Issue 1:
This:

extern crate iron;

use iron::{Request, Response, IronResult, Iron, status};
use std::net::ip::Ipv4Addr;

fn main() {
Iron::new(hello_world);

fn hello_world(_: &mut Request) -> IronResult<Response> {
Ok(Response::with(status::Ok, "hello world"))
}
}

compiles fine, but:

extern crate iron;

use iron::{Request, Response, IronResult, Iron, status};
use std::net::ip::Ipv4Addr;

fn main() {
Iron::new(hello_world).listen(Ipv4Addr(127, 0, 0, 1), 3000);

fn hello_world(_: &mut Request) -> IronResult<Response> {
Ok(Response::with(status::Ok, "hello world"))
}
}

ICEs with:

error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'no entry found for key', /Users/rustbuild/src/rust-buildbot/slave/nightly-mac/build/src/libstd/collections/hashmap/map.rs:1093

stack backtrace:
1: 0x10cebcd59 - rt::backtrace::imp::write::h189e19957ab9c695OLq
2: 0x10cec0071 - failure::on_fail::h03dc2437e5a88345n2q
3: 0x10d12ce95 - unwind::begin_unwind_inner::h033484cc1a8bac37Jud
4: 0x109a37e7e - unwind::begin_unwind::h7267044357685618810
5: 0x109f59800 - middle::ty::type_contents::tc_ty::h9dee7b4d0b2b2b26VCF
6: 0x109f58f3c - middle::ty::type_contents::tc_ty::h9dee7b4d0b2b2b26VCF
7: 0x109cdb5d6 - middle::ty::type_contents::h92aeb2c2b610e0e2QBF
8: 0x109ee9fe9 - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::consume_expr::h14245152794985074657
9: 0x109ee495f - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_expr::h5075202552449147342
10: 0x109eea03e - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::consume_expr::h14245152794985074657
11: 0x109ee495f - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_expr::h5075202552449147342
12: 0x109eea293 - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_local::h3960078952215051727
13: 0x109eea1c5 - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_block::h1681476813087692403
14: 0x109ee4ab8 - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_expr::h5075202552449147342
15: 0x109eedd7a - middle::trans::_match::create_bindings_map::h7c926dcc9743685daOi
16: 0x109e6336a - middle::trans::_match::trans_match::hda856724a8df18120Ji
17: 0x109e51b37 - middle::trans::expr::trans_rvalue_dps_unadjusted::hc9fadfddd28f4d57KO4
18: 0x109e12b9d - middle::trans::expr::trans_into::h61ab769bf22fa7c9iq3
19: 0x109e11e9c - middle::trans::controlflow::trans_stmt_semi::h690085bf4cf7dcecUCZ
20: 0x109e11520 - middle::trans::controlflow::trans_stmt::hf3294d619d4310c2HyZ
21: 0x109e12df8 - middle::trans::controlflow::trans_block::haf894db31e0a118dNDZ
22: 0x109e16e78 - middle::trans::controlflow::trans_while::h5f1f833bc693e3166NZ
23: 0x109e53a87 - middle::trans::expr::trans_rvalue_stmt_unadjusted::h429c506388a2e3d6LI4
24: 0x109e12c64 - middle::trans::expr::trans_into::h61ab769bf22fa7c9iq3
25: 0x109e12efd - middle::trans::controlflow::trans_block::haf894db31e0a118dNDZ
26: 0x109e51bad - middle::trans::expr::trans_rvalue_dps_unadjusted::hc9fadfddd28f4d57KO4
27: 0x109e12b9d - middle::trans::expr::trans_into::h61ab769bf22fa7c9iq3
28: 0x109e12efd - middle::trans::controlflow::trans_block::haf894db31e0a118dNDZ
29: 0x109ec399e - middle::trans::base::trans_closure::h7f2921f1f179d268ezf
30: 0x109e667b5 - middle::trans::closure::trans_expr_fn::hfa0708e282a88c7eLFj
31: 0x109e52a73 - middle::trans::expr::trans_rvalue_dps_unadjusted::hc9fadfddd28f4d57KO4
32: 0x109e50426 - middle::trans::expr::trans_unadjusted::hc4be1e5aa2eff2b4gb4
33: 0x109e14056 - middle::trans::expr::trans::h49becb6a5c7b0a40cu3
34: 0x109e497c4 - middle::trans::callee::trans_args::h82b5e82dbe357761802
35: 0x109e1b801 - middle::trans::callee::trans_call_inner::hd16d8c5fe60896ffbG2
36: 0x109e43814 - middle::trans::callee::trans_method_call::haf484f13878df218EB2
37: 0x109e51646 - middle::trans::expr::trans_rvalue_dps_unadjusted::hc9fadfddd28f4d57KO4
38: 0x109e12b9d - middle::trans::expr::trans_into::h61ab769bf22fa7c9iq3
39: 0x109e11e9c - middle::trans::controlflow::trans_stmt_semi::h690085bf4cf7dcecUCZ
40: 0x109e11520 - middle::trans::controlflow::trans_stmt::hf3294d619d4310c2HyZ
41: 0x109e12df8 - middle::trans::controlflow::trans_block::haf894db31e0a118dNDZ
42: 0x109e18076 - middle::trans::controlflow::trans_for::h5d5ba302e1abeed7cQZ
43: 0x109e53ac8 - middle::trans::expr::trans_rvalue_stmt_unadjusted::h429c506388a2e3d6LI4
44: 0x109e12c64 - middle::trans::expr::trans_into::h61ab769bf22fa7c9iq3
45: 0x109e12efd - middle::trans::controlflow::trans_block::haf894db31e0a118dNDZ
46: 0x109ec399e - middle::trans::base::trans_closure::h7f2921f1f179d268ezf
47: 0x109e0508a - middle::trans::base::trans_fn::hac9c962286515c42CKf
48: 0x109e06f5e - middle::trans::monomorphize::monomorphic_fn::h96fb22308c4a0853u5Y
49: 0x109e3dbcf - middle::trans::callee::trans_fn_ref_with_substs::hdc5652548ed88225tk2
50: 0x109e3a3ab - middle::trans::callee::trans_fn_ref::hf590bd91aa7c0fd4181
51: 0x109e1c24d - middle::trans::meth::trans_method_callee::h321387808d989836SRk
52: 0x109e439bb - middle::trans::callee::trans_method_call::closure.123984
53: 0x109e1a754 - middle::trans::callee::trans_call_inner::hd16d8c5fe60896ffbG2
54: 0x109e43814 - middle::trans::callee::trans_method_call::haf484f13878df218EB2
55: 0x109e51646 - middle::trans::expr::trans_rvalue_dps_unadjusted::hc9fadfddd28f4d57KO4
56: 0x109e12b9d - middle::trans::expr::trans_into::h61ab769bf22fa7c9iq3
57: 0x109e12efd - middle::trans::controlflow::trans_block::haf894db31e0a118dNDZ
58: 0x109e51bad - middle::trans::expr::trans_rvalue_dps_unadjusted::hc9fadfddd28f4d57KO4
59: 0x109e12b9d - middle::trans::expr::trans_into::h61ab769bf22fa7c9iq3
60: 0x109e12efd - middle::trans::controlflow::trans_block::haf894db31e0a118dNDZ
61: 0x109ec399e - middle::trans::base::trans_closure::h7f2921f1f179d268ezf
62: 0x109e667b5 - middle::trans::closure::trans_expr_fn::hfa0708e282a88c7eLFj
63: 0x109e52a73 - middle::trans::expr::trans_rvalue_dps_unadjusted::hc9fadfddd28f4d57KO4
64: 0x109e50426 - middle::trans::expr::trans_unadjusted::hc4be1e5aa2eff2b4gb4
65: 0x109e14056 - middle::trans::expr::trans::h49becb6a5c7b0a40cu3
66: 0x109e497c4 - middle::trans::callee::trans_args::h82b5e82dbe357761802
67: 0x109e1b801 - middle::trans::callee::trans_call_inner::hd16d8c5fe60896ffbG2
68: 0x109e429a7 - middle::trans::callee::trans_call::hc740554d018cb851wA2
69: 0x109e52201 - middle::trans::expr::trans_rvalue_dps_unadjusted::hc9fadfddd28f4d57KO4
70: 0x109e12b9d - middle::trans::expr::trans_into::h61ab769bf22fa7c9iq3
71: 0x109e11e9c - middle::trans::controlflow::trans_stmt_semi::h690085bf4cf7dcecUCZ
72: 0x109e11520 - middle::trans::controlflow::trans_stmt::hf3294d619d4310c2HyZ
73: 0x109e12df8 - middle::trans::controlflow::trans_block::haf894db31e0a118dNDZ
74: 0x109ec399e - middle::trans::base::trans_closure::h7f2921f1f179d268ezf
75: 0x109e0508a - middle::trans::base::trans_fn::hac9c962286515c42CKf
76: 0x109e06f5e - middle::trans::monomorphize::monomorphic_fn::h96fb22308c4a0853u5Y
77: 0x109e3dbcf - middle::trans::callee::trans_fn_ref_with_substs::hdc5652548ed88225tk2
78: 0x109e3a3ab - middle::trans::callee::trans_fn_ref::hf590bd91aa7c0fd4181
79: 0x109e1c24d - middle::trans::meth::trans_method_callee::h321387808d989836SRk
80: 0x109e439bb - middle::trans::callee::trans_method_call::closure.123984
81: 0x109e1a754 - middle::trans::callee::trans_call_inner::hd16d8c5fe60896ffbG2
82: 0x109e43814 - middle::trans::callee::trans_method_call::haf484f13878df218EB2
83: 0x109e51646 - middle::trans::expr::trans_rvalue_dps_unadjusted::hc9fadfddd28f4d57KO4
84: 0x109e12b9d - middle::trans::expr::trans_into::h61ab769bf22fa7c9iq3
85: 0x109e11e9c - middle::trans::controlflow::trans_stmt_semi::h690085bf4cf7dcecUCZ
86: 0x109e11520 - middle::trans::controlflow::trans_stmt::hf3294d619d4310c2HyZ
87: 0x109e12df8 - middle::trans::controlflow::trans_block::haf894db31e0a118dNDZ
88: 0x109ec399e - middle::trans::base::trans_closure::h7f2921f1f179d268ezf
89: 0x109e0508a - middle::trans::base::trans_fn::hac9c962286515c42CKf
90: 0x109e02805 - middle::trans::base::trans_item::h35195f56acc36a8eV3f
91: 0x109ecd4d8 - middle::trans::base::trans_crate::h6442820c0a274264r2g
92: 0x10a308615 - driver::driver::phase_4_translate_to_llvm::h8e1e0d5a654b87d1kAx
93: 0x10a300718 - driver::driver::compile_input::h1f2de5081accd1dcf7w
94: 0x10a389084 - driver::run_compiler::h00e7e552333d10b3yVA
95: 0x10a3871b6 - driver::run::closure.147372
96: 0x109a7034b - task::TaskBuilder<S>::try_future::closure.101547
97: 0x109a70233 - task::TaskBuilder<S>::spawn_internal::closure.101518
98: 0x10ad2179d - task::spawn_opts::closure.8528
99: 0x10d19495c - rust_try_inner
100: 0x10d194946 - rust_try
... <frames omitted>

I tried to debug this with @eddyb on IRC a few days ago, but haven't been able to make any progress.

Issue 2:
I hit an internal compiler error in rustc 0.12.0-nightly (d53874e 2014-10-02 01:22:20 +0000).

Notes:

trying to compile ncollide / nphysics. It wasn't finding crates, possibly because of ncollide recently switching to use cargo's 'feature' feature, so I was randomly prodding the Cargo.toml files trying to get it working. The internal error appears to happen when it's trying to abort after a legitimate error. This is on OSX 10.9.5.

src/nphysics_testbed2d.rs:9:1: 9:42 error: can't find crate for `ncollide`
src/nphysics_testbed2d.rs:9 extern crate "ncollide2df32" as ncollide;
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error
Build failed, waiting for other jobs to finish...
error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'no entry found for key', /Users/rustbuild/src/rust-buildbot/slave/nightly-mac/build/src/libstd/collections/hashmap/map.rs:1093

stack backtrace:
1: 0x110287a59 - rt::backtrace::imp::write::h049a27795fff38dbKPq
2: 0x11028ad91 - failure::on_fail::hf299c5c1cb208a9do6q
3: 0x11050e0f5 - unwind::begin_unwind_inner::h465f1e1474a7adb5VRd
4: 0x10cefc7cc - unwind::begin_unwind::h6224404741762780903
5: 0x10d3ddc7c - middle::ty::type_contents::tc_ty::h37c76a0b06a14d6cMjF
6: 0x10d3dd16e - middle::ty::type_contents::tc_ty::h37c76a0b06a14d6cMjF
7: 0x10d3dd16e - middle::ty::type_contents::tc_ty::h37c76a0b06a14d6cMjF
8: 0x10d3dd16e - middle::ty::type_contents::tc_ty::h37c76a0b06a14d6cMjF
9: 0x10d3dd3b2 - middle::ty::type_contents::tc_ty::h37c76a0b06a14d6cMjF
10: 0x10d17a43e - middle::ty::type_contents::h75766b281b690932HiF
11: 0x10d371d49 - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::consume_expr::h13012547343158736823
12: 0x10d36c8ef - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_expr::h6685391383007306325
13: 0x10d371d9e - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::consume_expr::h13012547343158736823
14: 0x10d36c8ef - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_expr::h6685391383007306325
15: 0x10d36ce87 - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_expr::h6685391383007306325
16: 0x10d375194 - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::mutate_expr::h9035542041730929236
17: 0x10d36cd94 - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_expr::h6685391383007306325
18: 0x10d371d9e - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::consume_expr::h13012547343158736823
19: 0x10d371f4c - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_block::h7738644643951441682
20: 0x10d36ca32 - middle::expr_use_visitor::ExprUseVisitor<'d, 't, TYPER>::walk_expr::h6685391383007306325
21: 0x10d375b2a - middle::trans::_match::create_bindings_map::hd25097ff54ccbcdasmi
22: 0x10d2ee38d - middle::trans::_match::trans_match::h0ba66424e9281343iii
23: 0x10d2dc3f9 - middle::trans::expr::trans_rvalue_dps_unadjusted::h5d6407e79a5cc35fui4
24: 0x10d29ef2d - middle::trans::expr::trans_into::h6eccb4310a02b305lU2
25: 0x10d29e24c - middle::trans::controlflow::trans_stmt_semi::hea41b09732ea710at0Y
26: 0x10d29d8c0 - middle::trans::controlflow::trans_stmt::h1b97b1c27514a134gWY
27: 0x10d29f198 - middle::trans::controlflow::trans_block::h337751839b4d81e3m1Y
28: 0x10d2dc476 - middle::trans::expr::trans_rvalue_dps_unadjusted::h5d6407e79a5cc35fui4
29: 0x10d29ef2d - middle::trans::expr::trans_into::h6eccb4310a02b305lU2
30: 0x10d29e24c - middle::trans::controlflow::trans_stmt_semi::hea41b09732ea710at0Y
31: 0x10d29d8c0 - middle::trans::controlflow::trans_stmt::h1b97b1c27514a134gWY
32: 0x10d29f198 - middle::trans::controlflow::trans_block::h337751839b4d81e3m1Y
33: 0x10d29f902 - middle::trans::controlflow::trans_if::h6b93397b0f18b64933Y
34: 0x10d2dc39e - middle::trans::expr::trans_rvalue_dps_unadjusted::h5d6407e79a5cc35fui4
35: 0x10d29ef2d - middle::trans::expr::trans_into::h6eccb4310a02b305lU2
36: 0x10d29f29d - middle::trans::controlflow::trans_block::h337751839b4d81e3m1Y
37: 0x10d29f902 - middle::trans::controlflow::trans_if::h6b93397b0f18b64933Y
38: 0x10d2dc39e - middle::trans::expr::trans_rvalue_dps_unadjusted::h5d6407e79a5cc35fui4
39: 0x10d29ef2d - middle::trans::expr::trans_into::h6eccb4310a02b305lU2
40: 0x10d29f29d - middle::trans::controlflow::trans_block::h337751839b4d81e3m1Y
41: 0x10d34c81a - middle::trans::base::trans_closure::hc49edb61d41084dfi7e
42: 0x10d2919c8 - middle::trans::base::trans_fn::h90875a4e9c0850f7Gif
43: 0x10d29376a - middle::trans::monomorphize::monomorphic_fn::h4f43084b40ed295c4sY
44: 0x10d2c9522 - middle::trans::callee::trans_fn_ref_with_substs::h9474b7d186580bbeuO1
45: 0x10d2c62cb - middle::trans::callee::trans_fn_ref::h677ee1a9dbc6c9254C1
46: 0x10d2a83c0 - middle::trans::meth::trans_method_callee::h282f920af2833d33tpk
47: 0x10d2ce6fb - middle::trans::callee::trans_method_call::closure.123396
48: 0x10d2a6a24 - middle::trans::callee::trans_call_inner::hc594d308e2d213b2ca2
49: 0x10d2ce564 - middle::trans::callee::trans_method_call::hcc48f7a83dff65e7F51
50: 0x10d2dbeff - middle::trans::expr::trans_rvalue_dps_unadjusted::h5d6407e79a5cc35fui4
51: 0x10d2dabe6 - middle::trans::expr::trans_unadjusted::h300bbfb3064e6e71jF3
52: 0x10d2a03f6 - middle::trans::expr::trans::h4cd050e04fe533fafY2
53: 0x10d2de450 - middle::trans::expr::trans_rvalue_stmt_unadjusted::h7457beeaca2ed7dfvc4
54: 0x10d29effc - middle::trans::expr::trans_into::h6eccb4310a02b305lU2
55: 0x10d29e24c - middle::trans::controlflow::trans_stmt_semi::hea41b09732ea710at0Y
56: 0x10d29d8c0 - middle::trans::controlflow::trans_stmt::h1b97b1c27514a134gWY
57: 0x10d29f198 - middle::trans::controlflow::trans_block::h337751839b4d81e3m1Y
58: 0x10d34c81a - middle::trans::base::trans_closure::hc49edb61d41084dfi7e
59: 0x10d2919c8 - middle::trans::base::trans_fn::h90875a4e9c0850f7Gif
60: 0x10d29376a - middle::trans::monomorphize::monomorphic_fn::h4f43084b40ed295c4sY
61: 0x10d2c9522 - middle::trans::callee::trans_fn_ref_with_substs::h9474b7d186580bbeuO1
62: 0x10d2c62cb - middle::trans::callee::trans_fn_ref::h677ee1a9dbc6c9254C1
63: 0x10d2a83c0 - middle::trans::meth::trans_method_callee::h282f920af2833d33tpk
64: 0x10d2ce6fb - middle::trans::callee::trans_method_call::closure.123396
65: 0x10d2a6a24 - middle::trans::callee::trans_call_inner::hc594d308e2d213b2ca2
66: 0x10d2ce564 - middle::trans::callee::trans_method_call::hcc48f7a83dff65e7F51
67: 0x10d2dbeff - middle::trans::expr::trans_rvalue_dps_unadjusted::h5d6407e79a5cc35fui4
68: 0x10d29ef2d - middle::trans::expr::trans_into::h6eccb4310a02b305lU2
69: 0x10d29e24c - middle::trans::controlflow::trans_stmt_semi::hea41b09732ea710at0Y
70: 0x10d29d8c0 - middle::trans::controlflow::trans_stmt::h1b97b1c27514a134gWY
71: 0x10d29f198 - middle::trans::controlflow::trans_block::h337751839b4d81e3m1Y
72: 0x10d29f902 - middle::trans::controlflow::trans_if::h6b93397b0f18b64933Y
73: 0x10d2dc39e - middle::trans::expr::trans_rvalue_dps_unadjusted::h5d6407e79a5cc35fui4
74: 0x10d29ef2d - middle::trans::expr::trans_into::h6eccb4310a02b305lU2
75: 0x10d29f29d - middle::trans::controlflow::trans_block::h337751839b4d81e3m1Y
76: 0x10d2a4414 - middle::trans::controlflow::trans_for::h2d44c78625f7e59bLdZ
77: 0x10d2de338 - middle::trans::expr::trans_rvalue_stmt_unadjusted::h7457beeaca2ed7dfvc4
78: 0x10d29effc - middle::trans::expr::trans_into::h6eccb4310a02b305lU2
79: 0x10d29e24c - middle::trans::controlflow::trans_stmt_semi::hea41b09732ea710at0Y
80: 0x10d29d8c0 - middle::trans::controlflow::trans_stmt::h1b97b1c27514a134gWY
81: 0x10d29f198 - middle::trans::controlflow::trans_block::h337751839b4d81e3m1Y
82: 0x10d34c81a - middle::trans::base::trans_closure::hc49edb61d41084dfi7e
83: 0x10d2919c8 - middle::trans::base::trans_fn::h90875a4e9c0850f7Gif
84: 0x10d29376a - middle::trans::monomorphize::monomorphic_fn::h4f43084b40ed295c4sY
85: 0x10d2c9522 - middle::trans::callee::trans_fn_ref_with_substs::h9474b7d186580bbeuO1
86: 0x10d2c62cb - middle::trans::callee::trans_fn_ref::h677ee1a9dbc6c9254C1
87: 0x10d2a83c0 - middle::trans::meth::trans_method_callee::h282f920af2833d33tpk
88: 0x10d2ce6fb - middle::trans::callee::trans_method_call::closure.123396
89: 0x10d2a6a24 - middle::trans::callee::trans_call_inner::hc594d308e2d213b2ca2
90: 0x10d2ce564 - middle::trans::callee::trans_method_call::hcc48f7a83dff65e7F51
91: 0x10d2dbeff - middle::trans::expr::trans_rvalue_dps_unadjusted::h5d6407e79a5cc35fui4
92: 0x10d29ef2d - middle::trans::expr::trans_into::h6eccb4310a02b305lU2
93: 0x10d29e24c - middle::trans::controlflow::trans_stmt_semi::hea41b09732ea710at0Y
94: 0x10d29d8c0 - middle::trans::controlflow::trans_stmt::h1b97b1c27514a134gWY
95: 0x10d29f198 - middle::trans::controlflow::trans_block::h337751839b4d81e3m1Y
96: 0x10d34c81a - middle::trans::base::trans_closure::hc49edb61d41084dfi7e
97: 0x10d2919c8 - middle::trans::base::trans_fn::h90875a4e9c0850f7Gif
98: 0x10d34e225 - middle::trans::meth::trans_impl::h32e5a4ac425ceae4Okk
99: 0x10d28f5d2 - middle::trans::base::trans_item::hc219df2cb1017ae3ZBf
100: 0x10d28f648 - middle::trans::base::trans_item::hc219df2cb1017ae3ZBf
... <frames omitted>

Could not compile nphysics_testbed2d.