Check the node type for !<?> tag in case user manually specifies it

lib/js-yaml/loader.js

@@ -1393,13 +1393,19 @@ function composeNode(state, parentIndent, nodeContext, allowToSeek, allowCompact
 
   if (state.tag !== null && state.tag !== '!') {
     if (state.tag === '?') {
+      // Implicit resolving is not allowed for non-scalar types, and '?'
+      // non-specific tag is only automatically assigned to plain scalars.
+      //
+      // We only need to check kind conformity in case user explicitly assigns '?'
+      // tag, for example like this: "!<?> [0]"
+      //
+      if (state.result !== null && state.kind !== 'scalar') {
+        throwError(state, 'unacceptable node kind for !<?> tag; it should be "scalar", not "' + state.kind + '"');
+      }
+
       for (typeIndex = 0, typeQuantity = state.implicitTypes.length; typeIndex < typeQuantity; typeIndex += 1) {
         type = state.implicitTypes[typeIndex];
 
-        // Implicit resolving is not allowed for non-scalar types, and '?'
-        // non-specific tag is only assigned to plain scalars. So, it isn't
-        // needed to check for 'kind' conformity.
-
         if (type.resolve(state.result)) { // `state.result` updated in resolver if matched
           state.result = type.construct(state.result);
           state.tag = type.tag;

test/issues/0525-2.js

@@ -0,0 +1,16 @@
+'use strict';
+
+
+var assert = require('assert');
+var yaml   = require('../../');
+
+
+test('Should check kind type when resolving !<?> tag', function () {
+  try {
+    yaml.safeLoad('!<?> [0]');
+  } catch (err) {
+    assert(err.stack.startsWith('YAMLException: unacceptable node kind for !<?> tag'));
+    return;
+  }
+  assert.fail(null, null, 'Expected an error to be thrown');
+});