Add --all-features flag to cargo

[esclear]

As (more or less) requested in #1173 I added a --all-features flag to cargo that builds all available features.

I hope I documented it in all the right places.

If there's something weird or wrong, please give me a heads up.

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[alexcrichton]

Thanks for the PR @esclear! Looking pretty good to me, but the println! may want to get converted into actually enabling all features? Can you also be sure to add some tests for this functionality as well?

cc @rust-lang/tools, a new flag to cargo

[esclear]

Well…
It does enable all featues, since it overwrites the features vec.
But you're right, one wouldn't want to see this kind of debugging information 😳.

I'll try to think of some test and get back to this PR.

[esclear]

@alexcrichton Removed the println! and added a simple test.

[brson]

Seems reasonable to me given the current design of features. It might be worth considering how this plays out with any future changes to cargo features. For example, some features may be mutually-incompatible. Cargo has no way to encode that today, but maybe not forever.

[sfackler]

This shouldn't impact this PR from landing, but here's one example of me forcing incompatible traits to help ease a rename (of e.g. feature openssl to feature with-openssl): https://github.com/sfackler/rust-postgres/blob/breaks/src/feature_check.rs

[esclear]

Given that exclusive features are already being discussed in #2980 this should be considered.

My main intent behind this flag was to simplify enabling all features while building crate documentation or testing.
I think in that case you'd still want all features to be built.

On the other hand, there might be problems when testing with exclusive features enabled.

In my opinion, the user would have to enable all of the needed features manually if there are any exclusive features.
In case one uses the --all-features flag when building a crate with exclusive features, cargo should warn the user and stop.

[alexcrichton]

Looking good! I think though that this'll also need to enable any optional dependencies as well as [feature]-style features. Perhaps this could look into using Method::Everything as that should enable all features by default as well?

[alexcrichton]

Could you also add a test for an optional dependency getting activated as well?

[alexcrichton]

(other than that though looks good to me)

[alexcrichton]

This dependency on "baz" may want to be removed because otherwise activating bar is the same as activating baz (e.g. --all-features should activate optional dependencies that aren't listed in [features])

[esclear]

Okay, now I get what you meant by that.

[alexcrichton]

Thanks! Could you squash the commits down as well?

[esclear]

I'll try, even though I merged multiple times now.

[esclear]

After some manual rebasing it should be fine now.

[esclear]

I removed baz from the feature dependencies of bar.

[alexcrichton]

@bors: r+ 1f8b398

Thanks!

[bors]

⌛ Testing commit 1f8b398 with merge e713e7f...

[bors]

☀️ Test successful - cargo-cross-linux, cargo-linux-32, cargo-linux-64, cargo-mac-32, cargo-mac-64, cargo-win-gnu-32, cargo-win-gnu-64, cargo-win-msvc-32, cargo-win-msvc-64
Approved by: alexcrichton
Pushing e713e7f to master...