[clang-tidy] Accessing checks not done for aliases of std::array

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

This patch aims to extend it for aliases such as:
 `using MyArray = std::array<int, 10>;`

Reviewed By: PiotrZSL

Differential Revision: https://reviews.llvm.org/D154297

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

@@ -49,7 +49,8 @@ void ProBoundsConstantArrayIndexCheck::registerMatchers(MatchFinder *Finder) {
       cxxOperatorCallExpr(
           hasOverloadedOperatorName("[]"),
           hasArgument(
-              0, hasType(cxxRecordDecl(hasName("::std::array")).bind("type"))),
+              0, hasType(hasUnqualifiedDesugaredType(recordType(hasDeclaration(
+                     cxxRecordDecl(hasName("::std::array")).bind("type")))))),
           hasArgument(1, expr().bind("index")))
           .bind("expr"),
       this);

clang-tools-extra/docs/ReleaseNotes.rst

@@ -321,6 +321,10 @@ Changes in existing checks
   :doc:`cppcoreguidelines-use-default-member-init
   <clang-tidy/checks/cppcoreguidelines/use-default-member-init>` instead.
 
+- Improved :doc:`cppcoreguidelines-pro-bounds-constant-array-index
+  <clang-tidy/checks/cppcoreguidelines/pro-bounds-constant-array-index>` check
+  to cover type aliases of ``std::array``.
+
 - Fixed a false positive in :doc:`cppcoreguidelines-slicing
   <clang-tidy/checks/cppcoreguidelines/slicing>` check when warning would be
   emitted in constructor for virtual base class initialization.

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

@@ -44,6 +44,28 @@ void f(std::array<int, 10> a, int pos) {
   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 = std::array<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
 }
 
 void g() {