fix Cursor's copy constructor

Summary:
The Cursor class didn't provide a copy constructor accepting a
"const Cursor&".  The existing constructor only accepted references to
non-const Cursor.

This updates the constructor to also accept "const Cursor&".  I also
made the template parameter checking more strict, so that it only
accepts other CursorBase classes.  This prevents the compiler from
thinking that a Cursor can be constructed from any other possible type
when performing overload resolution.

Test Plan: Ran all of the folly cursor tests.

Reviewed By: davejwatson@fb.com

FB internal diff: D1208428
Add control of floating point serialization to JSON serialization

Summary: Title.  Note that this is a no-op with default parameters because folly::toAppend(double, &dest) calls folly::toAppend(double, &dest, DtoaMode, numDigits) with DtoaMode = SHORTEST and numDigits = 0.

Test Plan: Tested new functionality in D1212547.

Reviewed By: kelarini@fb.com

FB internal diff: D1212617
update FOLLY_IS_TRIVIALLY_COPYABLE

Summary:
Let's make sure that boost version is intented to mean exactly
the same as `std::is_trivially_copyable` (see 9 [class] / 6) to avoid any
confusion (current boost path is more close to
`std::is_trivially_copy_constructible` than to
`std::is_trivially_copyable`;  UPD: unfortunately, old versions of boost
don't support `boost::has_trivial_move_constructor` and friends, so I
can't completely mimic `std::is_trivially_copyable` here).

As mentioned in the original comment, `__has_trivial_copy` returns 1 in
case of deleted copy ctor in clang (contradicts 12.8 [class.copy] / 13 +
8.4.2 [dcl.fct.def.default] / 4), which makes `FOLLY_IS_TRIVIALLY_COPYABLE`
accept `std::unique_ptr<>`; using `boost::has_trivial_destructor` would
at least save us from the problems in this case.

Alternative "solution" may be to rename `FOLLY_IS_TRIVIALLY_COPYABLE` to
`FOLLY_IS_TRIVIALLY_COPY_CONSTRUCTIBLE`, and make sure
`folly::small_vector` won't call dtor when memcopies the data around.

Test Plan: fbconfig --clang folly/test:small_vector_test && fbmake runtests_opt (fails in trunk, passes with this diff)

Reviewed By: pgriess@fb.com

FB internal diff: D1216158
Move thrift/lib/cpp/async to folly.

Summary:
Move the minimum amount of stuff and still have everything compile.  Would like to move TAsyncSocket/ServerSocket/SSL/UDP eventually, but not this round.

thrift async is used very widely now: thrift, proxygen, newer mysql async interface, even trying it out in memcache.  A common complaint is that it doesn't get wide enough notice under thrift/, so let's move it to folly/.  After moving TAsyncSocket, both HHVM and proxygen could avoid a dep on thrift as well.

Changes:
* mv files to folly/io/async
* remove 'T' prefix on classes/filenames
* change namespace to 'folly'
* remove any thrift references.

Tried this before in D470080, this time doesn't attempt to abstract libevent

@override-unit-failures

Test Plan:
fbconfig -r thrift; fbmake dev.
Will iterate on any other contbuild failures

Reviewed By: pgriess@fb.com

FB internal diff: D1195393
Make sure folly::dynamic arrays can be used with folly::gen

Summary:
Define a value_type for folly::dynamic to make arrays work with
folly::gen::from.

Test Plan:
- added new unit test
- fbconfig folly/test && fbmake runtests

Reviewed By: tjackson@fb.com

FB internal diff: D1216358
Introduce a merge() function for folly::sorted_vector_map

Summary:
Feed spends a non trivial amount of time merging two sorted_vector_maps. Writing code for this efficiently is actually a little tricky, and its much easier to maintain the simpler code. This adds merge() to folly so that its easy for feed and fast. Benchmarks with large input sizes show this is a gigantic win (moving from O(n^2) to O(n).

Test Plan: unit tests, benchmark

Reviewed By: delong.j@fb.com

FB internal diff: D1221725

@override-unit-failures
sorted_vector_types does not work with std::inserter

Summary:
The signature of insert(hint, const val& v) is wrong. It should return an iterator, not pair<iterator, bool>. This breaks std::inserter, making it impossible to use this for std::merge. I plan to create folly::merge (std::merge with stronger semantics when equal values are present in the two input ranges), so I need this fixed.

Given that the documentation claims this is a "drop in replacement" for std::map, I figure we should fix this.

Test Plan: reran unit tests

Reviewed By: delong.j@fb.com

FB internal diff: D1223396
folly::merge() - std::merge() with stronger guarantees (probably same implementation in practice)

Summary:
std::merge() does not guarantee the ordering when equal elements belong in two ranges(comparator(it_a, it_b) == comparator(it_b, it_a) == 0). For maps, it is important that we can specify the ordering (see array_merge in php, where we guarantee which array's value will be present in the output if a key is present in both inputs).

Also removes folly::merge that is specfic for sorted_vector_map since this will not be needed. NOTE: I expect this to break feed, will fix in a separate non-folly diff.

Test Plan: This implementation is directly ripped from cppreference.com, but unit tests added none-the-less. Specifically, one is added where the output is a std::map to demonstrate its usefulness.

Reviewed By: delong.j@fb.com

FB internal diff: D1223401

@override-unit-failures
sorted_vector_types have move inserts

Summary: sorted_vector_types were missing move inserts that come with std::map in c++11. This prevents me from using move iterators in folly::merge use case.

Test Plan: unit tests

Reviewed By: delong.j@fb.com

FB internal diff: D1223426
Move commited bits out of folly

Summary: Preparing to land the other diffs. No code changes here, just moving files around.

Test Plan: fbconfig bistro/common/cron/test bistro/common/cron/utils/test ; fbmake runtests

Reviewed By: yinwang@fb.com

FB internal diff: D1225159
Unbreak Symbolizer with small ElfCache

Test Plan: fbconfig -r folly/experimental/symbolizer && fbmake runtests_opt && fbmake runtests

Reviewed By: simpkins@fb.com

FB internal diff: D1224552

@override-unit-failures
Add constexpr specifier for small_vector::max_size

Summary: Now we could use small_vector::max_size in constant expressions

Test Plan: unittest

Reviewed By: delong.j@fb.com

FB internal diff: D1224274
range(), for making Range<T*> from arrays and std::vector

Summary: So people can more easily write functions which take contiguous values from memory.

Test Plan: Unit tests

Reviewed By: tudorb@fb.com

FB internal diff: D1217809