0x0000000100bdcc64 in vec::__extensions__::each_24341::_f660f04d53d71191::_04 ()
#43 0x0000000100d1ea90 in middle::trans::alt::trans_alt_inner::_a9d346c11893b647::_04 ()
#44 0x0000000100d1ded1 in middle::trans::alt::trans_alt::anon::expr_fn_30846 ()
#45 0x0000000100b8ca0f in middle::trans::base::with_scope::_996fb23bb7f2845::_04 ()
#46 0x0000000100c0e33f in middle::trans::alt::trans_alt::_9296d11856c4ec4::_04 ()
#47 0x0000000100c04fd2 in middle::trans::expr::trans_rvalue_dps_unadjusted::_ead42a4b3d1be38a::_04 ()
#48 0x0000000100bff841 in middle::trans::expr::trans_into_unadjusted::_ead42a4b3d1be38a::_04 ()
#49 0x0000000100b73177 in middle::trans::expr::trans_into::_ead42a4b3d1be38a::_04 ()
#50 0x0000000100b6fba2 in middle::trans::controlflow::trans_block::_2448b950a43ba10::_04 ()
#51 0x0000000100c9d86f in middle::trans::base::trans_closure::_de391e1ab6ebccc::_04 ()
#52 0x0000000100ac4296 in middle::trans::base::trans_fn::_f5531fab3be1a3c1::_04 ()
#53 0x0000000100abcdb9 in middle::trans::base::trans_item::_85f94bc13edd0::_04 ()
#54 0x0000000100cad24d in middle::trans::base::trans_mod::anon::expr_fn_28568 ()
#55 0x0000000100b71492 in vec::each_22729::anon::expr_fn_22735 ()
#56 0x0000000100b713ba in vec::as_imm_buf_22732::_2bccd72f7286ea4a::_04 ()
#57 0x0000000100b71298 in vec::each_22729::_74aecc843b4616d::_04 ()
#58 0x0000000100cac801 in middle::trans::base::trans_mod::_a57b1d56f5ce85ad::_04 ()
#59 0x0000000100abc4d1 in middle::trans::base::trans_item::_85f94bc13edd0::_04 ()
#60 0x0000000100cad24d in middle::trans::base::trans_mod::anon::expr_fn_28568 ()
#61 0x0000000100b71492 in vec::each_22729::anon::expr_fn_22735 ()
#62 0x0000000100b713ba in vec::as_imm_buf_22732::_2bccd72f7286ea4a::_04 ()
#63 0x0000000100b71298 in vec::each_22729::_74aecc843b4616d::_04 ()
#64 0x0000000100cac801 in middle::trans::base::trans_mod::_a57b1d56f5ce85ad::_04 ()
#65 0x0000000100abc4d1 in middle::trans::base::trans_item::_85f94bc13edd0::_04 ()
#66 0x0000000100cad24d in middle::trans::base::trans_mod::anon::expr_fn_28568 ()
#67 0x0000000100b71492 in vec::each_22729::anon::expr_fn_22735 ()
#68 0x0000000100b713ba in vec::as_imm_buf_22732::_2bccd72f7286ea4a::_04 ()
#69 0x0000000100b71298 in vec::each_22729::_74aecc843b4616d::_04 ()
#70 0x0000000100cac801 in middle::trans::base::trans_mod::_a57b1d56f5ce85ad::_04 ()
#71 0x0000000100cdf908 in middle::trans::base::trans_crate::_3c3db3d1abf0159a::_04 ()
#72 0x00000001015b6a3a in __morestack ()

I haven't gotten very far in tracking this down. It seems to have something to do with cross-crate static functions.

[nikomatsakis]

Oh, I think this may be a dup of #3446.

[nikomatsakis]

Oh, well, not precisely, but I think it's related to this FIXME in the code:

    // FIXME(#3446) -- I am pretty sure index 0 is not the right one,
    // if the static method is implemented on a generic type. (NDM)

[nikomatsakis]

I believe this is a minified example:

trait Deserializer {
    fn read_int() -> int;
}

trait Deserializable<D: Deserializer> {
    static fn deserialize(d: &D) -> self;
}

impl<D: Deserializer> int: Deserializable<D> {
    static fn deserialize(d: &D) -> int {
        return d.read_int();
    }
}

struct FromThinAir { dummy: () }

impl FromThinAir: Deserializer {
    fn read_int() -> int { 22 }
}

fn main() {
    let d = FromThinAir { dummy: () };
    let i: int = deserialize(&d);
    assert i == 22;
}

The stack track is slightly different owing to the fact that this is not the cross-crate case, but I think the relevant parts are the same:

#0  upcall_fail (expr=0x102b0ef50 "option::get none", file=0x101668170 "/Users/nmatsakis/versioned/rust-green/src/rustc/rustc.rc", line=1) at rust_upcall.cpp:94
#1  0x00000001001120f7 in rt::rustrt::rust_upcall_fail::_74a64c4360d2dcec::_04 ()
#2  0x000000010003c5c7 in rt::rt_fail_::_74a64c4360d2dcec::_04 ()
#3  0x0000000100b62952 in option::get_22339::_89c15131464a9573::_04 ()
#4  0x0000000100d3b2a5 in middle::trans::meth::method_from_methods::_6b67243aebfac69::_04 ()
#5  0x0000000100d38f98 in middle::trans::meth::method_with_name::_19b276bbd665a346::_04 ()
#6  0x0000000100bd2592 in middle::trans::meth::trans_static_method_callee::_f9ec6ca09ccac979::_04 ()
#7  0x0000000100bcb9bd in middle::trans::callee::trans::trans_def::_67363582be12cd36::_04 ()
#8  0x0000000100bcb4fe in middle::trans::callee::trans::_f48ed4270a0c3c0::_04 ()
#9  0x00000001015b78fa in __morestack ()

[nikomatsakis]

Fixing this is I think as "simple" as changing the [0] to be [x] where x is the number of bounds on the impl's type parameters (sigh, what a complex encoding we have) --- but finding out the number of impl type parameters is a bit of a pain. I think the right information is not available in the cross-crate case. So right now I'm experimenting with the best way to encode that.