Add support for merge keys

Merge keys are specified here[1] for YAML 1.1. While not part of
the YAML 1.2 specification, they're very useful and are supported
in other implementations[2][3][4] that target 1.2.

Support for merge keys is optional and disabled by default. It can
be enabled by defining YAML_CPP_SUPPORT_MERGE_KEYS, either directly
or by setting the CMake option YAML_CPP_SUPPORT_MERGE_KEYS=ON.

[1]: http://yaml.org/type/merge.html
[2]: https://github.com/go-yaml/yaml
[3]: https://github.com/ruby/psych
[4]: https://bitbucket.org/ruamel/yaml

.gitignore

@@ -1 +1,2 @@
 build/
+/tags

.travis.yml

@@ -5,6 +5,9 @@ os:
 compiler:
   - clang
   - gcc
+env:
+  - YAML_CPP_SUPPORT_MERGE_KEYS=ON
+  - YAML_CPP_SUPPORT_MERGE_KEYS=OFF
 before_install:
   - |
     if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then
@@ -17,7 +20,7 @@ before_install:
 before_script:
   - mkdir build
   - cd build
-  - cmake ..
+  - cmake .. -DYAML_CPP_SUPPORT_MERGE_KEYS=$YAML_CPP_SUPPORT_MERGE_KEYS
 script:
   - make
   - test/run-tests

CMakeLists.txt

@@ -41,6 +41,7 @@ enable_testing()
 option(YAML_CPP_BUILD_TESTS "Enable testing" ON)
 option(YAML_CPP_BUILD_TOOLS "Enable parse tools" ON)
 option(YAML_CPP_BUILD_CONTRIB "Enable contrib stuff in library" ON)
+option(YAML_CPP_SUPPORT_MERGE_KEYS "Support YAML merge keys ('<<') in yaml-cpp's executable targets. Use '#define YAML_CPP_SUPPORT_MERGE_KEYS' instead when linking from another project." OFF)
 
 ## Build options
 # --> General
@@ -97,6 +98,10 @@ else()
 	add_definitions(-DYAML_CPP_NO_CONTRIB)
 endif()
 
+if (YAML_CPP_SUPPORT_MERGE_KEYS)
+    add_definitions(-DYAML_CPP_SUPPORT_MERGE_KEYS)
+endif()
+
 set(library_sources
   ${sources}
   ${public_headers}
@@ -116,9 +121,10 @@ if(VERBOSE)
 	message(STATUS "contrib_private_headers: ${contrib_private_headers}")
 endif()
 
-include_directories(${YAML_CPP_SOURCE_DIR}/src)
-include_directories(${YAML_CPP_SOURCE_DIR}/include)
-
+if (CMAKE_VERSION VERSION_LESS 2.8.12)
+    include_directories(${YAML_CPP_SOURCE_DIR}/src)
+    include_directories(${YAML_CPP_SOURCE_DIR}/include)
+endif()
 
 
 ###
@@ -275,6 +281,14 @@ set(_INSTALL_DESTINATIONS
 ### Library
 ###
 add_library(yaml-cpp ${library_sources})
+
+if (NOT CMAKE_VERSION VERSION_LESS 2.8.12)
+    target_include_directories(yaml-cpp
+        PUBLIC $<BUILD_INTERFACE:${YAML_CPP_SOURCE_DIR}/include>
+               $<INSTALL_INTERFACE:${INCLUDE_INSTALL_ROOT_DIR}>
+        PRIVATE $<BUILD_INTERFACE:${YAML_CPP_SOURCE_DIR}/src>)
+endif()
+
 set_target_properties(yaml-cpp PROPERTIES
   COMPILE_FLAGS "${yaml_c_flags} ${yaml_cxx_flags}"
 )

include/yaml-cpp/exceptions.h

@@ -15,7 +15,7 @@
 
 // This is here for compatibility with older versions of Visual Studio
 // which don't support noexcept
-#ifdef _MSC_VER
+#if defined(_MSC_VER) && _MSC_VER < 1900
     #define YAML_CPP_NOEXCEPT _NOEXCEPT
 #else
     #define YAML_CPP_NOEXCEPT noexcept

include/yaml-cpp/node/detail/impl.h

@@ -32,7 +32,7 @@ struct get_idx<Key,
 
   static node* get(std::vector<node*>& sequence, const Key& key,
                    shared_memory_holder pMemory) {
-   if (key > sequence.size() || (key > 0 && !sequence[key-1]->is_defined()))
+    if (key > sequence.size() || (key > 0 && !sequence[key - 1]->is_defined()))
       return 0;
     if (key == sequence.size())
       sequence.push_back(&pMemory->create_node());
@@ -56,6 +56,37 @@ struct get_idx<Key, typename std::enable_if<std::is_signed<Key>::value>::type> {
   }
 };
 
+template <typename Key, typename Enable = void>
+struct remove_idx {
+  static bool remove(std::vector<node*>&, const Key&) { return false; }
+};
+
+template <typename Key>
+struct remove_idx<
+    Key, typename std::enable_if<std::is_unsigned<Key>::value &&
+                                 !std::is_same<Key, bool>::value>::type> {
+
+  static bool remove(std::vector<node*>& sequence, const Key& key) {
+    if (key >= sequence.size()) {
+      return false;
+    } else {
+      sequence.erase(sequence.begin() + key);
+      return true;
+    }
+  }
+};
+
+template <typename Key>
+struct remove_idx<Key,
+                  typename std::enable_if<std::is_signed<Key>::value>::type> {
+
+  static bool remove(std::vector<node*>& sequence, const Key& key) {
+    return key >= 0 ? remove_idx<std::size_t>::remove(
+                          sequence, static_cast<std::size_t>(key))
+                    : false;
+  }
+};
+
 template <typename T>
 inline bool node::equals(const T& rhs, shared_memory_holder pMemory) {
   T lhs;
@@ -129,21 +160,23 @@ inline node& node_data::get(const Key& key, shared_memory_holder pMemory) {
 
 template <typename Key>
 inline bool node_data::remove(const Key& key, shared_memory_holder pMemory) {
-  if (m_type != NodeType::Map)
-    return false;
+  if (m_type == NodeType::Sequence) {
+    return remove_idx<Key>::remove(m_sequence, key);
+  } else if (m_type == NodeType::Map) {
+    kv_pairs::iterator it = m_undefinedPairs.begin();
+    while (it != m_undefinedPairs.end()) {
+      kv_pairs::iterator jt = std::next(it);
+      if (it->first->equals(key, pMemory)) {
+        m_undefinedPairs.erase(it);
+      }
+      it = jt;
+    }
 
-  for (kv_pairs::iterator it = m_undefinedPairs.begin();
-       it != m_undefinedPairs.end();) {
-    kv_pairs::iterator jt = std::next(it);
-    if (it->first->equals(key, pMemory))
-      m_undefinedPairs.erase(it);
-    it = jt;
-  }
-
-  for (node_map::iterator it = m_map.begin(); it != m_map.end(); ++it) {
-    if (it->first->equals(key, pMemory)) {
-      m_map.erase(it);
-      return true;
+    for (node_map::iterator it = m_map.begin(); it != m_map.end(); ++it) {
+      if (it->first->equals(key, pMemory)) {
+        m_map.erase(it);
+        return true;
+      }
     }
   }
 

include/yaml-cpp/node/detail/iterator.h

@@ -8,19 +8,19 @@
 #endif
 
 #include "yaml-cpp/dll.h"
+#include "yaml-cpp/node/detail/node_iterator.h"
 #include "yaml-cpp/node/node.h"
 #include "yaml-cpp/node/ptr.h"
-#include "yaml-cpp/node/detail/node_iterator.h"
 #include <cstddef>
 #include <iterator>
 
+
 namespace YAML {
 namespace detail {
 struct iterator_value;
 
 template <typename V>
-class iterator_base : public std::iterator<std::forward_iterator_tag, V,
-                                           std::ptrdiff_t, V*, V> {
+class iterator_base {
 
  private:
   template <typename>
@@ -37,7 +37,11 @@ class iterator_base : public std::iterator<std::forward_iterator_tag, V,
   };
 
  public:
-  typedef typename iterator_base::value_type value_type;
+  using iterator_category = std::forward_iterator_tag;
+  using value_type = V;
+  using difference_type = std::ptrdiff_t;
+  using pointer = V*;
+  using reference = V;
 
  public:
   iterator_base() : m_iterator(), m_pMemory() {}
@@ -86,7 +90,7 @@ class iterator_base : public std::iterator<std::forward_iterator_tag, V,
   base_type m_iterator;
   shared_memory_holder m_pMemory;
 };
-}
-}
+}  // namespace detail
+}  // namespace YAML
 
 #endif  // VALUE_DETAIL_ITERATOR_H_62B23520_7C8E_11DE_8A39_0800200C9A66

include/yaml-cpp/node/detail/node.h

@@ -122,12 +122,23 @@ class node {
     // NOTE: this returns a non-const node so that the top-level Node can wrap
     // it, and returns a pointer so that it can be NULL (if there is no such
     // key).
-    return static_cast<const node_ref&>(*m_pRef).get(key, pMemory);
+    node* value = static_cast<const node_ref&>(*m_pRef).get(key, pMemory);
+#ifdef YAML_CPP_SUPPORT_MERGE_KEYS
+    if (!value || value->type() == NodeType::Undefined) {
+      return get_value_from_merge_key(key, value, pMemory);
+    }
+#endif
+    return value;
   }
   template <typename Key>
   node& get(const Key& key, shared_memory_holder pMemory) {
     node& value = m_pRef->get(key, pMemory);
     value.add_dependency(*this);
+#ifdef YAML_CPP_SUPPORT_MERGE_KEYS
+    if (value.type() == NodeType::Undefined) {
+      return *get_value_from_merge_key(key, &value, pMemory);
+    }
+#endif
     return value;
   }
   template <typename Key>
@@ -159,6 +170,33 @@ class node {
   }
 
  private:
+#ifdef YAML_CPP_SUPPORT_MERGE_KEYS
+  template <typename Key>
+  inline node* get_value_from_merge_key(const Key& key, node* currentValue,
+                                        shared_memory_holder pMemory) const {
+    node* mergeValue =
+      static_cast<const node_ref&>(*m_pRef).get(std::string("<<"), pMemory);
+    if (!mergeValue) {
+      return currentValue;
+    }
+    if (mergeValue->type() == NodeType::Map) {
+      return &mergeValue->get(key, pMemory);
+    }
+    if (mergeValue->type() == NodeType::Sequence) {
+      for (const_node_iterator it = mergeValue->begin();
+            it != mergeValue->end(); ++it) {
+        if (it->pNode && it->pNode->type() == NodeType::Map) {
+          node* value = it->pNode->get(key, pMemory);
+          if (value && value->type() != NodeType::Undefined) {
+            return value;
+          }
+        }
+      }
+    }
+    return currentValue;
+  }
+#endif
+
   shared_node_ref m_pRef;
   typedef std::set<node*> nodes;
   nodes m_dependencies;

src/contrib/graphbuilder.cpp

@@ -11,7 +11,7 @@ void* BuildGraphOfNextDocument(Parser& parser,
   if (parser.HandleNextDocument(eventHandler)) {
     return eventHandler.RootNode();
   } else {
-    return NULL;
+    return nullptr;
   }
 }
 }

src/contrib/graphbuilderadapter.cpp

@@ -49,7 +49,7 @@ void GraphBuilderAdapter::OnMapStart(const Mark &mark, const std::string &tag,
                                      EmitterStyle::value /* style */) {
   void *pNode = m_builder.NewMap(mark, tag, GetCurrentParent());
   m_containers.push(ContainerFrame(pNode, m_pKeyNode));
-  m_pKeyNode = NULL;
+  m_pKeyNode = nullptr;
   RegisterAnchor(anchor, pNode);
 }
 
@@ -62,7 +62,7 @@ void GraphBuilderAdapter::OnMapEnd() {
 
 void *GraphBuilderAdapter::GetCurrentParent() const {
   if (m_containers.empty()) {
-    return NULL;
+    return nullptr;
   }
   return m_containers.top().pContainer;
 }
@@ -83,7 +83,7 @@ void GraphBuilderAdapter::DispositionNode(void *pNode) {
   if (m_containers.top().isMap()) {
     if (m_pKeyNode) {
       m_builder.AssignInMap(pContainer, m_pKeyNode, pNode);
-      m_pKeyNode = NULL;
+      m_pKeyNode = nullptr;
     } else {
       m_pKeyNode = pNode;
     }

src/contrib/graphbuilderadapter.h

@@ -26,7 +26,7 @@ namespace YAML {
 class GraphBuilderAdapter : public EventHandler {
  public:
   GraphBuilderAdapter(GraphBuilderInterface& builder)
-      : m_builder(builder), m_pRootNode(NULL), m_pKeyNode(NULL) {}
+      : m_builder(builder), m_pRootNode(nullptr), m_pKeyNode(nullptr) {}
 
   virtual void OnDocumentStart(const Mark& mark) { (void)mark; }
   virtual void OnDocumentEnd() {}

src/emitterutils.cpp

@@ -134,12 +134,12 @@ void WriteCodePoint(ostream_wrapper& out, int codePoint) {
   if (codePoint < 0 || codePoint > 0x10FFFF) {
     codePoint = REPLACEMENT_CHARACTER;
   }
-  if (codePoint < 0x7F) {
+  if (codePoint <= 0x7F) {
     out << static_cast<char>(codePoint);
-  } else if (codePoint < 0x7FF) {
+  } else if (codePoint <= 0x7FF) {
     out << static_cast<char>(0xC0 | (codePoint >> 6))
         << static_cast<char>(0x80 | (codePoint & 0x3F));
-  } else if (codePoint < 0xFFFF) {
+  } else if (codePoint <= 0xFFFF) {
     out << static_cast<char>(0xE0 | (codePoint >> 12))
         << static_cast<char>(0x80 | ((codePoint >> 6) & 0x3F))
         << static_cast<char>(0x80 | (codePoint & 0x3F));

src/exceptions.cpp

@@ -2,7 +2,7 @@
 
 // This is here for compatibility with older versions of Visual Studio
 // which don't support noexcept
-#ifdef _MSC_VER
+#if defined(_MSC_VER) && _MSC_VER < 1900
     #define YAML_CPP_NOEXCEPT _NOEXCEPT
 #else
     #define YAML_CPP_NOEXCEPT noexcept

src/node_data.cpp

@@ -197,7 +197,7 @@ void node_data::insert(node& key, node& value, shared_memory_holder pMemory) {
 // indexing
 node* node_data::get(node& key, shared_memory_holder /* pMemory */) const {
   if (m_type != NodeType::Map) {
-    return NULL;
+    return nullptr;
   }
 
   for (node_map::const_iterator it = m_map.begin(); it != m_map.end(); ++it) {
@@ -205,7 +205,7 @@ node* node_data::get(node& key, shared_memory_holder /* pMemory */) const {
       return it->second;
   }
 
-  return NULL;
+  return nullptr;
 }
 
 node& node_data::get(node& key, shared_memory_holder pMemory) {
@@ -235,6 +235,14 @@ bool node_data::remove(node& key, shared_memory_holder /* pMemory */) {
   if (m_type != NodeType::Map)
     return false;
 
+  kv_pairs::iterator it = m_undefinedPairs.begin();
+  while (it != m_undefinedPairs.end()) {
+    kv_pairs::iterator jt = std::next(it);
+    if (it->first->is(key))
+      m_undefinedPairs.erase(it);
+    it = jt;
+  }
+
   for (node_map::iterator it = m_map.begin(); it != m_map.end(); ++it) {
     if (it->first->is(key)) {
       m_map.erase(it);

src/nodebuilder.cpp

@@ -11,8 +11,8 @@ namespace YAML {
 struct Mark;
 
 NodeBuilder::NodeBuilder()
-    : m_pMemory(new detail::memory_holder), m_pRoot(0), m_mapDepth(0) {
-  m_anchors.push_back(0);  // since the anchors start at 1
+    : m_pMemory(new detail::memory_holder), m_pRoot(nullptr), m_mapDepth(0) {
+  m_anchors.push_back(nullptr);  // since the anchors start at 1
 }
 
 NodeBuilder::~NodeBuilder() {}

src/ostream_wrapper.cpp

@@ -7,7 +7,7 @@
 namespace YAML {
 ostream_wrapper::ostream_wrapper()
     : m_buffer(1, '\0'),
-      m_pStream(0),
+      m_pStream(nullptr),
       m_pos(0),
       m_row(0),
       m_col(0),

src/scanner.cpp

@@ -282,7 +282,7 @@ Scanner::IndentMarker* Scanner::PushIndentTo(int column,
                                              IndentMarker::INDENT_TYPE type) {
   // are we in flow?
   if (InFlowContext()) {
-    return 0;
+    return nullptr;
   }
 
   std::unique_ptr<IndentMarker> pIndent(new IndentMarker(column, type));
@@ -291,12 +291,12 @@ Scanner::IndentMarker* Scanner::PushIndentTo(int column,
 
   // is this actually an indentation?
   if (indent.column < lastIndent.column) {
-    return 0;
+    return nullptr;
   }
   if (indent.column == lastIndent.column &&
       !(indent.type == IndentMarker::SEQ &&
         lastIndent.type == IndentMarker::MAP)) {
-    return 0;
+    return nullptr;
   }
 
   // push a start token

src/scanner.h

@@ -49,7 +49,7 @@ class Scanner {
     enum INDENT_TYPE { MAP, SEQ, NONE };
     enum STATUS { VALID, INVALID, UNKNOWN };
     IndentMarker(int column_, INDENT_TYPE type_)
-        : column(column_), type(type_), status(VALID), pStartToken(0) {}
+        : column(column_), type(type_), status(VALID), pStartToken(nullptr) {}
 
     int column;
     INDENT_TYPE type;

src/simplekey.cpp

@@ -5,7 +5,7 @@ namespace YAML {
 struct Mark;
 
 Scanner::SimpleKey::SimpleKey(const Mark& mark_, std::size_t flowLevel_)
-    : mark(mark_), flowLevel(flowLevel_), pIndent(0), pMapStart(0), pKey(0) {}
+    : mark(mark_), flowLevel(flowLevel_), pIndent(nullptr), pMapStart(nullptr), pKey(nullptr) {}
 
 void Scanner::SimpleKey::Validate() {
   // Note: pIndent will *not* be garbage here;

test/CMakeLists.txt

@@ -30,6 +30,7 @@ file(GLOB test_new_api_sources new-api/[a-z]*.cpp)
 list(APPEND test_sources ${test_new_api_sources})
 add_sources(${test_sources} ${test_headers})
 
+include_directories(${YAML_CPP_SOURCE_DIR}/src)
 include_directories(${YAML_CPP_SOURCE_DIR}/test)
 
 add_executable(run-tests

test/integration/load_node_test.cpp

@@ -185,6 +185,39 @@ TEST(LoadNodeTest, DereferenceIteratorError) {
   EXPECT_THROW(node.begin()->begin()->Type(), InvalidNode);
 }
 
+#ifdef YAML_CPP_SUPPORT_MERGE_KEYS
+TEST(NodeTest, MergeKeyScalarSupport) {
+  Node node = Load("{<<: {a: 1}}");
+  ASSERT_FALSE(!node["a"]);
+  EXPECT_EQ(1, node["a"].as<int>());
+}
+
+TEST(NodeTest, MergeKeyExistingKey) {
+  Node node = Load("{a: 1, <<: {a: 2}}");
+  ASSERT_FALSE(!node["a"]);
+  EXPECT_EQ(1, node["a"].as<int>());
+}
+
+TEST(NodeTest, MergeKeySequenceSupport) {
+  Node node = Load("<<: [{a: 1}, {a: 2, b: 3}]");
+  ASSERT_FALSE(!node["a"]);
+  ASSERT_FALSE(!node["b"]);
+  EXPECT_EQ(1, node["a"].as<int>());
+  EXPECT_EQ(3, node["b"].as<int>());
+}
+
+TEST(NodeTest, NestedMergeKeys) {
+  Node node = Load("{<<: {<<: {a: 1}}}");
+  ASSERT_FALSE(!node["a"]);
+  EXPECT_EQ(1, node["a"].as<int>());
+}
+#else
+TEST(NodeTest, MergeKeySupport) {
+  Node node = Load("{<<: {a: 1}}");
+  ASSERT_FALSE(node["a"]);
+}
+#endif
+
 TEST(NodeTest, EmitEmptyNode) {
   Node node;
   Emitter emitter;