fix(eslint-plugin): [prefer-nullish-coalescing] handle case when type…

… of left side is null or undefined (#7225)
typescript-eslint · Jul 17, 2023 · b62affe · b62affe
1 parent 0fef2e3
commit b62affe
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diff --git a/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts b/packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
@@ -310,6 +310,8 @@ export default util.createRule<Options, MessageIds>({
           .filter((flag): flag is number => flag !== undefined)
           .reduce((previous, flag) => previous | flag, 0);
         if (
+          type.flags !== ts.TypeFlags.Null &&
+          type.flags !== ts.TypeFlags.Undefined &&
           (type as ts.UnionOrIntersectionType).types.some(t =>
             tsutils.isTypeFlagSet(t, ignorableFlags),
           )

diff --git a/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts b/packages/eslint-plugin/tests/rules/prefer-nullish-coalescing.test.ts
@@ -1208,5 +1208,47 @@ x || y;
         },
       ],
     },
+    {
+      code: `
+declare const x: null;
+x || y;
+      `,
+      errors: [
+        {
+          messageId: 'preferNullishOverOr',
+        },
+      ],
+    },
+    {
+      code: `
+const x = undefined;
+x || y;
+      `,
+      errors: [
+        {
+          messageId: 'preferNullishOverOr',
+        },
+      ],
+    },
+    {
+      code: `
+null || y;
+      `,
+      errors: [
+        {
+          messageId: 'preferNullishOverOr',
+        },
+      ],
+    },
+    {
+      code: `
+undefined || y;
+      `,
+      errors: [
+        {
+          messageId: 'preferNullishOverOr',
+        },
+      ],
+    },
   ],
 });