Fix: findVisualStudio with pwsh constrained lang. mode

lib/find-visualstudio.js

@@ -126,23 +126,40 @@ VisualStudioFinder.prototype = {
   // Invoke the PowerShell script to get information about Visual Studio 2017
   // or newer installations
   findVisualStudio2017OrNewer: function findVisualStudio2017OrNewer (cb) {
-    var ps = path.join(process.env.SystemRoot, 'System32',
-      'WindowsPowerShell', 'v1.0', 'powershell.exe')
-    var csFile = path.join(__dirname, 'Find-VisualStudio.cs')
-    var psArgs = [
-      '-ExecutionPolicy',
-      'Unrestricted',
-      '-NoProfile',
-      '-Command',
-      '&{Add-Type -Path \'' + csFile + '\';' + '[VisualStudioConfiguration.Main]::PrintJson()}'
-    ]
+    const ps = path.join(process.env.SystemRoot, 'System32', 'WindowsPowerShell', 'v1.0', 'powershell.exe')
+    const csFile = path.join(__dirname, 'Find-VisualStudio.cs')
+    const basePsArgs = ['-ExecutionPolicy', 'Unrestricted', '-NoProfile', '-Command']
+    const findLanguageModePsCmd =
+      '&{ try { $ExecutionContext.SessionState.LanguageMode } catch { try { (Get-PSSessionConfiguration -Name Test).LanguageMode } catch { \'error\' } } }'
 
+    const psArgs = [...basePsArgs, findLanguageModePsCmd]
     this.log.silly('Running', ps, psArgs)
-    var child = execFile(ps, psArgs, { encoding: 'utf8' },
+    const childFindPsLanguageMode = execFile(
+      ps,
+      psArgs,
+      { encoding: 'utf8' },
       (err, stdout, stderr) => {
-        this.parseData(err, stdout, stderr, cb)
+        this.log.silly('PS stderr = %j', stderr)
+        if (err) {
+          this.log.silly('PS err = %j', err && (err.stack || err))
+          this.addLog(
+            'could not determine PowerShell LanguageMode, try re-running with \'--loglevel silly\' for more details')
+          return cb(null)
+        }
+        const findVscDataPsCmd = `&{Add-Type -Path '${csFile}';[VisualStudioConfiguration.Main]::PrintJson()}`
+        const psArgs = [...basePsArgs, findVscDataPsCmd]
+        // the Add-Type command requires powershell to run with languageMode == FullLanguage
+        // Because languageMode feature is not introduced yet in powershell v2, we can try to use it.
+        // If powershell v2 is not installed (a problem only if languageMode is not FullLanguage), then it is not
+        // possible to use feature Add-Type.
+        if (stdout.toString('utf8').trim().toLowerCase() !== 'fulllanguage') {
+          psArgs.unshift('-Version', '2')
+        }
+        this.log.silly('Running', ps, psArgs)
+        const child = execFile(ps, psArgs, { encoding: 'utf8' }, (err, stdout, stderr) => this.parseData(err, stdout, stderr, cb))
+        child.stdin.end()
       })
-    child.stdin.end()
+    childFindPsLanguageMode.stdin.end()
   },
 
   // Parse the output of the PowerShell script and look for an installation