fix(eslint-plugin): [no-unnecessary-condition] false positive when ar…

…ray predicate returns unknown (#2772)

packages/eslint-plugin/src/rules/no-unnecessary-condition.ts

@@ -450,6 +450,10 @@ export default createRule<Options, MessageId>({
           // Not a callable function
           return;
         }
+        // Predicate is always necessary if it involves `any` or `unknown`
+        if (returnTypes.some(t => isTypeAnyType(t) || isTypeUnknownType(t))) {
+          return;
+        }
         if (!returnTypes.some(isPossiblyFalsy)) {
           return context.report({
             node: callback,

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

@@ -235,6 +235,14 @@ function length(x: string) {
 function nonEmptyStrings(x: string[]) {
   return x.filter(length);
 }
+
+// filter-like predicate
+function count(
+  list: string[],
+  predicate: (value: string, index: number, array: string[]) => unknown,
+) {
+  return list.filter(predicate).length;
+}
     `,
     // Ignores non-array methods of the same name
     `