feat: add check to for-direction rule when the condition is in revers…

…e order
eslint · Nov 13, 2023 · 9617521 · 9617521
1 parent eb2279e
commit 9617521
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Showing 3 changed files with 38 additions and 4 deletions.
diff --git a/docs/src/rules/for-direction.md b/docs/src/rules/for-direction.md
@@ -24,6 +24,9 @@ for (var i = 10; i >= 0; i++) {
 for (var i = 0; i > 10; i++) {
 }
 
+for (var i = 0; 10 > i; i--) {
+}
+
 const n = -2;
 for (let i = 0; i < 10; i += n) {
 }
@@ -40,6 +43,9 @@ Examples of **correct** code for this rule:
 for (var i = 0; i < 10; i++) {
 }
 
+for (var i = 0; 10 > i; i++) { // with counter "i" on the right
+}
+
 for (let i = 10; i >= 0; i += this.step) { // direction unknown
 }
 

diff --git a/lib/rules/for-direction.js b/lib/rules/for-direction.js
@@ -101,20 +101,36 @@ module.exports = {
             }
             return 0;
         }
+
+        /**
+         * get the counter position in test
+         * @param {ASTNode} node the node to check
+         * @returns {"left" | "right"} the position of the counter respect to BinaryExpression
+         */
+        function getCounterPosition(node) {
+            if (node.update.type === "UpdateExpression" || node.update.type === "AssignmentExpression") {
+                if (node.update.argument && node.update.argument.type === "Identifier") {
+                    return node.test.left.name === node.update.argument.name ? "left" : "right";
+                }
+            }
+            return "left";
+        }
+
         return {
             ForStatement(node) {
 
-                if (node.test && node.test.type === "BinaryExpression" && node.test.left.type === "Identifier" && node.update) {
-                    const counter = node.test.left.name;
+                if (node.test && node.test.type === "BinaryExpression" && (node.test.left.type === "Identifier" || node.test.right.type === "Identifier") && node.update) {
+                    const counterPosition = getCounterPosition(node);
+                    const counter = node.test[counterPosition].name;
                     const operator = node.test.operator;
                     const update = node.update;
 
                     let wrongDirection;
 
                     if (operator === "<" || operator === "<=") {
-                        wrongDirection = -1;
+                        wrongDirection = counterPosition === "left" ? -1 : 1;
                     } else if (operator === ">" || operator === ">=") {
-                        wrongDirection = 1;
+                        wrongDirection = counterPosition === "left" ? 1 : -1;
                     } else {
                         return;
                     }

diff --git a/tests/lib/rules/for-direction.js b/tests/lib/rules/for-direction.js
@@ -28,6 +28,12 @@ ruleTester.run("for-direction", rule, {
         "for(var i = 10; i > 0; i--){}",
         "for(var i = 10; i >= 0; i--){}",
 
+        // test if '++', '--' with counter 'i' on the right side of test condition
+        "for(var i = 0; 10 > i; i++){}",
+        "for(var i = 0; 10 >= i; i++){}",
+        "for(var i = 10; 0 < i; i--){}",
+        "for(var i = 10; 0 <= i; i--){}",
+
         // test if '+=', '-=',
         "for(var i = 0; i < 10; i+=1){}",
         "for(var i = 0; i <= 10; i+=1){}",
@@ -82,6 +88,12 @@ ruleTester.run("for-direction", rule, {
         { code: "for(var i = 10; i > 10; i++){}", errors: [incorrectDirection] },
         { code: "for(var i = 10; i >= 0; i++){}", errors: [incorrectDirection] },
 
+        // test if '++', '--' with counter 'i' on the right side of test condition
+        { code: "for(var i = 0; 10 > i; i--){}", errors: [incorrectDirection] },
+        { code: "for(var i = 0; 10 >= i; i--){}", errors: [incorrectDirection] },
+        { code: "for(var i = 10; 10 < i; i++){}", errors: [incorrectDirection] },
+        { code: "for(var i = 10; 0 <= i; i++){}", errors: [incorrectDirection] },
+
         // test if '+=', '-='
         { code: "for(var i = 0; i < 10; i-=1){}", errors: [incorrectDirection] },
         { code: "for(var i = 0; i <= 10; i-=1){}", errors: [incorrectDirection] },