valid-expect-in-promise.ts

import { AST_NODE_TYPES, TSESLint, TSESTree } from '@typescript-eslint/utils';
import {
  KnownCallExpression,
  ModifierName,
  createRule,
  findTopMostCallExpression,
  getAccessorValue,
  getNodeName,
  isFunction,
  isIdentifier,
  isSupportedAccessor,
  isTypeOfJestFnCall,
  parseJestFnCall,
} from './utils';

type PromiseChainCallExpression = KnownCallExpression<
  'then' | 'catch' | 'finally'
>;

const isPromiseChainCall = (
  node: TSESTree.Node,
): node is PromiseChainCallExpression => {
  if (
    node.type === AST_NODE_TYPES.CallExpression &&
    node.callee.type === AST_NODE_TYPES.MemberExpression &&
    isSupportedAccessor(node.callee.property)
  ) {
    // promise methods should have at least 1 argument
    if (node.arguments.length === 0) {
      return false;
    }

    switch (getAccessorValue(node.callee.property)) {
      case 'then':
        return node.arguments.length < 3;
      case 'catch':
      case 'finally':
        return node.arguments.length < 2;
    }
  }

  return false;
};

const isTestCaseCallWithCallbackArg = (
  node: TSESTree.CallExpression,
  context: TSESLint.RuleContext<string, unknown[]>,
): boolean => {
  const jestCallFn = parseJestFnCall(node, context);

  if (jestCallFn?.type !== 'test') {
    return false;
  }

  const isJestEach = jestCallFn.members.some(
    s => getAccessorValue(s) === 'each',
  );

  if (
    isJestEach &&
    node.callee.type !== AST_NODE_TYPES.TaggedTemplateExpression
  ) {
    // isJestEach but not a TaggedTemplateExpression, so this must be
    // the `jest.each([])()` syntax which this rule doesn't support due
    // to its complexity (see jest-community/eslint-plugin-jest#710)
    // so we return true to trigger bailout
    return true;
  }

  const [, callback] = node.arguments;

  const callbackArgIndex = Number(isJestEach);

  return (
    callback &&
    isFunction(callback) &&
    callback.params.length === 1 + callbackArgIndex
  );
};

const isPromiseMethodThatUsesValue = (
  node: TSESTree.AwaitExpression | TSESTree.ReturnStatement,
  identifier: TSESTree.Identifier,
): boolean => {
  const { name } = identifier;

  if (node.argument === null) {
    return false;
  }

  if (
    node.argument.type === AST_NODE_TYPES.CallExpression &&
    node.argument.arguments.length > 0
  ) {
    const nodeName = getNodeName(node.argument);

    if (['Promise.all', 'Promise.allSettled'].includes(nodeName as string)) {
      const [firstArg] = node.argument.arguments;

      if (
        firstArg.type === AST_NODE_TYPES.ArrayExpression &&
        firstArg.elements.some(nod => isIdentifier(nod, name))
      ) {
        return true;
      }
    }

    if (
      ['Promise.resolve', 'Promise.reject'].includes(nodeName as string) &&
      node.argument.arguments.length === 1
    ) {
      return isIdentifier(node.argument.arguments[0], name);
    }
  }

  return isIdentifier(node.argument, name);
};

/**
 * Attempts to determine if the runtime value represented by the given `identifier`
 * is `await`ed within the given array of elements
 */
const isValueAwaitedInElements = (
  name: string,
  elements:
    | TSESTree.ArrayExpression['elements']
    | TSESTree.CallExpression['arguments'],
): boolean => {
  for (const element of elements) {
    if (
      element.type === AST_NODE_TYPES.AwaitExpression &&
      isIdentifier(element.argument, name)
    ) {
      return true;
    }

    if (
      element.type === AST_NODE_TYPES.ArrayExpression &&
      isValueAwaitedInElements(name, element.elements)
    ) {
      return true;
    }
  }

  return false;
};

/**
 * Attempts to determine if the runtime value represented by the given `identifier`
 * is `await`ed as an argument along the given call expression
 */
const isValueAwaitedInArguments = (
  name: string,
  call: TSESTree.CallExpression,
): boolean => {
  let node: TSESTree.Node = call;

  while (node) {
    if (node.type === AST_NODE_TYPES.CallExpression) {
      if (isValueAwaitedInElements(name, node.arguments)) {
        return true;
      }

      node = node.callee;
    }

    if (node.type !== AST_NODE_TYPES.MemberExpression) {
      break;
    }

    node = node.object;
  }

  return false;
};

const getLeftMostCallExpression = (
  call: TSESTree.CallExpression,
): TSESTree.CallExpression => {
  let leftMostCallExpression: TSESTree.CallExpression = call;
  let node: TSESTree.Node = call;

  while (node) {
    if (node.type === AST_NODE_TYPES.CallExpression) {
      leftMostCallExpression = node;
      node = node.callee;
    }

    if (node.type !== AST_NODE_TYPES.MemberExpression) {
      break;
    }

    node = node.object;
  }

  return leftMostCallExpression;
};

/**
 * Attempts to determine if the runtime value represented by the given `identifier`
 * is `await`ed or `return`ed within the given `body` of statements
 */
const isValueAwaitedOrReturned = (
  identifier: TSESTree.Identifier,
  body: TSESTree.Statement[],
  context: TSESLint.RuleContext<string, unknown[]>,
): boolean => {
  const { name } = identifier;

  for (const node of body) {
    // skip all nodes that are before this identifier, because they'd probably
    // be affecting a different runtime value (e.g. due to reassignment)
    if (node.range[0] <= identifier.range[0]) {
      continue;
    }

    if (node.type === AST_NODE_TYPES.ReturnStatement) {
      return isPromiseMethodThatUsesValue(node, identifier);
    }

    if (node.type === AST_NODE_TYPES.ExpressionStatement) {
      // it's possible that we're awaiting the value as an argument
      if (node.expression.type === AST_NODE_TYPES.CallExpression) {
        if (isValueAwaitedInArguments(name, node.expression)) {
          return true;
        }

        const leftMostCall = getLeftMostCallExpression(node.expression);
        const jestFnCall = parseJestFnCall(node.expression, context);

        if (
          jestFnCall?.type === 'expect' &&
          leftMostCall.arguments.length > 0 &&
          isIdentifier(leftMostCall.arguments[0], name)
        ) {
          if (
            jestFnCall.members.some(m => {
              const v = getAccessorValue(m);

              return v === ModifierName.resolves || v === ModifierName.rejects;
            })
          ) {
            return true;
          }
        }
      }

      if (
        node.expression.type === AST_NODE_TYPES.AwaitExpression &&
        isPromiseMethodThatUsesValue(node.expression, identifier)
      ) {
        return true;
      }

      // (re)assignment changes the runtime value, so if we've not found an
      // await or return already we act as if we've reached the end of the body
      if (node.expression.type === AST_NODE_TYPES.AssignmentExpression) {
        // unless we're assigning to the same identifier, in which case
        // we might be chaining off the existing promise value
        if (
          isIdentifier(node.expression.left, name) &&
          getNodeName(node.expression.right)?.startsWith(`${name}.`) &&
          isPromiseChainCall(node.expression.right)
        ) {
          continue;
        }

        break;
      }
    }

    if (
      node.type === AST_NODE_TYPES.BlockStatement &&
      isValueAwaitedOrReturned(identifier, node.body, context)
    ) {
      return true;
    }
  }

  return false;
};

const findFirstBlockBodyUp = (
  node: TSESTree.Node,
): TSESTree.BlockStatement['body'] => {
  let parent: TSESTree.Node['parent'] = node;

  while (parent) {
    if (parent.type === AST_NODE_TYPES.BlockStatement) {
      return parent.body;
    }

    parent = parent.parent;
  }

  /* istanbul ignore next */
  throw new Error(
    `Could not find BlockStatement - please file a github issue at https://github.com/jest-community/eslint-plugin-jest`,
  );
};

const isDirectlyWithinTestCaseCall = (
  node: TSESTree.Node,
  context: TSESLint.RuleContext<string, unknown[]>,
): boolean => {
  let parent: TSESTree.Node['parent'] = node;

  while (parent) {
    if (isFunction(parent)) {
      parent = parent.parent;

      return (
        parent?.type === AST_NODE_TYPES.CallExpression &&
        isTypeOfJestFnCall(parent, context, ['test'])
      );
    }

    parent = parent.parent;
  }

  return false;
};

const isVariableAwaitedOrReturned = (
  variable: TSESTree.VariableDeclarator,
  context: TSESLint.RuleContext<string, unknown[]>,
): boolean => {
  const body = findFirstBlockBodyUp(variable);

  // it's pretty much impossible for us to track destructuring assignments,
  // so we return true to bailout gracefully
  if (!isIdentifier(variable.id)) {
    return true;
  }

  return isValueAwaitedOrReturned(variable.id, body, context);
};

export default createRule({
  name: __filename,
  meta: {
    docs: {
      category: 'Best Practices',
      description:
        'Ensure promises that have expectations in their chain are valid',
      recommended: 'error',
    },
    messages: {
      expectInFloatingPromise:
        'This promise should either be returned or awaited to ensure the expects in its chain are called',
    },
    type: 'suggestion',
    schema: [],
  },
  defaultOptions: [],
  create(context) {
    let inTestCaseWithDoneCallback = false;
    // an array of booleans representing each promise chain we enter, with the
    // boolean value representing if we think a given chain contains an expect
    // in it's body.
    //
    // since we only care about the inner-most chain, we represent the state in
    // reverse with the inner-most being the first item, as that makes it
    // slightly less code to assign to by not needing to know the length
    const chains: boolean[] = [];

    return {
      CallExpression(node: TSESTree.CallExpression) {
        // there are too many ways that the done argument could be used with
        // promises that contain expect that would make the promise safe for us
        if (isTestCaseCallWithCallbackArg(node, context)) {
          inTestCaseWithDoneCallback = true;

          return;
        }

        // if this call expression is a promise chain, add it to the stack with
        // value of "false", as we assume there are no expect calls initially
        if (isPromiseChainCall(node)) {
          chains.unshift(false);

          return;
        }

        // if we're within a promise chain, and this call expression looks like
        // an expect call, mark the deepest chain as having an expect call
        if (
          chains.length > 0 &&
          isTypeOfJestFnCall(node, context, ['expect'])
        ) {
          chains[0] = true;
        }
      },
      'CallExpression:exit'(node: TSESTree.CallExpression) {
        // there are too many ways that the "done" argument could be used to
        // make promises containing expects safe in a test for us to be able to
        // accurately check, so we just bail out completely if it's present
        if (inTestCaseWithDoneCallback) {
          if (isTypeOfJestFnCall(node, context, ['test'])) {
            inTestCaseWithDoneCallback = false;
          }

          return;
        }

        if (!isPromiseChainCall(node)) {
          return;
        }

        // since we're exiting this call expression (which is a promise chain)
        // we remove it from the stack of chains, since we're unwinding
        const hasExpectCall = chains.shift();

        // if the promise chain we're exiting doesn't contain an expect,
        // then we don't need to check it for anything
        if (!hasExpectCall) {
          return;
        }

        const { parent } = findTopMostCallExpression(node);

        // if we don't have a parent (which is technically impossible at runtime)
        // or our parent is not directly within the test case, we stop checking
        // because we're most likely in the body of a function being defined
        // within the test, which we can't track
        if (!parent || !isDirectlyWithinTestCaseCall(parent, context)) {
          return;
        }

        switch (parent.type) {
          case AST_NODE_TYPES.VariableDeclarator: {
            if (isVariableAwaitedOrReturned(parent, context)) {
              return;
            }

            break;
          }

          case AST_NODE_TYPES.AssignmentExpression: {
            if (
              parent.left.type === AST_NODE_TYPES.Identifier &&
              isValueAwaitedOrReturned(
                parent.left,
                findFirstBlockBodyUp(parent),
                context,
              )
            ) {
              return;
            }

            break;
          }

          case AST_NODE_TYPES.ExpressionStatement:
            break;

          case AST_NODE_TYPES.ReturnStatement:
          case AST_NODE_TYPES.AwaitExpression:
          default:
            return;
        }

        context.report({
          messageId: 'expectInFloatingPromise',
          node: parent,
        });
      },
    };
  },
});