Implement NoUnusedFragments

 - unit tests as well.

 #6

Author: jhgg

graphql/core/validation/rules.py

@@ -171,7 +171,55 @@ class KnownFragmentNames(ValidationRule):
 
 
 class NoUnusedFragments(ValidationRule):
-    pass
+    def __init__(self, context):
+        super(NoUnusedFragments, self).__init__(context)
+        self.fragment_definitions = []
+        self.spreads_within_operation = []
+        self.fragment_adjacencies = {}
+        self.spread_names = set()
+
+    def enter_OperationDefinition(self, *args):
+        self.spread_names = set()
+        self.spreads_within_operation.append(self.spread_names)
+
+    def enter_FragmentDefinition(self, node, *args):
+        self.fragment_definitions.append(node)
+        self.spread_names = set()
+        self.fragment_adjacencies[node.name.value] = self.spread_names
+
+    def enter_FragmentSpread(self, node, *args):
+        self.spread_names.add(node.name.value)
+
+    def leave_Document(self, *args):
+        fragment_names_used = set()
+
+        def reduce_spread_fragments(spreads):
+            for fragment_name in spreads:
+                if fragment_name in fragment_names_used:
+                    continue
+
+                fragment_names_used.add(fragment_name)
+                if fragment_name in self.fragment_adjacencies:
+                    reduce_spread_fragments(self.fragment_adjacencies[fragment_name])
+
+        for spreads in self.spreads_within_operation:
+            reduce_spread_fragments(spreads)
+
+        errors = [
+            GraphQLError(
+                self.unused_fragment_message(fragment_definition.name.value),
+                [fragment_definition]
+            )
+            for fragment_definition in self.fragment_definitions
+            if fragment_definition.name.value not in fragment_names_used
+        ]
+
+        if errors:
+            return errors
+
+    @staticmethod
+    def unused_fragment_message(fragment_name):
+        return 'Fragment "{}" is never used.'.format(fragment_name)
 
 
 class PossibleFragmentSpreads(ValidationRule):

tests/core_validation/test_no_unused_fragments.py

@@ -0,0 +1,143 @@
+from graphql.core.language.location import SourceLocation
+from graphql.core.validation.rules import NoUnusedFragments
+from utils import expect_passes_rule, expect_fails_rule
+
+
+def unused_fragment(fragment_name, line, column):
+    return {
+        'message': NoUnusedFragments.unused_fragment_message(fragment_name),
+        'locations': [SourceLocation(line, column)]
+    }
+
+
+def test_all_fragment_names_are_used():
+    expect_passes_rule(NoUnusedFragments, '''
+      {
+        human(id: 4) {
+          ...HumanFields1
+          ... on Human {
+            ...HumanFields2
+          }
+        }
+      }
+      fragment HumanFields1 on Human {
+        name
+        ...HumanFields3
+      }
+      fragment HumanFields2 on Human {
+        name
+      }
+      fragment HumanFields3 on Human {
+        name
+      }
+    ''')
+
+
+def test_all_fragment_names_are_used_by_multiple_operations():
+    expect_passes_rule(NoUnusedFragments, '''
+      query Foo {
+        human(id: 4) {
+          ...HumanFields1
+        }
+      }
+      query Bar {
+        human(id: 4) {
+          ...HumanFields2
+        }
+      }
+      fragment HumanFields1 on Human {
+        name
+        ...HumanFields3
+      }
+      fragment HumanFields2 on Human {
+        name
+      }
+      fragment HumanFields3 on Human {
+        name
+      }
+   ''')
+
+
+def test_contains_unknown_fragments():
+    expect_fails_rule(NoUnusedFragments, '''
+      query Foo {
+        human(id: 4) {
+          ...HumanFields1
+        }
+      }
+      query Bar {
+        human(id: 4) {
+          ...HumanFields2
+        }
+      }
+      fragment HumanFields1 on Human {
+        name
+        ...HumanFields3
+      }
+      fragment HumanFields2 on Human {
+        name
+      }
+      fragment HumanFields3 on Human {
+        name
+      }
+      fragment Unused1 on Human {
+        name
+      }
+      fragment Unused2 on Human {
+        name
+      }
+    ''', [
+        unused_fragment('Unused1', 22, 7),
+        unused_fragment('Unused2', 25, 7),
+    ])
+
+
+def test_contains_unknown_fragments_with_ref_cycle():
+    expect_fails_rule(NoUnusedFragments, '''
+      query Foo {
+        human(id: 4) {
+          ...HumanFields1
+        }
+      }
+      query Bar {
+        human(id: 4) {
+          ...HumanFields2
+        }
+      }
+      fragment HumanFields1 on Human {
+        name
+        ...HumanFields3
+      }
+      fragment HumanFields2 on Human {
+        name
+      }
+      fragment HumanFields3 on Human {
+        name
+      }
+      fragment Unused1 on Human {
+        name
+        ...Unused2
+      }
+      fragment Unused2 on Human {
+        name
+        ...Unused1
+      }
+    ''', [
+        unused_fragment('Unused1', 22, 7),
+        unused_fragment('Unused2', 26, 7),
+    ])
+
+
+def test_contains_unknown_and_undefined_fragments():
+    expect_fails_rule(NoUnusedFragments, '''
+      query Foo {
+        human(id: 4) {
+          ...bar
+        }
+      }
+      fragment foo on Human {
+        name
+      }
+    ''', [
+        unused_fragment('foo', 7, 7)
+    ])