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Josh GoldbergJamesHenry
Josh Goldberg
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feat(eslint-plugin): added new rule unbound-method (typescript-eslint#204)
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‎packages/eslint-plugin/README.md

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@@ -152,6 +152,7 @@ Then you should add `airbnb` (or `airbnb-base`) to your `extends` section of `.e
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| [`@typescript-eslint/promise-function-async`](./docs/rules/promise-function-async.md) | Requires any function or method that returns a Promise to be marked async. (`promise-function-async` from TSLint) | | | :thought_balloon: |
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| [`@typescript-eslint/restrict-plus-operands`](./docs/rules/restrict-plus-operands.md) | When adding two variables, operands must both be of type number or of type string. (`restrict-plus-operands` from TSLint) | | | :thought_balloon: |
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| [`@typescript-eslint/type-annotation-spacing`](./docs/rules/type-annotation-spacing.md) | Require consistent spacing around type annotations (`typedef-whitespace` from TSLint) | :heavy_check_mark: | :wrench: | |
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| [`@typescript-eslint/unbound-method`](./docs/rules/unbound-method.md) | Enforces unbound methods are called with their expected scope. (`no-unbound-method` from TSLint) | :heavy_check_mark: | | :thought_balloon: |
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| [`@typescript-eslint/unified-signatures`](./docs/rules/unified-signatures.md) | Warns for any two overloads that could be unified into one. (`unified-signatures` from TSLint) | | | |
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<!-- end rule list -->

‎packages/eslint-plugin/ROADMAP.md

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| [`no-submodule-imports`] | 🌓 | [`import/no-internal-modules`] (slightly different) |
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| [`no-switch-case-fall-through`] | 🌟 | [`no-fallthrough`][no-fallthrough] |
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| [`no-this-assignment`] | ✅ | [`@typescript-eslint/no-this-alias`] |
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| [`no-unbound-method`] | 🛑 | N/A |
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| [`no-unbound-method`] | ✅ | [`@typescript-eslint/unbound-method`] |
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| [`no-unnecessary-class`] | ✅ | [`@typescript-eslint/no-extraneous-class`] |
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| [`no-unsafe-any`] | 🛑 | N/A |
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| [`no-unsafe-finally`] | 🌟 | [`no-unsafe-finally`][no-unsafe-finally] |
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[`@typescript-eslint/no-namespace`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-namespace.md
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[`@typescript-eslint/no-non-null-assertion`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-non-null-assertion.md
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[`@typescript-eslint/no-triple-slash-reference`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-triple-slash-reference.md
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[`@typescript-eslint/unbound-method`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/unbound-method.md
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[`@typescript-eslint/no-unnecessary-type-assertion`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-unnecessary-type-assertion.md
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[`@typescript-eslint/no-var-requires`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-var-requires.md
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[`@typescript-eslint/type-annotation-spacing`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/type-annotation-spacing.md

‎packages/eslint-plugin/docs/rules/unbound-method.md

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# Enforces unbound methods are called with their expected scope (unbound-method)
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Warns when a method is used outside of a method call.
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Class functions don't preserve the class scope when passed as standalone variables.
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## Rule Details
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Examples of **incorrect** code for this rule
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```ts
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class MyClass {
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public log(): void {
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console.log(this);
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}
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}
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const instance = new MyClass();
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// This logs the global scope (`window`/`global`), not the class instance
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const myLog = instance.log;
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myLog();
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// This log might later be called with an incorrect scope
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const { log } = instance;
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```
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Examples of **correct** code for this rule
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```ts
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class MyClass {
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public logUnbound(): void {
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console.log(this);
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}
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public logBound = () => console.log(this);
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}
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const instance = new MyClass();
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// logBound will always be bound with the correct scope
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const { logBound } = instance;
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logBound();
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// .bind and lambdas will also add a correct scope
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const dotBindLog = instance.log.bind(instance);
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const innerLog = () => instance.log();
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```
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## Options
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The rule accepts an options object with the following property:
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- `ignoreStatic` to not check whether `static` methods are correctly bound
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### `ignoreStatic`
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Examples of **correct** code for this rule with `{ ignoreStatic: true }`:
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```ts
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class OtherClass {
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static log() {
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console.log(OtherClass);
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}
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}
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// With `ignoreStatic`, statics are assumed to not rely on a particular scope
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const { log } = OtherClass;
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log();
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```
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### Example
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```json
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{
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"@typescript-eslint/unbound-method": [
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"error",
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{
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"ignoreStatic": true
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}
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]
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}
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```
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## When Not To Use It
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If your code intentionally waits to bind methods after use, such as by passing a `scope: this` along with the method, you can disable this rule.
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## Related To
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- TSLint: [no-unbound-method](https://palantir.github.io/tslint/rules/no-unbound-method/)

‎packages/eslint-plugin/src/rules/unbound-method.ts

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import { TSESTree, AST_NODE_TYPES } from '@typescript-eslint/typescript-estree';
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import * as tsutils from 'tsutils';
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import * as ts from 'typescript';
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import * as util from '../util';
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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interface Config {
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ignoreStatic: boolean;
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}
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type Options = [Config];
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type MessageIds = 'unbound';
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export default util.createRule<Options, MessageIds>({
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name: 'unbound-method',
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meta: {
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docs: {
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category: 'Best Practices',
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description:
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'Enforces unbound methods are called with their expected scope.',
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tslintName: 'no-unbound-method',
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recommended: 'error',
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},
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messages: {
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unbound:
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'Avoid referencing unbound methods which may cause unintentional scoping of `this`.',
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},
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schema: [
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{
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type: 'object',
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properties: {
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ignoreStatic: {
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type: 'boolean',
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},
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},
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additionalProperties: false,
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},
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],
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type: 'problem',
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},
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defaultOptions: [
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{
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ignoreStatic: false,
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},
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],
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create(context, [{ ignoreStatic }]) {
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const parserServices = util.getParserServices(context);
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const checker = parserServices.program.getTypeChecker();
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return {
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[AST_NODE_TYPES.MemberExpression](node: TSESTree.MemberExpression) {
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if (isSafeUse(node)) {
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return;
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}
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const originalNode = parserServices.esTreeNodeToTSNodeMap.get(node);
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const symbol = checker.getSymbolAtLocation(originalNode);
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if (symbol && isDangerousMethod(symbol, ignoreStatic)) {
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context.report({
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messageId: 'unbound',
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node,
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});
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}
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},
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};
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},
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});
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function isDangerousMethod(symbol: ts.Symbol, ignoreStatic: boolean) {
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const { valueDeclaration } = symbol;
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switch (valueDeclaration.kind) {
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case ts.SyntaxKind.MethodDeclaration:
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case ts.SyntaxKind.MethodSignature:
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return !(
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ignoreStatic &&
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tsutils.hasModifier(
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valueDeclaration.modifiers,
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ts.SyntaxKind.StaticKeyword,
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)
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);
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}
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return false;
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}
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function isSafeUse(node: TSESTree.Node): boolean {
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const parent = node.parent!;
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switch (parent.type) {
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case AST_NODE_TYPES.IfStatement:
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case AST_NODE_TYPES.ForStatement:
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case AST_NODE_TYPES.MemberExpression:
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case AST_NODE_TYPES.UpdateExpression:
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case AST_NODE_TYPES.WhileStatement:
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return true;
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case AST_NODE_TYPES.CallExpression:
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return parent.callee === node;
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case AST_NODE_TYPES.ConditionalExpression:
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return parent.test === node;
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case AST_NODE_TYPES.LogicalExpression:
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return parent.operator !== '||';
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case AST_NODE_TYPES.TaggedTemplateExpression:
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return parent.tag === node;
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case AST_NODE_TYPES.TSNonNullExpression:
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case AST_NODE_TYPES.TSAsExpression:
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case AST_NODE_TYPES.TSTypeAssertion:
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return isSafeUse(parent);
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}
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return false;
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}

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