feat: logical-assignment-operators to report expressions with 3 opera…

…nds (#17600)

* fix: logical-assignment-operators to report expressions with 3 operands

* Apply suggestions from code review

Co-authored-by: Milos Djermanovic <milos.djermanovic@gmail.com>

* test: add more `??` test cases

* docs: add explanation of always option

* Update docs/src/rules/logical-assignment-operators.md

Co-authored-by: Nicholas C. Zakas <nicholas@humanwhocodes.com>

---------

Co-authored-by: Milos Djermanovic <milos.djermanovic@gmail.com>
Co-authored-by: Nicholas C. Zakas <nicholas@humanwhocodes.com>

docs/src/rules/logical-assignment-operators.md

@@ -10,7 +10,7 @@ For example `a = a || b` can be shortened to `a ||= b`.
 
 ## Rule Details
 
-This rule requires or disallows logical assignment operator shorthand.  
+This rule requires or disallows logical assignment operator shorthand.
 
 ### Options
 
@@ -27,6 +27,9 @@ Object option (only available if string option is set to `"always"`):
 
 #### always
 
+This option checks for expressions that can be shortened using logical assignment operator. For example, `a = a || b` can be shortened to `a ||= b`.
+Expressions with associativity such as `a = a || b || c` are reported as being able to be shortened to `a ||= b || c` unless the evaluation order is explicitly defined using parentheses, such as `a = (a || b) || c`.
+
 Examples of **incorrect** code for this rule with the default `"always"` option:
 
 ::: incorrect
@@ -40,6 +43,9 @@ a = a ?? b
 a || (a = b)
 a && (a = b)
 a ?? (a = b)
+a = a || b || c
+a = a && b && c
+a = a ?? b ?? c
 ```
 
 :::
@@ -58,6 +64,8 @@ a = b || c
 a || (b = c)
 
 if (a) a = b
+
+a = (a || b) || c
 ```
 
 :::

lib/rules/logical-assignment-operators.js

@@ -150,6 +150,31 @@ function isInsideWithBlock(node) {
     return node.parent.type === "WithStatement" && node.parent.body === node ? true : isInsideWithBlock(node.parent);
 }
 
+/**
+ * Gets the leftmost operand of a consecutive logical expression.
+ * @param {SourceCode} sourceCode The ESLint source code object
+ * @param {LogicalExpression} node LogicalExpression
+ * @returns {Expression} Leftmost operand
+ */
+function getLeftmostOperand(sourceCode, node) {
+    let left = node.left;
+
+    while (left.type === "LogicalExpression" && left.operator === node.operator) {
+
+        if (astUtils.isParenthesised(sourceCode, left)) {
+
+            /*
+             * It should have associativity,
+             * but ignore it if use parentheses to make the evaluation order clear.
+             */
+            return left;
+        }
+        left = left.left;
+    }
+    return left;
+
+}
+
 //------------------------------------------------------------------------------
 // Rule Definition
 //------------------------------------------------------------------------------
@@ -318,7 +343,10 @@ module.exports = {
 
             // foo = foo || bar
             "AssignmentExpression[operator='='][right.type='LogicalExpression']"(assignment) {
-                if (!astUtils.isSameReference(assignment.left, assignment.right.left)) {
+                const leftOperand = getLeftmostOperand(sourceCode, assignment.right);
+
+                if (!astUtils.isSameReference(assignment.left, leftOperand)
+                ) {
                     return;
                 }
 
@@ -342,10 +370,10 @@ module.exports = {
                         yield ruleFixer.insertTextBefore(assignmentOperatorToken, assignment.right.operator);
 
                         // -> foo ||= bar
-                        const logicalOperatorToken = getOperatorToken(assignment.right);
+                        const logicalOperatorToken = getOperatorToken(leftOperand.parent);
                         const firstRightOperandToken = sourceCode.getTokenAfter(logicalOperatorToken);
 
-                        yield ruleFixer.removeRange([assignment.right.range[0], firstRightOperandToken.range[0]]);
+                        yield ruleFixer.removeRange([leftOperand.parent.range[0], firstRightOperandToken.range[0]]);
                     }
                 };
 

tests/lib/rules/logical-assignment-operators.js

@@ -354,6 +354,28 @@ ruleTester.run("logical-assignment-operators", rule, {
         }, {
             code: "a.b = a.b || c",
             options: ["never"]
+        },
+
+        // 3 or more operands
+        {
+            code: "a = a && b || c",
+            options: ["always"]
+        },
+        {
+            code: "a = a && b && c || d",
+            options: ["always"]
+        },
+        {
+            code: "a = (a || b) || c", // Allow if parentheses are used.
+            options: ["always"]
+        },
+        {
+            code: "a = (a && b) && c", // Allow if parentheses are used.
+            options: ["always"]
+        },
+        {
+            code: "a = (a ?? b) ?? c", // Allow if parentheses are used.
+            options: ["always"]
         }
     ],
     invalid: [
@@ -1511,6 +1533,151 @@ ruleTester.run("logical-assignment-operators", rule, {
                     output: "(a.b.c ||= d) as number"
                 }]
             }]
+        },
+
+        // 3 or more operands
+        {
+            code: "a = a || b || c",
+            output: "a ||= b || c",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "||=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = a && b && c",
+            output: "a &&= b && c",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "&&=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = a ?? b ?? c",
+            output: "a ??= b ?? c",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "??=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = a || b && c",
+            output: "a ||= b && c",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "||=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = a || b || c || d",
+            output: "a ||= b || c || d",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "||=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = a && b && c && d",
+            output: "a &&= b && c && d",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "&&=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = a ?? b ?? c ?? d",
+            output: "a ??= b ?? c ?? d",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "??=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = a || b || c && d",
+            output: "a ||= b || c && d",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "||=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = a || b && c || d",
+            output: "a ||= b && c || d",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "||=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = (a) || b || c",
+            output: "a ||= b || c",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "||=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = a || (b || c) || d",
+            output: "a ||= (b || c) || d",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "||=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = (a || b || c)",
+            output: "a ||= (b || c)",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "||=" },
+                suggestions: []
+            }]
+        },
+        {
+            code: "a = ((a) || (b || c) || d)",
+            output: "a ||= ((b || c) || d)",
+            options: ["always"],
+            errors: [{
+                messageId: "assignment",
+                type: "AssignmentExpression",
+                data: { operator: "||=" },
+                suggestions: []
+            }]
         }
     ]
 });