Quickchecking crate CLI

[shnewto]

Prior to this commit the quickchecking crate used for generating proprty tests for bindgen was a [lib] target and had configurations that required commenting/uncommenting code to enable/disable. This meant it was inconvienent/prohibitive to configure the property tests on a per-run basis. This commit reorganizes the quickchecking crate to provide both [lib] and [[bin]] targets in order to expose those configurations through a CLI.

The configurations that are exposed through the [[bin]] target's CLI are:

• Count/number of tests to run.
• Directory to provide fuzzed headers
• Generation range corresponding to the range quickcheck uses to
• generate arbitrary.

Usage from the tests/quickchecking directory

quickchecking 0.2.0
Bindgen property tests with quickcheck. Generate random valid C code and pass it to the csmith/predicate.py script

USAGE:
    quickchecking [OPTIONS]

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

OPTIONS:
    -c, --count <COUNT>    Count / number of tests to run. Running a fuzzed header through the predicate.py script can
                           take a long time, especially if the generation range is large. Increase this number if you're
                           willing to wait a while. [default: 2]
    -p, --path <PATH>      Optional. Preserve generated headers for inspection, provide directory path for header
                           output. [default: None] 
    -r, --range <RANGE>    Sets the range quickcheck uses during generation. Corresponds to things like arbitrary usize
                           and arbitrary vector length. This number doesn't have to grow much for that execution time to
                           increase significantly. [default: 32]

Because the actual work of running the property tests moved to the [[bin]]
target, rather than duplicate that code in the quickchecking crate's tests
directory, some actual (very basic) tests for the quickchecking crate were
added.

*Note: I'm not attached to any of the option flags, if there are better characters/words for any of the options I've exposed I'll be happy to revise!

Also, I'm not sure how palatable the "global singleton" is for managing context (output path) across tests in the lib.rs file. Very open to suggestions on how to manage that if it's not an acceptable approach.

Thanks for taking a look, looking forward to feedback!

Closes #1168

r? @fitzgen

[shnewto]

For sanity here are a couple fuzzed headers generated with the state of the current code.
https://gist.github.com/snewt/8afbf552c8f40974a9fdd903e63beec6

[fitzgen]

Looks great!

Now that the tests are about the quickchecking crate itself, rather than actually quickchecking bindgen, we should run cargo test in CI instead of cargo check.

Once you add that, you can comment @bors-servo r=fitzgen and the PR will get tested and merged.

Thanks!

[fitzgen]

Looks great!

Now that the tests are about the quickchecking crate itself, rather than actually quickchecking bindgen, we should run cargo test in CI instead of cargo check.

Once you add that, you can comment @bors-servo r=fitzgen and the PR will get tested and merged.

Thanks!

[fitzgen]

@bors-servo delegate+

[bors-servo]

✌️ @snewt can now approve this pull request

[shnewto]

@fitzgen ah awesome, can do (this evening).

[shnewto]

@bors-servo r=fitzgen

[bors-servo]

📌 Commit 2c77652 has been approved by fitzgen

[bors-servo]

⌛️ Testing commit 2c77652 with merge a59205e...

[bors-servo]

☀️ Test successful - status-travis
Approved by: fitzgen
Pushing a59205e to master...