Summary:
[Folly] Tweak `partial` to avoid a poorly-understood build failure on macos with clang++ and libc++.

```
In file included from folly/functional/test/PartialTest.cpp:19:
In file included from folly/folly/Function.h:230:
folly/functional/Invoke.h:65:25: error: attempt to use a deleted function
      noexcept(noexcept(std::mem_fn(f)(static_cast<A&&>(a)...)))
                        ^
folly/functional/Partial.h:41:19: note: in instantiation of exception specification for 'operator()<int (int &, int &, int &), Foo, const Foo &, const int &, const int &, int &>' requested here
      -> decltype(invoke(
                  ^
folly/functional/Partial.h:65:56: note: while substituting deduced template arguments into function template 'invokeForward' [with Self = const folly::detail::partial::Partial<int (Foo::*)(int &, int &, int &), std::__1::tuple<Foo, int, int> > &, I = <0, 1, 2>, Args = <int &>]
  auto operator()(CArgs&&... cargs) const& -> decltype(invokeForward(
                                                       ^
folly/functional/test/PartialTest.cpp:59:21: note: while substituting deduced template arguments into function template 'operator()' [with CArgs = <int &>]
  EXPECT_EQ(1234, p0(four));
                    ^
type_traits:1743:5: note: '~__nat' has been explicitly marked deleted here
    ~__nat() = delete;
    ^
```

Reviewed By: chadaustin

Differential Revision: D23722804

fbshipit-source-id: 7b3d6307a46fa12eadea13db327f10aafb89691c

Summary:
The getuid and getgid are defined as returning uid_t and gid_t. Defining these
types here will prevent downstream consumer from having to redefine these
types for Windows.

(Note: this ignores all push blocking failures!)

Reviewed By: yfeldblum, Orvid

Differential Revision: D23693492

fbshipit-source-id: 1ec9221509bffdd5f6d241c4bc08d7809cdb6162

Summary: no need to install when not building tests

Reviewed By: wez

Differential Revision: D23714375

fbshipit-source-id: 6f34ab59ed2155df5646ad279d1347e904f393c4

Summary: [Folly] Cache python-import in `getExecutor` so that it happens only once overall rather than once per call.

Reviewed By: nanshu

Differential Revision: D23657508

fbshipit-source-id: 06d3bd53303cac9c10fff74f4e6daaeccdc59471

Summary: required. not installed with CMake ExternalProject anymore

Reviewed By: xttjsn

Differential Revision: D23700095

fbshipit-source-id: 807105a1e3d4bd837a35e39c6dced53744edd8de

Summary:
in getdeps we currently don't build and run the tests
There are a few issues:
  1. we need to also build tests for fizz, wangle, mvfst since proxygen tests include headers only exported if building tests in dependencies
  2. we use `ExternalProject_add` for gtest/gmock. but doesn't seem to be playing nicely with getdeps

Reviewed By: dddmello, mjoras

Differential Revision: D16934955

fbshipit-source-id: fb1c52237f9f0c71da86643409972c94d16e6a71

Summary: properly find the required GMock version (1.8.0) and allow building tests in getdeps

Reviewed By: mjoras

Differential Revision: D16935741

fbshipit-source-id: 46f62511e2feaf553d028e286a862aa5b30393c6

Summary: also always install fizz test headers for mvfst and proxygen tests to consume without needing to build fizz tests

Reviewed By: yfeldblum

Differential Revision: D23676344

fbshipit-source-id: 7ae78c81c2d67bb8da135fcd69d4be119b50a27e

Summary: they were all transitively pulling it from folly

Reviewed By: mjoras

Differential Revision: D23683292

fbshipit-source-id: 2085a580584891b3fd0960c14505c0f675a11bd5

Summary:
This diff introduces a callback, `CertificateIdentityVerifier` that can probe peer end-entity certificates during a TLS handshake in `AsyncSSLSocket`.

The verifier gets called only if regular chain verification (OpenSSL's and a `HandshakeCB`'s) succeeds and can return a `Try` with a `CertificateIdentityVerifierException` to indicate that a failure occurred. `AsyncSSLSocket` will then fail the TLS handshake.

The diff also adds a new `AsyncSSLSocket` constructor with a new `Options` parameter that groups together some optional properties, including the verifier. We can eventually refactor the other constructors to use it too.

Reviewed By: mingtaoy

Differential Revision: D22821714

fbshipit-source-id: b63b141862b5703eb5274fb6ef8aa98934a55df0

Summary:
exception_tracer is currently gated on FOLLY_USE_SYMBOLIZER, and when
I enabled it, I didn't notice the CMake build of Folly on macOS
stopped working.

Fix it by adding correct conditionals, and removing the removed
std::unexpected_handler.

Reviewed By: yfeldblum, lnicco

Differential Revision: D23690777

fbshipit-source-id: 76ada7911ac33de3b1e8b0a73cebf3c2d04a58ef

Summary: As the main purpose of write callback is to signal the buffer is on longer needed and may be released (https://fburl.com/diffusion/ahbbb6oy). Release the buffer then calling the write callback seems more reasonable

Differential Revision: D23411380

fbshipit-source-id: c9b421716368253eafb4ecb8b72f48c8b47c2f9f

Summary:
This API allows for an easier way to configure EventBase without a need to introduce yet another constructor with variable amount of arguments.

In particular, we have an ad-hoc constructor for overriding just the wheel timer interval, but it's not possible to override it in other constructors.

Reviewed By: yfeldblum

Differential Revision: D23511659

fbshipit-source-id: 2f8de3a527ee07dbf2dc19f2e369014793d906c1

Summary:
needed by a few projects [wangle, mvfst, proxygen]

it's already in lfs
https://www.internalfb.com/intern/diffusion/FBS/browse/master/fbcode/tools/lfs/.lfs-pointers?lines=41

Reviewed By: mzlee

Differential Revision: D23676343

fbshipit-source-id: 0fa04d4224f27e756f683924af0c21ea63a90647

Summary:
Fixes across the codebase to allow for r-value qualified getVia.

Change is behaviour neutral - getVia is already destructive internally.

Reviewed By: yfeldblum

Differential Revision: D23605722

fbshipit-source-id: 75dfe6faca1c888eae9b262552372dd557eb6933

Summary: Moving CoReturn and CoThrow helpers for use with GTest. CoReturn() and CoThrow() work similar to Return() and Throw() provided in GTest framework.

Reviewed By: yfeldblum

Differential Revision: D23502840

fbshipit-source-id: 3e5f35135d8291543b91d3615e86398d794a7ba9

Summary:
Enable FOLLY_USE_SYMBOLIZER on macOS and teach SafeStackTracePrinter
to use `backtrace_symbols_fd` on non-ELF platforms.

Reviewed By: luciang

Differential Revision: D23017169

fbshipit-source-id: 1ad6cbf6d9ad11276d95b821095e37a86c8bb862

Summary:
Before: While the Xcode constants are pretty well standardized, discoverability and use within folly is non-trivial.
We have constants for various other attributes about the OS and target platform, so add a sane mapping for Apple targets as well.

Reviewed By: yfeldblum

Differential Revision: D23605949

fbshipit-source-id: cd4212dd30d9ec6a3c48a6d7a787a67fdeb9dd1f

Summary: [Folly] Some static-asserts in `Executor::KeepAlive`: standard-layout, pointer-size, pointer-align.

Reviewed By: LeeHowes

Differential Revision: D23656740

fbshipit-source-id: ff6c5aa3de01a37144fe8ef0961f06d13938654a

Summary: For consistency with get() make getTryVia r-value qualified and move the result out. This has the benefit of removing surprise copies in code that already operated on a temporary future but ended up with an l-value reference to copy from as a result of this operation.

Reviewed By: ispeters

Differential Revision: D23610051

fbshipit-source-id: a11344b9c8680f9498abc307ba1c7c793e3403e1

Summary: [Folly] Cut explicit `main` from test programs in `folly/gen/test/` and prefer the linked-in version.

Reviewed By: simpkins

Differential Revision: D23643891

fbshipit-source-id: 20152ae4feeeccd43038580043d45759c39c075c

Summary: This makes sense on systems without `backtrace` and with LLVM libunwind implementations.

Reviewed By: yfeldblum

Differential Revision: D23625739

fbshipit-source-id: 6ec50c94c73bda227118ffc36d6856bcd8dd0d8b

Summary:
`std::shared_ptr` has an aliasing constructor, but `std::weak_ptr`
has none.  This diff implements a helper function that implements the
functionality.  For libstdc++ it uses ABI-specific hacks to avoid the
need to construct a temporary `std::shared_ptr`.

Reviewed By: yfeldblum

Differential Revision: D23580416

fbshipit-source-id: 71712270519b0e7522d8019a5c356679c7dc5397

Summary:
[Folly] Decay char-array and trivial args to `throw_exception` and `terminate_with`.

The motivation is to ensure smaller call-site code size in the common cases, where the solitary argument is a string literal. Extend to cases where arguments are numbers and the like as well, since that is simple enough and is something that `Function` already does.

Reviewed By: aary

Differential Revision: D23550096

fbshipit-source-id: d3a2066dc28dc4cfac6b65e2b8972613ce55d06c

Summary: [Folly] `byte`, backported from `std::byte` in C++17.

Reviewed By: Alfus, vitaut

Differential Revision: D23535105

fbshipit-source-id: 056c634362b2ca226306a97ae9994a4631d07ee5

Summary: In newer versions of the windows STL, this gets included in <thread>, so explicitly include it in Unistd.h and remove the definition of getpid.

Reviewed By: yfeldblum

Differential Revision: D23498073

fbshipit-source-id: 5fe07dbbaa9fb1bf5c904286bd15beccbf1d1615

Summary:
[Folly] Revise invoke to be an invoker rather than a function, and therefore insusceptible to ADL, and revise invocability traits for compile-time perf.

Do the same for apply and applicability traits.

Reviewed By: Mizuchi

Differential Revision: D23334895

fbshipit-source-id: 4d3241a3f34a7bede44f8ab54a30a3074d9fd3ed

Summary: [Folly] Tweaks to hash primitives: twang, jenkins_rev, fnv

Reviewed By: ot, luciang

Differential Revision: D23290185

fbshipit-source-id: 080dfa8a5f357065473f3973654c91d01c683c3c

Summary:
When grabbing an iterator when the map is empty, size is zero but we
still create a copy of the elem_ pointer which is invalid to do when the size
is zero (since the writer could overwrite the pointer upon first insertion).
This diff checks whether the iterator would be empty and if so avoid grabbing
that pointer.

Reviewed By: yfeldblum

Differential Revision: D23520616

fbshipit-source-id: 5b3f2bc3a9b935920e7fd616e64fadafd7775a75

Summary: Honestly I haven't spent time to understand why this order needs to be acq_rel, but (1) it's the same as the one used in the other keepAliveRelease in this file (2) this ordering is free for read-modify-write operations (3) TSAN said this works :)

Reviewed By: yfeldblum

Differential Revision: D23495784

fbshipit-source-id: 8bdcafb14b27e6c0f8838ed478364821cd39f9a9

Summary:
[Folly] Fix the `reentrant_allocator` internal loop, which when finding a new head node would incorrectly preserve the free `offset` corresponding to the previous head.

Hat tip to hpmv for the report.

Differential Revision: D23593517

fbshipit-source-id: b4fc701f08056184225e7feac32d60aabf7ea6cc

Summary:
Remove the old `fbcode_builder_config.py` file used by the previous
incarnation of fbcode_builder.  This file hasn't been used in a while now.
Folly instead builds with `build/fbcode_builder/getdeps.py`, which uses the
configuration file at `build/fbcode_builder/manifests/folly`

Reviewed By: wez

Differential Revision: D23591355

fbshipit-source-id: b2e193c7dc54dcf481557984b5833fa92ff4049c

Summary:
Add a small top-level build.sh script that invokes
build/fbcode_builder/getdeps.py to perform the build.  This primarily helps
make the getdeps build process more discoverable to users.

Also document this script in README.md

Reviewed By: yfeldblum

Differential Revision: D23484822

fbshipit-source-id: 6013ace6d80d7d3d80aa87d4c6269ac106814cf0

Summary:
Update the `README.md` file in the fbcode_builder subdirectory to document the
current getdeps.py build system rather than the older fbcode_builder scripts
that required each project to keep their own python-based build files in their
project directory.

Reviewed By: chadaustin, wez

Differential Revision: D23591356

fbshipit-source-id: 75a099a10793e68a2b59696682010c4dff47ec69

Differential Revision:
D23489967 (https://github.com/facebook/folly/commit/65bb1505d3f64d9248bc1f7a04abc212db518676)

Original commit changeset: db11c9c5946e

fbshipit-source-id: 4970fc7de479a51d4acf91b2871ff0c15712130e

Summary:
The code in `FindDoubleConversion.cmake` called
`FIND_PACKAGE_HANDLE_STANDARD_ARGS()` with the wrong arguments.  The first
argument must match the package name: since this file is called
`FindDoubleConversion` the first argument must be `DoubleConversion`.

Previously this code was passing in `DOUBLE_CONVERSION`, causing it to set
`DOUBLE_CONVERSION_FOUND` instead of `DoubleConversion_FOUND`.  Since this
module did not set `DoubleConversion_FOUND` the `find_package()` call assumed
it always succeeded, even when the double-conversion library was not found.

Also remove the extra status message.  `FIND_PACKAGE_HANDLE_STANDARD_ARGS()`
already prints out a status message as long as `find_package()` was called
without the `QUIET` argument.

Reviewed By: yfeldblum

Differential Revision: D23588980

fbshipit-source-id: 8c088930b1b01c027403c3e425f1924f6149f72a

Summary:
Update FindGflags.cmake to work on recent CentOS and RedHat distributions.

On these distributions the CMake package configuration installed by the
gflags-devel RPM is slightly broken, and sets `gflags_INCLUDE_DIR` to a
directory that does not exist.  This happens because `/lib64` is symlinked to
`/usr/lib64`, and CMake ends up searching `/lib64` before `/usr/lib64` by
default when searching for packages.  Therefore it finds `gflags-config.cmake`
via the `/lib64` symlink.  However, `gflags-config.cmake` computes the include
directory relative to where its config file was found, and this relative path
computation only works when using the actual `/usr/lib64` path where it was
installed.  When found via `/lib64` it returns a bogus `//include` path that
does not exist.

This updates `FindGflags.cmake` to verify if the `gflags_INCLUDE_DIR` path
actually exists, and set it to a sane location instead.

This also updates the code to use the `gflags-shared` target that is exported
by the default gflags package configuration if it was only built as a shared
library.

Pull Request resolved: https://github.com/facebook/folly/pull/1409

Reviewed By: yfeldblum

Differential Revision: D23588288

fbshipit-source-id: b68a717953ae0521f568d7bcfd05ca33cd6dc578

Summary:
FOLLY_USE_SYMBOLIZER is a poor guard for the existence of execinfo.h
and backtrace(3), which is widely available on unix platforms, but not
available on Android NDK. Instead, introduce FOLLY_HAVE_BACKTRACE and
have CMake detect its availability.

Reviewed By: yfeldblum, luciang

Differential Revision: D23361495

fbshipit-source-id: 4409363f3eaa754977a93e1f006c5911d8e32020

Summary: Darwin libc doesn't implement quick_exit, so use std::_Exit instead.

Reviewed By: yfeldblum

Differential Revision: D23592838

fbshipit-source-id: bda318216239965e14b4c97ca184a2303353ed73

Summary: For consistency with get() make getTryVia r-value qualified and move the result out. This has the benefit of removing surprise copies in code that already operated on a temporary future but ended up with an l-value reference to copy from as a result of this operation.

Reviewed By: yfeldblum

Differential Revision: D23489967

fbshipit-source-id: db11c9c5946edd402103b3aa4140c0a1db5aae5e