@GrahamcOfBorg build carnix

The changes to features in carnix 0.6.4 cause an error in my Rust project when building the num-complex crate as an indirect dependency.

project
 |
 +-- chrono
 |    |
 |    `-- num
 |         |
 |         `-- num-complex
 |
 `-- ndarray
      |
      `-- num-complex

Building src/lib.rs (num-complex)
Running rustc --crate-name num_complex src/lib.rs --crate-type lib -C opt-level=3 -C metadata=b465201f42 -C extra-filename=-b465201f42 --cfg feature="rustc-serialize" --cfg feature="default" --out-dir target/lib --emit=dep-info,link -L dependency=target/deps --extern num_traits=/nix/store/8j3a9q8gjsf4l5iyn84x72ycnj9zdpwj-rust_num-traits-0.1.42/lib/libnum_traits-cd53366641.rlib --cap-lints allow --color always
error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead? (see issue #27812)
  --> src/lib.rs:20:1
   |
20 | extern crate rustc_serialize;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add #![feature(rustc_private)] to the crate attributes to enable

error: aborting due to previous error

builder for ‘/nix/store/9ahmk3pwakplbsa7p851glb08fcg532i-rust_num-complex-0.1.41.drv’ failed with exit code 101
cannot build derivation ‘/nix/store/s95h8rhcpd6sz7hzw5s52mmy89vf89mw-rust_fuzzyd-0.13.0.drv’: 1 dependencies couldn't be built
error: build of ‘/nix/store/s95h8rhcpd6sz7hzw5s52mmy89vf89mw-rust_fuzzyd-0.13.0.drv’ failed

Building my project with carnix 0.6.1 works fine, and 0.5.2 before that.

Building src/lib.rs (num-complex)
Running rustc --crate-name num_complex src/lib.rs --crate-type lib -C opt-level=3 -C metadata=b465201f42 -C extra-filename=-b465201f42 --out-dir target/lib --emit=dep-info,link -L dependency=target/deps --extern num_traits=/nix/store/4jk3mkvgnbqamfnwng2gw01yy3pbr6dl-rust_num-traits-0.1.42/lib/libnum_traits-cd53366641.rlib --cap-lints allow --color always
installing
post-installation fixup
shrinking RPATHs of ELF executables and libraries in /nix/store/nssfaramr4abs3xkhls1q4yqxwshlwj6-rust_num-complex-0.1.41
strip is /nix/store/mdyy001q67hiks0g24ra53z7ckm4jfr4-binutils-2.28.1/bin/strip
stripping (with command strip and flags -S) in /nix/store/nssfaramr4abs3xkhls1q4yqxwshlwj6-rust_num-complex-0.1.41/lib
patching script interpreter paths in /nix/store/nssfaramr4abs3xkhls1q4yqxwshlwj6-rust_num-complex-0.1.41
checking for references to /tmp/nix-build-rust_num-complex-0.1.41.drv-0 in /nix/store/nssfaramr4abs3xkhls1q4yqxwshlwj6-rust_num-complex-0.1.41...
building path(s) ‘/nix/store/a94q4jagrzq21xn43f0k3rs4f0w6xi24-rust_num-integer-0.1.35’
unpacking sources
unpacking source archive /nix/store/j7v77a00h3cn91w19i9jjl5zajix0n2h-num-integer-0.1.35.tar.gz
source root is num-integer-0.1.35.tar.gz
patching sources
configuring
no configure script, doing nothing
building

Comparing the rustc commands shows that 0.6.4 added --cfg feature="rustc-serialize".

- Running rustc --crate-name num_complex src/lib.rs --crate-type lib -C opt-level=3 -C metadata=b465201f42 -C extra-filename=-b465201f42 --out-dir target/lib --emit=dep-info,link -L dependency=target/deps --extern num_traits=/nix/store/4jk3mkvgnbqamfnwng2gw01yy3pbr6dl-rust_num-traits-0.1.42/lib/libnum_traits-cd53366641.rlib --cap-lints allow --color always
+ Running rustc --crate-name num_complex src/lib.rs --crate-type lib -C opt-level=3 -C metadata=b465201f42 -C extra-filename=-b465201f42 --cfg feature="rustc-serialize" --cfg feature="default" --out-dir target/lib --emit=dep-info,link -L dependency=target/deps --extern num_traits=/nix/store/8j3a9q8gjsf4l5iyn84x72ycnj9zdpwj-rust_num-traits-0.1.42/lib/libnum_traits-cd53366641.rlib --cap-lints allow --color always

I'm not sure which is doing the wrong thing:

• 0.6.1 wrongly fails to enable a default feature and compiles, or
• 0.6.4 wrongly enables a default feature and the build fails.

I don't want to hijack this PR with a bug discussion, so if there's a better place to discuss, I can open a github issue or pijul discussion or whatever else is preferred and create an SSCCE.

I am bit worried about the file sizes that are getting bigger and bigger with each release of carnix:

$ wc -l carnix-0.6.4/Cargo.lock carnix.nix
551 Cargo.lock
1508 carnix.nix
$ wc -c carnix.nix Cargo.lock
72813 carnix.nix
24678 Cargo.lock

Out of experience I know, that git does not like large generated text files.
Also nix will take longer to evaluate.

@Mic92: this is because rust "features" are normally handled by Cargo. The first versions of Carnix computed them once and for all, but this was incorrect because they might depend on the platform. The last release (0.6.4) is supposed to shrink them a little, at least in bytes if not in lines, by using more appropriate features of Nix.

Some more context: in Rust, crates can have "features", which are supposed to be monotonic (i.e. features can't conflict), and might depend on the platform, or on other features, or sometimes on features in their dependent crates. In addition to that, some crates also have default features, which is a list of features activated unless specified otherwise.

Carnix 0.6.0 used an ugly idea to compute features: each crate A wanting a feature F from a dependency B would cause carnix to add a line of the form A.F.from_B = true, or sometimes A.F.from_B = hasFeature A G if feature F depends on whether feature G of A is active.

Carnix 0.6.4 does a better job by collecting features for all crates by passing them to feature-computing functions, which in turn pass them over to the dependencies' feature-computing function.

@boxofrox: I'd try it out. Do you use any feature from chrono from your "project" crate?

@P-E-Meunier I see. It also looks a more readable then older versions.

@boxofrox: I'd try it out. Do you use any feature from chrono from your "project" crate?

chrono 0.4.0 doesn't have any features to enable that I'm aware of. chrono does depend on the num crate, and disables default features in num [1], likewise, ndarray disables default features of num-complex [2].

However, num optionally depends on num-complex as a default feature or complex feature [3], but doesn't disable default features in num-complex. So, here we might have a conflict: num -> num-complex(default) and ndarray -> num-complex(no-default), but I'm pretty sure num shouldn't be pulling in num-complex as a dependency in my project, since chrono disabled default features of its num dependency chrono -> num(no-default) -> "no dep on num-complex".

I'll create an SSCCE on github and post a link.

[1]: https://github.com/chronotope/chrono/blob/master/Cargo.toml#L24
[2]: https://github.com/bluss/rust-ndarray/blob/master/Cargo.toml#L28
[3]: https://github.com/rust-num/num/blob/master/Cargo.toml#L46

[package]
authors = ["Justin Charette <charetjc@gmail.com>"]
name = "fuzzyd"
version = "0.13.1"
[[bin]]
name = "fuzzyd"
path = "src/bin/fuzzyd/main.rs"
[[bin]]
name = "fuzzy-debug"
path = "src/bin/fuzzy-debug.rs"
[dependencies]
as_num = "0.2.3"
assert_matches = "1.1.0"
bytes = "0.4.3"
chrono = "0.4.0"
clap = "2.23.3"
csv = "0.15.0"
error-chain = "0.11.0"
flexi_logger = "0.6.9"
futures = "0.1.13"
futures-cpupool = "0.1.8"
http-box = "0.1.5"
httparse = "1.2.2"
humansize = "1.0.1"
itertools = "0.7.6"
log = "0.4.1"
mysql_async = "0.12.0"
native-tls = "0.1.2"
ndarray = "0.11.1"
nom = "3.0.0"
revord = "0.0.2"
serde = "1.0.6"
serde_derive = "1.0.6"
serde_json = "1.0.2"
serde_yaml = "0.7.1"
textwrap = "0.9.0"
time = "0.1.37"
tokio-core = "0.1.7"
tokio-io = "0.1.1"
tokio-service = "0.1.0"
tokio-timer = "0.1.1"
tokio-tls = "0.1.2"

@boxofrox: it's ok, I can reproduce. I believe it's fixed in Carnix 0.6.5.

(also, some of @Mic92's comments are implemented in 0.6.5)

replaced by #34568

One more comment to note that Carnix 0.6.5 resolves my issue regarding 0.6.4. Many thanks @P-E-Meunier.