explicit-length-check: Check Boolean(foo.length) (#951)

Author: fisker

docs/rules/explicit-length-check.md

@@ -79,6 +79,10 @@ const isNotEmpty = 0 < foo.length;
 const isNotEmpty = 1 <= foo.length;
 ```
 
+```js
+const isNotEmpty = Boolean(foo.length);
+```
+
 ```js
 // Negative style is forbidden too
 const isNotEmpty = !(foo.length === 0);

rules/explicit-length-check.js

@@ -11,12 +11,22 @@ const messages = {
 };
 
 const isLogicNot = node =>
+	node &&
 	node.type === 'UnaryExpression' &&
 	node.operator === '!';
 const isLogicNotArgument = node =>
-	node.parent &&
 	isLogicNot(node.parent) &&
 	node.parent.argument === node;
+const isBooleanCall = node =>
+	node &&
+	node.type === 'CallExpression' &&
+	node.callee &&
+	node.callee.type === 'Identifier' &&
+	node.callee.name === 'Boolean' &&
+	node.arguments.length === 1;
+const isBooleanCallArgument = node =>
+	isBooleanCall(node.parent) &&
+	node.parent.arguments[0] === node;
 const isCompareRight = (node, operator, value) =>
 	node.type === 'BinaryExpression' &&
 	node.operator === operator &&
@@ -62,9 +72,16 @@ const lengthSelector = [
 
 function getBooleanAncestor(node) {
 	let isNegative = false;
-	while (isLogicNotArgument(node)) {
-		isNegative = !isNegative;
-		node = node.parent;
+	// eslint-disable-next-line no-constant-condition
+	while (true) {
+		if (isLogicNotArgument(node)) {
+			isNegative = !isNegative;
+			node = node.parent;
+		} else if (isBooleanCallArgument(node)) {
+			node = node.parent;
+		} else {
+			break;
+		}
 	}
 
 	return {node, isNegative};
@@ -117,7 +134,12 @@ function getLengthCheckNode(node) {
 }
 
 function isBooleanNode(node) {
-	if (isLogicNot(node) || isLogicNotArgument(node)) {
+	if (
+		isLogicNot(node) ||
+		isLogicNotArgument(node) ||
+		isBooleanCall(node) ||
+		isBooleanCallArgument(node)
+	) {
 		return true;
 	}
 

test/explicit-length-check.js

@@ -39,6 +39,9 @@ test({
 		// Not boolean
 		'const bar = foo.length',
 		'const bar = +foo.length',
+		'const x = Boolean(foo.length, foo.length)',
+		'const x = new Boolean(foo.length)',
+		'const x = NotBoolean(foo.length)',
 
 		// Checking 'non-zero'
 		'if (foo.length > 0) {}',
@@ -119,5 +122,11 @@ test.visualize([
 	'const isEmpty = foo.length < 1;',
 	'bar(foo.length >= 1)',
 	'bar(!foo.length || foo.length)',
-	'const bar = void !foo.length;'
+	'const bar = void !foo.length;',
+	'const isNotEmpty = Boolean(foo.length)',
+	'const isNotEmpty = Boolean(foo.length || bar)',
+	'const isEmpty = Boolean(!foo.length)',
+	'const isEmpty = Boolean(foo.length === 0)',
+	'const isNotEmpty = !Boolean(foo.length === 0)',
+	'const isEmpty = !Boolean(!Boolean(foo.length === 0))'
 ]);

test/snapshots/explicit-length-check.js.md

@@ -891,3 +891,99 @@ Generated by [AVA](https://avajs.dev).
     > 1 | const bar = void !foo.length;␊
         |                  ^^^^^^^^^^^ Use `.length === 0` when checking length is zero.␊
     `
+
+## explicit-length-check - #15
+
+> Snapshot 1
+
+    `␊
+    Input:␊
+      1 | const isNotEmpty = Boolean(foo.length)␊
+    ␊
+    Output:␊
+      1 | const isNotEmpty = foo.length > 0␊
+    ␊
+    Error 1/1:␊
+    > 1 | const isNotEmpty = Boolean(foo.length)␊
+        |                    ^^^^^^^^^^^^^^^^^^^ Use `.length > 0` when checking length is not zero.␊
+    `
+
+## explicit-length-check - #16
+
+> Snapshot 1
+
+    `␊
+    Input:␊
+      1 | const isNotEmpty = Boolean(foo.length || bar)␊
+    ␊
+    Output:␊
+      1 | const isNotEmpty = Boolean(foo.length > 0 || bar)␊
+    ␊
+    Error 1/1:␊
+    > 1 | const isNotEmpty = Boolean(foo.length || bar)␊
+        |                            ^^^^^^^^^^ Use `.length > 0` when checking length is not zero.␊
+    `
+
+## explicit-length-check - #17
+
+> Snapshot 1
+
+    `␊
+    Input:␊
+      1 | const isEmpty = Boolean(!foo.length)␊
+    ␊
+    Output:␊
+      1 | const isEmpty = foo.length === 0␊
+    ␊
+    Error 1/1:␊
+    > 1 | const isEmpty = Boolean(!foo.length)␊
+        |                 ^^^^^^^^^^^^^^^^^^^^ Use `.length === 0` when checking length is zero.␊
+    `
+
+## explicit-length-check - #18
+
+> Snapshot 1
+
+    `␊
+    Input:␊
+      1 | const isEmpty = Boolean(foo.length === 0)␊
+    ␊
+    Output:␊
+      1 | const isEmpty = foo.length === 0␊
+    ␊
+    Error 1/1:␊
+    > 1 | const isEmpty = Boolean(foo.length === 0)␊
+        |                 ^^^^^^^^^^^^^^^^^^^^^^^^^ Use `.length === 0` when checking length is zero.␊
+    `
+
+## explicit-length-check - #19
+
+> Snapshot 1
+
+    `␊
+    Input:␊
+      1 | const isNotEmpty = !Boolean(foo.length === 0)␊
+    ␊
+    Output:␊
+      1 | const isNotEmpty = foo.length > 0␊
+    ␊
+    Error 1/1:␊
+    > 1 | const isNotEmpty = !Boolean(foo.length === 0)␊
+        |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `.length > 0` when checking length is not zero.␊
+    `
+
+## explicit-length-check - #20
+
+> Snapshot 1
+
+    `␊
+    Input:␊
+      1 | const isEmpty = !Boolean(!Boolean(foo.length === 0))␊
+    ␊
+    Output:␊
+      1 | const isEmpty = foo.length === 0␊
+    ␊
+    Error 1/1:␊
+    > 1 | const isEmpty = !Boolean(!Boolean(foo.length === 0))␊
+        |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `.length === 0` when checking length is zero.␊
+    `