fix: don't ignore engines with yarn v2+

lib/create-options.js

@@ -19,10 +19,6 @@ function createOptions(cwd, context) {
   options.env['TEMP'] = context.npmConfigTmp;
   options.env['TMP'] = context.npmConfigTmp;
   options.env['TMPDIR'] = context.npmConfigTmp;
-  // Explicitly tell yarn to ignore the "engines" field in `package.json`.
-  // If dependencies of tested modules have set it and CITGM is testing an
-  // unreleased version of Node.js, this prevents `yarn install` from failing.
-  options.env['YARN_IGNORE_ENGINES'] = 'true';
 
   if (context.options.nodedir) {
     const nodedir = path.resolve(process.cwd(), context.options.nodedir);

lib/lookup.json

@@ -133,6 +133,7 @@
     "maintainers": "mafintosh"
   },
   "ember-cli": {
+    "envVar": { "YARN_IGNORE_ENGINES": "true" },
     "prefix": "v",
     "flaky": ["win32", "rhel", "sles"],
     "master": true,

lib/package-manager/install.js

@@ -2,14 +2,48 @@
 
 const path = require('path');
 
+const semverLt = require('semver/functions/lt');
 const stripAnsi = require('strip-ansi');
 
 const createOptions = require('../create-options');
 const spawn = require('../spawn');
+const { spawnSync } = require('child_process');
 const timeout = require('../timeout');
 
 const envSeparator = process.platform === 'win32' ? ';' : ':';
 
+function getVersion(packageManager, context) {
+  const options = createOptions(
+    path.join(context.path, context.module.name),
+    context
+  );
+  const packageManagerBin =
+    packageManager === 'npm' ? context.npmPath : context.yarnPath;
+
+  const binDirectory = path.dirname(packageManagerBin);
+  options.env.PATH = `${binDirectory}${envSeparator}${process.env.PATH}`;
+  options.encoding = 'utf8';
+
+  const proc = spawnSync(packageManagerBin, ['--version'], options);
+  if (proc.status !== 0) {
+    context.emit(
+      'data',
+      'warn',
+      `${context.module.name} ${packageManager}:`,
+      `Unable to determine ${packageManager} version:\n${proc.stdout}` +
+        `\n${proc.stderr}`
+    );
+    return undefined;
+  }
+  context.emit(
+    'data',
+    'verbose',
+    `${context.module.name} ${packageManager}:`,
+    `${packageManager} version ${proc.stdout}`
+  );
+  return proc.stdout;
+}
+
 function install(packageManager, context) {
   return new Promise((resolve, reject) => {
     const options = createOptions(
@@ -34,6 +68,14 @@ function install(packageManager, context) {
     if (packageManager === 'npm') {
       args.push('--no-audit');
       args.push('--no-fund');
+    } else if (packageManager === 'yarn') {
+      // Tell yarn versions earlier than v2 to ignore the "engines" field in
+      // `package.json` (if present) to allow installation with unreleased
+      // versions of Node.js.
+      const version = getVersion(packageManager, context);
+      if (version && semverLt(version, '2.0.0', { includePrerelease: true })) {
+        options.env['YARN_IGNORE_ENGINES'] = 'true';
+      }
     }
 
     if (context.module.install) {

test/test-create-options.js

@@ -35,7 +35,6 @@ test('create-options:', (t) => {
   env['TEMP'] = 'npm_config_tmp';
   env['TMP'] = 'npm_config_tmp';
   env['TMPDIR'] = 'npm_config_tmp';
-  env['YARN_IGNORE_ENGINES'] = 'true';
   // Set dynamically to support Windows.
   env['npm_config_nodedir'] = path.resolve(process.cwd(), nodePath);