// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -verify=expected,both            %s
// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -verify=expected,both -std=c++20 %s
// RUN: %clang_cc1 -verify=ref,both            %s
// RUN: %clang_cc1 -verify=ref,both -std=c++20 %s

constexpr int m = 3;
constexpr const int *foo[][5] = {
  {nullptr, &m, nullptr, nullptr, nullptr},
  {nullptr, nullptr, &m, nullptr, nullptr},
  {nullptr, nullptr, nullptr, &m, nullptr},
};

static_assert(foo[0][0] == nullptr, "");
static_assert(foo[0][1] == &m, "");
static_assert(foo[0][2] == nullptr, "");
static_assert(foo[0][3] == nullptr, "");
static_assert(foo[0][4] == nullptr, "");
static_assert(foo[1][0] == nullptr, "");
static_assert(foo[1][1] == nullptr, "");
static_assert(foo[1][2] == &m, "");
static_assert(foo[1][3] == nullptr, "");
static_assert(foo[1][4] == nullptr, "");
static_assert(foo[2][0] == nullptr, "");
static_assert(foo[2][1] == nullptr, "");
static_assert(foo[2][2] == nullptr, "");
static_assert(foo[2][3] == &m, "");
static_assert(foo[2][4] == nullptr, "");

constexpr int afterEnd[] = {1,2,3};
static_assert(&afterEnd[3] == afterEnd + 3, "");

constexpr int ZeroSizeArray[] = {};

constexpr int SomeInt[] = {1};
constexpr int getSomeInt() { return *SomeInt; }
static_assert(getSomeInt() == 1, "");

/// A init list for a primitive value.
constexpr int f{5};
static_assert(f == 5, "");


constexpr int getElement(int i) {
  int values[] = {1, 4, 9, 16, 25, 36};
  return values[i];
}
static_assert(getElement(1) == 4, "");
static_assert(getElement(5) == 36, "");

constexpr int data[] = {5, 4, 3, 2, 1};
constexpr int getElement(const int *Arr, int index) {
  return *(Arr + index);
}

constexpr int derefPtr(const int *d) {
  return *d;
}
static_assert(derefPtr(data) == 5, "");

/// Make sure we can refer to the one-past-the-end element
/// and then return back to the end of the array.
static_assert((&data[5])[-1] == 1, "");

constexpr int storePtr() {
  int b[] = {1,2,3,4};
  int *c = b;

  *c = 4;
  return *c;
}
static_assert(storePtr() == 4, "");


static_assert(getElement(data, 1) == 4, "");
static_assert(getElement(data, 4) == 1, "");

constexpr int getElementFromEnd(const int *Arr, int size, int index) {
  return *(Arr + size - index - 1);
}
static_assert(getElementFromEnd(data, 5, 0) == 1, "");
static_assert(getElementFromEnd(data, 5, 4) == 5, "");

constexpr int getFirstElem(const int *a) {
  return a[0]; // both-note {{read of dereferenced null pointer}}
}
static_assert(getFirstElem(nullptr) == 1, ""); // both-error {{not an integral constant expression}} \
                                               // both-note {{in call to}}

constexpr static int arr[2] = {1,2};
constexpr static int arr2[2] = {3,4};
constexpr int *p1 = nullptr;
constexpr int *p2 = p1 + 1; // both-error {{must be initialized by a constant expression}} \
                            // both-note {{cannot perform pointer arithmetic on null pointer}}
constexpr int *p3 = p1 + 0;
constexpr int *p4 = p1 - 0;
constexpr int *p5 =  0 + p1;
constexpr int *p6 =  0 - p1; // both-error {{invalid operands to binary expression}}

constexpr int const * ap1 = &arr[0];
constexpr int const * ap2 = ap1 + 3; // both-error {{must be initialized by a constant expression}} \
                                     // both-note {{cannot refer to element 3 of array of 2}}

constexpr auto ap3 = arr - 1; // both-error {{must be initialized by a constant expression}} \
                              // both-note {{cannot refer to element -1}}
constexpr int k1 = &arr[1] - &arr[0];
static_assert(k1 == 1, "");
static_assert((&arr[0] - &arr[1]) == -1, "");

constexpr int k2 = &arr2[1] - &arr[0]; // both-error {{must be initialized by a constant expression}} \
                                       // both-note {{arithmetic involving unrelated objects}}

static_assert((arr + 0) == arr, "");
static_assert(&arr[0] == arr, "");
static_assert(*(&arr[0]) == 1, "");
static_assert(*(&arr[1]) == 2, "");

constexpr const int *OOB = (arr + 3) - 3; // both-error {{must be initialized by a constant expression}} \
                                          // both-note {{cannot refer to element 3 of array of 2 elements}}

template<typename T>
constexpr T getElementOf(T* array, int i) {
  return array[i];
}
static_assert(getElementOf(foo[0], 1) == &m, "");


template <typename T, int N>
constexpr T& getElementOfArray(T (&array)[N], int I) {
  return array[I];
}
static_assert(getElementOfArray(foo[2], 3) == &m, "");


static_assert(data[0] == 4, ""); // both-error{{failed}} \
                                 // both-note{{5 == 4}}

constexpr int dynamic[] = {
  f, 3, 2 + 5, data[3], *getElementOf(foo[2], 3)
};
static_assert(dynamic[0] == f, "");
static_assert(dynamic[3] == 2, "");


constexpr int dependent[4] = {
  0, 1, dependent[0], dependent[1]
};
static_assert(dependent[2] == dependent[0], "");
static_assert(dependent[3] == dependent[1], "");

union { char x[]; } r = {0};

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wc99-extensions"
#pragma clang diagnostic ignored "-Winitializer-overrides"
constexpr int DI[] = {
  [0] = 10,
  [1] = 20,
  30,
  40,
  [1] = 50
};
static_assert(DI[0] == 10, "");
static_assert(DI[1] == 50, "");
static_assert(DI[2] == 30, "");
static_assert(DI[3] == 40, "");

constexpr int addThreeElements(const int v[3]) {
  return v[0] + v[1] + v[2];
}
constexpr int is[] = {10, 20, 30 };
static_assert(addThreeElements(is) == 60, "");

struct fred {
  char s [6];
  int n;
};

struct fred y [] = { [0] = { .s[0] = 'q' } };
#pragma clang diagnostic pop

namespace indices {
  constexpr int first[] = {1};
  constexpr int firstValue = first[2]; // both-error {{must be initialized by a constant expression}} \
                                       // both-note {{cannot refer to element 2 of array of 1}}

  constexpr int second[10] = {17};
  constexpr int secondValue = second[10];// both-error {{must be initialized by a constant expression}} \
                                         // both-note {{read of dereferenced one-past-the-end pointer}} \

  constexpr int negative = second[-2]; // both-error {{must be initialized by a constant expression}} \
                                       // both-note {{cannot refer to element -2 of array of 10}}
};

namespace DefaultInit {
  template <typename T, unsigned N>
  struct B {
    T a[N];
  };

  int f() {
     constexpr B<int,10> arr = {};
     constexpr int x = arr.a[0];
  }
};

class A {
public:
  int a;
  constexpr A(int m = 2) : a(10 + m) {}
};
class AU {
public:
  int a;
  constexpr AU() : a(5 / 0) {} // both-warning {{division by zero is undefined}} \
                               // both-note 2{{division by zero}} \
                               // both-error {{never produces a constant expression}}
};
class B {
public:
  A a[2];
  constexpr B() {}
};
constexpr B b;
static_assert(b.a[0].a == 12, "");
static_assert(b.a[1].a == 12, "");

class BU {
public:
  AU a[2];
  constexpr BU() {} // both-note {{in call to 'AU()'}}
};
constexpr BU bu; // both-error {{must be initialized by a constant expression}} \
                 // both-note {{in call to 'BU()'}}

namespace IncDec {
  constexpr int getNextElem(const int *A, int I) {
    const int *B = (A + I);
    ++B;
    return *B;
  }
  constexpr int E[] = {1,2,3,4};

  static_assert(getNextElem(E, 1) == 3, "");

  constexpr int getFirst() {
    const int *e = E;
    return *(e++);
  }
  static_assert(getFirst() == 1, "");

  constexpr int getFirst2() {
    const int *e = E;
    e++;
    return *e;
  }
  static_assert(getFirst2() == 2, "");

  constexpr int getSecond() {
    const int *e = E;
    return *(++e);
  }
  static_assert(getSecond() == 2, "");

  constexpr int getSecond2() {
    const int *e = E;
    ++e;
    return *e;
  }
  static_assert(getSecond2() == 2, "");

  constexpr int getLast() {
    const int *e = E + 3;
    return *(e--);
  }
  static_assert(getLast() == 4, "");

  constexpr int getLast2() {
    const int *e = E + 3;
    e--;
    return *e;
  }
  static_assert(getLast2() == 3, "");

  constexpr int getSecondToLast() {
    const int *e = E + 3;
    return *(--e);
  }
  static_assert(getSecondToLast() == 3, "");

  constexpr int getSecondToLast2() {
    const int *e = E + 3;
    --e;
    return *e;
  }
  static_assert(getSecondToLast2() == 3, "");

  constexpr int bad1() { // both-error {{never produces a constant expression}}
    const int *e =  E + 3;
    e++; // This is fine because it's a one-past-the-end pointer
    return *e; // both-note 2{{read of dereferenced one-past-the-end pointer}}
  }
  static_assert(bad1() == 0, ""); // both-error {{not an integral constant expression}} \
                                  // both-note {{in call to}}

  constexpr int bad2() { // both-error {{never produces a constant expression}}
    const int *e = E + 4;
    e++; // both-note 2{{cannot refer to element 5 of array of 4 elements}}
    return *e; // This is UB as well
  }
  static_assert(bad2() == 0, ""); // both-error {{not an integral constant expression}} \
                                  // both-note {{in call to}}

  constexpr int bad3() { // both-error {{never produces a constant expression}}
    const int *e = E;
    e--; // both-note 2{{cannot refer to element -1 of array of 4 elements}}
    return *e; // This is UB as well
  }
   static_assert(bad3() == 0, ""); // both-error {{not an integral constant expression}} \
                                   // both-note {{in call to}}

  constexpr int nullptr1(bool Pre) {
    int *a = nullptr;
    if (Pre)
      ++a; // both-note {{arithmetic on null pointer}}
    else
      a++; // both-note {{arithmetic on null pointer}}
    return 1;
  }
  static_assert(nullptr1(true) == 1, ""); // both-error {{not an integral constant expression}} \
                                          // both-note {{in call to}}

  static_assert(nullptr1(false) == 1, ""); // both-error {{not an integral constant expression}} \
                                           // both-note {{in call to}}
};

namespace ZeroInit {
  struct A {
    int *p[2];
  };
  constexpr A a = {};
  static_assert(a.p[0] == nullptr, "");
  static_assert(a.p[1] == nullptr, "");

  struct B {
    double f[2];
  };
  constexpr B b = {};
  static_assert(b.f[0] == 0.0, "");
  static_assert(b.f[1] == 0.0, "");
}

namespace ArrayInitLoop {
  struct X {
      int arr[3];
  };
  constexpr X f(int &r) {
      return {++r, ++r, ++r};
  }
  constexpr int g() {
      int n = 0;
      auto [a, b, c] = f(n).arr;
      return a + b + c;
  }
  static_assert(g() == 6, "");
}

namespace StringZeroFill {
  struct A {
    char c[6];
  };
  constexpr A a = { "abc" };
  static_assert(a.c[0] == 'a', "");
  static_assert(a.c[1] == 'b', "");
  static_assert(a.c[2] == 'c', "");
  static_assert(a.c[3] == '\0', "");
  static_assert(a.c[4] == '\0', "");
  static_assert(a.c[5] == '\0', "");

  constexpr char b[6] = "foo";
  static_assert(b[0] == 'f', "");
  static_assert(b[1] == 'o', "");
  static_assert(b[2] == 'o', "");
  static_assert(b[3] == '\0', "");
  static_assert(b[4] == '\0', "");
  static_assert(b[5] == '\0', "");
}

namespace NoInitMapLeak {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdivision-by-zero"
#pragma clang diagnostic ignored "-Wc++20-extensions"
  constexpr int testLeak() { // both-error {{never produces a constant expression}}
    int a[2];
    a[0] = 1;
    // interrupts interpretation.
    (void)(1 / 0); // both-note 2{{division by zero}}

    return 1;
  }
#pragma clang diagnostic pop
  static_assert(testLeak() == 1, ""); // both-error {{not an integral constant expression}} \
                                      // both-note {{in call to 'testLeak()'}}

  constexpr int a[] = {1,2,3,4/0,5}; // both-error {{must be initialized by a constant expression}} \
                                     // both-note {{division by zero}} \
                                     // ref-note {{declared here}}

  /// FIXME: This should fail in the new interpreter as well.
  constexpr int b = a[0]; // ref-error {{must be initialized by a constant expression}} \
                          // ref-note {{is not a constant expression}} \
                          // ref-note {{declared here}}
  static_assert(b == 1, ""); // ref-error {{not an integral constant expression}} \
                             // ref-note {{not a constant expression}}

  constexpr int f() { // both-error {{never produces a constant expression}}
    int a[] = {19,2,3/0,4}; // both-note 2{{division by zero}} \
                            // both-warning {{is undefined}}
    return 1;
  }
  static_assert(f() == 1, ""); // both-error {{not an integral constant expression}} \
                               // both-note {{in call to}}
}

namespace Incomplete {
  struct Foo {
    char c;
    int a[];
  };

  constexpr Foo F{};
  constexpr const int *A = F.a; // both-error {{must be initialized by a constant expression}} \
                                // both-note {{array-to-pointer decay of array member without known bound}}

  constexpr const int *B = F.a + 1; // both-error {{must be initialized by a constant expression}} \
                                    // both-note {{array-to-pointer decay of array member without known bound}}

  constexpr int C = *F.a; // both-error {{must be initialized by a constant expression}} \
                          // both-note {{array-to-pointer decay of array member without known bound}}

  struct X {
    int a;
    int b[];
  };
  extern X x;
  constexpr int *xb = x.b; // both-error {{must be initialized by a constant expression}} \
                           // both-note {{array-to-pointer decay of array member without known bound}}


  /// These are from test/SemaCXX/constant-expression-cxx11.cpp
  extern int arr[];
  constexpr int *c = &arr[1]; // both-error  {{must be initialized by a constant expression}} \
                              // both-note {{indexing of array without known bound}}
  constexpr int *d = &arr[1]; // both-error  {{must be initialized by a constant expression}} \
                              // both-note {{indexing of array without known bound}}
  constexpr int *e = arr + 1; // both-error  {{must be initialized by a constant expression}} \
                              // both-note {{indexing of array without known bound}}
}

namespace GH69115 {
  /// This used to crash because we were trying to emit destructors for the
  /// array.
  constexpr int foo() {
    int arr[2][2] = {1, 2, 3, 4};
    return 0;
  }
  static_assert(foo() == 0, "");

  /// Test that we still emit the destructors for multi-dimensional
  /// composite arrays.
#if __cplusplus >= 202002L
  constexpr void assert(bool C) {
    if (C)
      return;
    // Invalid in constexpr.
    (void)(1 / 0); // both-warning {{undefined}}
  }

  class F {
  public:
    int a;
    int *dtor;
    int &idx;
    constexpr F(int a, int *dtor, int &idx) : a(a), dtor(dtor), idx(idx) {}
    constexpr ~F() noexcept(false){
      dtor[idx] = a;
      ++idx;
    }
  };
  constexpr int foo2() {
    int dtorIndices[] = {0, 0, 0, 0};
    int idx = 0;

    {
      F arr[2][2] = {F(1, dtorIndices, idx),
                     F(2, dtorIndices, idx),
                     F(3, dtorIndices, idx),
                     F(4, dtorIndices, idx)};
    }

    /// Reverse-reverse order.
    assert(idx == 4);
    assert(dtorIndices[0] == 4);
    assert(dtorIndices[1] == 3);
    assert(dtorIndices[2] == 2);
    assert(dtorIndices[3] == 1);

    return 0;
  }
  static_assert(foo2() == 0, "");
#endif
}

namespace NonConstReads {
#if __cplusplus >= 202002L
  void *p = nullptr; // both-note {{declared here}}

  int arr[!p]; // both-error {{not allowed at file scope}} \
               // both-warning {{variable length arrays}} \
               // both-note {{read of non-constexpr variable 'p'}}
  int z; // both-note {{declared here}}
  int a[z]; // both-error {{not allowed at file scope}} \
            // both-warning {{variable length arrays}} \
            // both-note {{read of non-const variable 'z'}}
#else
  void *p = nullptr;
  int arr[!p]; // both-error {{not allowed at file scope}}
  int z;
  int a[z]; // both-error {{not allowed at file scope}}
#endif

  const int y = 0;
  int yy[y];
}

namespace SelfComparison {
  struct S {
    int field;
    static int static_field;
    int array[4];
  };

  struct T {
    int field;
    static int static_field;
    int array[4];
    S s;
  };

  int struct_test(S s1, S s2, S *s3, T t) {
    return s3->array[t.field] == s3->array[t.field];  // both-warning {{self-comparison always evaluates to true}}
  };
}

namespace LocalIndex {
  void test() {
    const int const_subscript = 3;
    int array[2]; // both-note {{declared here}}
    array[const_subscript] = 0;  // both-warning {{array index 3 is past the end of the array (that has type 'int[2]')}}
  }
}

namespace LocalVLA {
  struct Foo {
    int x;
    Foo(int x) : x(x) {}
  };
  struct Elidable {
    Elidable();
  };

  void foo(int size) {
    Elidable elidableDynArray[size];
#if __cplusplus >= 202002L
     // both-note@-3 {{declared here}}
     // both-warning@-3 {{variable length array}}
     // both-note@-4 {{function parameter 'size' with unknown value}}
#endif
  }

  void f (unsigned int m) {
    int e[2][m];
#if __cplusplus >= 202002L
     // both-note@-3 {{declared here}}
     // both-warning@-3 2{{variable length array}}
     // both-note@-4 {{function parameter 'm' with unknown value}}
#endif
    e[0][0] = 0;
  }
}

char melchizedek[2];
typedef decltype(melchizedek[1] - melchizedek[0]) ptrdiff_t;
constexpr ptrdiff_t d1 = &melchizedek[1] - &melchizedek[0]; // ok
constexpr ptrdiff_t d3 = &melchizedek[0] - &melchizedek[1]; // ok

/// GH#88018
const int SZA[] = {};
void testZeroSizedArrayAccess() { unsigned c = SZA[4]; }

#if __cplusplus >= 202002L
constexpr int test_multiarray2() { // both-error {{never produces a constant expression}}
  int multi2[2][1]; // both-note {{declared here}}
  return multi2[2][0]; // both-note {{cannot access array element of pointer past the end of object}} \
                       // both-warning {{array index 2 is past the end of the array (that has type 'int[2][1]')}}
}

/// Same but with a dummy pointer.
int multi22[2][2]; // both-note {{declared here}}
int test_multiarray22() {
  return multi22[2][0]; // both-warning {{array index 2 is past the end of the array (that has type 'int[2][2]')}}
}

#endif

namespace ArrayMemberAccess {
  struct A {
    int x;
  };
  void f(const A (&a)[]) {
    bool cond = a->x;
  }
}

namespace OnePastEndSub {
  struct A {};
  constexpr A a[3][3];
  constexpr int diff2 = &a[1][3] - &a[1][0]; /// Used to crash.
}

static int same_entity_2[3];
constexpr int *get2() {
  // This is a redeclaration of the same entity, even though it doesn't
  // inherit the type of the prior declaration.
  extern int same_entity_2[];
  return same_entity_2;
}
static_assert(get2() == same_entity_2, "failed to find previous decl");

constexpr int zs[2][2][2][2] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 };
constexpr int fail(const int &p) {
  return (&p)[64]; // both-note 2{{cannot refer to element 64 of array of 2 elements}} \
                   // both-note {{cannot refer to element 65 of array of 2 elements}} \
                   // both-note {{cannot refer to element 66 of array of 2 elements}}
}
static_assert(fail(*(&(&(*(*&(&zs[2] - 1)[0] + 2 - 2))[2])[-1][2] - 2)) == 11, ""); // both-error {{not an integral constant expression}} \
                                                                                    // both-note {{in call to}}


static_assert(fail( // both-error {{not an integral constant expression}} \
                    // both-note {{in call to 'fail(zs[1][1][0][0])'}}
      *(*(*((*
  (zs + 1))     /// int[2][2][2]
      + 1)      /// int[2][2]
      + 2 - 2)  /// int[2]
      + 2 - 2)  /// int
      ));

static_assert(fail( // both-error {{not an integral constant expression}} \
                    // both-note {{in call to 'fail(zs[1][0][0][1])'}}
      *(*(*((*
  (zs + 1))     /// int[2][2][2]
      + 0)      /// int[2][2]
      + 2 - 2)  /// int[2]
      + 1)      /// int
      ));

static_assert(fail( // both-error {{not an integral constant expression}} \
                    // both-note {{in call to 'fail(zs[1][0][0][2])'}}
      *(*(*((*
  (zs + 1))     /// int[2][2][2]
      + 0)      /// int[2][2]
      + 2 - 2)  /// int[2]
      + 2)      /// int
      ));

namespace ZeroIndex {
  constexpr char foo(const char *a) {
    return a[0];
  }
  constexpr const char *f = "abc";
  static_assert(foo(f + 1) == 'b', "");
}

namespace MultiDimArrayOffset {
#define assert(x) (x ? void(0) : __builtin_abort())
  struct R {
    int a;
  };

  template<typename T>
  class view {
  public:
    T* V;
    T* current;

    constexpr view(T*V) : V(V), current(V) {}

    constexpr void operator+=(unsigned N) {
      current += N;
    }

    constexpr auto operator*() {
      return *current;
    }

  };

  constexpr int foo() {
    R buffer[2][4] = {{1, 2, 3, 4}, {5, 6, 7, 8}};

    auto A = buffer;
    A += 1;
    assert((**A).a == 5);
    assert(buffer == buffer + 1 - 1);

    assert(--A+0 == buffer+0);

    view V(buffer);
    assert(*V == &buffer[0][0]);
    V += 1;
    assert(*V == &buffer[1][0]);
    assert(*(V.current) == &buffer[1][0]);
    return 1;
  }
  static_assert(foo() == 1, "");
}

namespace ZeroSizeTypes {
  constexpr int (*p1)[0] = 0, (*p2)[0] = 0;
  constexpr int k = p2 - p1; // both-error {{constexpr variable 'k' must be initialized by a constant expression}} \
                             // both-note {{subtraction of pointers to type 'int[0]' of zero size}} \
                             // both-warning {{subtraction of pointers to type 'int[0]' of zero size has undefined behavior}}

  int arr[5][0];
  constexpr int f() { // both-error {{never produces a constant expression}}
    return &arr[3] - &arr[0]; // both-note {{subtraction of pointers to type 'int[0]' of zero size}} \
                              // both-warning {{subtraction of pointers to type 'int[0]' of zero size has undefined behavior}}
  }

  constexpr int z[0]{};
  static_assert((z - z) == 0);
}

namespace InvalidIndex {
  constexpr int foo(int i) { // both-error {{no return statement in constexpr function}}
    int a[] = {1,2,3};
    return a[_z]; // both-error {{use of undeclared identifier}}
  }
  static_assert(foo(0) == 1, "");
}

namespace PointerSubscript {
  template<typename T>
  constexpr T foo() {
    T ss[] = {{}, {}, {}};
    T *s = &ss[0];

    return s[2];
  }
  static_assert(foo<int>() == 0);
  struct S{};
  static_assert((foo<S>(), true));
}

namespace OnePastEndDiag {

  constexpr int a(const int *b) {
    return *b; // both-note {{read of dereferenced one-past-the-end pointer}}
  }
  constexpr int foo[] = {1,2};
  constexpr int k = a(foo + 2); // both-error {{must be initialized by a constant expression}} \
                                // both-note {{in call to 'a(&foo[2])'}}
}

namespace DiscardedSubScriptExpr {
  constexpr bool foo() { // both-error {{never produces a constant expression}}
    int a[2] = {};
    (void)a[3]; // both-note {{cannot refer to element 3 of array of 2 elements in a constant expression}}
    return true;
  }
}

namespace ZeroSizeArrayRead {
  constexpr char str[0] = {};
  constexpr  unsigned checksum(const char *s) {
    unsigned result = 0;
    for (const char *p = s; *p != '\0'; ++p) { // both-note {{read of dereferenced one-past-the-end pointer}}
      result += *p;
    }
    return result;
  }
  constexpr unsigned C = checksum(str); // both-error {{must be initialized by a constant expression}} \
                                        // both-note {{in call to}}

  constexpr const char *p1 = &str[0];
  constexpr const char *p2 = &str[1]; // both-error {{must be initialized by a constant expression}} \
                                      // both-note {{cannot refer to element 1 of array of 0 elements in a constant expression}}

  constexpr char s[] = {};
  static_assert(s[0] == '0', ""); // both-error {{not an integral constant expression}} \
                                  // both-note {{read of dereferenced one-past-the-end pointer}}
}

namespace FAM {
  char *strchr(const char *, int);

  struct A {
    char n, a[2];
  };
  struct B {
    int n;
    struct A a[]; // both-note {{here}}
  };

  const struct B b = {0, {{1, {2, 3}}, {4, {5, 6}}}};
  void foo(void) { int sch = 0 != strchr(b.a[1].a, '\0'); }

  int foo2() {
    struct B b = {0, {{1, {2, 3}}, {4, {5, 6}}}}; // both-error {{initialization of flexible array member is not allowed}}
    return 1;
  }
}