execute.mjs

import { forEach, isCollection } from 'iterall';
import inspect from '../jsutils/inspect';
import memoize3 from '../jsutils/memoize3';
import invariant from '../jsutils/invariant';
import devAssert from '../jsutils/devAssert';
import isInvalid from '../jsutils/isInvalid';
import isNullish from '../jsutils/isNullish';
import isPromise from '../jsutils/isPromise';
import isObjectLike from '../jsutils/isObjectLike';
import promiseReduce from '../jsutils/promiseReduce';
import promiseForObject from '../jsutils/promiseForObject';
import { addPath, pathToArray } from '../jsutils/Path';
import { GraphQLError } from '../error/GraphQLError';
import { locatedError } from '../error/locatedError';
import { Kind } from '../language/kinds';
import { assertValidSchema } from '../type/validate';
import { SchemaMetaFieldDef, TypeMetaFieldDef, TypeNameMetaFieldDef } from '../type/introspection';
import { GraphQLIncludeDirective, GraphQLSkipDirective } from '../type/directives';
import { isObjectType, isAbstractType, isLeafType, isListType, isNonNullType } from '../type/definition';
import { typeFromAST } from '../utilities/typeFromAST';
import { getOperationRootType } from '../utilities/getOperationRootType';
import { getVariableValues, getArgumentValues, getDirectiveValues } from './values';
/**
 * Terminology
 *
 * "Definitions" are the generic name for top-level statements in the document.
 * Examples of this include:
 * 1) Operations (such as a query)
 * 2) Fragments
 *
 * "Operations" are a generic name for requests in the document.
 * Examples of this include:
 * 1) query,
 * 2) mutation
 *
 * "Selections" are the definitions that can appear legally and at
 * single level of the query. These include:
 * 1) field references e.g "a"
 * 2) fragment "spreads" e.g. "...c"
 * 3) inline fragment "spreads" e.g. "...on Type { a }"
 */

/**
 * Data that must be available at all points during query execution.
 *
 * Namely, schema of the type system that is currently executing,
 * and the fragments defined in the query document
 */

export function execute(argsOrSchema, document, rootValue, contextValue, variableValues, operationName, fieldResolver, typeResolver) {
  /* eslint-enable no-redeclare */
  // Extract arguments from object args if provided.
  return arguments.length === 1 ? executeImpl(argsOrSchema) : executeImpl({
    schema: argsOrSchema,
    document: document,
    rootValue: rootValue,
    contextValue: contextValue,
    variableValues: variableValues,
    operationName: operationName,
    fieldResolver: fieldResolver,
    typeResolver: typeResolver
  });
}

function executeImpl(args) {
  var schema = args.schema,
      document = args.document,
      rootValue = args.rootValue,
      contextValue = args.contextValue,
      variableValues = args.variableValues,
      operationName = args.operationName,
      fieldResolver = args.fieldResolver,
      typeResolver = args.typeResolver; // If arguments are missing or incorrect, throw an error.

  assertValidExecutionArguments(schema, document, variableValues); // If a valid execution context cannot be created due to incorrect arguments,
  // a "Response" with only errors is returned.

  var exeContext = buildExecutionContext(schema, document, rootValue, contextValue, variableValues, operationName, fieldResolver, typeResolver); // Return early errors if execution context failed.

  if (Array.isArray(exeContext)) {
    return {
      errors: exeContext
    };
  } // Return a Promise that will eventually resolve to the data described by
  // The "Response" section of the GraphQL specification.
  //
  // If errors are encountered while executing a GraphQL field, only that
  // field and its descendants will be omitted, and sibling fields will still
  // be executed. An execution which encounters errors will still result in a
  // resolved Promise.


  var data = executeOperation(exeContext, exeContext.operation, rootValue);
  return buildResponse(exeContext, data);
}
/**
 * Given a completed execution context and data, build the { errors, data }
 * response defined by the "Response" section of the GraphQL specification.
 */


function buildResponse(exeContext, data) {
  if (isPromise(data)) {
    return data.then(function (resolved) {
      return buildResponse(exeContext, resolved);
    });
  }

  return exeContext.errors.length === 0 ? {
    data: data
  } : {
    errors: exeContext.errors,
    data: data
  };
}
/**
 * Essential assertions before executing to provide developer feedback for
 * improper use of the GraphQL library.
 */


export function assertValidExecutionArguments(schema, document, rawVariableValues) {
  document || devAssert(0, 'Must provide document'); // If the schema used for execution is invalid, throw an error.

  assertValidSchema(schema); // Variables, if provided, must be an object.

  rawVariableValues == null || isObjectLike(rawVariableValues) || devAssert(0, 'Variables must be provided as an Object where each property is a variable value. Perhaps look to see if an unparsed JSON string was provided.');
}
/**
 * Constructs a ExecutionContext object from the arguments passed to
 * execute, which we will pass throughout the other execution methods.
 *
 * Throws a GraphQLError if a valid execution context cannot be created.
 */

export function buildExecutionContext(schema, document, rootValue, contextValue, rawVariableValues, operationName, fieldResolver, typeResolver) {
  var operation;
  var hasMultipleAssumedOperations = false;
  var fragments = Object.create(null);

  for (var _i2 = 0, _document$definitions2 = document.definitions; _i2 < _document$definitions2.length; _i2++) {
    var definition = _document$definitions2[_i2];

    switch (definition.kind) {
      case Kind.OPERATION_DEFINITION:
        if (!operationName && operation) {
          hasMultipleAssumedOperations = true;
        } else if (!operationName || definition.name && definition.name.value === operationName) {
          operation = definition;
        }

        break;

      case Kind.FRAGMENT_DEFINITION:
        fragments[definition.name.value] = definition;
        break;
    }
  }

  if (!operation) {
    if (operationName) {
      return [new GraphQLError("Unknown operation named \"".concat(operationName, "\"."))];
    }

    return [new GraphQLError('Must provide an operation.')];
  }

  if (hasMultipleAssumedOperations) {
    return [new GraphQLError('Must provide operation name if query contains multiple operations.')];
  }

  var coercedVariableValues = getVariableValues(schema, operation.variableDefinitions || [], rawVariableValues || {}, {
    maxErrors: 50
  });

  if (coercedVariableValues.errors) {
    return coercedVariableValues.errors;
  }

  return {
    schema: schema,
    fragments: fragments,
    rootValue: rootValue,
    contextValue: contextValue,
    operation: operation,
    variableValues: coercedVariableValues.coerced,
    fieldResolver: fieldResolver || defaultFieldResolver,
    typeResolver: typeResolver || defaultTypeResolver,
    errors: []
  };
}
/**
 * Implements the "Evaluating operations" section of the spec.
 */

function executeOperation(exeContext, operation, rootValue) {
  var type = getOperationRootType(exeContext.schema, operation);
  var fields = collectFields(exeContext, type, operation.selectionSet, Object.create(null), Object.create(null));
  var path = undefined; // Errors from sub-fields of a NonNull type may propagate to the top level,
  // at which point we still log the error and null the parent field, which
  // in this case is the entire response.
  //
  // Similar to completeValueCatchingError.

  try {
    var result = operation.operation === 'mutation' ? executeFieldsSerially(exeContext, type, rootValue, path, fields) : executeFields(exeContext, type, rootValue, path, fields);

    if (isPromise(result)) {
      return result.then(undefined, function (error) {
        exeContext.errors.push(error);
        return Promise.resolve(null);
      });
    }

    return result;
  } catch (error) {
    exeContext.errors.push(error);
    return null;
  }
}
/**
 * Implements the "Evaluating selection sets" section of the spec
 * for "write" mode.
 */


function executeFieldsSerially(exeContext, parentType, sourceValue, path, fields) {
  return promiseReduce(Object.keys(fields), function (results, responseName) {
    var fieldNodes = fields[responseName];
    var fieldPath = addPath(path, responseName);
    var result = resolveField(exeContext, parentType, sourceValue, fieldNodes, fieldPath);

    if (result === undefined) {
      return results;
    }

    if (isPromise(result)) {
      return result.then(function (resolvedResult) {
        results[responseName] = resolvedResult;
        return results;
      });
    }

    results[responseName] = result;
    return results;
  }, Object.create(null));
}
/**
 * Implements the "Evaluating selection sets" section of the spec
 * for "read" mode.
 */


function executeFields(exeContext, parentType, sourceValue, path, fields) {
  var results = Object.create(null);
  var containsPromise = false;

  for (var _i4 = 0, _Object$keys2 = Object.keys(fields); _i4 < _Object$keys2.length; _i4++) {
    var responseName = _Object$keys2[_i4];
    var fieldNodes = fields[responseName];
    var fieldPath = addPath(path, responseName);
    var result = resolveField(exeContext, parentType, sourceValue, fieldNodes, fieldPath);

    if (result !== undefined) {
      results[responseName] = result;

      if (!containsPromise && isPromise(result)) {
        containsPromise = true;
      }
    }
  } // If there are no promises, we can just return the object


  if (!containsPromise) {
    return results;
  } // Otherwise, results is a map from field name to the result of resolving that
  // field, which is possibly a promise. Return a promise that will return this
  // same map, but with any promises replaced with the values they resolved to.


  return promiseForObject(results);
}
/**
 * Given a selectionSet, adds all of the fields in that selection to
 * the passed in map of fields, and returns it at the end.
 *
 * CollectFields requires the "runtime type" of an object. For a field which
 * returns an Interface or Union type, the "runtime type" will be the actual
 * Object type returned by that field.
 */


export function collectFields(exeContext, runtimeType, selectionSet, fields, visitedFragmentNames) {
  for (var _i6 = 0, _selectionSet$selecti2 = selectionSet.selections; _i6 < _selectionSet$selecti2.length; _i6++) {
    var selection = _selectionSet$selecti2[_i6];

    switch (selection.kind) {
      case Kind.FIELD:
        {
          if (!shouldIncludeNode(exeContext, selection)) {
            continue;
          }

          var name = getFieldEntryKey(selection);

          if (!fields[name]) {
            fields[name] = [];
          }

          fields[name].push(selection);
          break;
        }

      case Kind.INLINE_FRAGMENT:
        {
          if (!shouldIncludeNode(exeContext, selection) || !doesFragmentConditionMatch(exeContext, selection, runtimeType)) {
            continue;
          }

          collectFields(exeContext, runtimeType, selection.selectionSet, fields, visitedFragmentNames);
          break;
        }

      case Kind.FRAGMENT_SPREAD:
        {
          var fragName = selection.name.value;

          if (visitedFragmentNames[fragName] || !shouldIncludeNode(exeContext, selection)) {
            continue;
          }

          visitedFragmentNames[fragName] = true;
          var fragment = exeContext.fragments[fragName];

          if (!fragment || !doesFragmentConditionMatch(exeContext, fragment, runtimeType)) {
            continue;
          }

          collectFields(exeContext, runtimeType, fragment.selectionSet, fields, visitedFragmentNames);
          break;
        }
    }
  }

  return fields;
}
/**
 * Determines if a field should be included based on the @include and @skip
 * directives, where @skip has higher precedence than @include.
 */

function shouldIncludeNode(exeContext, node) {
  var skip = getDirectiveValues(GraphQLSkipDirective, node, exeContext.variableValues);

  if (skip && skip.if === true) {
    return false;
  }

  var include = getDirectiveValues(GraphQLIncludeDirective, node, exeContext.variableValues);

  if (include && include.if === false) {
    return false;
  }

  return true;
}
/**
 * Determines if a fragment is applicable to the given type.
 */


function doesFragmentConditionMatch(exeContext, fragment, type) {
  var typeConditionNode = fragment.typeCondition;

  if (!typeConditionNode) {
    return true;
  }

  var conditionalType = typeFromAST(exeContext.schema, typeConditionNode);

  if (conditionalType === type) {
    return true;
  }

  if (isAbstractType(conditionalType)) {
    return exeContext.schema.isPossibleType(conditionalType, type);
  }

  return false;
}
/**
 * Implements the logic to compute the key of a given field's entry
 */


function getFieldEntryKey(node) {
  return node.alias ? node.alias.value : node.name.value;
}
/**
 * Resolves the field on the given source object. In particular, this
 * figures out the value that the field returns by calling its resolve function,
 * then calls completeValue to complete promises, serialize scalars, or execute
 * the sub-selection-set for objects.
 */


function resolveField(exeContext, parentType, source, fieldNodes, path) {
  var fieldNode = fieldNodes[0];
  var fieldName = fieldNode.name.value;
  var fieldDef = getFieldDef(exeContext.schema, parentType, fieldName);

  if (!fieldDef) {
    return;
  }

  var resolveFn = fieldDef.resolve || exeContext.fieldResolver;
  var info = buildResolveInfo(exeContext, fieldDef, fieldNodes, parentType, path); // Get the resolve function, regardless of if its result is normal
  // or abrupt (error).

  var result = resolveFieldValueOrError(exeContext, fieldDef, fieldNodes, resolveFn, source, info);
  return completeValueCatchingError(exeContext, fieldDef.type, fieldNodes, info, path, result);
}

export function buildResolveInfo(exeContext, fieldDef, fieldNodes, parentType, path) {
  // The resolve function's optional fourth argument is a collection of
  // information about the current execution state.
  return {
    fieldName: fieldDef.name,
    fieldNodes: fieldNodes,
    returnType: fieldDef.type,
    parentType: parentType,
    path: path,
    schema: exeContext.schema,
    fragments: exeContext.fragments,
    rootValue: exeContext.rootValue,
    operation: exeContext.operation,
    variableValues: exeContext.variableValues
  };
} // Isolates the "ReturnOrAbrupt" behavior to not de-opt the `resolveField`
// function. Returns the result of resolveFn or the abrupt-return Error object.

export function resolveFieldValueOrError(exeContext, fieldDef, fieldNodes, resolveFn, source, info) {
  try {
    // Build a JS object of arguments from the field.arguments AST, using the
    // variables scope to fulfill any variable references.
    // TODO: find a way to memoize, in case this field is within a List type.
    var args = getArgumentValues(fieldDef, fieldNodes[0], exeContext.variableValues); // The resolve function's optional third argument is a context value that
    // is provided to every resolve function within an execution. It is commonly
    // used to represent an authenticated user, or request-specific caches.

    var _contextValue = exeContext.contextValue;
    var result = resolveFn(source, args, _contextValue, info);
    return isPromise(result) ? result.then(undefined, asErrorInstance) : result;
  } catch (error) {
    return asErrorInstance(error);
  }
} // Sometimes a non-error is thrown, wrap it as an Error instance to ensure a
// consistent Error interface.

function asErrorInstance(error) {
  if (error instanceof Error) {
    return error;
  }

  return new Error('Unexpected error value: ' + inspect(error));
} // This is a small wrapper around completeValue which detects and logs errors
// in the execution context.


function completeValueCatchingError(exeContext, returnType, fieldNodes, info, path, result) {
  try {
    var completed;

    if (isPromise(result)) {
      completed = result.then(function (resolved) {
        return completeValue(exeContext, returnType, fieldNodes, info, path, resolved);
      });
    } else {
      completed = completeValue(exeContext, returnType, fieldNodes, info, path, result);
    }

    if (isPromise(completed)) {
      // Note: we don't rely on a `catch` method, but we do expect "thenable"
      // to take a second callback for the error case.
      return completed.then(undefined, function (error) {
        return handleFieldError(error, fieldNodes, path, returnType, exeContext);
      });
    }

    return completed;
  } catch (error) {
    return handleFieldError(error, fieldNodes, path, returnType, exeContext);
  }
}

function handleFieldError(rawError, fieldNodes, path, returnType, exeContext) {
  var error = locatedError(asErrorInstance(rawError), fieldNodes, pathToArray(path)); // If the field type is non-nullable, then it is resolved without any
  // protection from errors, however it still properly locates the error.

  if (isNonNullType(returnType)) {
    throw error;
  } // Otherwise, error protection is applied, logging the error and resolving
  // a null value for this field if one is encountered.


  exeContext.errors.push(error);
  return null;
}
/**
 * Implements the instructions for completeValue as defined in the
 * "Field entries" section of the spec.
 *
 * If the field type is Non-Null, then this recursively completes the value
 * for the inner type. It throws a field error if that completion returns null,
 * as per the "Nullability" section of the spec.
 *
 * If the field type is a List, then this recursively completes the value
 * for the inner type on each item in the list.
 *
 * If the field type is a Scalar or Enum, ensures the completed value is a legal
 * value of the type by calling the `serialize` method of GraphQL type
 * definition.
 *
 * If the field is an abstract type, determine the runtime type of the value
 * and then complete based on that type
 *
 * Otherwise, the field type expects a sub-selection set, and will complete the
 * value by evaluating all sub-selections.
 */


function completeValue(exeContext, returnType, fieldNodes, info, path, result) {
  // If result is an Error, throw a located error.
  if (result instanceof Error) {
    throw result;
  } // If field type is NonNull, complete for inner type, and throw field error
  // if result is null.


  if (isNonNullType(returnType)) {
    var completed = completeValue(exeContext, returnType.ofType, fieldNodes, info, path, result);

    if (completed === null) {
      throw new Error("Cannot return null for non-nullable field ".concat(info.parentType.name, ".").concat(info.fieldName, "."));
    }

    return completed;
  } // If result value is null-ish (null, undefined, or NaN) then return null.


  if (isNullish(result)) {
    return null;
  } // If field type is List, complete each item in the list with the inner type


  if (isListType(returnType)) {
    return completeListValue(exeContext, returnType, fieldNodes, info, path, result);
  } // If field type is a leaf type, Scalar or Enum, serialize to a valid value,
  // returning null if serialization is not possible.


  if (isLeafType(returnType)) {
    return completeLeafValue(returnType, result);
  } // If field type is an abstract type, Interface or Union, determine the
  // runtime Object type and complete for that type.


  if (isAbstractType(returnType)) {
    return completeAbstractValue(exeContext, returnType, fieldNodes, info, path, result);
  } // If field type is Object, execute and complete all sub-selections.


  /* istanbul ignore else */
  if (isObjectType(returnType)) {
    return completeObjectValue(exeContext, returnType, fieldNodes, info, path, result);
  } // Not reachable. All possible output types have been considered.


  /* istanbul ignore next */
  invariant(false, 'Cannot complete value of unexpected output type: ' + inspect(returnType));
}
/**
 * Complete a list value by completing each item in the list with the
 * inner type
 */


function completeListValue(exeContext, returnType, fieldNodes, info, path, result) {
  if (!isCollection(result)) {
    throw new GraphQLError("Expected Iterable, but did not find one for field ".concat(info.parentType.name, ".").concat(info.fieldName, "."));
  } // This is specified as a simple map, however we're optimizing the path
  // where the list contains no Promises by avoiding creating another Promise.


  var itemType = returnType.ofType;
  var containsPromise = false;
  var completedResults = [];
  forEach(result, function (item, index) {
    // No need to modify the info object containing the path,
    // since from here on it is not ever accessed by resolver functions.
    var fieldPath = addPath(path, index);
    var completedItem = completeValueCatchingError(exeContext, itemType, fieldNodes, info, fieldPath, item);

    if (!containsPromise && isPromise(completedItem)) {
      containsPromise = true;
    }

    completedResults.push(completedItem);
  });
  return containsPromise ? Promise.all(completedResults) : completedResults;
}
/**
 * Complete a Scalar or Enum by serializing to a valid value, returning
 * null if serialization is not possible.
 */


function completeLeafValue(returnType, result) {
  var serializedResult = returnType.serialize(result);

  if (isInvalid(serializedResult)) {
    throw new Error("Expected a value of type \"".concat(inspect(returnType), "\" but ") + "received: ".concat(inspect(result)));
  }

  return serializedResult;
}
/**
 * Complete a value of an abstract type by determining the runtime object type
 * of that value, then complete the value for that type.
 */


function completeAbstractValue(exeContext, returnType, fieldNodes, info, path, result) {
  var resolveTypeFn = returnType.resolveType || exeContext.typeResolver;
  var contextValue = exeContext.contextValue;
  var runtimeType = resolveTypeFn(result, contextValue, info, returnType);

  if (isPromise(runtimeType)) {
    return runtimeType.then(function (resolvedRuntimeType) {
      return completeObjectValue(exeContext, ensureValidRuntimeType(resolvedRuntimeType, exeContext, returnType, fieldNodes, info, result), fieldNodes, info, path, result);
    });
  }

  return completeObjectValue(exeContext, ensureValidRuntimeType(runtimeType, exeContext, returnType, fieldNodes, info, result), fieldNodes, info, path, result);
}

function ensureValidRuntimeType(runtimeTypeOrName, exeContext, returnType, fieldNodes, info, result) {
  var runtimeType = typeof runtimeTypeOrName === 'string' ? exeContext.schema.getType(runtimeTypeOrName) : runtimeTypeOrName;

  if (!isObjectType(runtimeType)) {
    throw new GraphQLError("Abstract type ".concat(returnType.name, " must resolve to an Object type at runtime for field ").concat(info.parentType.name, ".").concat(info.fieldName, " with ") + "value ".concat(inspect(result), ", received \"").concat(inspect(runtimeType), "\". ") + "Either the ".concat(returnType.name, " type should provide a \"resolveType\" function or each possible type should provide an \"isTypeOf\" function."), fieldNodes);
  }

  if (!exeContext.schema.isPossibleType(returnType, runtimeType)) {
    throw new GraphQLError("Runtime Object type \"".concat(runtimeType.name, "\" is not a possible type for \"").concat(returnType.name, "\"."), fieldNodes);
  }

  return runtimeType;
}
/**
 * Complete an Object value by executing all sub-selections.
 */


function completeObjectValue(exeContext, returnType, fieldNodes, info, path, result) {
  // If there is an isTypeOf predicate function, call it with the
  // current result. If isTypeOf returns false, then raise an error rather
  // than continuing execution.
  if (returnType.isTypeOf) {
    var isTypeOf = returnType.isTypeOf(result, exeContext.contextValue, info);

    if (isPromise(isTypeOf)) {
      return isTypeOf.then(function (resolvedIsTypeOf) {
        if (!resolvedIsTypeOf) {
          throw invalidReturnTypeError(returnType, result, fieldNodes);
        }

        return collectAndExecuteSubfields(exeContext, returnType, fieldNodes, path, result);
      });
    }

    if (!isTypeOf) {
      throw invalidReturnTypeError(returnType, result, fieldNodes);
    }
  }

  return collectAndExecuteSubfields(exeContext, returnType, fieldNodes, path, result);
}

function invalidReturnTypeError(returnType, result, fieldNodes) {
  return new GraphQLError("Expected value of type \"".concat(returnType.name, "\" but got: ").concat(inspect(result), "."), fieldNodes);
}

function collectAndExecuteSubfields(exeContext, returnType, fieldNodes, path, result) {
  // Collect sub-fields to execute to complete this value.
  var subFieldNodes = collectSubfields(exeContext, returnType, fieldNodes);
  return executeFields(exeContext, returnType, result, path, subFieldNodes);
}
/**
 * A memoized collection of relevant subfields with regard to the return
 * type. Memoizing ensures the subfields are not repeatedly calculated, which
 * saves overhead when resolving lists of values.
 */


var collectSubfields = memoize3(_collectSubfields);

function _collectSubfields(exeContext, returnType, fieldNodes) {
  var subFieldNodes = Object.create(null);
  var visitedFragmentNames = Object.create(null);

  for (var _i8 = 0; _i8 < fieldNodes.length; _i8++) {
    var node = fieldNodes[_i8];

    if (node.selectionSet) {
      subFieldNodes = collectFields(exeContext, returnType, node.selectionSet, subFieldNodes, visitedFragmentNames);
    }
  }

  return subFieldNodes;
}
/**
 * If a resolveType function is not given, then a default resolve behavior is
 * used which attempts two strategies:
 *
 * First, See if the provided value has a `__typename` field defined, if so, use
 * that value as name of the resolved type.
 *
 * Otherwise, test each possible type for the abstract type by calling
 * isTypeOf for the object being coerced, returning the first type that matches.
 */


export var defaultTypeResolver = function defaultTypeResolver(value, contextValue, info, abstractType) {
  // First, look for `__typename`.
  if (isObjectLike(value) && typeof value.__typename === 'string') {
    return value.__typename;
  } // Otherwise, test each possible type.


  var possibleTypes = info.schema.getPossibleTypes(abstractType);
  var promisedIsTypeOfResults = [];

  for (var i = 0; i < possibleTypes.length; i++) {
    var type = possibleTypes[i];

    if (type.isTypeOf) {
      var isTypeOfResult = type.isTypeOf(value, contextValue, info);

      if (isPromise(isTypeOfResult)) {
        promisedIsTypeOfResults[i] = isTypeOfResult;
      } else if (isTypeOfResult) {
        return type;
      }
    }
  }

  if (promisedIsTypeOfResults.length) {
    return Promise.all(promisedIsTypeOfResults).then(function (isTypeOfResults) {
      for (var _i9 = 0; _i9 < isTypeOfResults.length; _i9++) {
        if (isTypeOfResults[_i9]) {
          return possibleTypes[_i9];
        }
      }
    });
  }
};
/**
 * If a resolve function is not given, then a default resolve behavior is used
 * which takes the property of the source object of the same name as the field
 * and returns it as the result, or if it's a function, returns the result
 * of calling that function while passing along args and context value.
 */

export var defaultFieldResolver = function defaultFieldResolver(source, args, contextValue, info) {
  // ensure source is a value for which property access is acceptable.
  if (isObjectLike(source) || typeof source === 'function') {
    var property = source[info.fieldName];

    if (typeof property === 'function') {
      return source[info.fieldName](args, contextValue, info);
    }

    return property;
  }
};
/**
 * This method looks up the field on the given type definition.
 * It has special casing for the two introspection fields, __schema
 * and __typename. __typename is special because it can always be
 * queried as a field, even in situations where no other fields
 * are allowed, like on a Union. __schema could get automatically
 * added to the query type, but that would require mutating type
 * definitions, which would cause issues.
 */

export function getFieldDef(schema, parentType, fieldName) {
  if (fieldName === SchemaMetaFieldDef.name && schema.getQueryType() === parentType) {
    return SchemaMetaFieldDef;
  } else if (fieldName === TypeMetaFieldDef.name && schema.getQueryType() === parentType) {
    return TypeMetaFieldDef;
  } else if (fieldName === TypeNameMetaFieldDef.name) {
    return TypeNameMetaFieldDef;
  }

  return parentType.getFields()[fieldName];
}