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Josh GoldbergJamesHenry
Josh Goldberg
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JamesHenry
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feat(eslint-plugin): added new rule use-default-type-parameter (typescript-eslint#562)
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‎packages/eslint-plugin/README.md

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@@ -160,6 +160,7 @@ Then you should add `airbnb` (or `airbnb-base`) to your `extends` section of `.e
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| [`@typescript-eslint/no-this-alias`](./docs/rules/no-this-alias.md) | Disallow aliasing `this` | | | |
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| [`@typescript-eslint/no-type-alias`](./docs/rules/no-type-alias.md) | Disallow the use of type aliases | | | |
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| [`@typescript-eslint/no-unnecessary-qualifier`](./docs/rules/no-unnecessary-qualifier.md) | Warns when a namespace qualifier is unnecessary | | :wrench: | :thought_balloon: |
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| [`@typescript-eslint/no-unnecessary-type-arguments`](./docs/rules/no-unnecessary-type-arguments.md) | Warns if an explicitly specified type argument is the default for that type parameter | | :wrench: | :thought_balloon: |
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| [`@typescript-eslint/no-unnecessary-type-assertion`](./docs/rules/no-unnecessary-type-assertion.md) | Warns if a type assertion does not change the type of an expression | | :wrench: | :thought_balloon: |
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| [`@typescript-eslint/no-unused-vars`](./docs/rules/no-unused-vars.md) | Disallow unused variables | :heavy_check_mark: | | |
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| [`@typescript-eslint/no-use-before-define`](./docs/rules/no-use-before-define.md) | Disallow the use of variables before they are defined | :heavy_check_mark: | | |

‎packages/eslint-plugin/ROADMAP.md

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@@ -99,7 +99,7 @@
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| [`triple-equals`] | 🌟 | [`eqeqeq`][eqeqeq] |
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| [`typeof-compare`] | 🌟 | [`valid-typeof`][valid-typeof] |
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| [`unnecessary-constructor`] | 🌟 | [`no-useless-constructor`][no-useless-constructor] |
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| [`use-default-type-parameter`] | 🛑 | N/A |
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| [`use-default-type-parameter`] | ✅ | [`@typescript-eslint/no-unnecessary-type-arguments`] |
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| [`use-isnan`] | 🌟 | [`use-isnan`][use-isnan] |
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<sup>[1]</sup> The ESLint rule also supports silencing with an extra set of parens (`if ((foo = bar)) {}`)<br>
@@ -617,6 +617,7 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
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[`@typescript-eslint/require-await`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/require-await.md
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[`@typescript-eslint/no-for-in-array`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-for-in-array.md
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[`@typescript-eslint/no-unnecessary-qualifier`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-unnecessary-qualifier.md
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[`@typescript-eslint/no-unnecessary-type-arguments`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-unnecessary-type-arguments.md
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[`@typescript-eslint/semi`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/semi.md
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[`@typescript-eslint/no-floating-promises`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-floating-promises.md
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‎packages/eslint-plugin/docs/rules/no-unnecessary-type-arguments.md

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# Enforces that types will not to be used (no-unnecessary-type-arguments)
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Warns if an explicitly specified type argument is the default for that type parameter.
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## Rule Details
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Type parameters in TypeScript may specify a default value.
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For example:
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```ts
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function f<T = number>() {}
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```
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It is redundant to provide an explicit type parameter equal to that default.
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Examples of **incorrect** code for this rule:
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```ts
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function f<T = number>() {}
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f<number>();
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function g<T = number, U = string>() {}
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g<string, string>();
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class C<T = number> {}
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function h(c: C<number>) {}
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new C<number>();
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class D extends C<number> {}
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interface I<T = number> {}
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class Impl implements I<number> {}
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```
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Examples of **correct** code for this rule:
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```ts
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function f<T = number>() {}
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f<string>();
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function g<T = number, U = string>() {}
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g<number, number>();
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class C<T = number> {}
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new C<string>();
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class D extends C<string> {}
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interface I<T = number> {}
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class Impl implements I<string> {}
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```
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## Related to
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- TSLint: [use-default-type-parameter](https://palantir.github.io/tslint/rules/use-default-type-parameter)

‎packages/eslint-plugin/src/configs/all.json

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"@typescript-eslint/no-this-alias": "error",
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"@typescript-eslint/no-type-alias": "error",
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"@typescript-eslint/no-unnecessary-qualifier": "error",
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"@typescript-eslint/no-unnecessary-type-arguments": "error",
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"@typescript-eslint/no-unnecessary-type-assertion": "error",
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"no-unused-vars": "off",
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"@typescript-eslint/no-unused-vars": "error",

‎packages/eslint-plugin/src/rules/indent-new-do-not-use/BinarySearchTree.ts

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@@ -17,7 +17,7 @@ export interface TreeValue {
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* can easily be swapped out.
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*/
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export class BinarySearchTree {
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private rbTree = createTree<TreeValue, number>();
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private rbTree = createTree<TreeValue>();
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/**
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* Inserts an entry into the tree.

‎packages/eslint-plugin/src/rules/index.ts

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@@ -58,6 +58,7 @@ import typeAnnotationSpacing from './type-annotation-spacing';
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import typedef from './typedef';
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import unboundMethod from './unbound-method';
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import unifiedSignatures from './unified-signatures';
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import useDefaultTypeParameter from './no-unnecessary-type-arguments';
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export default {
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'adjacent-overload-signatures': adjacentOverloadSignatures,
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'no-this-alias': noThisAlias,
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'no-type-alias': noTypeAlias,
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'no-unnecessary-qualifier': noUnnecessaryQualifier,
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'no-unnecessary-type-arguments': useDefaultTypeParameter,
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'no-unnecessary-type-assertion': noUnnecessaryTypeAssertion,
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'no-unused-vars': noUnusedVars,
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'no-use-before-define': noUseBeforeDefine,
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'require-array-sort-compare': requireArraySortCompare,
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'require-await': requireAwait,
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'restrict-plus-operands': restrictPlusOperands,
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semi: semi,
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'strict-boolean-expressions': strictBooleanExpressions,
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'triple-slash-reference': tripleSlashReference,
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'type-annotation-spacing': typeAnnotationSpacing,
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typedef: typedef,
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'unbound-method': unboundMethod,
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'unified-signatures': unifiedSignatures,
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semi: semi,
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typedef: typedef,
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};

‎packages/eslint-plugin/src/rules/no-unnecessary-type-arguments.ts

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import { TSESTree } from '@typescript-eslint/experimental-utils';
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import * as tsutils from 'tsutils';
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import ts from 'typescript';
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import * as util from '../util';
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import { findFirstResult } from '../util';
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interface ArgsAndParams {
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typeArguments: ts.NodeArray<ts.TypeNode>;
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typeParameters: readonly ts.TypeParameterDeclaration[];
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}
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type ExtendingClassLikeDeclaration = ts.ClassLikeDeclaration & {
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heritageClauses: ts.NodeArray<ts.HeritageClause>;
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};
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type ParameterCapableTSNode =
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| ts.CallExpression
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| ts.NewExpression
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| ts.TypeReferenceNode
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| ts.ExpressionWithTypeArguments;
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type MessageIds = 'unnecessaryTypeParameter';
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export default util.createRule<[], MessageIds>({
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name: 'no-unnecessary-type-arguments',
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meta: {
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docs: {
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description:
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'Warns if an explicitly specified type argument is the default for that type parameter',
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category: 'Best Practices',
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recommended: false,
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},
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fixable: 'code',
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messages: {
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unnecessaryTypeParameter:
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'This is the default value for this type parameter, so it can be omitted.',
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},
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schema: [],
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type: 'suggestion',
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},
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defaultOptions: [],
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create(context) {
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const parserServices = util.getParserServices(context);
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const checker = parserServices.program.getTypeChecker();
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function checkTSArgsAndParameters(
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esParameters: TSESTree.TSTypeParameterInstantiation,
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{ typeArguments, typeParameters }: ArgsAndParams,
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): void {
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// Just check the last one. Must specify previous type parameters if the last one is specified.
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const i = typeArguments.length - 1;
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const arg = typeArguments[i];
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const param = typeParameters[i];
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// TODO: would like checker.areTypesEquivalent. https://github.com/Microsoft/TypeScript/issues/13502
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if (
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param.default === undefined ||
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param.default.getText() !== arg.getText()
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) {
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return;
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}
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context.report({
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fix: fixer =>
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fixer.removeRange(
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i === 0
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? [typeArguments.pos - 1, typeArguments.end + 1]
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: [typeArguments[i - 1].end, arg.end],
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),
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messageId: 'unnecessaryTypeParameter',
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node: esParameters!.params[i],
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});
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}
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return {
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TSTypeParameterInstantiation(node) {
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const parentDeclaration = parserServices.esTreeNodeToTSNodeMap.get(
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node.parent!,
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) as ExtendingClassLikeDeclaration | ParameterCapableTSNode;
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const expression = tsutils.isClassLikeDeclaration(parentDeclaration)
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? parentDeclaration.heritageClauses[0].types[0]
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: parentDeclaration;
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const argsAndParams = getArgsAndParameters(expression, checker);
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if (argsAndParams !== undefined) {
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checkTSArgsAndParameters(node, argsAndParams);
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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 getArgsAndParameters(
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node: ParameterCapableTSNode,
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checker: ts.TypeChecker,
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): ArgsAndParams | undefined {
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const typeParameters = getTypeParametersFromNode(node, checker);
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return typeParameters === undefined
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? undefined
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: { typeArguments: node.typeArguments!, typeParameters };
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}
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function getTypeParametersFromNode(
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node: ParameterCapableTSNode,
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checker: ts.TypeChecker,
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) {
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if (ts.isExpressionWithTypeArguments(node)) {
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return getTypeParametersFromType(node.expression, checker);
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}
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if (ts.isTypeReferenceNode(node)) {
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return getTypeParametersFromType(node.typeName, checker);
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}
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return getTypeParametersFromCall(node, checker);
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}
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function getTypeParametersFromType(
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type: ts.EntityName | ts.Expression | ts.ClassDeclaration,
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checker: ts.TypeChecker,
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): readonly ts.TypeParameterDeclaration[] | undefined {
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const sym = getAliasedSymbol(checker.getSymbolAtLocation(type)!, checker);
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if (sym === undefined || sym.declarations === undefined) {
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return undefined;
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}
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return findFirstResult(sym.declarations, decl =>
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tsutils.isClassLikeDeclaration(decl) ||
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ts.isTypeAliasDeclaration(decl) ||
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ts.isInterfaceDeclaration(decl)
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? decl.typeParameters
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: undefined,
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);
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}
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function getTypeParametersFromCall(
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node: ts.CallExpression | ts.NewExpression,
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checker: ts.TypeChecker,
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): readonly ts.TypeParameterDeclaration[] | undefined {
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const sig = checker.getResolvedSignature(node);
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const sigDecl = sig === undefined ? undefined : sig.getDeclaration();
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if (sigDecl === undefined) {
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return ts.isNewExpression(node)
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? getTypeParametersFromType(node.expression, checker)
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: undefined;
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}
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return sigDecl.typeParameters;
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}
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function getAliasedSymbol(
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symbol: ts.Symbol,
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checker: ts.TypeChecker,
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): ts.Symbol | undefined {
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return tsutils.isSymbolFlagSet(symbol, ts.SymbolFlags.Alias)
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? checker.getAliasedSymbol(symbol)
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: symbol;
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}

‎packages/eslint-plugin/src/util/misc.ts

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);
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}
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/** Returns the first non-`undefined` result. */
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export function findFirstResult<T, U>(
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inputs: T[],
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getResult: (t: T) => U | undefined,
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): U | undefined {
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for (const element of inputs) {
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const result = getResult(element);
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if (result !== undefined) {
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return result;
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}
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}
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return undefined;
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}
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/**
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* Gets a string name representation of the name of the given MethodDefinition
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* or ClassProperty node, with handling for computed property names.

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