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cargo fix: Prevent fixing in mixed up transition steps #5778

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alexcrichton opened this issue Jul 23, 2018 · 4 comments · Fixed by #5824
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cargo fix: Prevent fixing in mixed up transition steps #5778

alexcrichton opened this issue Jul 23, 2018 · 4 comments · Fixed by #5824
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@alexcrichton
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Edition Preview 2

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@alexcrichton
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A common problem we're seeing in the 2018 transition is that steps are performed out of order, rendering cargo fix not too useful any more! I think we should implement two important fixes in cargo fix to remedy the situation:

  • First, Cargo should be able to deduce a set of "interesting crates" which are actually being fixed. This is driven by the -p arguments on the command line.
  • Next, if these crates have the 2018 edition enabled and --prepare-for is passed, then an error is generated. You can't prepare for an edition if you're already in the 2018 edition!
  • And finally, if the crate is compiled but doesn't have #![feature(rust_2018_preview)] inside it then we should either warn or fail compilation.

This should hopefully fix the bugs of "you enabled the edition too early" or "you forgot to enable the feature gate"!
@alexcrichton alexcrichton added this to the Edition Preview 2 milestone Jul 23, 2018
@alexcrichton
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cc @killercup

@alexcrichton alexcrichton mentioned this issue Jul 26, 2018
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@alexcrichton alexcrichton mentioned this issue Jul 28, 2018
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@johnthagen
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Next, if these crates have the 2018 edition enabled and --prepare-for is passed, then an error is generated. You can't prepare for an edition if you're already in the 2018 edition!

Wanted to share anecdotal support for this feature. When I was doing a transition of a crate, it was very natural to up-arrow in the terminal and pull down my first cargo fix --prepare-for 2018 ... command even after I added the edition to my Cargo.toml. I'd expect others to make this small mistake as well.

@johnthagen johnthagen mentioned this issue Jul 28, 2018
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@alexcrichton
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Yes currently I'm not sure if we've got the best ergonomics. Another option would be to issue a warning and keep going (without the lint group), but that runs more risk of causing hundreds of errors I think than the annoyance of tweaking arguments.

@johnthagen
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Yeah, I feel like shooting for a "fail-fast" error in this case with a good message would be the best IMO.

alexcrichton added a commit to alexcrichton/cargo that referenced this issue Jul 31, 2018
@alexcrichton
Add more diagnostics to smooth edition transition
fa7a387 
This commit adds two diagnostics in particular to ease the transition into the
2018 edition. The current transition process is pretty particular and must be
done carefully, so let's try to automate things to make it as painless as
possible! Notably the new diagnostics are:

* If you `cargo fix --prepare-for 2018` a crate which already has the 2018
  edition enabled, then an error is generated. This is because the compiler
  can't prepare for the 2018 edition if you're already in the 2018 edition, the
  lints won't have a chance to fire. You can only execute `--prepare-for 2018`
  over crates in the 2015 edition.

* If you `cargo fix --prepare-for 2018` and have forgotten the
  `rust_2018_preview` feature, a warning is issued. The lints don't fire unless
  the feature is enabled, so this is intended to warn in this situation to
  ensure that lints fire as much as they can.

After this commit if `cargo fix --prepare-for` exits successfully with zero
warnings then crates should be guaranteed to be compatible!

Closes rust-lang#5778
@alexcrichton alexcrichton self-assigned this Jul 31, 2018
bors added a commit that referenced this issue Jul 31, 2018
@bors
Auto merge of #5824 - alexcrichton:careful-transition, r=alexcrichton
9bbab73 
Add more diagnostics to smooth edition transition

This commit adds two diagnostics in particular to ease the transition into the
2018 edition. The current transition process is pretty particular and must be
done carefully, so let's try to automate things to make it as painless as
possible! Notably the new diagnostics are:

* If you `cargo fix --prepare-for 2018` a crate which already has the 2018
  edition enabled, then an error is generated. This is because the compiler
  can't prepare for the 2018 edition if you're already in the 2018 edition, the
  lints won't have a chance to fire. You can only execute `--prepare-for 2018`
  over crates in the 2015 edition.

* If you `cargo fix --prepare-for 2018` and have forgotten the
  `rust_2018_preview` feature, a warning is issued. The lints don't fire unless
  the feature is enabled, so this is intended to warn in this situation to
  ensure that lints fire as much as they can.

After this commit if `cargo fix --prepare-for` exits successfully with zero
warnings then crates should be guaranteed to be compatible!

Closes #5778
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Add more diagnostics to smooth edition transition alexcrichton/cargo
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