fix(no-promise-reject): new Promises and throw statements are now also checked (#848)

Author: RebeccaStevens

docs/rules/no-promise-reject.md

@@ -2,15 +2,13 @@
 
 <!-- end auto-generated rule header -->
 
-This rule disallows use of `Promise.reject()`.
+This rule disallows rejecting promises.
 
 ## Rule Details
 
 It is useful when using an `Option` type (something like `{ value: T } | { error: Error }`)
 for handling errors. In this case a promise should always resolve with an `Option` and never reject.
 
-This rule should be used in conjunction with [`no-throw-statements`](./no-throw-statements.md).
-
 ### ❌ Incorrect
 
 <!-- eslint-skip -->

src/rules/no-promise-reject.ts

@@ -8,7 +8,12 @@ import {
   type NamedCreateRuleCustomMeta,
   type RuleResult,
 } from "#/utils/rule";
-import { isIdentifier, isMemberExpression } from "#/utils/type-guards";
+import { getEnclosingFunction, getEnclosingTryStatement } from "#/utils/tree";
+import {
+  isFunctionLike,
+  isIdentifier,
+  isMemberExpression,
+} from "#/utils/type-guards";
 
 /**
  * The name of this rule.
@@ -39,7 +44,7 @@ const defaultOptions: Options = [{}];
  * The possible error messages.
  */
 const errorMessages = {
-  generic: "Unexpected reject, return an error instead.",
+  generic: "Unexpected rejection, resolve an error instead.",
 } as const;
 
 /**
@@ -67,6 +72,7 @@ function checkCallExpression(
   return {
     context,
     descriptors:
+      // TODO: Better Promise type detection.
       isMemberExpression(node.callee) &&
       isIdentifier(node.callee.object) &&
       isIdentifier(node.callee.property) &&
@@ -77,12 +83,65 @@ function checkCallExpression(
   };
 }
 
+/**
+ * Check if the given NewExpression is for a Promise and it has a callback that rejects.
+ */
+function checkNewExpression(
+  node: TSESTree.NewExpression,
+  context: Readonly<RuleContext<keyof typeof errorMessages, Options>>,
+): RuleResult<keyof typeof errorMessages, Options> {
+  return {
+    context,
+    descriptors:
+      // TODO: Better Promise type detection.
+      isIdentifier(node.callee) &&
+      node.callee.name === "Promise" &&
+      node.arguments[0] !== undefined &&
+      isFunctionLike(node.arguments[0]) &&
+      node.arguments[0].params.length === 2
+        ? [{ node: node.arguments[0].params[1]!, messageId: "generic" }]
+        : [],
+  };
+}
+
+/**
+ * Check if the given ThrowStatement violates this rule.
+ */
+function checkThrowStatement(
+  node: TSESTree.ThrowStatement,
+  context: Readonly<RuleContext<keyof typeof errorMessages, Options>>,
+): RuleResult<keyof typeof errorMessages, Options> {
+  const enclosingFunction = getEnclosingFunction(node);
+  if (enclosingFunction?.async !== true) {
+    return { context, descriptors: [] };
+  }
+
+  const enclosingTryStatement = getEnclosingTryStatement(node);
+  if (
+    enclosingTryStatement === null ||
+    getEnclosingFunction(enclosingTryStatement) !== enclosingFunction ||
+    enclosingTryStatement.handler === null
+  ) {
+    return {
+      context,
+      descriptors: [{ node, messageId: "generic" }],
+    };
+  }
+
+  return {
+    context,
+    descriptors: [],
+  };
+}
+
 // Create the rule.
 export const rule = createRule<keyof typeof errorMessages, Options>(
   name,
   meta,
   defaultOptions,
   {
     CallExpression: checkCallExpression,
+    NewExpression: checkNewExpression,
+    ThrowStatement: checkThrowStatement,
   },
 );

src/utils/tree.ts

@@ -24,6 +24,7 @@ import {
   isTSTypeAnnotation,
   isTSTypeLiteral,
   isTSTypeReference,
+  isTryStatement,
   isVariableDeclaration,
 } from "./type-guards";
 
@@ -52,7 +53,21 @@ export function isInFunctionBody(
   node: TSESTree.Node,
   async?: boolean,
 ): boolean {
-  const functionNode = getAncestorOfType(
+  const functionNode = getEnclosingFunction(node);
+
+  return (
+    functionNode !== null &&
+    (async === undefined || functionNode.async === async)
+  );
+}
+
+/**
+ * Get the function the given node is in.
+ *
+ * Will return null if not in a function.
+ */
+export function getEnclosingFunction(node: TSESTree.Node) {
+  return getAncestorOfType(
     (
       n,
       c,
@@ -62,10 +77,17 @@ export function isInFunctionBody(
       | TSESTree.FunctionExpression => isFunctionLike(n) && n.body === c,
     node,
   );
+}
 
-  return (
-    functionNode !== null &&
-    (async === undefined || functionNode.async === async)
+/**
+ * Get the function the given node is in.
+ *
+ * Will return null if not in a function.
+ */
+export function getEnclosingTryStatement(node: TSESTree.Node) {
+  return getAncestorOfType(
+    (n, c): n is TSESTree.TryStatement => isTryStatement(n) && n.block === c,
+    node,
   );
 }
 

src/utils/type-guards.ts

@@ -237,6 +237,12 @@ export function isThrowStatement(
   return node.type === AST_NODE_TYPES.ThrowStatement;
 }
 
+export function isTryStatement(
+  node: TSESTree.Node,
+): node is TSESTree.TryStatement {
+  return node.type === AST_NODE_TYPES.TryStatement;
+}
+
 export function isTSArrayType(
   node: TSESTree.Node,
 ): node is TSESTree.TSArrayType {
@@ -440,3 +446,12 @@ export function isObjectConstructorType(type: Type | null): boolean {
 export function isFunctionLikeType(type: Type | null): boolean {
   return type !== null && type.getCallSignatures().length > 0;
 }
+
+export function isPromiseType(type: Type | null): boolean {
+  return (
+    type !== null &&
+    (((type.symbol as unknown) !== undefined &&
+      type.symbol.name === "Promise") ||
+      (isUnionType(type) && type.types.some(isPromiseType)))
+  );
+}