1 files changed, 80 insertions, 0 deletions
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/no-comparison-or-assignment-inside-ok.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/no-comparison-or-assignment-inside-ok.js
new file mode 100644
index 0000000000..9bab06b000
--- /dev/null
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/no-comparison-or-assignment-inside-ok.js
@@ -0,0 +1,80 @@
+/**
+ * @fileoverview Don't allow accidental assignments inside `ok()`,
+ *               and encourage people to use appropriate alternatives
+ *               when using comparisons between 2 values.
+ *
+ * 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";
+
+const operatorToAssertionMap = {
+  "==": "Assert.equal",
+  "===": "Assert.strictEqual",
+  "!=": "Assert.notEqual",
+  "!==": "Assert.notStrictEqual",
+  ">": "Assert.greater",
+  "<": "Assert.less",
+  "<=": "Assert.lessOrEqual",
+  ">=": "Assert.greaterOrEqual",
+};
+
+module.exports = {
+  meta: {
+    docs: {
+      url: "https://firefox-source-docs.mozilla.org/code-quality/lint/linters/eslint-plugin-mozilla/rules/no-comparison-or-assignment-inside-ok.html",
+    },
+    fixable: "code",
+    messages: {
+      assignment:
+        "Assigning to a variable inside ok() is odd - did you mean to compare the two?",
+      comparison:
+        "Use dedicated assertion methods rather than ok(a {{operator}} b).",
+    },
+    schema: [],
+    type: "suggestion",
+  },
+
+  create(context) {
+    const exprs = new Set(["BinaryExpression", "AssignmentExpression"]);
+    return {
+      CallExpression(node) {
+        if (node.callee.type != "Identifier" || node.callee.name != "ok") {
+          return;
+        }
+        let firstArg = node.arguments[0];
+        if (!exprs.has(firstArg.type)) {
+          return;
+        }
+        if (firstArg.type == "AssignmentExpression") {
+          context.report({
+            node: firstArg,
+            messageId: "assignment",
+          });
+        } else if (
+          firstArg.type == "BinaryExpression" &&
+          operatorToAssertionMap.hasOwnProperty(firstArg.operator)
+        ) {
+          context.report({
+            node,
+            messageId: "comparison",
+            data: { operator: firstArg.operator },
+            fix: fixer => {
+              let left = context.sourceCode.getText(firstArg.left);
+              let right = context.sourceCode.getText(firstArg.right);
+              return [
+                fixer.replaceText(firstArg, left + ", " + right),
+                fixer.replaceText(
+                  node.callee,
+                  operatorToAssertionMap[firstArg.operator]
+                ),
+              ];
+            },
+          });
+        }
+      },
+    };
+  },
+};