[clang-tidy] Fix false positive for cppcoreguidelines-pro-bounds-pointer-arithmetic (#127394)

this PR fixes #126424
for `ArraySubScriptExpr`, `hasBase` Matcher will get right operand when
it is not integer type, but is not for sure that left operand is integer
type. For the example code below `hasBase` will get `r` for the
Subsequent matching and causing false positive.
```
template <typename R>
int f(std::map<R*, int>& map, R* r) {
  return map[r];
}
```
so is needed to see if index is integer type to avoid this situation.

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

@@ -42,7 +42,8 @@ void ProBoundsPointerArithmeticCheck::registerMatchers(MatchFinder *Finder) {
       arraySubscriptExpr(
           hasBase(ignoringImpCasts(
               anyOf(AllPointerTypes,
-                    hasType(decayedType(hasDecayedType(pointerType())))))))
+                    hasType(decayedType(hasDecayedType(pointerType())))))),
+          hasIndex(hasType(isInteger())))
           .bind("expr"),
       this);
 }

clang-tools-extra/docs/ReleaseNotes.rst

@@ -216,6 +216,11 @@ Changes in existing checks
   <clang-tidy/checks/cppcoreguidelines/missing-std-forward>` check by adding a
   flag to specify the function used for forwarding instead of ``std::forward``.
    
+- Improved :doc:`cppcoreguidelines-pro-bounds-pointer-arithmetic
+  <clang-tidy/checks/cppcoreguidelines/pro-bounds-pointer-arithmetic>` check by
+  fixing false positives when calling indexing operators that do not perform
+  pointer arithmetic in template, for example ``std::map::operator[]``.
+
 - Improved :doc:`cppcoreguidelines-rvalue-reference-param-not-moved
   <clang-tidy/checks/cppcoreguidelines/rvalue-reference-param-not-moved>` check
   by adding a flag to specify the function used for moving instead of

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-bounds-pointer-arithmetic.cpp

@@ -87,3 +87,25 @@ void okay() {
 
   for(int ii : a) ; // OK, pointer arithmetic generated by compiler
 }
+
+namespace gh126424 {
+
+namespace std {
+template <typename, typename>
+class pair {};
+
+template <typename Key, typename Value>
+class map {
+  public:
+   using value_type = pair<Key, Value>;
+   value_type& operator[](const Key& key);
+   value_type& operator[](Key&& key);
+ };
+}
+
+template <typename R>
+int f(std::map<R*, int>& map, R* r) {
+  return map[r]; // OK
+}
+
+}