Do not touch get() calls on 'this' object.

[sbenza]

Summary

These calls are part of the implementation of the smart pointer itself
and chaning it is likely to be wrong.
Example:

T& operator*() const { return *get(); }

[djasper]

Makes sense.

[sbenza]

Submitted as r207525

clang-tidy/misc/RedundantSmartptrGet.cpp

 namespace tidy {
 
 namespace {
 internal::Matcher<Expr> callToGet(internal::Matcher<Decl> OnClass) {
   return memberCallExpr(
              on(expr(anyOf(hasType(OnClass),
                            hasType(qualType(pointsTo(decl(OnClass).bind(
                                "ptr_to_ptr")))))).bind("smart_pointer")),
+             unless(callee(memberExpr(hasObjectExpression(thisExpr())))),
              callee(methodDecl(hasName("get")))).bind("redundant_get");
 }
 
 void registerMatchersForGetArrowStart(MatchFinder *Finder,
                                       MatchFinder::MatchCallback *Callback) {
   const auto QuacksLikeASmartptr = recordDecl(
       recordDecl().bind("duck_typing"),
       has(methodDecl(hasName("operator->"),

test/clang-tidy/redundant-smartptr-get.cpp

void Positive() {
   bb = nullptr != sp->get();
   // CHECK: :[[@LINE-1]]:19: warning: Redundant get() call on smart pointer.
   // CHECK: nullptr != sp->get();
 }
 
 // CHECK-NOT: warning
 
 void Negative() {
+  struct NegPtr {
+    int* get();
+    int* operator->() {
+      return &*this->get();
+    }
+    int& operator*() {
+      return *get();
+    }
+  };
+
   std::unique_ptr<Bar>* u;
   u->get()->Do();
 
   Fail1().get()->Do();
   Fail2().get()->Do();
   const Bar& b = *Fail1().get();
   (*Fail2().get()).Do();
 
   int_ptr ip;
   bool bb = std::unique_ptr<int>().get() == NULL;
   bb = ip.get() == nullptr;
   bb = u->get() == NULL;
 }