fix(eslint-plugin): [no-unnec-type-assert] handle JSX attributes

packages/eslint-plugin/package.json

@@ -50,6 +50,7 @@
     "@types/json-schema": "^7.0.3",
     "@types/marked": "^0.7.1",
     "@types/prettier": "^1.18.2",
+    "@types/react": "^16.9.2",
     "chalk": "^3.0.0",
     "marked": "^0.7.0",
     "prettier": "*",

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

@@ -1,6 +1,7 @@
 import { TSESTree } from '@typescript-eslint/experimental-utils';
 import {
   isCallExpression,
+  isJsxExpression,
   isNewExpression,
   isObjectType,
   isObjectFlagSet,
@@ -117,6 +118,8 @@ export default util.createRule<Options, MessageIds>({
         return parent.type
           ? checker.getTypeFromTypeNode(parent.type)
           : undefined;
+      } else if (isJsxExpression(parent)) {
+        return checker.getContextualType(parent);
       } else if (
         ![ts.SyntaxKind.TemplateSpan, ts.SyntaxKind.JsxExpression].includes(
           parent.kind,

packages/eslint-plugin/tests/RuleTester.ts

@@ -44,6 +44,7 @@ class RuleTester extends TSESLint.RuleTester {
   ): void {
     const errorMessage = `Do not set the parser at the test level unless you want to use a parser other than ${parser}`;
 
+    // standardise the valid tests as objects
     tests.valid = tests.valid.map(test => {
       if (typeof test === 'string') {
         return {

packages/eslint-plugin/tests/fixtures/tsconfig.json

@@ -1,10 +1,15 @@
 {
   "compilerOptions": {
+    "jsx": "preserve",
     "target": "es5",
     "module": "commonjs",
     "strict": true,
     "esModuleInterop": true,
     "lib": ["es2015", "es2017", "esnext"],
     "experimentalDecorators": true
-  }
+  },
+  "include": [
+    "file.ts",
+    "react.tsx"
+  ]
 }

packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts

@@ -1,3 +1,4 @@
+import { clearCaches } from '@typescript-eslint/parser';
 import path from 'path';
 import rule from '../../src/rules/no-unnecessary-type-assertion';
 import { RuleTester } from '../RuleTester';
@@ -12,6 +13,12 @@ const ruleTester = new RuleTester({
   parser: '@typescript-eslint/parser',
 });
 
+// make sure each test is completely isolated
+// there was some weird behaviour with the mixed ts/tsx test cases without this
+afterEach(() => {
+  clearCaches();
+});
+
 ruleTester.run('no-unnecessary-type-assertion', rule, {
   valid: [
     'const foo = 3 as number;',
@@ -117,6 +124,19 @@ function testFunction(_param: string | null): void { /* noop */ }
 const value = 'test' as string | null | undefined
 testFunction(value!)
     `,
+    // https://github.com/typescript-eslint/typescript-eslint/issues/982
+    {
+      code: `
+const React = require("react");
+
+function Test(props: {
+  id?: null | string | number;
+}) {
+  return <div key={props.id!} />;
+};
+      `,
+      filename: path.join(rootDir, 'react.tsx'),
+    },
   ],
 
   invalid: [
@@ -327,5 +347,33 @@ class Mx {
         },
       ],
     },
+    // https://github.com/typescript-eslint/typescript-eslint/issues/982
+    {
+      code: `
+const React = require("react");
+
+function Test(props: {
+  id?: string | number;
+}) {
+  return <div key={props.id!} />;
+};
+      `,
+      output: `
+const React = require("react");
+
+function Test(props: {
+  id?: string | number;
+}) {
+  return <div key={props.id} />;
+};
+      `,
+      errors: [
+        {
+          messageId: 'contextuallyUnnecessary',
+          line: 7,
+        },
+      ],
+      filename: path.join(rootDir, 'react.tsx'),
+    },
   ],
 });

yarn.lock

@@ -1425,6 +1425,19 @@
   resolved "https://registry.yarnpkg.com/@types/prettier/-/prettier-1.18.3.tgz#64ff53329ce16139f17c3db9d3e0487199972cd8"
   integrity sha512-48rnerQdcZ26odp+HOvDGX8IcUkYOCuMc2BodWYTe956MqkHlOGAG4oFQ83cjZ0a4GAgj7mb4GUClxYd2Hlodg==
 
+"@types/prop-types@*":
+  version "15.7.2"
+  resolved "https://registry.yarnpkg.com/@types/prop-types/-/prop-types-15.7.2.tgz#0e58ae66773d7fd7c372a493aff740878ec9ceaa"
+  integrity sha512-f8JzJNWVhKtc9dg/dyDNfliTKNOJSLa7Oht/ElZdF/UbMUmAH3rLmAk3ODNjw0mZajDEgatA03tRjB4+Dp/tzA==
+
+"@types/react@^16.9.2":
+  version "16.9.2"
+  resolved "https://registry.yarnpkg.com/@types/react/-/react-16.9.2.tgz#6d1765431a1ad1877979013906731aae373de268"
+  integrity sha512-jYP2LWwlh+FTqGd9v7ynUKZzjj98T8x7Yclz479QdRhHfuW9yQ+0jjnD31eXSXutmBpppj5PYNLYLRfnZJvcfg==
+  dependencies:
+    "@types/prop-types" "*"
+    csstype "^2.2.0"
+
 "@types/semver@^6.0.1":
   version "6.0.2"
   resolved "https://registry.yarnpkg.com/@types/semver/-/semver-6.0.2.tgz#5e8b09f0e4af53034b1d0fb9977a277847836205"
@@ -2794,6 +2807,11 @@ cssstyle@^1.0.0:
   dependencies:
     cssom "0.3.x"
 
+csstype@^2.2.0:
+  version "2.6.6"
+  resolved "https://registry.yarnpkg.com/csstype/-/csstype-2.6.6.tgz#c34f8226a94bbb10c32cc0d714afdf942291fc41"
+  integrity sha512-RpFbQGUE74iyPgvr46U9t1xoQBM8T4BL8SxrN66Le2xYAPSaDJJKeztV3awugusb3g3G9iL8StmkBBXhcbbXhg==
+
 currently-unhandled@^0.4.1:
   version "0.4.1"
   resolved "https://registry.yarnpkg.com/currently-unhandled/-/currently-unhandled-0.4.1.tgz#988df33feab191ef799a61369dd76c17adf957ea"