Fix various bugs around empty structs and patterns

[petrochenkov]

Fixes #28692
Fixes #28992
Fixes some other similar issues (see the tests)

[breaking-change], needs crater run (cc @brson or @alexcrichton )

The pattern with parens UnitVariant(..) for unit variants seems to be popular in rustc (see the second commit), but mostly used by one person (@nikomatsakis), according to git blame. If it causes breakage on crates.io I'll add an exceptional case for it.

[rust-highfive]

r? @pnkfelix

(rust_highfive has picked a reviewer for you, use r? to override)

[nikomatsakis]

Heh, yeah, I like to do Foo(..) if I only care about the variant, so that it is forwards compatible with adding parameters later (which happens pretty regularly).

[pnkfelix]

This PR looks fine to me. It does need a crater run.

(I have not yet successfully run crater but I'm wiling to give it another shot.)

[bors]

☔ The latest upstream changes (presumably #28846) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

Rebased.

[pnkfelix]

@petrochenkov great; I am seeing if I can do a crater run now with it.

[alexcrichton]

I've made a new needs-crater tag on GitHub so we can keep track of which PRs need a crater run so we know how to move them forward

[bors]

☔ The latest upstream changes (presumably #29217) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

Rebased.

[bors]

☔ The latest upstream changes (presumably #29581) made this pull request unmergeable. Please resolve the merge conflicts.

[pnkfelix]

@petrochenkov thanks for rebasing

[pnkfelix]

I did a crater run (on the revisions from before the rebase).

Zero regressions.

crater results here: https://gist.github.com/pnkfelix/4b800d1faf17eb494d8e

---

Update: I just looked at those results again, and realized that, if I understand them correctly, they are saying that all crates failed to build on both of my compilers. :(

I'm not quite sure what I did wrong, if anything. I'll try a new run on the rebased versions.

[pnkfelix]

(So, r=me after next rebase.)

---

Update: see above comment. The aforementioned crater run seemed problematic, not b/c of this PR, but probably user error.

[petrochenkov]

Rebased.

[bors]

☔ The latest upstream changes (presumably #29763) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

Rebased.

@alexcrichton, could you run crater on this?

[alexcrichton]

Starting a crater run.

[bors]

☔ The latest upstream changes (presumably #29387) made this pull request unmergeable. Please resolve the merge conflicts.

[alexcrichton]

Crater reports eight root regressions with as many as up to 34. I glanced at the root ones and they at least all look legitimate.

Perhaps that error could be a warning for a few cycles? Seems like a good bugfix to have, but may be good to give fair warning.

[petrochenkov]

Rebased.

[petrochenkov]

ping @pnkfelix
beta is soon

[pnkfelix]

@bors r+

[bors]

📌 Commit af96402 has been approved by pnkfelix

[bors]

⌛ Testing commit af96402 with merge f0fcef8...

[bors]

💔 Test failed - auto-mac-32-opt

[petrochenkov]

fatal: unable to connect to github.com:
github.com[0: 192.30.252.130]: errno=Operation timed out

Needs retry

[bluss]

@bors retry

[bors]

⌛ Testing commit af96402 with merge e9ac440...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt

[bluss]

It looks like it's a breaking change anyway, conv 0.3.1 0.3.0 + git

src/errors.rs:576:17: 576:32 warning: `NegOverflow` does not name a tuple variant or a tuple struct [E0164]
src/errors.rs:576             Err(NegOverflow(..)) => T::neg_infinity(),
                                  ^~~~~~~~~~~~~~~
src/errors.rs:576:17: 576:32 help: run `rustc --explain E0164` to see a detailed explanation
src/errors.rs:576:17: 576:32 note: this warning will become a HARD ERROR in a future release. See RFC 218 for det
ails.
src/errors.rs:576             Err(NegOverflow(..)) => T::neg_infinity(),
                                  ^~~~~~~~~~~~~~~
src/errors.rs:577:17: 577:32 warning: `PosOverflow` does not name a tuple variant or a tuple struct [E0164]
src/errors.rs:577             Err(PosOverflow(..)) => T::pos_infinity(),
                                  ^~~~~~~~~~~~~~~
src/errors.rs:577:17: 577:32 help: run `rustc --explain E0164` to see a detailed explanation
src/errors.rs:577:17: 577:32 note: this warning will become a HARD ERROR in a future release. See RFC 218 for details.
src/errors.rs:577             Err(PosOverflow(..)) => T::pos_infinity(),
                                  ^~~~~~~~~~~~~~~
src/errors.rs:602:17: 602:32 warning: `NegOverflow` does not name a tuple variant or a tuple struct [E0164]
src/errors.rs:602             Err(NegOverflow(..)) => T::saturated_min(),
                                  ^~~~~~~~~~~~~~~
src/errors.rs:602:17: 602:32 help: run `rustc --explain E0164` to see a detailed explanation
src/errors.rs:602:17: 602:32 note: this warning will become a HARD ERROR in a future release. See RFC 218 for details.
src/errors.rs:602             Err(NegOverflow(..)) => T::saturated_min(),
                                  ^~~~~~~~~~~~~~~
src/errors.rs:603:17: 603:32 warning: `PosOverflow` does not name a tuple variant or a tuple struct [E0164]
src/errors.rs:603             Err(PosOverflow(..)) => T::saturated_max(),
                                  ^~~~~~~~~~~~~~~
src/errors.rs:603:17: 603:32 help: run `rustc --explain E0164` to see a detailed explanation
src/errors.rs:603:17: 603:32 note: this warning will become a HARD ERROR in a future release. See RFC 218 for details.
src/errors.rs:603             Err(PosOverflow(..)) => T::saturated_max(),
                                  ^~~~~~~~~~~~~~~
src/errors.rs:574:9: 578:10 error: non-exhaustive patterns: `Err(_)` not covered [E0004]
src/errors.rs:574         match self.map_err(Into::into) {
src/errors.rs:575             Ok(v) => v,
src/errors.rs:576             Err(NegOverflow(..)) => T::neg_infinity(),
src/errors.rs:577             Err(PosOverflow(..)) => T::pos_infinity(),
src/errors.rs:578         }
src/errors.rs:574:9: 578:10 help: run `rustc --explain E0004` to see a detailed explanation
src/errors.rs:600:9: 604:10 error: non-exhaustive patterns: `Err(_)` not covered [E0004]
src/errors.rs:600         match self.map_err(Into::into) {
src/errors.rs:601             Ok(v) => v,
src/errors.rs:602             Err(NegOverflow(..)) => T::saturated_min(),
src/errors.rs:603             Err(PosOverflow(..)) => T::saturated_max(),
src/errors.rs:604         }

[petrochenkov]

Hm, the warning should not affect exhaustiveness check, I'll investigate what happens.

[bluss]

I apologise if I'm pointing to the wrong PR, but it seems related.