Cargo improvements and bugs

[jethrogb]

This is a tracking issue for proposed changes to cargo that could aid
portability.

• Conditional compilation based on a dependent's choices.
• Target-specific cargo features
• Make std fully pluggable #4

• Post Make Cargo aware of standard library dependencies rust-lang/rfcs#1133 concerns
  • Explicit standard library dependencies rust-lang/cargo#5002: Explicit standard library dependencies
  • Implicit standard library dependencies rust-lang/cargo#5003: Implicit standard library dependencies
  • Not clear how to [patch] sources other than crates-io rust-lang/cargo#4499: @Ericson2314 left comment about [patch] for std-lib libraries, thinks issue might by closed in mistake cause cannot find docs
• build-dependencies and dependencies should not have features unified rust-lang/cargo#4866: cross compilation totally breaks build.rs
  • build-dependencies and dependencies should not have features unified rust-lang/cargo#4866 (comment) shows that Cargo.lock doesn't handle platform-specific dependencies properly either

[Ericson2314]

At the end of rust-lang/rfcs#1133 I carved off some stand-alone issues that can be addressed relatively independently. (edit added above).

---

@jethrogb seeing you copied my issues in to the OP, I embellished that and removed from here. In general, I was wondering what you think of non-authors editing the OP. It's convenient to put things there, also but don't want to put words into other people's mouths, so no obvious solution IMO.

[jethrogb]

jamesmunns/rfcs#1

https://internals.rust-lang.org/t/pre-rfc-std-aware-cargo/9450