feat: for-direction rule add check for condition in reverse order (#1…

…7755) feat: add check to for-direction rule when the condition is in reverse order
eslint · Nov 17, 2023 · a7a883b · a7a883b
1 parent 1452dc9
commit a7a883b
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Showing 3 changed files with 48 additions and 17 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
@@ -101,30 +101,37 @@ module.exports = {
             }
             return 0;
         }
+
         return {
             ForStatement(node) {
 
-                if (node.test && node.test.type === "BinaryExpression" && node.test.left.type === "Identifier" && node.update) {
-                    const counter = node.test.left.name;
-                    const operator = node.test.operator;
-                    const update = node.update;
+                if (node.test && node.test.type === "BinaryExpression" && node.update) {
+                    for (const counterPosition of ["left", "right"]) {
+                        if (node.test[counterPosition].type !== "Identifier") {
+                            continue;
+                        }
 
-                    let wrongDirection;
+                        const counter = node.test[counterPosition].name;
+                        const operator = node.test.operator;
+                        const update = node.update;
 
-                    if (operator === "<" || operator === "<=") {
-                        wrongDirection = -1;
-                    } else if (operator === ">" || operator === ">=") {
-                        wrongDirection = 1;
-                    } else {
-                        return;
-                    }
+                        let wrongDirection;
+
+                        if (operator === "<" || operator === "<=") {
+                            wrongDirection = counterPosition === "left" ? -1 : 1;
+                        } else if (operator === ">" || operator === ">=") {
+                            wrongDirection = counterPosition === "left" ? 1 : -1;
+                        } else {
+                            return;
+                        }
 
-                    if (update.type === "UpdateExpression") {
-                        if (getUpdateDirection(update, counter) === wrongDirection) {
+                        if (update.type === "UpdateExpression") {
+                            if (getUpdateDirection(update, counter) === wrongDirection) {
+                                report(node);
+                            }
+                        } else if (update.type === "AssignmentExpression" && getAssignmentDirection(update, counter) === wrongDirection) {
                             report(node);
                         }
-                    } else if (update.type === "AssignmentExpression" && getAssignmentDirection(update, counter) === wrongDirection) {
-                        report(node);
                     }
                 }
             }

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){}",
@@ -44,6 +50,9 @@ ruleTester.run("for-direction", rule, {
         "for(var i = 0; i < MAX; i -= ~2);",
         "for(var i = 0, n = -1; i < MAX; i += -n);",
 
+        // test if '+=', '-=' with counter 'i' on the right side of test condition
+        "for(var i = 0; 10 > i; i+=1){}",
+
         // test if no update.
         "for(var i = 10; i > 0;){}",
         "for(var i = 10; i >= 0;){}",
@@ -82,6 +91,12 @@ 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] },
@@ -96,6 +111,9 @@ ruleTester.run("for-direction", rule, {
         { code: "for(var i = MIN; i <= MAX; i-=true){}", errors: [incorrectDirection] },
         { code: "for(var i = 0; i < 10; i-=+5e-7){}", errors: [incorrectDirection] },
         { code: "for(var i = 0; i < MAX; i += (2 - 3));", errors: [incorrectDirection] },
-        { code: "var n = -2; for(var i = 0; i < 10; i += n);", errors: [incorrectDirection] }
+        { code: "var n = -2; for(var i = 0; i < 10; i += n);", errors: [incorrectDirection] },
+
+        // test if '+=', '-=' with counter 'i' on the right side of test condition
+        { code: "for(var i = 0; 10 > i; i-=1){}", errors: [incorrectDirection] }
     ]
 });