feat(no-misused-observables): new rule like no-misused-promises

Author: JasonWeinzierl

README.md

@@ -100,6 +100,7 @@ The package includes the following rules.
 | [no-implicit-any-catch](docs/rules/no-implicit-any-catch.md)           | Disallow implicit `any` error parameters in `catchError` operators.                                       | ✅ 🔒 | 🔧 | 💡 | 💭 |    |
 | [no-index](docs/rules/no-index.md)                                     | Disallow importing index modules.                                                                         | ✅ 🔒 |    |    |    |    |
 | [no-internal](docs/rules/no-internal.md)                               | Disallow importing internal modules.                                                                      | ✅ 🔒 | 🔧 | 💡 |    |    |
+| [no-misused-observables](docs/rules/no-misused-observables.md)         | Disallow Observables in places not designed to handle them.                                               |      |    |    | 💭 |    |
 | [no-nested-subscribe](docs/rules/no-nested-subscribe.md)               | Disallow calling `subscribe` within a `subscribe` callback.                                               | ✅ 🔒 |    |    | 💭 |    |
 | [no-redundant-notify](docs/rules/no-redundant-notify.md)               | Disallow sending redundant notifications from completed or errored observables.                           | ✅ 🔒 |    |    | 💭 |    |
 | [no-sharereplay](docs/rules/no-sharereplay.md)                         | Disallow unsafe `shareReplay` usage.                                                                      | ✅ 🔒 |    |    |    |    |

docs/rules/no-misused-observables.md

@@ -0,0 +1,15 @@
+# Disallow Observables in places not designed to handle them (`rxjs-x/no-misused-observables`)
+
+💭 This rule requires [type information](https://typescript-eslint.io/linting/typed-linting).
+
+<!-- end auto-generated rule header -->
+
+## Options
+
+<!-- begin auto-generated rule options list -->
+
+| Name            | Description                             | Type    | Default |
+| :-------------- | :-------------------------------------- | :------ | :------ |
+| `checksSpreads` | Disallow `...` spreading an Observable. | Boolean | `true`  |
+
+<!-- end auto-generated rule options list -->

src/index.ts

@@ -27,6 +27,7 @@ import { noIgnoredTakewhileValueRule } from './rules/no-ignored-takewhile-value'
 import { noImplicitAnyCatchRule } from './rules/no-implicit-any-catch';
 import { noIndexRule } from './rules/no-index';
 import { noInternalRule } from './rules/no-internal';
+import { noMisusedObservablesRule } from './rules/no-misused-observables';
 import { noNestedSubscribeRule } from './rules/no-nested-subscribe';
 import { noRedundantNotifyRule } from './rules/no-redundant-notify';
 import { noSharereplayRule } from './rules/no-sharereplay';
@@ -74,6 +75,7 @@ const plugin = {
     'no-implicit-any-catch': noImplicitAnyCatchRule,
     'no-index': noIndexRule,
     'no-internal': noInternalRule,
+    'no-misused-observables': noMisusedObservablesRule,
     'no-nested-subscribe': noNestedSubscribeRule,
     'no-redundant-notify': noRedundantNotifyRule,
     'no-sharereplay': noSharereplayRule,

src/rules/no-misused-observables.ts

@@ -0,0 +1,53 @@
+import { TSESLint } from '@typescript-eslint/utils';
+import { getTypeServices } from '../etc';
+import { ruleCreator } from '../utils';
+
+// The implementation of this rule is similar to typescript-eslint's no-misused-promises. MIT License.
+// https://github.com/typescript-eslint/typescript-eslint/blob/fcd6cf063a774f73ea00af23705117a197f826d4/packages/eslint-plugin/src/rules/no-misused-promises.ts
+
+const defaultOptions: readonly {
+  checksSpreads?: boolean;
+}[] = [];
+
+export const noMisusedObservablesRule = ruleCreator({
+  defaultOptions,
+  meta: {
+    docs: {
+      description: 'Disallow Observables in places not designed to handle them.',
+      requiresTypeChecking: true,
+    },
+    messages: {
+      forbiddenSpread: 'Expected a non-Observable value to be spread into an object.',
+    },
+    schema: [
+      {
+        properties: {
+          checksSpreads: { type: 'boolean', default: true, description: 'Disallow `...` spreading an Observable.' },
+        },
+        type: 'object',
+      },
+    ],
+    type: 'problem',
+  },
+  name: 'no-misused-observables',
+  create: (context) => {
+    const { couldBeObservable } = getTypeServices(context);
+    const [config = {}] = context.options;
+    const { checksSpreads = true } = config;
+
+    const spreadChecks: TSESLint.RuleListener = {
+      SpreadElement: (node) => {
+        if (couldBeObservable(node.argument)) {
+          context.report({
+            messageId: 'forbiddenSpread',
+            node: node.argument,
+          });
+        }
+      },
+    };
+
+    return {
+      ...(checksSpreads ? spreadChecks : {}),
+    };
+  },
+});

tests/rules/no-misused-observables.test.ts

@@ -0,0 +1,48 @@
+import { stripIndent } from 'common-tags';
+import { noMisusedObservablesRule } from '../../src/rules/no-misused-observables';
+import { fromFixture } from '../etc';
+import { ruleTester } from '../rule-tester';
+
+ruleTester({ types: true }).run('no-misused-observables', noMisusedObservablesRule, {
+  valid: [
+    {
+      code: stripIndent`
+        // spread; explicitly allowed
+        import { of } from "rxjs";
+
+        const source = of(42);
+        const foo = { ...source };
+      `,
+      options: [{ checksSpreads: false }],
+    },
+    stripIndent`
+      // unrelated
+      const foo = { bar: 42 };
+      const baz = { ...foo };
+    `,
+  ],
+  invalid: [
+    fromFixture(
+      stripIndent`
+        // spread variable
+        import { of } from "rxjs";
+
+        const source = of(42);
+        const foo = { ...source };
+                         ~~~~~~ [forbiddenSpread]
+      `,
+    ),
+    fromFixture(
+      stripIndent`
+        // spread call function
+        import { of } from "rxjs";
+
+        function source() {
+          return of(42);
+        }
+        const foo = { ...source() };
+                         ~~~~~~~~ [forbiddenSpread]
+      `,
+    ),
+  ],
+});