objc 0.2.7 dependency fails to build

[aclysma]

The current workaround is to force cargo to use 0.2.6

cargo update -p objc --precise 0.2.6

[aclysma]

Found a better fix. Apparently specifying objc = "0.2.6" still permits upgrading to anything < 1.0.0. However a more explicit version requirement can be specified: objc = ">=0.2,<0.2.7"

This avoids users having to force updating to a particular version and for now builds out-of-the-box, but it may be worth asking the maintainer of objc if there is a better solution, and if this is a known problem.

[SSheldon]

@aclysma the metal-rs crate has been renamed to metal! The version of it and cocoa that you're using are a couple years old and unfortunately exercised the unsound behavior that is no longer allowed in objc 0.2.7, described in SSheldon/rust-objc#62.

If you switch to using the metal crate with a version 0.16 or higher (which accordingly uses cocoa 0.19), you will be able to use objc 0.2.7 and you'll be safe from this undefined behavior.

[aclysma]

Updated to use metal instead of metal-rs in a080e49 and this fixed the build problem. Thanks so much for the help!