From 0c86b68a6e2435eb03b681b51b099b552b521adc Mon Sep 17 00:00:00 2001
From: Stephen Wade <stephen@stephenwade.me>
Date: Sat, 14 Aug 2021 19:16:11 -0400
Subject: [PATCH] Chore: Replace old syntax for Array flat/flatMap (#14614)

---
 lib/linter/apply-disable-directives.js | 19 ++-----------------
 lib/linter/linter.js                   |  3 +--
 lib/linter/node-event-generator.js     |  4 +---
 lib/rules/max-lines.js                 | 16 +---------------
 4 files changed, 5 insertions(+), 37 deletions(-)

diff --git a/lib/linter/apply-disable-directives.js b/lib/linter/apply-disable-directives.js
index de81c24447f..20085ed4fe9 100644
--- a/lib/linter/apply-disable-directives.js
+++ b/lib/linter/apply-disable-directives.js
@@ -96,20 +96,6 @@ function createCommentRemoval(directives, commentToken) {
     };
 }
 
-/**
- * Returns a new array formed by applying a given callback function to each element of the array, and then flattening the result by one level.
- * TODO(stephenwade): Replace this with array.flatMap when we drop support for Node v10
- * @param {any[]} array The array to process
- * @param {Function} fn The function to use
- * @returns {any[]} The result array
- */
-function flatMap(array, fn) {
-    const mapped = array.map(fn);
-    const flattened = [].concat(...mapped);
-
-    return flattened;
-}
-
 /**
  * Parses details from directives to create output Problems.
  * @param {Directive[]} allDirectives Unused directives to be removed.
@@ -118,8 +104,7 @@ function flatMap(array, fn) {
 function processUnusedDisableDirectives(allDirectives) {
     const directiveGroups = groupByParentComment(allDirectives);
 
-    return flatMap(
-        directiveGroups,
+    return directiveGroups.flatMap(
         directives => {
             const { parentComment } = directives[0].unprocessedDirective;
             const remainingRuleIds = new Set(parentComment.ruleIds);
@@ -247,7 +232,7 @@ module.exports = ({ directives, disableFixes, problems, reportUnusedDisableDirec
         .map(directive => Object.assign({}, directive, { unprocessedDirective: directive }))
         .sort(compareLocations);
 
-    const lineDirectives = flatMap(directives, directive => {
+    const lineDirectives = directives.flatMap(directive => {
         switch (directive.type) {
             case "disable":
             case "enable":
diff --git a/lib/linter/linter.js b/lib/linter/linter.js
index ae564b6610b..a140b4b1bef 100644
--- a/lib/linter/linter.js
+++ b/lib/linter/linter.js
@@ -1310,8 +1310,7 @@ class Linter {
         const text = ensureText(textOrSourceCode);
         const preprocess = options.preprocess || (rawText => [rawText]);
 
-        // TODO(stephenwade): Replace this with array.flat() when we drop support for Node v10
-        const postprocess = options.postprocess || (array => [].concat(...array));
+        const postprocess = options.postprocess || (messagesList => messagesList.flat());
         const filterCodeBlock =
             options.filterCodeBlock ||
             (blockFilename => blockFilename.endsWith(".js"));
diff --git a/lib/linter/node-event-generator.js b/lib/linter/node-event-generator.js
index 8b619fdff83..9b058247b3e 100644
--- a/lib/linter/node-event-generator.js
+++ b/lib/linter/node-event-generator.js
@@ -37,9 +37,7 @@ const esquery = require("esquery");
  * @returns {any[]} The union of the input arrays
  */
 function union(...arrays) {
-
-    // TODO(stephenwade): Replace this with arrays.flat() when we drop support for Node v10
-    return [...new Set([].concat(...arrays))];
+    return [...new Set(arrays.flat())];
 }
 
 /**
diff --git a/lib/rules/max-lines.js b/lib/rules/max-lines.js
index 8bd5a1c95f4..0837dd1f0fd 100644
--- a/lib/rules/max-lines.js
+++ b/lib/rules/max-lines.js
@@ -137,20 +137,6 @@ module.exports = {
             return [];
         }
 
-        /**
-         * Returns a new array formed by applying a given callback function to each element of the array, and then flattening the result by one level.
-         * TODO(stephenwade): Replace this with array.flatMap when we drop support for Node v10
-         * @param {any[]} array The array to process
-         * @param {Function} fn The function to use
-         * @returns {any[]} The result array
-         */
-        function flatMap(array, fn) {
-            const mapped = array.map(fn);
-            const flattened = [].concat(...mapped);
-
-            return flattened;
-        }
-
         return {
             "Program:exit"() {
                 let lines = sourceCode.lines.map((text, i) => ({
@@ -173,7 +159,7 @@ module.exports = {
                 if (skipComments) {
                     const comments = sourceCode.getAllComments();
 
-                    const commentLines = flatMap(comments, comment => getLinesWithoutCode(comment));
+                    const commentLines = comments.flatMap(getLinesWithoutCode);
 
                     lines = lines.filter(
                         l => !commentLines.includes(l.lineNumber)