feat(eslint-plugin): [no-unnesc-cond] check array predicates by default

typescript-eslint · Feb 7, 2020 · 8f676df · 8f676df
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diff --git a/packages/eslint-plugin/docs/rules/no-unnecessary-condition.md b/packages/eslint-plugin/docs/rules/no-unnecessary-condition.md
@@ -28,6 +28,12 @@ function bar<T>(arg: string) {
   // arg can never be nullish, so ?. is unnecessary
   return arg?.length;
 }
+
+// Checks array predicate return types, where possible
+[
+  [1, 2],
+  [3, 4],
+].filter(t => t); // number[] is always truthy
 ```
 
 Examples of **correct** code for this rule:
@@ -50,6 +56,8 @@ function bar(arg?: string | null) {
   // Necessary, since arg might be nullish
   return arg?.length;
 }
+
+[0, 1, 2, 3].filter(t => t); // number can be truthy or falsy
 ```
 
 ## Options
@@ -74,19 +82,6 @@ for (; true; ) {}
 do {} while (true);
 ```
 
-- `checkArrayPredicates` (default: `false`) - if set checks that the return value from certain array method callbacks (`filter`, `find`, `some`, `every`) is necessarily conditional.
-
-```ts
-// Valid: numbers can be truthy or falsy.
-[0, 1, 2, 3].filter(t => t);
-
-// Invalid: arrays are always falsy.
-[
-  [1, 2],
-  [3, 4],
-].filter(t => t);
-```
-
 ## When Not To Use It
 
 The main downside to using this rule is the need for type information.

diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts b/packages/eslint-plugin/src/rules/no-unnecessary-condition.ts
@@ -61,7 +61,6 @@ export type Options = [
   {
     allowConstantLoopConditions?: boolean;
     ignoreRhs?: boolean;
-    checkArrayPredicates?: boolean;
   },
 ];
 
@@ -96,9 +95,6 @@ export default createRule<Options, MessageId>({
           ignoreRhs: {
             type: 'boolean',
           },
-          checkArrayPredicates: {
-            type: 'boolean',
-          },
         },
         additionalProperties: false,
       },
@@ -125,13 +121,9 @@ export default createRule<Options, MessageId>({
     {
       allowConstantLoopConditions: false,
       ignoreRhs: false,
-      checkArrayPredicates: false,
     },
   ],
-  create(
-    context,
-    [{ allowConstantLoopConditions, checkArrayPredicates, ignoreRhs }],
-  ) {
+  create(context, [{ allowConstantLoopConditions, ignoreRhs }]) {
     const service = getParserServices(context);
     const checker = service.program.getTypeChecker();
     const sourceCode = context.getSourceCode();
@@ -299,8 +291,6 @@ export default createRule<Options, MessageId>({
     function shouldCheckCallback(node: TSESTree.CallExpression): boolean {
       const { callee } = node;
       return (
-        // option is on
-        !!checkArrayPredicates &&
         // looks like `something.filter` or `something.find`
         callee.type === AST_NODE_TYPES.MemberExpression &&
         callee.property.type === AST_NODE_TYPES.Identifier &&

diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts
@@ -91,20 +91,7 @@ function test(a: string) {
     /**
      * Predicate functions
      **/
-    // valid, with the flag off
     `
-[1,3,5].filter(() => true);
-[1,2,3].find(() => false);
-function truthy() {
-  return [];
-}
-function falsy() {}
-[1,3,5].filter(truthy);
-[1,2,3].find(falsy);
-`,
-    {
-      options: [{ checkArrayPredicates: true }],
-      code: `
 // with literal arrow function
 [0,1,2].filter(x => x);
 
@@ -117,22 +104,16 @@ function length(x: string) {
 // with non-literal array
 function nonEmptyStrings(x: string[]) {
   return x.filter(length);
-}
-`,
-    },
+}`,
     // Ignores non-array methods of the same name
-    {
-      options: [{ checkArrayPredicates: true }],
-      code: `
+    `
 const notArray = {
   filter: (func: () => boolean) => func(),
   find: (func: () => boolean) => func(),
 };
 notArray.filter(() => true);
 notArray.find(() => true);
 `,
-    },
-
     // Nullish coalescing operator
     `
 function test(a: string | null) {
@@ -336,7 +317,6 @@ function test(a: never) {
 
     // Predicate functions
     {
-      options: [{ checkArrayPredicates: true }],
       code: `
 [1,3,5].filter(() => true);
 [1,2,3].find(() => { return false; });
@@ -363,7 +343,6 @@ function nothing3(x: [string, string]) {
       ],
     },
     {
-      options: [{ checkArrayPredicates: true }],
       code: `
 function truthy() {
   return [];
@@ -380,7 +359,6 @@ function falsy() {}
     // Supports generics
     // TODO: fix this
     //     {
-    //       options: [{ checkArrayPredicates: true }],
     //       code: `
     // const isTruthy = <T>(t: T) => T;
     // // Valid: numbers can be truthy or falsy (0).