Implement more traits for function pointers

[petrochenkov]

Closes #26082

[rust-highfive]

r? @aturon

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[alexcrichton]

Can you measure the metadata size before/after this patch? I'm a little worried about these being so rarely used but having a relatively significant cost in terms of metadata size.

[petrochenkov]

Size of libcore.rlib:
before: 20,958,680 bytes
after: 26,644,788 byte
after with all ABIs except for "Rust" and "C" removed: 21,947,498 bytes
after with all ABIs except for "Rust" and "C" and functions with >5 arguments removed: 21,461,438 bytes

[alexcrichton]

How about we stick to just Rust, C, and <5 arguments for now? I think we can also cut down on the number of traits implemented to the bare bones as well, I don't think these necessarily need to be at the same parity as raw pointers (e.g. are we really using function pointers as keys in hash maps?).

[petrochenkov]

How about we stick to just Rust, C, and <5 arguments for now?

Good, it was the back-up plan from the beginning.

are we really using function pointers as keys in hash maps

We aren't, because they don't implement Hash!

I think we can also cut down on the number of traits implemented to the bare bones as well, I don't think these necessarily need to be at the same parity as raw pointer

I'd prefer not to do this, libcore size is not a holy grail after all. What increase in size of libcore do you consider acceptable?
Here's my chart of usefulness for these impls.
Clone (+ 150kb) - was already implemented
PartialEq/Eq (+ 300kb) - was partially implemented
Debug (+ 150kb) - needed if you want to assert_eq that PartialEq above or derive Debug for a containing struct.
PartialOrd/Ord (+ 300kb) or Hash (+ 150kb) are needed to have any kind of set of fn pointers or structs containing them (hash set, tree set, sorted array).
fmt::Pointer (+ 150kb) - needed mostly for consistency with data pointers.

[alexcrichton]

OK, seems reasonable, I guess we can try to figure out how to control metadata size later.

@bors: r+ bc7c430

Thanks!

[bors]

⌛ Testing commit bc7c430 with merge bf60883...

[bors]

💔 Test failed - auto-win-gnu-64-opt

[alexcrichton]

@bors: retry

On Mon, Sep 14, 2015 at 6:38 PM, bors notifications@github.com wrote:

[image: 💔] Test failed - auto-win-gnu-64-opt
http://buildbot.rust-lang.org/builders/auto-win-gnu-64-opt/builds/1409

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#28268 (comment).

[bors]

⌛ Testing commit bc7c430 with merge 8320345...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, 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