Macros Won't Build in no_std

[mriise]

While trying to build with a common no_std target thumbv6m-none-eabi.
Changing data-encoding-macro-internal's Cargo.toml to use the the alloc feature allowed for a clean build.
data-encoding = { version = "2.3", path = "../..", default-features = false, features = ["alloc"] }

thumbv6m-none-eabi should probably be added to the CI build list for next time around :)

[mriise]

Aaaaand I just read your comment multiformats/rust-multibase#25 (comment)

[ia0]

The macro doesn't need the alloc feature to work, so it shouldn't be necessary to change its dependencies.

The problem is due to rust-lang/cargo#7915 where cargo leaks features of compile-time dependencies like proc-macro. The current fix is to use the host_dep unstable feature for now until it gets stable. Does this fix your issue?

[mriise]

@ia0 yes, I was going to close this with my last comment but figured it might be good for anyone else who comes across the problem. Maybe a quick note in the README for the macro lib to prevent others falling into the same hole?

[ia0]

Good point. I updated the README and documentation.