Add != to YAMLParser's basic_collection_iterator.

...and mark it as merely an input_iterator rather than a forward_iterator,
since it is destructive. And then rewrite == to take advantage of that.

Patch by Alex Denisov!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256913 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/YAMLParser.h

@@ -305,7 +305,7 @@ class KeyValueNode final : public Node {
 /// increment() which must set CurrentEntry to 0 to create an end iterator.
 template <class BaseT, class ValueT>
 class basic_collection_iterator
-    : public std::iterator<std::forward_iterator_tag, ValueT> {
+    : public std::iterator<std::input_iterator_tag, ValueT> {
 public:
   basic_collection_iterator() : Base(nullptr) {}
   basic_collection_iterator(BaseT *B) : Base(B) {}
@@ -326,11 +326,24 @@ class basic_collection_iterator
     return Base->CurrentEntry;
   }
 
+  /// Note on EqualityComparable:
+  ///
+  /// The iterator is not re-entrant,
+  /// it is meant to be used for parsing YAML on-demand
+  /// Once iteration started - it can point only to one entry at a time
+  /// hence Base.CurrentEntry and Other.Base.CurrentEntry are equal
+  /// iff Base and Other.Base are equal.
+  bool operator==(const basic_collection_iterator &Other) const {
+    if (Base && (Base == Other.Base)) {
+      assert((Base->CurrentEntry == Other.Base->CurrentEntry)
+             && "Equal Bases expected to point to equal Entries");
+    }
+
+    return Base == Other.Base;
+  }
+
   bool operator!=(const basic_collection_iterator &Other) const {
-    if (Base != Other.Base)
-      return true;
-    return (Base && Other.Base) &&
-           Base->CurrentEntry != Other.Base->CurrentEntry;
+    return !(Base == Other.Base);
   }
 
   basic_collection_iterator &operator++() {

unittests/Support/YAMLParserTest.cpp

@@ -260,4 +260,76 @@ TEST(YAMLParser, DiagnosticFilenameFromBufferID) {
   EXPECT_EQ("buffername.yaml", GeneratedDiag.getFilename());
 }
 
+TEST(YAMLParser, SameNodeIteratorOperatorNotEquals) {
+  SourceMgr SM;
+  yaml::Stream Stream("[\"1\", \"2\"]", SM);
+
+  yaml::SequenceNode *Node = dyn_cast<yaml::SequenceNode>(
+                                              Stream.begin()->getRoot());
+
+  auto Begin = Node->begin();
+  auto End = Node->end();
+
+  EXPECT_TRUE(Begin != End);
+  EXPECT_FALSE(Begin != Begin);
+  EXPECT_FALSE(End != End);
+}
+
+TEST(YAMLParser, SameNodeIteratorOperatorEquals) {
+  SourceMgr SM;
+  yaml::Stream Stream("[\"1\", \"2\"]", SM);
+
+  yaml::SequenceNode *Node = dyn_cast<yaml::SequenceNode>(
+                                              Stream.begin()->getRoot());
+
+  auto Begin = Node->begin();
+  auto End = Node->end();
+
+  EXPECT_FALSE(Begin == End);
+  EXPECT_TRUE(Begin == Begin);
+  EXPECT_TRUE(End == End);
+}
+
+TEST(YAMLParser, DifferentNodesIteratorOperatorNotEquals) {
+  SourceMgr SM;
+  yaml::Stream Stream("[\"1\", \"2\"]", SM);
+  yaml::Stream AnotherStream("[\"1\", \"2\"]", SM);
+
+  yaml::SequenceNode *Node = dyn_cast<yaml::SequenceNode>(
+                                                  Stream.begin()->getRoot());
+  yaml::SequenceNode *AnotherNode = dyn_cast<yaml::SequenceNode>(
+                                              AnotherStream.begin()->getRoot());
+
+  auto Begin = Node->begin();
+  auto End = Node->end();
+
+  auto AnotherBegin = AnotherNode->begin();
+  auto AnotherEnd = AnotherNode->end();
+
+  EXPECT_TRUE(Begin != AnotherBegin);
+  EXPECT_TRUE(Begin != AnotherEnd);
+  EXPECT_FALSE(End != AnotherEnd);
+}
+
+TEST(YAMLParser, DifferentNodesIteratorOperatorEquals) {
+  SourceMgr SM;
+  yaml::Stream Stream("[\"1\", \"2\"]", SM);
+  yaml::Stream AnotherStream("[\"1\", \"2\"]", SM);
+
+  yaml::SequenceNode *Node = dyn_cast<yaml::SequenceNode>(
+                                                    Stream.begin()->getRoot());
+  yaml::SequenceNode *AnotherNode = dyn_cast<yaml::SequenceNode>(
+                                             AnotherStream.begin()->getRoot());
+
+  auto Begin = Node->begin();
+  auto End = Node->end();
+
+  auto AnotherBegin = AnotherNode->begin();
+  auto AnotherEnd = AnotherNode->end();
+
+  EXPECT_FALSE(Begin == AnotherBegin);
+  EXPECT_FALSE(Begin == AnotherEnd);
+  EXPECT_TRUE(End == AnotherEnd);
+}
+
 } // end namespace llvm