clang-tidy: accessing checks not done for aliases of `std::array`

[sousajo]

Summary

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

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

[Eugene.Zelenko]

Please mention this change in Release Notes.

[PiotrZSL]

Looks good, probably hasCanonicalType would be sufficient but hasUnqualifiedDesugaredType will also do a job.
Release notes need to be updated.

[sousajo]

Thanks ^^ added the release note. Can someone please land it for me?

Jorge Pinto Sousa <[e-mail]>

[sousajo]

while landing it, if someone feels that the release note can/should be reworded please feel free to do so.

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

Finder->addMatcher(arraySubscriptExpr(hasBase(ignoringImpCasts(hasType(
                                         unless(hasAncestor(decl(isImplicit()))))
                          .bind("expr"),
                      this);
 
   Finder->addMatcher(
       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);
 }
 
 void ProBoundsConstantArrayIndexCheck::check(
     const MatchFinder::MatchResult &Result) {
   const auto *Matched = Result.Nodes.getNodeAs<Expr>("expr");

clang-tools-extra/docs/ReleaseNotes.rst

 - Deprecated :doc:`cert-dcl21-cpp
   <clang-tidy/checks/cert/dcl21-cpp>` check.
 
 - Deprecated C.48 enforcement from :doc:`cppcoreguidelines-prefer-member-initializer
   <clang-tidy/checks/cppcoreguidelines/prefer-member-initializer>`. Please use
   :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.
 
 - Deprecated check-local options `HeaderFileExtensions`
   in :doc:`google-build-namespaces
   <clang-tidy/checks/google/build-namespaces>` check.
   Global options of the same name should be used instead.

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

void f(std::array<int, 10> a, int pos) {
 
   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 = 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() {
   int a[10];
   for (int i = 0; i < 10; ++i) {
     a[i] = i;
     // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: do not use array subscript when the index is not an integer constant expression
     // CHECK-FIXES: gsl::at(a, i) = i;