[clang-tidy] Access checks not done classes derived of std::array

Index accessing checks are not performed for derived classes of
of `std::array`, as only `std::array` itself and its aliases
seems to be checked.

This patch aims to extend it for derived classes such as:
```
template<class T, size_t N>
class DerivedArray : public std::array<T, N> {};
```

Reviewed By: PiotrZSL

Differential Revision: https://reviews.llvm.org/D156624

clang-tools-extra/clang-tidy/cppcoreguidelines/ProBoundsConstantArrayIndexCheck.cpp

@@ -48,9 +48,8 @@ void ProBoundsConstantArrayIndexCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
       cxxOperatorCallExpr(
           hasOverloadedOperatorName("[]"),
-          hasArgument(
-              0, hasType(hasUnqualifiedDesugaredType(recordType(hasDeclaration(
-                     cxxRecordDecl(hasName("::std::array")).bind("type")))))),
+          callee(cxxMethodDecl(
+              ofClass(cxxRecordDecl(hasName("::std::array")).bind("type")))),
           hasArgument(1, expr().bind("index")))
           .bind("expr"),
       this);

clang-tools-extra/docs/ReleaseNotes.rst

@@ -202,6 +202,10 @@ Changes in existing checks
   <clang-tidy/checks/cppcoreguidelines/pro-bounds-array-to-pointer-decay>` check
   to ignore predefined expression (e.g., ``__func__``, ...).
 
+- Improved :doc:`cppcoreguidelines-pro-bounds-constant-array-index
+  <clang-tidy/checks/cppcoreguidelines/pro-bounds-constant-array-index>` check
+  to perform checks on derived classes of  ``std::array``.
+
 - Improved :doc:`cppcoreguidelines-pro-type-member-init
   <clang-tidy/checks/cppcoreguidelines/pro-type-member-init>` check to ignore
   dependent delegate constructors.

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-bounds-constant-array-index.cpp

@@ -23,6 +23,9 @@ constexpr int const_index(int base) {
   return base + 3;
 }
 
+template<class T, size_t N>
+class DerivedArray : public std::array<T, N> {};
+
 void f(std::array<int, 10> a, int pos) {
   a [ pos / 2 /*comment*/] = 1;
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not use array subscript when the index is not an integer constant expression [cppcoreguidelines-pro-bounds-constant-array-index]
@@ -68,6 +71,81 @@ void f(std::array<int, 10> a, int pos) {
   m[const_index(6)] = 3; // OK, constant index and inside bounds
 }
 
+template<class T, size_t N>
+class PrivateDerivedArray : std::array<T, N> {
+public:
+  T& operator[](size_t n){
+    return std::array<T, N>::operator[](static_cast<int>(n));
+  };
+  T& at(size_t n) {
+    return std::array<T, N>::at(static_cast<int>(n));
+  };
+};
+
+void f_derived(DerivedArray<int, 10> a, int pos) {
+  a [ pos / 2 /*comment*/] = 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not use array subscript when the index is not an integer constant expression [cppcoreguidelines-pro-bounds-constant-array-index]
+  int j = a[pos - 1];
+  // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: do not use array subscript when the index is not an integer constant expression
+
+  a.at(pos-1) = 2; // OK, at() instead of []
+  gsl::at(a, pos-1) = 2; // OK, gsl::at() instead of []
+
+  a[-1] = 3;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: std::array<> index -1 is negative [cppcoreguidelines-pro-bounds-constant-array-index]
+  a[10] = 4;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: std::array<> index 10 is past the end of the array (which contains 10 elements) [cppcoreguidelines-pro-bounds-constant-array-index]
+
+  a[const_index(7)] = 3;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: std::array<> index 10 is past the end of the array (which contains 10 elements)
+
+  a[0] = 3; // OK, constant index and inside bounds
+  a[1] = 3; // OK, constant index and inside bounds
+  a[9] = 3; // OK, constant index and inside bounds
+  a[const_index(6)] = 3; // OK, constant index and inside bounds
+
+  using MyArray = DerivedArray<int, 10>;
+  MyArray m{};
+  m [ pos / 2 /*comment*/] = 1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not use array subscript when the index is not an integer constant expression [cppcoreguidelines-pro-bounds-constant-array-index]
+  int jj = m[pos - 1];
+  // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: do not use array subscript when the index is not an integer constant expression
+
+  m.at(pos-1) = 2; // OK, at() instead of []
+  gsl::at(m, pos-1) = 2; // OK, gsl::at() instead of []
+  m[-1] = 3;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: std::array<> index -1 is negative [cppcoreguidelines-pro-bounds-constant-array-index]
+  m[10] = 4;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: std::array<> index 10 is past the end of the array (which contains 10 elements) [cppcoreguidelines-pro-bounds-constant-array-index]
+
+  m[const_index(7)] = 3;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: std::array<> index 10 is past the end of the array (which contains 10 elements)
+
+  m[0] = 3; // OK, constant index and inside bounds
+  m[1] = 3; // OK, constant index and inside bounds
+  m[9] = 3; // OK, constant index and inside bounds
+  m[const_index(6)] = 3; // OK, constant index and inside bounds
+
+  using MyPrivateArray = PrivateDerivedArray<int, 10>;
+  MyPrivateArray pm{};
+  pm [ pos / 2 /*comment*/] = 1;
+  int jjj = pm[pos - 1];
+
+  pm.at(pos-1) = 2; // OK, at() instead of []
+  pm[-1] = 3;
+  pm[10] = 4;
+
+  pm[const_index(7)] = 3;
+
+  pm[0] = 3; // OK, constant index and inside bounds
+  pm[1] = 3; // OK, constant index and inside bounds
+  pm[9] = 3; // OK, constant index and inside bounds
+  pm[const_index(6)] = 3; // OK, constant index and inside bounds
+}
+
+
+
+
 void g() {
   int a[10];
   for (int i = 0; i < 10; ++i) {