Cargo environment variables doesn't trigger a rebuild on update

[ishitatsuyuki]

Rust Version

rustc 1.16.0-dev (0f8a29647 2017-01-28)

Disclaimer: homemade build

Affected Version of clap

2.20.1

Expected Behavior Summary

Changing version/description in Cargo.toml should trigger a rebuild with app_from_crate!() macro and others.

Actual Behavior Summary

Nothing happens.

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A quick hack that can trick the compiler:

include_str!("../Cargo.toml");

This is not universal though, since this assumes the main source is src/main.rs.

The real solution would require hooking into the compiler (via plugin/proc-macro) and alter the filemap.
It's likely a rustc design fault, so we can also file an issue on them instead.

For the meanwhile, put a big warning in docs.

[kbknapp]

Thanks for mentioning this, I'll add it to the upcoming round of doc changes!