Replace all uses of `fail` with `die!`, then remove `fail` and rename `die!` to `fail!`

[bstrie]

fail is becoming a macro as per #3627, but first all uses of the fail keyword must be removed. There's a new macro named die! that can do the job of fail. Make the switch, then remove the fail keyword from the parser and mass-rename die! to fail!.

[nickdesaulniers]

Can I get dibs on this?

[bstrie]

@nickdesaulniers you can!

[nickdesaulniers]

Just an update on the state of this bug:

Step 1: Replace instances of fail with die!(), DONE TESTS GREEN
Step 2: Remove fail keyword, DONE TESTS GREEN
Step 3: Mass replace die!() with fail!(), IN PROGRESS

This will be three separate commits, many changes, will probably take some time to review. I also missed a few instances of fail from step one but caught them in step 2. Tests are still green in both commits. Hope this is not an issue. Do all of these commits need to be rebased?

[bstrie]

Actually, I may have overlooked one step. You may need to wait for a new snapshot before you can complete step 3, because the stage0 compiler currently has no idea what the die!() macro is so it'll just choke. For now, I think you'll need to back up to steps 1 and 2, and then insert a step 2.5 where you define the die!() macro as an identical alternative to fail!(), but don't actually use the new macro anywhere. Only once a new snapshot has been produced with knowledge of die!() can you then actually begin using it.

[nickdesaulniers]

@brson, so duplicate die macro as fail macro in libsyntax/ext/expand.rs? I'm closing pull request #4721 , will issue a new one.

[bstrie]

Actually, until the fail keyword is entirely removed from the stage0 compiler it will probably yell at you even for having the fail! macro defined at all. So you really need to take these steps:

1. Convert all fail to die!
2. Remove fail as a keyword
3. Wait for a snapshot
4. Add fail! macro
5. Wait for a snapshot
6. Rename all die! to fail!

The joys of self-hosting!

[brson]

I think it can be done in one snap

1. Convert fail calls to die!
2. Remove fail
3. Duplicate die! as fail! (but don't use it)
4. Snapshot
5. Replace die! with fail!
6. Remove die!

[nickdesaulniers]

Pull request #4744 was just merged. Waiting on a snapshot (@brson). In the meantime, I think all new code based on top of this is going to have to use die!() for a short time, then start using fail!(). Do all rust devs need to be aware of this...?

[Dretch]

Could fail just be a regular function? What magic does it do that requires it to be a syntax-extension/macro/magical-!-thing?

Edit: Never mind I found some explanations here: #2232