[NFC][Clang] Fix static analyzer tool remark about missing user-defined assignment operator

[Manna]

Summary

Reported by Coverity:

Copy without assign
This class has a user-defined copy constructor but no user-defined assignment operator. If the copy constructor is necessary to manage owned resources then a corresponding assignment operator is usually required. If an object of this type is assigned memory leaks and/or use-after-free errors may occur. Note that a compiler-generated assignment operator will perform only a bit-wise copy for any fields that do not have their own assignment operators defined.

Class has user-written copy constructor but no user-written assignment operator

copy_without_assign: Class <unnamed>::DeclUseTracker has a user-written copy constructor <unnamed>::DeclUseTracker::DeclUseTracker(<unnamed>::DeclUseTracker const &) =delete but no corresponding user-written assignment operator.

[aaron.ballman]

LGTM! It's not strictly needed (the move constructor causes the implicit assignment operator to be deleted: https://eel.is/c++draft/class.copy.assign#2.sentence-2), but I think it's more clear to be explicit.

[Manna]

Thank you @aaron.ballman for reviews and feedback.

[Manna]

The lit test failure seem unrelated to my fix:
https://buildkite.com/llvm-project/premerge-checks/builds/146438#0187786e-2f04-40a2-acf1-78eee9f00e7f

Failed Tests (1):

Clang :: SemaCXX/warn-unsafe-buffer-usage-fixits-pre-increment.cpp

clang/lib/Analysis/UnsafeBufferUsage.cpp

class DeclUseTracker {
 
   // Allocate on the heap for easier move.
   std::unique_ptr<UseSetTy> Uses{std::make_unique<UseSetTy>()};
   DefMapTy Defs{};
 
 public:
   DeclUseTracker() = default;
   DeclUseTracker(const DeclUseTracker &) = delete; // Let's avoid copies.
+  DeclUseTracker &operator=(const DeclUseTracker &) = delete;
   DeclUseTracker(DeclUseTracker &&) = default;
   DeclUseTracker &operator=(DeclUseTracker &&) = default;
 
   // Start tracking a freshly discovered DRE.
   void discoverUse(const DeclRefExpr *DRE) { Uses->insert(DRE); }
 
   // Stop tracking the DRE as it's been fully figured out.
   void claimUse(const DeclRefExpr *DRE) {