Fix: no-useless-rest-spread about holes (fixes #14)

Author: mysticatea

lib/rules/no-useless-rest-spread.js

@@ -21,6 +21,15 @@ function isCommaToken(token) {
     return token.type === "Punctuator" && token.value === ","
 }
 
+/**
+ * Check whether a given node is a hole.
+ * @param {ASTNode|null} element The node to check.
+ * @returns {boolean} `true` if the node is a hole.
+ */
+function isHole(element) {
+    return element == null
+}
+
 /**
  * Gets the last token of the given node's elements.
  * This skips trailing commas.
@@ -50,6 +59,11 @@ function defineFixer(sourceCode, node) {
     return (fixer) => {
         const child = node.argument
 
+        // If the inner array includes holes, do nothing.
+        if (child.elements != null && child.elements.some(isHole)) {
+            return null
+        }
+
         // Remove this element if it's empty.
         if ((child.elements || child.properties).length === 0) {
             const next = sourceCode.getTokenAfter(node)

tests/lib/rules/no-useless-rest-spread.js

@@ -116,5 +116,37 @@ ruleTester.run("no-useless-rest-spread", rule, {
             output: "let obj = { ...b}",
             errors: ["Redundant spread property."],
         },
+
+        // Don't auto-fix if the inner array has holes.
+        {
+            code: "let list = [a, ...[,]]",
+            output: null,
+            errors: ["Redundant spread element."],
+        },
+        {
+            code: "let list = [a, ...[b,,c]]",
+            output: null,
+            errors: ["Redundant spread element."],
+        },
+        {
+            code: "foo(a, ...[,])",
+            output: null,
+            errors: ["Redundant spread element."],
+        },
+        {
+            code: "let [a, ...[,]] = list",
+            output: null,
+            errors: ["Redundant rest element."],
+        },
+        {
+            code: "let [a, ...[,]] = list",
+            output: null,
+            errors: ["Redundant rest element."],
+        },
+        {
+            code: "function foo(a, ...[,]) {}",
+            output: null,
+            errors: ["Redundant rest parameter."],
+        },
     ],
 })