[ADT] Fix circular include dependency by using std::array. NFC

[zyounan]

Summary

2db6b34ea introduces circular dependency on llvm::ArrayRef. By inspecting commit history,
it appears that we have some issue using deduction guide on std::array.
Why don't we try std::array with explicit template arguments?

[zyounan]

Pipeline failed due to missing include header llvm/ADT/Hashing.h

In file included from /var/lib/buildkite-agent/builds/llvm-project/clang-tools-extra/clangd/Config.cpp:9:
/var/lib/buildkite-agent/builds/llvm-project/clang-tools-extra/clangd/Config.h:158:18: error: no member named 'hash_combine' in namespace 'llvm'
    return llvm::hash_combine(Val.Kind, Val.Location, Val.MountPoint);

This header was included by ArrayRef.h which is included by STLExtras.h before.

#include "llvm/ADT/Hashing.h"

I don't think it's a good idea to dive into every TU and revise this include dependency. Let's add this to STLExtras.h directly.

[zyounan]

Add header llvm/ADT/Hashing.h, which is included by ArrayRef.h before. This header may be dependent by some TUs indirectly.

[zyounan]

Ping. Is this OK for trunk?

[JDevlieghere]

LGTM

[zyounan]

In D141352#4053069, @JDevlieghere wrote:

LGTM

Thanks. Can you help me commit this PR?

[zyounan]

Ping again. Sorry I don't have commit access to main branch.

[zyounan]

Fix issue

[zyounan]

Can anyone else help me to commit this PR? I mean we should land this patch ASAP, as many of PRs are now depending on llvm::ArrayRef without including ADT/ArrayRef.h but ADT/STLExtras.h, which would make it extremely harder to resolve this circular dependency later.

Patch D139553 is a good example to demonstrate this.

/repo/llvm-project/llvm/include/llvm/MC/SubtargetFeature.h:192:32: error: no template named 'ArrayRef'
  void addFeaturesVector(const ArrayRef<std::string> OtherFeatures);
                               ^
/repo/llvm-project/llvm/lib/MC/SubtargetFeature.cpp:45:25: error: out-of-line definition of 'addFeaturesVector' does not match any declaration in 'llvm::SubtargetFeatures'
void SubtargetFeatures::addFeaturesVector(
                        ^~~~~~~~~~~~~~~~~
2 errors generated.

I have updated this patch to fix this new issue.

@eklepilkina, please note that this patch doesn't have functional changes but add a header.

Also ping @JDevlieghere again.

---

Sorry for my silly mistake, I don't know that Phabricator drops the author info. Please use zyounan<[e-mail]> for the commit. Thank you again for your time.

llvm/include/llvm/ADT/STLExtras.h

 ///
 /// No library is required when using these functions.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_STLEXTRAS_H
 #define LLVM_ADT_STLEXTRAS_H
 
-#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/STLForwardCompat.h"
 #include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/identity.h"
 #include "llvm/ADT/iterator.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Config/abi-breaking.h"
 #include "llvm/Support/ErrorHandling.h"
 #include <algorithm>
+#include <array>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <cstdlib>
 #include <functional>
 #include <initializer_list>
 #include <iterator>
 #include <limits>
struct zip_first : public zip_common<zip_first<Iters...>, Iters...> {
   zip_first(Iters &&... ts) : Base(std::forward<Iters>(ts)...) {}
 };
 
 template <typename... Iters>
 class zip_shortest : public zip_common<zip_shortest<Iters...>, Iters...> {
   template <size_t... Ns>
   bool test(const zip_shortest<Iters...> &other,
             std::index_sequence<Ns...>) const {
-    return all_of(llvm::ArrayRef<bool>({std::get<Ns>(this->iterators) !=
+    return all_of(
+        std::array<bool, sizeof...(Ns)>({std::get<Ns>(this->iterators) !=
                                          std::get<Ns>(other.iterators)...}),
-                  identity<bool>{});
   }
 
 public:
   using Base = zip_common<zip_shortest<Iters...>, Iters...>;
 
   zip_shortest(Iters &&... ts) : Base(std::forward<Iters>(ts)...) {}
 
   bool operator==(const zip_shortest<Iters...> &other) const {