[clang-tools-extra] [clang-tidy] Add readability-pointer-to-ref check (PR #182068)

[via cfe-commits]

================
@@ -0,0 +1,199 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "PointerToRefCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::readability {
+
+namespace {
+
+/// Visitor that classifies how a pointer parameter is used in a function body.
+/// It detects:
+///   - Dereferences (operator*, operator->)
+///   - Null checks (if(ptr), ptr != nullptr, assert(ptr), etc.)
+///   - Pointer arithmetic
+///   - Being passed to other functions as a pointer
+///   - Address-of or array subscript usage
+class PointerUsageVisitor : public RecursiveASTVisitor<PointerUsageVisitor> {
+public:
+  explicit PointerUsageVisitor(const ParmVarDecl *Param) : Param(Param) {}
+
+  bool isDereferenced() const { return Dereferenced; }
+  bool isNullChecked() const { return NullChecked; }
+  bool isUsedAsPointer() const { return UsedAsPointer; }
+
+  bool VisitUnaryOperator(const UnaryOperator *UO) {
+    if (UO->getOpcode() == UO_Deref && refersToParam(UO->getSubExpr()))
+      Dereferenced = true;
+    return true;
----------------
zeyi2 wrote:

IMO we should handle `&` here? WDYT?
```cpp
if (UO->getOpcode() == UO_AddrOf && refersToParam(SubExp))
  UsedAsPointer = true;
```

https://github.com/llvm/llvm-project/pull/182068