Default features of dependencies get pulled in for no reason

[nox]

When building webrender_traits with servo/webrender#430, even running cargo build --no-default-features --features serde_derive ends up building serde_codegen with its feature with-syntex. This should not happen.

[nox]

Cc @alexcrichton

[alexcrichton]

Hm what version of Cargo are you using actually? I just used cargo 0.13.0-nightly (cbe47ed 2016-09-29) locally and got:

features: {
  offscreen_gl_context v0.4.4: {"serde", "serde_serialization", "default"}
  unicode-xid v0.0.3: {"default"}
  serde v0.8.11: {"std", "default"}
  app_units v0.3.0: {"default"}
  byteorder v0.5.3: {"std", "default"}
  uuid v0.3.1: {"rand", "v4"}
  bincode v0.6.0: {"serde", "rustc-serialize", "default"}
  libc v0.2.16: {"use_std", "default"}
  serde_codegen v0.8.11: {"with-syn"}
  webrender_traits v0.6.0 (file:///home/alex/code/lol): {"serde_derive"}
  x11 v2.8.0: {"xlib"}
  log v0.3.6: {"use_std", "default"}
  syn v0.8.7: {"quote", "unicode-xid", "aster", "printing", "default", "visit", "parsing"}
}

which looks correct? Maybe we fixed this bug? (not that I remember it)

[nox]

@alexcrichton

cargo 0.13.0-nightly (ebcf0a8 2016-10-03)

And in Cargo.lock:

[[package]]
name = "serde_codegen"
version = "0.8.11"
source = "registry+https://github.com/rust-lang/crates.io-index"
dependencies = [
 "quote 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
 "serde_codegen_internals 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "syn 0.8.7 (registry+https://github.com/rust-lang/crates.io-index)",
 "syntex 0.44.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "syntex_syntax 0.44.0 (registry+https://github.com/rust-lang/crates.io-index)",
]

[alexcrichton]

Hm it looks like there's something else in play here because it works if I use the exact Cargo.toml from webrender_traits. What Cargo.toml are you building from again to reproduce?

[nox]

The one in 94437c4bbbee843e172dfc306b113a13a8a840c8, which is the tip of the PR I linked.

[nox]

I wonder if that is related to #1197, it's certainly similar.

[alexcrichton]

If the "bug" is that syntex_syntax is mentioned in Cargo.lock then that's not a bug. There exists a mode to build webrender_traits which builds the syntex_syntax crate, so it must be in the lock file.

[nox]

I see! Now that makes sense. Closing this then!