planning

node_modules/graphql/validation/rules/UniqueFieldDefinitionNamesRule.js.flow

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+// @flow strict
+import { GraphQLError } from '../../error/GraphQLError';
+
+import type { ASTVisitor } from '../../language/visitor';
+import type {
+  NameNode,
+  FieldDefinitionNode,
+  InputValueDefinitionNode,
+} from '../../language/ast';
+
+import type { GraphQLNamedType } from '../../type/definition';
+import {
+  isObjectType,
+  isInterfaceType,
+  isInputObjectType,
+} from '../../type/definition';
+
+import type { SDLValidationContext } from '../ValidationContext';
+
+/**
+ * Unique field definition names
+ *
+ * A GraphQL complex type is only valid if all its fields are uniquely named.
+ */
+export function UniqueFieldDefinitionNamesRule(
+  context: SDLValidationContext,
+): ASTVisitor {
+  const schema = context.getSchema();
+  const existingTypeMap = schema ? schema.getTypeMap() : Object.create(null);
+  const knownFieldNames = Object.create(null);
+
+  return {
+    InputObjectTypeDefinition: checkFieldUniqueness,
+    InputObjectTypeExtension: checkFieldUniqueness,
+    InterfaceTypeDefinition: checkFieldUniqueness,
+    InterfaceTypeExtension: checkFieldUniqueness,
+    ObjectTypeDefinition: checkFieldUniqueness,
+    ObjectTypeExtension: checkFieldUniqueness,
+  };
+
+  function checkFieldUniqueness(node: {
+    +name: NameNode,
+    +fields?: $ReadOnlyArray<InputValueDefinitionNode | FieldDefinitionNode>,
+    ...
+  }) {
+    const typeName = node.name.value;
+
+    if (!knownFieldNames[typeName]) {
+      knownFieldNames[typeName] = Object.create(null);
+    }
+
+    // istanbul ignore next (See: 'https://github.com/graphql/graphql-js/issues/2203')
+    const fieldNodes = node.fields ?? [];
+    const fieldNames = knownFieldNames[typeName];
+
+    for (const fieldDef of fieldNodes) {
+      const fieldName = fieldDef.name.value;
+
+      if (hasField(existingTypeMap[typeName], fieldName)) {
+        context.reportError(
+          new GraphQLError(
+            `Field "${typeName}.${fieldName}" already exists in the schema. It cannot also be defined in this type extension.`,
+            fieldDef.name,
+          ),
+        );
+      } else if (fieldNames[fieldName]) {
+        context.reportError(
+          new GraphQLError(
+            `Field "${typeName}.${fieldName}" can only be defined once.`,
+            [fieldNames[fieldName], fieldDef.name],
+          ),
+        );
+      } else {
+        fieldNames[fieldName] = fieldDef.name;
+      }
+    }
+
+    return false;
+  }
+}
+
+function hasField(type: GraphQLNamedType, fieldName: string): boolean {
+  if (isObjectType(type) || isInterfaceType(type) || isInputObjectType(type)) {
+    return type.getFields()[fieldName] != null;
+  }
+  return false;
+}