From 2cda91f1c55d5995c6316621c5ca02cd69406680 Mon Sep 17 00:00:00 2001
From: Joshua Chen <sidachen2003@gmail.com>
Date: Thu, 9 Mar 2023 22:19:47 -0500
Subject: [PATCH] feat(eslint-plugin): [no-unnecessary-cond] check logical
 assignments

---
 .../src/rules/no-unnecessary-condition.ts     |  13 ++
 .../rules/no-unnecessary-condition.test.ts    | 117 ++++++++++++++++++
 2 files changed, 130 insertions(+)

diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts b/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
index 4951e281af4e..6af9bc0e9e09 100644
--- a/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
+++ b/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
@@ -636,7 +636,20 @@ export default createRule<Options, MessageId>({
       checkOptionalChain(node, node.callee, '');
     }
 
+    function checkAssignmentExpression(
+      node: TSESTree.AssignmentExpression,
+    ): void {
+      // Similar to checkLogicalExpressionForUnnecessaryConditionals, since
+      // a ||= b is equivalent to a || (a = b)
+      if (['||=', '&&='].includes(node.operator)) {
+        checkNode(node.left);
+      } else if (node.operator === '??=') {
+        checkNodeForNullish(node.left);
+      }
+    }
+
     return {
+      AssignmentExpression: checkAssignmentExpression,
       BinaryExpression: checkIfBinaryExpressionIsNecessaryConditional,
       CallExpression: checkCallExpression,
       ConditionalExpression: (node): void => checkNode(node.test),
diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
index 96cad00c908b..e3647102305b 100644
--- a/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
@@ -548,6 +548,18 @@ interface Foo {
 type OptionalFoo = Foo | undefined;
 declare const foo: OptionalFoo;
 foo?.[1]?.length;
+    `,
+    `
+declare let foo: number | null;
+foo ??= 1;
+    `,
+    `
+declare let foo: number;
+foo ||= 1;
+    `,
+    `
+declare let foo: number;
+foo &&= 1;
     `,
     // https://github.com/typescript-eslint/typescript-eslint/issues/6264
     `
@@ -1676,5 +1688,110 @@ function getElem(dict: Record<string, { foo: string }>, key: string) {
         },
       ],
     },
+    {
+      code: `
+declare let foo: {};
+foo ??= 1;
+      `,
+      errors: [
+        {
+          messageId: 'neverNullish',
+          line: 3,
+          endLine: 3,
+          column: 1,
+          endColumn: 4,
+        },
+      ],
+    },
+    {
+      code: `
+declare let foo: number;
+foo ??= 1;
+      `,
+      errors: [
+        {
+          messageId: 'neverNullish',
+          line: 3,
+          endLine: 3,
+          column: 1,
+          endColumn: 4,
+        },
+      ],
+    },
+    {
+      code: `
+declare let foo: null;
+foo ??= null;
+      `,
+      errors: [
+        {
+          messageId: 'alwaysNullish',
+          line: 3,
+          endLine: 3,
+          column: 1,
+          endColumn: 4,
+        },
+      ],
+    },
+    {
+      code: `
+declare let foo: {};
+foo ||= 1;
+      `,
+      errors: [
+        {
+          messageId: 'alwaysTruthy',
+          line: 3,
+          endLine: 3,
+          column: 1,
+          endColumn: 4,
+        },
+      ],
+    },
+    {
+      code: `
+declare let foo: null;
+foo ||= null;
+      `,
+      errors: [
+        {
+          messageId: 'alwaysFalsy',
+          line: 3,
+          endLine: 3,
+          column: 1,
+          endColumn: 4,
+        },
+      ],
+    },
+    {
+      code: `
+declare let foo: {};
+foo &&= 1;
+      `,
+      errors: [
+        {
+          messageId: 'alwaysTruthy',
+          line: 3,
+          endLine: 3,
+          column: 1,
+          endColumn: 4,
+        },
+      ],
+    },
+    {
+      code: `
+declare let foo: null;
+foo &&= null;
+      `,
+      errors: [
+        {
+          messageId: 'alwaysFalsy',
+          line: 3,
+          endLine: 3,
+          column: 1,
+          endColumn: 4,
+        },
+      ],
+    },
   ],
 });