[Account] Use IArgumentCompleter to implement the Environment parameter auto completer.

src/Accounts/Accounts.Test/ArgumentCompleterTests.ps1

@@ -107,5 +107,5 @@ function Get-EnvironmentCompleterResult
     $command = Get-Command -Name $CmdletName
     $environmentCompleterAttribute = $command.Parameters.$ParameterName.Attributes | Where-Object { $_.GetType() -eq [Microsoft.Azure.Commands.Profile.Common.EnvironmentCompleterAttribute]}
 
-    return $environmentCompleterAttribute.ScriptBlock.Invoke().CompletionText
+    return $environmentCompleterAttribute.CompleteArgument($CmdletName, $ParameterName, "", $null, $null).CompletionText
 }

src/Accounts/Accounts/Common/EnvironmentCompleterAttribute.cs

@@ -1,20 +1,23 @@
 using Microsoft.Azure.Commands.Common.Authentication.Abstractions;
 using Microsoft.Azure.Commands.Common.Authentication.Models;
 using Microsoft.Azure.Commands.ResourceManager.Common;
+using System.Collections;
+using System.Collections.Generic;
 using System.Linq;
 using System.Management.Automation;
+using System.Management.Automation.Language;
 
 namespace Microsoft.Azure.Commands.Profile.Common
 {
     /// <summary>
     /// This attribute will allow the user to autocomplete the values for valid Azure Environment names when applied to Environment related cmdlet parameters.
     /// </summary>
-    public class EnvironmentCompleterAttribute : ArgumentCompleterAttribute
+    public class EnvironmentCompleterAttribute : ArgumentCompleterAttribute, IArgumentCompleter
     {
         /// <summary>
         /// Initializes a new instance of <see cref="EnvironmentCompleterAttribute" /> .
         /// </summary>
-        public EnvironmentCompleterAttribute() : base(CreateScriptBlock())
+        public EnvironmentCompleterAttribute() : base(typeof(EnvironmentCompleterAttribute))
         {
         }
 
@@ -28,13 +31,16 @@ public static string[] GetEnvironments()
             return profileClient.ListEnvironments(null).Select(x => x.Name).ToArray();
         }
 
-        private static ScriptBlock CreateScriptBlock()
+        /// <summary>
+        /// Implementations CompleteArgument function of the <see cref="IArgumentCompleter"/>.
+        /// </summary>
+        public IEnumerable<CompletionResult> CompleteArgument(string commandName, string parameterName, string wordToComplete, CommandAst commandAst, IDictionary fakeBoundParameters)
         {
-            string script = "param($commandName, $parameterName, $wordToComplete, $commandAst, $fakeBoundParameter)\n" +
-                "$environments = [Microsoft.Azure.Commands.Profile.Common.EnvironmentCompleterAttribute]::GetEnvironments()\n" +
-                "$environments | Where-Object { $_ -Like \"$wordToComplete*\" } | ForEach-Object { [System.Management.Automation.CompletionResult]::new($_, $_, 'ParameterValue', $_) }";
-            ScriptBlock scriptBlock = ScriptBlock.Create(script);
-            return scriptBlock;
+            IEnumerable<string> names = GetEnvironments().Where(env => env.ToLower().StartsWith(wordToComplete.ToLower())) ;
+            foreach (string name in names)
+            {
+                yield return new CompletionResult(name, name, CompletionResultType.ParameterValue, name);
+            }
         }
     }
 }