Implement .. in tuple (struct) patterns (RFC 1492)

[petrochenkov]

cc #33627
r? @nikomatsakis

plugin-[breaking-change] cc #31645 @Manishearth

[Manishearth]

Since this implements an RfC, it will need to land soon, right? In that case, we probably should make a batch soon after this gets approved -- so if you have other PRs you want to make, now is the time!

[bors]

☔ The latest upstream changes (presumably #33654) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

Rebased.

[nikomatsakis]

Nit: s/presents/is present/

[nikomatsakis]

Not that there is anything wrong with it, but I am surprised by this choice; I would have expected Vec<P<Pat>> and Option<Vec<P<Pat>>>, where the second set of patterns come after the ... Did you consider this and find that the current optional usize works out better (or just that you prefer it)? Anyway, it seems ok as is, just wanted to toss an alternative out there.

[petrochenkov]

One allocation, the variant itself is more compact (6 ptrs vs 4 ptrs), simpler traversal (no vec1.chain(vec2)).

[nikomatsakis]

Looks good. r=me with the add'l tests listed and nits addressed, though we should decide whether S(foo, ..,) is legal syntax.

[petrochenkov]

Updated.
(pat, ..,) is still illegal, but that can be relaxed at any moment.

[aturon]

My vote: let's keep it illegal and thereby start conservatively.

[pnkfelix]

I concur with @aturon; plus both syntaxes are feature gated so even if change wasn't a conservative extension we would still be within bounds to change it later

[nikomatsakis]

OK. Seems weird to me to permit trailing commas but only sometimes, but I bow to the will of the masses!

[nikomatsakis]

@bors r+

[bors]

📌 Commit 4983025 has been approved by nikomatsakis

[Manishearth]

@bors r-

hold on, plugin breaking. I'll batch these up tomorrow morning

Only #33351 needs to be included for now if someone else wants to do it

[nikomatsakis]

D'oh, sorry @Manishearth
On May 23, 2016 2:32 PM, "Manish Goregaokar" notifications@github.com
wrote:

@bors https://github.com/bors r-

hold on, plugin breaking. I'll batch these up tomorrow morning

Only #33351 #33351 needs to be
included for now if someone else wants to do it

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#33639 (comment)