PowerShell · dkattan · May 30, 2022 · May 31, 2022 · May 31, 2022 · May 31, 2022
diff --git a/src/System.Management.Automation/engine/Attributes.cs b/src/System.Management.Automation/engine/Attributes.cs
@@ -1595,7 +1595,6 @@ public abstract class CachedValidValuesGeneratorBase : IValidateSetValuesGenerat
         // Cached valid values.
         private string[] _validValues;
         private readonly int _validValuesCacheExpiration;
-
         /// <summary>
         /// Initializes a new instance of the <see cref="CachedValidValuesGeneratorBase"/> class.
         /// </summary>
@@ -1655,7 +1654,7 @@ public sealed class ValidateSetAttribute : ValidateEnumeratedArgumentsAttribute
         // of 'validValuesGenerator'.
         private readonly string[] _validValues;
         private readonly IValidateSetValuesGenerator validValuesGenerator = null;
-
+        private readonly ScriptBlock validValuesScript;
         // The valid values generator cache works across 'ValidateSetAttribute' instances.
         private static readonly ConcurrentDictionary<Type, IValidateSetValuesGenerator> s_ValidValuesGeneratorCache =
             new ConcurrentDictionary<Type, IValidateSetValuesGenerator>();
@@ -1686,11 +1685,36 @@ public IList<string> ValidValues
         {
             get
             {
-                if (validValuesGenerator == null)
+                if (validValuesGenerator == null && validValuesScript == null)
                 {
                     return _validValues;
                 }
 
+                if (validValuesScript is not null)
+                {
+                    var validValuesFromScript = new List<string>();
+                    var customResults = validValuesScript.Invoke();
+                    if (customResults == null || customResults.Count == 0)
+                    {
+                        validValuesFromScript = null;
+                    }
+
+                    foreach (var customResult in customResults)
+                    {
+                        var resultAsString = LanguagePrimitives.ConvertTo<string>(customResult);
+                        if (resultAsString != null)
+                        {
+                            validValuesFromScript.Add(resultAsString);
+                            continue;
+                        }
+
+                        var resultToString = customResult.ToString();
+                        validValuesFromScript.Add(resultToString);
+                    }
+
+                    return validValuesFromScript;
+                }
+
                 var validValuesLocal = validValuesGenerator.GetValidValues();
 
                 if (validValuesLocal == null)
@@ -1790,6 +1814,16 @@ public ValidateSetAttribute(Type valuesGeneratorType)
             validValuesGenerator = s_ValidValuesGeneratorCache.GetOrAdd(
                 valuesGeneratorType, static (key) => (IValidateSetValuesGenerator)Activator.CreateInstance(key));
         }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ValidateSetAttribute"/> class.
+        /// </summary>
+        /// <param name="scriptBlock">ScriptBlock that generates list of valid values</param>
+        /// <exception cref="ArgumentNullException">For null arguments.</exception>
+        public ValidateSetAttribute(ScriptBlock scriptBlock)
+        {
+            validValuesScript = scriptBlock;
+        }
     }
 
     /// <summary>

@@ -1645,6 +1645,10 @@ private static Attribute NewValidateSetAttribute(AttributeAst ast)
                         typeof(System.Management.Automation.IValidateSetValuesGenerator).FullName);
                 }
             }
+            else if (ast.PositionalArguments.Count == 1 && ast.PositionalArguments[0] is ScriptBlockExpressionAst scriptBlockAst)
+            {
+                result = new ValidateSetAttribute(scriptBlockAst.ScriptBlock.GetScriptBlock());
+            }
             else
             {
                 // 'ValidateSet("value1","value2", IgnoreCase=$false)' is supported in scripts.

diff --git a/test/powershell/Host/TabCompletion/TabCompletion.Tests.ps1 b/test/powershell/Host/TabCompletion/TabCompletion.Tests.ps1
@@ -1096,6 +1096,15 @@ switch ($x)
             $res.CompletionMatches[1].CompletionText | Should -BeExactly 'dog'
         }
 
+        It "Tab completion for validateSet attribute with ScriptBlock" {
+            function foo { param([ValidateSet({'cat','dog'})]$p) }
+            $inputStr = "foo "
+            $res = TabExpansion2 -inputScript $inputStr -cursorColumn $inputStr.Length
+            $res.CompletionMatches | Should -HaveCount 2
+            $res.CompletionMatches[0].CompletionText | Should -BeExactly 'cat'
+            $res.CompletionMatches[1].CompletionText | Should -BeExactly 'dog'
+        }
+
         It "Tab completion for validateSet attribute takes precedence over enums" {
             function foo { param([ValidateSet('DarkBlue','DarkCyan')][ConsoleColor]$p) }
             $inputStr = "foo "