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RFC: More flow-friendly thenable checking. #699

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merged 1 commit into from
Jan 27, 2017
Merged

RFC: More flow-friendly thenable checking. #699

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56 changes: 31 additions & 25 deletions src/execution/execute.js
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Original file line number Diff line number Diff line change
Expand Up @@ -341,8 +341,9 @@ function executeFieldsSerially(
if (result === undefined) {
return results;
}
if (isThenable(result)) {
return ((result: any): Promise<*>).then(resolvedResult => {
const promise = getPromise(result);
if (promise) {
return promise.then(resolvedResult => {
results[responseName] = resolvedResult;
return results;
});
Expand Down Expand Up @@ -382,7 +383,7 @@ function executeFields(
return results;
}
results[responseName] = result;
if (isThenable(result)) {
if (getPromise(result)) {
containsPromise = true;
}
return results;
Expand Down Expand Up @@ -688,12 +689,13 @@ function completeValueCatchingError(
path,
result
);
if (isThenable(completed)) {
const promise = getPromise(completed);
if (promise) {
// If `completeValueWithLocatedError` returned a rejected promise, log
// the rejection error and resolve to null.
// 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: any): Promise<*>).then(undefined, error => {
return promise.then(undefined, error => {
exeContext.errors.push(error);
return Promise.resolve(null);
});
Expand Down Expand Up @@ -726,8 +728,9 @@ function completeValueWithLocatedError(
path,
result
);
if (isThenable(completed)) {
return ((completed: any): Promise<*>).then(
const promise = getPromise(completed);
if (promise) {
return promise.then(
undefined,
error => Promise.reject(
locatedError(error, fieldNodes, responsePathAsArray(path))
Expand Down Expand Up @@ -770,8 +773,9 @@ function completeValue(
result: mixed
): mixed {
// If result is a Promise, apply-lift over completeValue.
if (isThenable(result)) {
return ((result: any): Promise<*>).then(
const promise = getPromise(result);
if (promise) {
return promise.then(
resolved => completeValue(
exeContext,
returnType,
Expand Down Expand Up @@ -900,7 +904,7 @@ function completeListValue(
item
);

if (!containsPromise && isThenable(completedItem)) {
if (!containsPromise && getPromise(completedItem)) {
containsPromise = true;
}
completedResults.push(completedItem);
Expand Down Expand Up @@ -944,11 +948,9 @@ function completeAbstractValue(
returnType.resolveType(result, exeContext.contextValue, info) :
defaultResolveTypeFn(result, exeContext.contextValue, info, returnType);

if (isThenable(runtimeType)) {
// Cast to Promise
const runtimeTypePromise: Promise<?GraphQLObjectType | string> =
(runtimeType: any);
return runtimeTypePromise.then(resolvedRuntimeType =>
const promise = getPromise(runtimeType);
if (promise) {
return promise.then(resolvedRuntimeType =>
completeObjectValue(
exeContext,
ensureValidRuntimeType(
Expand Down Expand Up @@ -1033,8 +1035,9 @@ function completeObjectValue(
if (returnType.isTypeOf) {
const isTypeOf = returnType.isTypeOf(result, exeContext.contextValue, info);

if (isThenable(isTypeOf)) {
return ((isTypeOf: any): Promise<boolean>).then(isTypeOfResult => {
const promise = getPromise(isTypeOf);
if (promise) {
return promise.then(isTypeOfResult => {
if (!isTypeOfResult) {
throw invalidReturnTypeError(returnType, result, fieldNodes);
}
Expand Down Expand Up @@ -1122,8 +1125,9 @@ function defaultResolveTypeFn(
if (type.isTypeOf) {
const isTypeOfResult = type.isTypeOf(value, context, info);

if (isThenable(isTypeOfResult)) {
promisedIsTypeOfResults[i] = isTypeOfResult;
const promise = getPromise(isTypeOfResult);
if (promise) {
promisedIsTypeOfResults[i] = promise;
} else if (isTypeOfResult) {
return type;
}
Expand Down Expand Up @@ -1160,13 +1164,15 @@ function (source, args, context, info) {
};

/**
* Checks to see if this object acts like a Promise, i.e. has a "then"
* function.
* Only returns the value if it acts like a Promise, i.e. has a "then" function,
* otherwise returns void.
*/
function isThenable(value: mixed): boolean {
return typeof value === 'object' &&
value !== null &&
typeof value.then === 'function';
function getPromise<T>(value: Promise<T> | mixed): Promise<T> | void {
if (typeof value === 'object' &&
value !== null &&
typeof value.then === 'function') {
return (value: any);
}
}

/**
Expand Down