Add tests, reworked key_to_string function

include/yaml-cpp/node/impl.h

@@ -47,7 +47,7 @@ inline Node::Node(const Node& rhs)
 
 inline Node::Node(Zombie) : m_isValid(false), m_pNode(NULL) {}
 
-inline Node::Node(Zombie, std::string key)
+inline Node::Node(Zombie, const std::string& key)
     : m_isValid(false), m_invalidKey(key), m_pNode(NULL) {}
 
 inline Node::Node(detail::node& node, detail::shared_memory_holder pMemory)
@@ -374,15 +374,25 @@ inline typename to_value_t<T>::return_type to_value(const T& t) {
 }
 }
 
-template<typename Key>
-std::string key_to_string(const Key& key) {
-  std::stringstream ss;
-  if (is_streamable<std::stringstream, Key>::value) {
+template<typename Key, bool Streamable>
+struct key_to_string_impl {
+  static std::string impl(const Key& key) {
+    std::stringstream ss;
     ss << key;
     return ss.str();
-  } else {
+  }
+};
+
+template<typename Key>
+struct key_to_string_impl<Key, false> {
+  static std::string impl(const Key&) {
     return std::string();
   }
+};
+
+template<typename Key>
+std::string key_to_string(const Key& key) {
+  return key_to_string_impl<Key, is_streamable<std::stringstream, Key>::value>().impl(key);
 }
 
 // indexing

include/yaml-cpp/node/node.h

@@ -8,7 +8,6 @@
 #endif
 
 #include <stdexcept>
-#include <string>
 
 #include "yaml-cpp/dll.h"
 #include "yaml-cpp/emitterstyle.h"
@@ -117,7 +116,7 @@ class YAML_CPP_API Node {
  private:
   enum Zombie { ZombieNode };
   explicit Node(Zombie);
-  explicit Node(Zombie, std::string);
+  explicit Node(Zombie, const std::string&);
   explicit Node(detail::node& node, detail::shared_memory_holder pMemory);
 
   void EnsureNodeExists() const;
@@ -132,6 +131,7 @@ class YAML_CPP_API Node {
 
  private:
   bool m_isValid;
+  // string representation of invalid key, if the node is invalid
   std::string m_invalidKey;
   mutable detail::shared_memory_holder m_pMemory;
   mutable detail::node* m_pNode;

test/integration/error_messages_test.cpp

@@ -0,0 +1,54 @@
+#include "specexamples.h"
+#include "yaml-cpp/yaml.h"  // IWYU pragma: keep
+
+#include "gtest/gtest.h"
+
+#define EXPECT_THROW_EXCEPTION(exception_type, statement, message) \
+  ASSERT_THROW(statement, exception_type);                         \
+  try {                                                            \
+    statement;                                                     \
+  } catch (const exception_type& e) {                              \
+    EXPECT_EQ(e.msg, message);                                     \
+  }
+
+namespace YAML {
+namespace {
+
+TEST(ErrorMessageTest, Ex9_1_BadSubscriptErrorMessage) {
+  Node doc = Load(ex9_1);
+
+  // Test that printable key is part of error message
+  EXPECT_THROW_EXCEPTION(YAML::BadSubscript, doc["first"]["second"]["fourth"],
+                         "operator[] call on a scalar (key: 'fourth')");
+  
+  EXPECT_THROW_EXCEPTION(YAML::BadSubscript, doc["first"]["second"][37],
+                         "operator[] call on a scalar (key: '37')");
+
+
+  // Non-printable key is not included in error message
+  EXPECT_THROW_EXCEPTION(YAML::BadSubscript,
+                         doc["first"]["second"][std::vector<int>()],
+                         "operator[] call on a scalar");
+
+  EXPECT_THROW_EXCEPTION(YAML::BadSubscript, doc["first"]["second"][Node()],
+                         "operator[] call on a scalar");
+}
+
+TEST(ErrorMessageTest, Ex9_1_InvalidNodeErrorMessage) {
+  const Node doc = Load(ex9_1);
+
+  // Test that printable key is part of error message
+  EXPECT_THROW_EXCEPTION(YAML::InvalidNode, doc["first"]["fourth"].as<int>(),
+                         "invalid node - first invalid key: 'fourth'");
+  
+  EXPECT_THROW_EXCEPTION(YAML::InvalidNode, doc["first"][37].as<int>(),
+                         "invalid node - first invalid key: '37'");
+ 
+  // Non-printable key is not included in error message
+  EXPECT_THROW_EXCEPTION(YAML::InvalidNode,
+                         doc["first"][std::vector<int>()].as<int>(),
+                         "invalid node; this may result from using a map "
+                         "iterator as a sequence iterator, or vice-versa");
+}
+}   
+}

test/specexamples.h

@@ -843,4 +843,9 @@ const char *ex8_22 =
     " - nested\n"
     "mapping: !!map\n"
     " foo: bar\n";
+
+const char *ex9_1 =
+    "first:\n"
+    "   second: 1\n"
+    "   third: 2\n";
 }