cargo nightly does not resolve nuklear-sys

[brson]

nuklear-backend-gfx 0.1.3 does not build on nightly, but does on stable. The reason seems to be that Cargo is not downloading and building nuklear-sys. Here's the output from a failed run:

    Updating registry `https://github.com/rust-lang/crates.io-index`
 Downloading gfx_window_glutin v0.12.0
 Downloading gfx_device_gl v0.11.2
 Downloading glutin v0.6.2
 Downloading nuklear-rust v0.1.5
 Downloading gfx v0.12.1
 Downloading gfx_core v0.4.0
 Downloading draw_state v0.6.0
 Downloading bitflags v0.6.0
 Downloading gfx_gl v0.3.1
 Downloading gl_generator v0.5.2
 Downloading khronos_api v1.0.0
 Downloading xml-rs v0.3.4
 Downloading libc v0.2.17
 Downloading shared_library v0.1.5
 Downloading x11-dl v2.9.0
 Downloading wayland-kbd v0.3.6
 Downloading osmesa-sys v0.1.2
 Downloading wayland-client v0.5.12
 Downloading wayland-window v0.2.3
 Downloading dlib v0.3.0
 Downloading libloading v0.2.4
 Downloading target_build_utils v0.1.2
 Downloading serde_json v0.8.3
 Downloading phf v0.7.17
 Downloading dtoa v0.2.2
 Downloading serde v0.8.14
 Downloading num-traits v0.1.36
 Downloading phf_shared v0.7.17
 Downloading phf_codegen v0.7.17
 Downloading phf_generator v0.7.17
 Downloading crossbeam v0.2.10
 Downloading wayland-sys v0.5.11
 Downloading wayland-scanner v0.5.11
   Compiling semver v0.1.20
   Compiling bitflags v0.6.0
   Compiling crossbeam v0.2.10
   Compiling khronos_api v1.0.0
   Compiling pkg-config v0.3.8
   Compiling phf_shared v0.7.17
   Compiling winapi v0.2.8
   Compiling bitflags v0.7.0
   Compiling winapi-build v0.1.1
   Compiling x11-dl v2.9.0
   Compiling phf v0.7.17
   Compiling dtoa v0.2.2
   Compiling kernel32-sys v0.2.2
   Compiling byteorder v0.5.3
   Compiling serde v0.8.14
   Compiling lazy_static v0.1.16
   Compiling num-traits v0.1.36
   Compiling log v0.3.6
   Compiling rustc_version v0.1.7
   Compiling draw_state v0.6.0
   Compiling itoa v0.1.1
   Compiling tempfile v2.1.4
   Compiling libc v0.2.17
   Compiling gfx_core v0.4.0
   Compiling lazy_static v0.2.1
   Compiling xml-rs v0.3.4
   Compiling shared_library v0.1.5
   Compiling nuklear-rust v0.1.5
error[E0463]: can't find crate for `nuklear_sys`
 --> /home/brian/.cargo/registry/src/github.com-1ecc6299db9ec823/nuklear-rust-0.1.5/src/lib.rs:5:1
  |
5 | extern crate nuklear_sys;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate

error: aborting due to previous error

And here's what happened when I used stable cargo:

 Downloading nuklear-sys v1.156.0
 Downloading gcc v0.3.37
   Compiling lazy_static v0.2.1
   Compiling serde v0.8.14
   Compiling libc v0.2.17
   Compiling crossbeam v0.2.10
   Compiling winapi v0.2.8
   Compiling log v0.3.6
   Compiling num-traits v0.1.36
   Compiling shared_library v0.1.5
   Compiling itoa v0.1.1
   Compiling osmesa-sys v0.1.2
   Compiling khronos_api v1.0.0
   Compiling winapi-build v0.1.1
   Compiling byteorder v0.5.3
   Compiling kernel32-sys v0.2.2
   Compiling semver v0.1.20
   Compiling rand v0.3.14
   Compiling phf_shared v0.7.17
   Compiling rustc_version v0.1.7
   Compiling phf v0.7.17
   Compiling pkg-config v0.3.8
   Compiling lazy_static v0.1.16
   Compiling bitflags v0.6.0
   Compiling draw_state v0.6.0
   Compiling x11-dl v2.9.0
   Compiling phf_generator v0.7.17
   Compiling tempfile v2.1.4
   Compiling bitflags v0.7.0
   Compiling gfx_core v0.4.0
   Compiling xml-rs v0.3.4
   Compiling wayland-scanner v0.5.11
   Compiling gl_generator v0.5.2
   Compiling phf_codegen v0.7.17
   Compiling target_build_utils v0.1.2
   Compiling gfx_gl v0.3.1
...

cc @snuk182

[snuk182]

Just checked the previous nuklear-rust version, 0.1.3, it is built fine with today's nightly. The main difference is in the nested project versioning. I've synced the nuklear-sys version to the one of C nuklear (0.1.4 -> 1.156.0), while the general project's one only minor-incremented (0.1.4 -> 0.1.5).

[alexcrichton]

This... is a fascinating regression. Caused by #3123 accidentally it turns out the index contains a version requirement from nuklear-rust to nuklear-sys with ^1.156.0. The Cargo.toml of the nuklear-rust, however, indicates a version requirement of 0.1.3. We previously never looked at Cargo.toml but that PR started doing so, causing the discrepancy!