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Provide way to disable nightly cfg #175

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Nemo157 opened this issue Apr 27, 2019 · 2 comments · Fixed by #176
Closed

Provide way to disable nightly cfg #175

Nemo157 opened this issue Apr 27, 2019 · 2 comments · Fixed by #176

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@Nemo157
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Nemo157 commented Apr 27, 2019

In futures we're attempting to treat the nightly compiler as stable using RUSTFLAGS="-Z allow-features=" to ensure future compatibility with Rust 1.36. Unfortunately this is failing in CI because of proc-macro2 unconditionally activating its own nightly cfg and attempting to use an unstable feature.

It would be great if we could somehow disable this feature no matter what channel of Rust we happen to be building with.
@Nemo157 Nemo157 mentioned this issue Apr 27, 2019
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Nemo157 added a commit to Nemo157/futures-rs that referenced this issue Apr 27, 2019
@Nemo157
Allow proc_macro_span feature
5052c98 
Workaround for dtolnay/proc-macro2#175
@Nemo157 Nemo157 mentioned this issue Apr 27, 2019
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Nemo157 added a commit to Nemo157/futures-rs that referenced this issue Apr 27, 2019
@Nemo157
Allow proc_macro_span feature
e3bf8fb 
Workaround for dtolnay/proc-macro2#175
Nemo157 added a commit to rust-lang/futures-rs that referenced this issue Apr 27, 2019
@Nemo157
Allow proc_macro_span feature
f68d824 
Workaround for dtolnay/proc-macro2#175
@dtolnay
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dtolnay commented Apr 27, 2019

I would accept a PR to parse RUSTFLAGS in our build script and look for whether proc_macro_span is present in allow-features.

If that won't work, alternatively we could expose an opt-out through RUSTFLAGS:

RUSTFLAGS='--cfg no_opportunistic_nightly'

@Nemo157
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Nemo157 commented Apr 27, 2019

Parsing RUSTFLAGS sounds reasonable if the build script has access to it, I’ll take a look at doing that tomorrow.

@Nemo157 Nemo157 mentioned this issue Apr 28, 2019
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@taiki-e taiki-e mentioned this issue Aug 29, 2019
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bors bot added a commit to taiki-e/pin-project that referenced this issue Aug 29, 2019
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Merge #54
558a833 
54: Detect if the proc_macro_def_site feature is not disallowed by -Zallow-features r=taiki-e a=taiki-e

Apart from what I mentioned in #53 (comment), there are cases where you want to completely avoid using the nightly function in the first place.

Refs: dtolnay/proc-macro2#175

Co-authored-by: Taiki Endo <te316e89@gmail.com>
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Detect if the user has disallowed usage of the proc_macro_span feature Nemo157/proc-macro2
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@Nemo157 @dtolnay