Warn in Typescript when using Array.flat() or .flatMap() without polyfill (#37558)

* Warn in Typescript when using Array.flat() or .flatMap() without polyfill

* Update ecma version provided to babel in eslint

* Update per review comments

packages/eslint-config-kibana/.eslintrc.js

@@ -7,11 +7,11 @@ module.exports = {
   plugins: ['@kbn/eslint-plugin-eslint'],
 
   parserOptions: {
-    ecmaVersion: 6
+    ecmaVersion: 2018
   },
 
   env: {
-    es6: true
+    es6: true,
   },
 
   rules: {

packages/eslint-config-kibana/javascript.js

@@ -44,8 +44,7 @@ module.exports = {
 
       parserOptions: {
         sourceType: 'module',
-        ecmaVersion: 6,
-        ecmaFeatures: { experimentalObjectRestSpread: true },
+        ecmaVersion: 2018,
       },
 
       rules: {

packages/eslint-config-kibana/typescript.js

@@ -42,9 +42,8 @@ module.exports = {
 
       parserOptions: {
         sourceType: 'module',
-        ecmaVersion: 6,
+        ecmaVersion: 2018,
         ecmaFeatures: {
-          experimentalObjectRestSpread: true,
           jsx: true
         },
         // NOTE: That is to avoid a known performance issue related with the `ts.Program` used by

packages/kbn-eslint-plugin-eslint/rules/__tests__/disallow_license_headers.js

@@ -24,7 +24,7 @@ const dedent = require('dedent');
 const ruleTester = new RuleTester({
   parser: 'babel-eslint',
   parserOptions: {
-    ecmaVersion: 2015,
+    ecmaVersion: 2018,
   },
 });
 

packages/kbn-eslint-plugin-eslint/rules/__tests__/no_restricted_paths.js

@@ -35,7 +35,7 @@ const ruleTester = new RuleTester({
   parser: 'babel-eslint',
   parserOptions: {
     sourceType: 'module',
-    ecmaVersion: 2015,
+    ecmaVersion: 2018,
   },
 });
 

packages/kbn-eslint-plugin-eslint/rules/__tests__/require_license_header.js

@@ -24,7 +24,7 @@ const dedent = require('dedent');
 const ruleTester = new RuleTester({
   parser: 'babel-eslint',
   parserOptions: {
-    ecmaVersion: 2015,
+    ecmaVersion: 2018,
   },
 });
 

src/core/public/utils/integration_tests/__fixtures__/frozen_object_mutation/tsconfig.json

@@ -3,7 +3,7 @@
     "strict": true,
     "skipLibCheck": true,
     "lib": [
-      "esnext"
+      "es2018"
     ]
   },
   "files": [

tsconfig.json

@@ -20,8 +20,9 @@
     "strict": true,
     // enables "core language features"
     "lib": [
-      // ESNext auto includes previous versions all the way back to es5
-      "esnext",
+      // ES2018 includes previous versions all the way back to es5
+      // We are not using esnext because @babel/polyfill is on core-js 2, not 3
+      "es2018",
       // includes support for browser APIs
       "dom"
     ],

x-pack/plugins/apm/public/components/app/ServiceDetails/MetricsChart.tsx

@@ -57,8 +57,8 @@ function getYTickFormatter(chart: GenericMetricsChart) {
   switch (chart.yUnit) {
     case 'bytes': {
       const max = Math.max(
-        ...chart.series.flatMap(series =>
-          series.data.map(coord => coord.y || 0)
+        ...chart.series.map(({ data }) =>
+          Math.max(...data.map(({ y }) => y || 0))
         )
       );
       return getFixedByteFormatter(max);

x-pack/plugins/canvas/public/lib/aeroelastic/tsconfig.json

@@ -2,7 +2,7 @@
   "extends": "../../../../../tsconfig",
   "compilerOptions": {
     "module": "commonjs",
-    "lib": ["esnext", "dom"],
+    "lib": ["es2018", "dom"],
     "noImplicitAny": true,
     "strictNullChecks": true,
     "strictFunctionTypes": false,

x-pack/plugins/code/public/reducers/symbol.ts

@@ -73,10 +73,11 @@ const generateStructureTree: (symbols: SymbolInformation[]) => any = symbols =>
     if (result) {
       return result;
     } else {
-      const subTree = tree
-        .filter(s => s.members)
-        .map(s => s.members)
-        .flat();
+      // TODO: Use Array.flat once supported
+      const subTree = tree.reduce(
+        (s, t) => (t.members ? s.concat(t.members) : s),
+        [] as SymbolWithMembers[]
+      );
       if (subTree.length > 0) {
         return findContainer(subTree, containerName);
       } else {