Non-consecutive crate IDs triggering assert

[sfackler]

building rust-postgres/rust-postgres@650a030 triggers an assert inside of metadata::encoder:

task 'rustc' failed at 'assertion failed: `(left == right) && (right == left)` (left: `4`, right: `3`)', /home/sfackler/rust/rust/src/librustc/metadata/encoder.rs:1492
stack backtrace:
   1:     0x7f22ec4d88f0 - rt::backtrace::imp::write::h5dfe62f829bb8926qRa::v0.11.pre
   2:     0x7f22ec43a130 - rt::unwind::begin_unwind_inner::h656188078345464dTra::v0.11.pre
   3:     0x7f22ec439db0 - rt::unwind::begin_unwind_fmt::h0fa0fd6a17be09cb3qa::v0.11.pre
   4:     0x7f22ed5e0db0 - metadata::encoder::encode_metadata_inner::hf63f8d88e8b7eaa5o48::v0.11.pre
   5:     0x7f22ecf63b90 - metadata::encoder::encode_metadata::h6c0dd041c1ff6bb4S38::v0.11.pre
   6:     0x7f22ecf624e0 - middle::trans::base::write_metadata::h0a375886de86b464zbq::v0.11.pre
   7:     0x7f22ecf64190 - middle::trans::base::trans_crate::h03cceaf99acd8b6fugq::v0.11.pre
   8:     0x7f22ed697bb0 - driver::driver::phase_4_translate_to_llvm::h7b7bc374e3942267cAe::v0.11.pre
   9:     0x7f22ed699e20 - driver::driver::compile_input::h5aefc635514c08cd1Pe::v0.11.pre
  10:     0x7f22ed6be200 - run_compiler::h54519610e6366e1flom::v0.11.pre
  11:     0x7f22ed6d5900 - main_args::closure.91936
  12:     0x7f22ed6d4230 - monitor::closure.91821
  13:     0x7f22ed6cfb10 - task::TaskBuilder::try::closure.91587
  14:     0x7f22ef43fb90 - task::spawn_opts::closure.7971
  15:     0x7f22ec4d3920 - rt::task::Task::run::closure.40115
  16:     0x7f22ec4df4e0 - rust_try
  17:     0x7f22ec4d3760 - rt::task::Task::run::h88d5577d7084e0bafi8::v0.11.pre
  18:     0x7f22ef43f960 - task::spawn_opts::closure.7944
  19:     0x7f22ec4d7430 - rt::thread::thread_start::hc0c9989a147641340W8::v0.11.pre
  20:     0x7f22ebe13fe0 - start_thread
  21:     0x7f22ec10ece9 - clone
  22:                0x0 - <unknown>

Moving the #[phase(syntax)] extern crate rust_phf to the bottom of the crate list suppresses the issue. It looks like syntax-only crates are still taking a crate ID in creader which is creating "holes" at link-time. I tried simply removing the assert that tripped but that broke the world.

[sfackler]

cc @alexcrichton

[alexcrichton]

I think that I have a fix for this, but I'm unable to reproduce in a smaller test case. Do you know of a way to minimize to something other than rust-postgres?

[sfackler]

I poked around a tiny bit last night but didn't find a repo. I'd imagine that it'd just be "link against a ton of crates with a syntax one somewhere in the middle". I can try to make another repro tonight.

[sfackler]

Here's a very minimal test case:

#![feature(phase)]

#[phase(syntax)]
extern crate fourcc;
#[phase(syntax, link)]
extern crate log;