[clang-tidy] Make 'modernize-use-nullptr' check work on multiple nested implicit cast expressions.

[hokein]

Summary

For some test cases like:

 int func(int, void*, void*);
(double)func(0, 0, 0);

The AST contains several ImplicitCastExprs, so we should not only check on the first sub expression.

`-CStyleCastExpr 0x7fe43a088938 <line:6:3, col:24> 'double' <NoOp>
     `-ImplicitCastExpr 0x7fe43a088920 <col:11, col:24> 'double' <IntegralToFloating>
       `-CallExpr 0x7fe43a0888a0 <col:11, col:24> 'int'
         |-ImplicitCastExpr 0x7fe43a088888 <col:11> 'int (*)(int, void *, void *)' <FunctionToPointerDecay>
         | `-DeclRefExpr 0x7fe43a0887d8 <col:11> 'int (int, void *, void *)' lvalue Function 0x7fe43a0886f0 'func1' 'int (int, void *, void *)'
         |-IntegerLiteral 0x7fe43a088800 <col:17> 'int' 0
         |-ImplicitCastExpr 0x7fe43a0888e0 <col:20> 'void *' <NullToPointer>
         | `-IntegerLiteral 0x7fe43a088820 <col:20> 'int' 0
         `-ImplicitCastExpr 0x7fe43a0888f8 <col:23> 'void *' <NullToPointer>
           `-IntegerLiteral 0x7fe43a088840 <col:23> 'int' 0

[alexfh]

LG

clang-tidy/modernize/UseNullptrCheck.cpp

if (SM.isMacroBodyExpansion(StartLoc) && SM.isMacroBodyExpansion(EndLoc)) {
       EndLoc = SM.getFileLoc(EndLoc);
     }
 
     if (!isReplaceableRange(StartLoc, EndLoc, SM)) {
       return skipSubTree();
     }
     replaceWithNullptr(Check, SM, StartLoc, EndLoc);
 
-    return skipSubTree();
+    return true;
   }
 
 private:
   bool skipSubTree() {
     PruneSubtree = true;
     return true;
   }
 

test/clang-tidy/modernize-use-nullptr-basic.cpp

void test_const_pointers() {
   // CHECK-MESSAGES: :[[@LINE-1]]:31: warning: use nullptr
   // CHECK-FIXES: const int *const_p5 = (int*)nullptr;
   int *t;
   const int *const_p6 = static_cast<int*>(t ? t : static_cast<int*>(0));
   // CHECK-MESSAGES: :[[@LINE-1]]:69: warning: use nullptr
   // CHECK-FIXES: const int *const_p6 = static_cast<int*>(t ? t : static_cast<int*>(nullptr));
 }
 
+void test_nested_implicit_cast_expr() {
+  int func0(void*, void*);
+  int func1(int, void*, void*);
+
+  (double)func1(0, 0, 0);
+  // CHECK-MESSAGES: :[[@LINE-1]]:20: warning: use nullptr
+  // CHECK-MESSAGES: :[[@LINE-2]]:23: warning: use nullptr
+  // CHECK-FIXES: (double)func1(0, nullptr, nullptr);
+  (double)func1(func0(0, 0), 0, 0);
+  // CHECK-MESSAGES: :[[@LINE-1]]:23: warning: use nullptr
+  // CHECK-MESSAGES: :[[@LINE-2]]:26: warning: use nullptr
+  // CHECK-MESSAGES: :[[@LINE-3]]:30: warning: use nullptr
+  // CHECK-MESSAGES: :[[@LINE-4]]:33: warning: use nullptr
+  // CHECK-FIXES: (double)func1(func0(nullptr, nullptr), nullptr, nullptr);
+}
 
 // FIXME: currently, the check doesn't work as it should with templates.
 template<typename T>
 class A {
  public:
   A(T *p = NULL) {}
 
   void f() {