From 1543117874047726a6bc1b71bd2f68779f266591 Mon Sep 17 00:00:00 2001
From: Brad Zacher <brad.zacher@gmail.com>
Date: Sun, 8 Mar 2020 18:41:15 -0700
Subject: [PATCH] =?UTF-8?q?feat(eslint-plugin):=20[no-unsafe-member-access?=
 =?UTF-8?q?]=20report=20any=20typed=E2=80=A6=20(#1683)?=
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---
 .../docs/rules/no-unsafe-member-access.md     | 11 +++
 .../src/rules/no-unsafe-member-access.ts      | 36 ++++++++-
 .../rules/no-unsafe-member-access.test.ts     | 74 +++++++++++++++++++
 3 files changed, 120 insertions(+), 1 deletion(-)

diff --git a/packages/eslint-plugin/docs/rules/no-unsafe-member-access.md b/packages/eslint-plugin/docs/rules/no-unsafe-member-access.md
index e99b2536c16..29c8ea3dd97 100644
--- a/packages/eslint-plugin/docs/rules/no-unsafe-member-access.md
+++ b/packages/eslint-plugin/docs/rules/no-unsafe-member-access.md
@@ -23,6 +23,11 @@ nestedAny.prop['a'];
 
 const key = 'a';
 nestedAny.prop[key];
+
+// usng an any to access a member is unsafe
+const arr = [1, 2, 3];
+arr[anyVar];
+nestedAny[anyVar];
 ```
 
 Examples of **correct** code for this rule:
@@ -35,6 +40,12 @@ nestedAny.prop['a'];
 
 const key = 'a';
 nestedAny.prop[key];
+
+const arr = [1, 2, 3];
+arr[1];
+const idx = 1;
+arr[idx];
+arr[idx++];
 ```
 
 ## Related to
diff --git a/packages/eslint-plugin/src/rules/no-unsafe-member-access.ts b/packages/eslint-plugin/src/rules/no-unsafe-member-access.ts
index 298cd97561e..3d3b0c7e723 100644
--- a/packages/eslint-plugin/src/rules/no-unsafe-member-access.ts
+++ b/packages/eslint-plugin/src/rules/no-unsafe-member-access.ts
@@ -1,4 +1,7 @@
-import { TSESTree } from '@typescript-eslint/experimental-utils';
+import {
+  TSESTree,
+  AST_NODE_TYPES,
+} from '@typescript-eslint/experimental-utils';
 import * as util from '../util';
 
 const enum State {
@@ -19,6 +22,8 @@ export default util.createRule({
     messages: {
       unsafeMemberExpression:
         'Unsafe member access {{property}} on an any value',
+      unsafeComputedMemberAccess:
+        'Computed name {{property}} resolves to an any value',
     },
     schema: [],
   },
@@ -69,6 +74,35 @@ export default util.createRule({
 
     return {
       'MemberExpression, OptionalMemberExpression': checkMemberExpression,
+      ':matches(MemberExpression, OptionalMemberExpression)[computed = true] > *.property'(
+        node: TSESTree.Expression,
+      ): void {
+        if (
+          // x[1]
+          node.type === AST_NODE_TYPES.Literal ||
+          // x[1++] x[++x] etc
+          // FUN FACT - **all** update expressions return type number, regardless of the argument's type,
+          // because JS engines return NaN if there the argument is not a number.
+          node.type === AST_NODE_TYPES.UpdateExpression
+        ) {
+          // perf optimizations - literals can obviously never be `any`
+          return;
+        }
+
+        const tsNode = esTreeNodeToTSNodeMap.get(node);
+        const type = checker.getTypeAtLocation(tsNode);
+
+        if (util.isTypeAnyType(type)) {
+          const propertyName = sourceCode.getText(node);
+          context.report({
+            node,
+            messageId: 'unsafeComputedMemberAccess',
+            data: {
+              property: `[${propertyName}]`,
+            },
+          });
+        }
+      },
     };
   },
 });
diff --git a/packages/eslint-plugin/tests/rules/no-unsafe-member-access.test.ts b/packages/eslint-plugin/tests/rules/no-unsafe-member-access.test.ts
index 641e0492e5a..484d4690c16 100644
--- a/packages/eslint-plugin/tests/rules/no-unsafe-member-access.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-unsafe-member-access.test.ts
@@ -15,8 +15,16 @@ const ruleTester = new RuleTester({
 
 ruleTester.run('no-unsafe-member-access', rule, {
   valid: [
+    'function foo(x: { a: number }, y: any) { x[y++] }',
     'function foo(x: { a: number }) { x.a }',
     'function foo(x?: { a: number }) { x?.a }',
+    'function foo(x: { a: number }) { x["a"] }',
+    'function foo(x?: { a: number }) { x?.["a"] }',
+    'function foo(x: { a: number }, y: string) { x[y] }',
+    'function foo(x?: { a: number }, y: string) { x?.[y] }',
+    'function foo(x: string[]) { x[1] }',
+    'function foo(x?: string[]) { x?.[1++] }',
+    'function foo(x?: string[]) { x?.[(1 as any)++] }',
   ],
   invalid: [
     ...batchedSingleLineTests({
@@ -81,5 +89,71 @@ function foo(x: any) { x['a']['b']['c'] }
         },
       ],
     }),
+    ...batchedSingleLineTests({
+      code: `
+function foo(x: { a: number }, y: any) { x[y] }
+function foo(x?: { a: number }, y: any) { x?.[y] }
+function foo(x: { a: number }, y: any) { x[y += 1] }
+function foo(x: { a: number }, y: any) { x[1 as any] }
+function foo(x: { a: number }, y: any) { x[y()] }
+function foo(x: string[], y: any) { x[y] }
+      `,
+      errors: [
+        {
+          messageId: 'unsafeComputedMemberAccess',
+          data: {
+            property: '[y]',
+          },
+          line: 2,
+          column: 44,
+          endColumn: 45,
+        },
+        {
+          messageId: 'unsafeComputedMemberAccess',
+          data: {
+            property: '[y]',
+          },
+          line: 3,
+          column: 47,
+          endColumn: 48,
+        },
+        {
+          messageId: 'unsafeComputedMemberAccess',
+          data: {
+            property: '[y += 1]',
+          },
+          line: 4,
+          column: 44,
+          endColumn: 50,
+        },
+        {
+          messageId: 'unsafeComputedMemberAccess',
+          data: {
+            property: '[1 as any]',
+          },
+          line: 5,
+          column: 44,
+          endColumn: 52,
+        },
+        {
+          messageId: 'unsafeComputedMemberAccess',
+          data: {
+            property: '[y()]',
+          },
+          line: 6,
+          column: 44,
+          endColumn: 47,
+        },
+        {
+          messageId: 'unsafeComputedMemberAccess',
+          data: {
+            property: '[y]',
+          },
+          line: 7,
+          column: 39,
+          endColumn: 40,
+        },
+      ],
+    }),
   ],
 });