fix(eslint-plugin): [no-unnecessary-condition] false positives with b…

…randed types (typescript-eslint#7293)
MBuchalik · Aug 13, 2023 · 7545695 · 7545695
1 parent 479f9f6
commit 7545695
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diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts b/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
@@ -31,6 +31,9 @@ const isPossiblyFalsy = (type: ts.Type): boolean =>
     // PossiblyFalsy flag includes literal values, so exclude ones that
     // are definitely truthy
     .filter(t => !isTruthyLiteral(t))
+    // Intersections like `string & {}` can also be possibly falsy,
+    // requiring us to look into the intersection.
+    .flatMap(type => tsutils.intersectionTypeParts(type))
     .some(type => isTypeFlagSet(type, ts.TypeFlags.PossiblyFalsy));
 
 const isPossiblyTruthy = (type: ts.Type): boolean =>

diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
@@ -83,6 +83,11 @@ const result2 = foo() == null;
     necessaryConditionTest('null | object'),
     necessaryConditionTest('undefined | true'),
     necessaryConditionTest('void | true'),
+    // "branded" type
+    necessaryConditionTest('string & {}'),
+    necessaryConditionTest('string & { __brand: string }'),
+    necessaryConditionTest('number & {}'),
+    necessaryConditionTest('boolean & {}'),
 
     necessaryConditionTest('any'), // any
     necessaryConditionTest('unknown'), // unknown