1 files changed, 129 insertions, 0 deletions
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/prefer-boolean-length-check.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/prefer-boolean-length-check.js
new file mode 100644
index 0000000000..0e2685ec28
--- /dev/null
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/prefer-boolean-length-check.js
@@ -0,0 +1,129 @@
+/**
+ * @fileoverview Prefer boolean length check
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+"use strict";
+
+function funcForBooleanLength(context, node, conditionCheck) {
+  let newText = "";
+  const sourceCode = context.getSourceCode();
+  switch (node.operator) {
+    case ">":
+      if (node.right.value == 0) {
+        if (conditionCheck) {
+          newText = sourceCode.getText(node.left);
+        } else {
+          newText = "!!" + sourceCode.getText(node.left);
+        }
+      } else {
+        newText = "!" + sourceCode.getText(node.right);
+      }
+      break;
+    case "<":
+      if (node.right.value == 0) {
+        newText = "!" + sourceCode.getText(node.left);
+      } else if (conditionCheck) {
+        newText = sourceCode.getText(node.right);
+      } else {
+        newText = "!!" + sourceCode.getText(node.right);
+      }
+      break;
+    case "==":
+      if (node.right.value == 0) {
+        newText = "!" + sourceCode.getText(node.left);
+      } else {
+        newText = "!" + sourceCode.getText(node.right);
+      }
+      break;
+    case "!=":
+      if (node.right.value == 0) {
+        if (conditionCheck) {
+          newText = sourceCode.getText(node.left);
+        } else {
+          newText = "!!" + sourceCode.getText(node.left);
+        }
+      } else if (conditionCheck) {
+        newText = sourceCode.getText(node.right);
+      } else {
+        newText = "!!" + sourceCode.getText(node.right);
+      }
+      break;
+  }
+  return newText;
+}
+
+module.exports = {
+  meta: {
+    docs: {
+      url: "https://firefox-source-docs.mozilla.org/code-quality/lint/linters/eslint-plugin-mozilla/prefer-boolean-length-check.html",
+    },
+    fixable: "code",
+    messages: {
+      preferBooleanCheck: "Prefer boolean length check",
+    },
+    schema: [],
+    type: "suggestion",
+  },
+
+  create(context) {
+    const conditionStatement = [
+      "IfStatement",
+      "WhileStatement",
+      "DoWhileStatement",
+      "ForStatement",
+      "ForInStatement",
+      "ConditionalExpression",
+    ];
+
+    return {
+      BinaryExpression(node) {
+        if (
+          ["==", "!=", ">", "<"].includes(node.operator) &&
+          ((node.right.type == "Literal" &&
+            node.right.value == 0 &&
+            node.left.property?.name == "length") ||
+            (node.left.type == "Literal" &&
+              node.left.value == 0 &&
+              node.right.property?.name == "length"))
+        ) {
+          if (
+            conditionStatement.includes(node.parent.type) ||
+            (node.parent.type == "LogicalExpression" &&
+              conditionStatement.includes(node.parent.parent.type))
+          ) {
+            context.report({
+              node,
+              fix: fixer => {
+                let generateExpression = funcForBooleanLength(
+                  context,
+                  node,
+                  true
+                );
+
+                return fixer.replaceText(node, generateExpression);
+              },
+              messageId: "preferBooleanCheck",
+            });
+          } else {
+            context.report({
+              node,
+              fix: fixer => {
+                let generateExpression = funcForBooleanLength(
+                  context,
+                  node,
+                  false
+                );
+                return fixer.replaceText(node, generateExpression);
+              },
+              messageId: "preferBooleanCheck",
+            });
+          }
+        }
+      },
+    };
+  },
+};