[clang] [-Wunsafe-buffer-usage] Add unique_ptr <T[]> accesses (PR #156773)

[via cfe-commits]

================
@@ -1318,6 +1319,88 @@ static bool isSupportedVariable(const DeclRefExpr &Node) {
   return D != nullptr && isa<VarDecl>(D);
 }
 
+static bool isUniquePtrArray(const CXXRecordDecl *RecordDecl) {
+  if (!RecordDecl || !RecordDecl->isInStdNamespace() ||
+      RecordDecl->getNameAsString() != "unique_ptr")
+    return false;
+
+  const ClassTemplateSpecializationDecl *class_template_specialization_decl =
+      dyn_cast<ClassTemplateSpecializationDecl>(RecordDecl);
+  if (!class_template_specialization_decl)
+    return false;
+
+  const TemplateArgumentList &template_args =
+      class_template_specialization_decl->getTemplateArgs();
+  if (template_args.size() == 0)
+    return false;
+
+  const TemplateArgument &first_arg = template_args[0];
+  if (first_arg.getKind() != TemplateArgument::Type)
+    return false;
+
+  QualType referred_type = first_arg.getAsType();
+  return referred_type->isArrayType();
+}
+
+class UniquePtrArrayAccessGadget : public WarningGadget {
+  static constexpr const char *const AccessorTag = "unique_ptr_array_access";
+  const CXXOperatorCallExpr *AccessorExpr;
+
+public:
+  UniquePtrArrayAccessGadget(const MatchResult &Result)
+      : WarningGadget(Kind::UniquePtrArrayAccess),
+        AccessorExpr(Result.getNodeAs<CXXOperatorCallExpr>(AccessorTag)) {
+    assert(AccessorExpr &&
+           "UniquePtrArrayAccessGadget requires a matched CXXOperatorCallExpr");
+  }
+
+  static bool classof(const Gadget *G) {
+    return G->getKind() == Kind::UniquePtrArrayAccess;
+  }
+
+  static bool matches(const Stmt *S, const ASTContext &Ctx,
+                      MatchResult &Result) {
+
+    const CXXOperatorCallExpr *OpCall = dyn_cast<CXXOperatorCallExpr>(S);
+    if (!OpCall || OpCall->getOperator() != OO_Subscript)
+      return false;
+
+    const Expr *Callee = OpCall->getCallee()->IgnoreParenImpCasts();
+    if (!Callee)
+      return false;
+
+    const CXXMethodDecl *Method =
+        dyn_cast_or_null<CXXMethodDecl>(OpCall->getDirectCallee());
+    if (!Method)
+      return false;
+
+    if (Method->getNameAsString() != "operator[]")
----------------
shreya-jain wrote:

Used `FunctionDecl::getOverloadedOperator`

https://github.com/llvm/llvm-project/pull/156773