Convert GN's deps iterator to work with range-based for loops.

tools/gn/deps_iterator.h

Index: tools/gn/deps_iterator.h
diff --git a/tools/gn/deps_iterator.h b/tools/gn/deps_iterator.h
index 5fc3c01e019f33eff2e9714bc4fb9fbf8d6d1fd4..1c3a75e141747c3faa5e86bb0e3f8db5255853a3 100644
--- a/tools/gn/deps_iterator.h
+++ b/tools/gn/deps_iterator.h
@@ -10,52 +10,64 @@
 
 class Target;
 
-// Iterates over the deps of a target.
+// Provides an iterator for iterating over multiple LabelTargetVectors to
+// make it convenient to iterate over all deps of a target.
 //
-// Since there are multiple kinds of deps, this iterator allows looping over
-// each one in one loop.
+// This works by maintaining a simple stack of vectors (since we have a fixed
+// number of deps types). When the stack is empty, we've reached the end. This
+// means that the default-constructed iterator == end() for any sequence.
 class DepsIterator {
  public:
-  enum LinkedOnly {
-    LINKED_ONLY,
-  };
+  // Creates an empty iterator.
+  DepsIterator();
 
-  // Iterate over public, private, and data deps.
-  explicit DepsIterator(const Target* t);
+  // Iterate over the deps in the given vectors. If passing less than three,
+  // pad with nulls.
+  DepsIterator(const LabelTargetVector* a,
+               const LabelTargetVector* b,
+               const LabelTargetVector* c);
 
-  // Iterate over the public and private linked deps, but not the data deps.
-  DepsIterator(const Target* t, LinkedOnly);
-
-  // Returns true when there are no more targets.
-  bool done() const {
-    return !vect_stack_[0];
-  }
-
-  // Advance to the next position. This assumes !done().
+  // Prefix increment operator. This assumes there are more items (i.e.
+  // *this != DepsIterator()).
   //
   // For internal use, this function tolerates an initial index equal to the
   // length of the current vector. In this case, it will advance to the next
   // one.
-  void Advance();
+  DepsIterator& operator++();
 
-  // The current dependency.
-  const LabelTargetPair& pair() const {
+  // Comparison for STL-based loops.
+  bool operator!=(const DepsIterator& other) {
+    return current_index_ != other.current_index_ ||
+        vect_stack_[0] != other.vect_stack_[0] ||
+        vect_stack_[1] != other.vect_stack_[1] ||
+        vect_stack_[2] != other.vect_stack_[2];
+  }
+
+  // Dereference operator for STL-compatible iterators.
+  const LabelTargetPair& operator*() const {
     DCHECK_LT(current_index_, vect_stack_[0]->size());
     return (*vect_stack_[0])[current_index_];
   }
 
-  // The pointer to the current dependency.
-  const Target* target() const { return pair().ptr; }
-
-  // The label of the current dependency.
-  const Label& label() const { return pair().label; }
-
  private:
   const LabelTargetVector* vect_stack_[3];
 
   size_t current_index_;
+};
+
+// Provides a virtual container implementing begin() and end() for a
+// sequence of deps. This can then be used in range-based for loops.
+class DepsIteratorRange {
+ public:
+  explicit DepsIteratorRange(const DepsIterator& b);
+  ~DepsIteratorRange();
+
+  const DepsIterator& begin() const { return begin_; }
+  const DepsIterator& end() const { return end_; }
 
-  DISALLOW_COPY_AND_ASSIGN(DepsIterator);
+ private:
+  DepsIterator begin_;
+  DepsIterator end_;
 };
 
 #endif  // TOOLS_GN_DEPS_ITERATOR_H_