Implement KnownDirectives validation rule

Author: dittos

graphql/core/validation/rules.py

@@ -176,7 +176,42 @@ class NoUnusedVariables(ValidationRule):
 
 
 class KnownDirectives(ValidationRule):
-    pass
+    def enter_Directive(self, node, key, parent, path, ancestors):
+        directive_def = None
+        for definition in self.context.get_schema().get_directives():
+            if definition.name == node.name.value:
+                directive_def = definition
+                break
+        if not directive_def:
+            return GraphQLError(
+                self.message(node.name.value),
+                [node]
+            )
+        applied_to = ancestors[-1]
+        if isinstance(applied_to, ast.OperationDefinition) and not directive_def.on_operation:
+            return GraphQLError(
+                self.misplaced_directive_message(node.name.value, 'operation'),
+                [node]
+            )
+        if isinstance(applied_to, ast.Field) and not directive_def.on_field:
+            return GraphQLError(
+                self.misplaced_directive_message(node.name.value, 'field'),
+                [node]
+            )
+        if (isinstance(applied_to, (ast.FragmentSpread, ast.InlineFragment, ast.FragmentDefinition)) and
+                not directive_def.on_fragment):
+            return GraphQLError(
+                self.misplaced_directive_message(node.name.value, 'fragment'),
+                [node]
+            )
+
+    @staticmethod
+    def message(directive_name):
+        return 'Unknown directive "{}".'.format(directive_name)
+
+    @staticmethod
+    def misplaced_directive_message(directive_name, placement):
+        return 'Directive "{}" may not be used on "{}".'.format(directive_name, placement)
 
 
 class KnownArgumentNames(ValidationRule):

tests/core_validation/test_known_directives.py

@@ -1,5 +1,3 @@
-import pytest
-
 from graphql.core.language.location import SourceLocation
 from graphql.core.validation.rules import KnownDirectives
 from utils import expect_passes_rule, expect_fails_rule
@@ -46,9 +44,6 @@ def test_with_known_directives():
     ''')
 
 
-@pytest.mark.skipif(not hasattr(KnownDirectives, "message"),
-                    reason=("KnownDirectives.message has not yet been "
-                            "implemented"))
 def test_with_unknown_directive():
     expect_fails_rule(KnownDirectives, '''
       {
@@ -59,9 +54,6 @@ def test_with_unknown_directive():
     ''', [unknown_directive('unknown', 3, 13)])
 
 
-@pytest.mark.skipif(not hasattr(KnownDirectives, "message"),
-                    reason=("KnownDirectives.message has not yet been "
-                            "implemented"))
 def test_with_many_unknown_directives():
     expect_fails_rule(KnownDirectives, '''
       {
@@ -91,10 +83,6 @@ def test_with_well_placed_directives():
     ''')
 
 
-@pytest.mark.skipif(not hasattr(KnownDirectives,
-                                "misplaced_directive_message"),
-                    reason=("KnownDirectives.misplaced_directive_message has "
-                            "not yet been implemented"))
 def test_with_misplaced_directives():
     expect_fails_rule(KnownDirectives, '''
       query Foo @include(if: true) {