PowerShell · adityapatwardhan · May 9, 2023 · Sep 4, 2022 · Sep 6, 2022 · Sep 6, 2022
diff --git a/src/System.Management.Automation/engine/Utils.cs b/src/System.Management.Automation/engine/Utils.cs
@@ -1561,11 +1561,14 @@ public static class InternalTestHooks
         internal static bool UseDebugAmsiImplementation;
         internal static bool BypassAppLockerPolicyCaching;
         internal static bool BypassOnlineHelpRetrieval;
-        internal static bool ThrowHelpCultureNotSupported;
         internal static bool ForcePromptForChoiceDefaultOption;
         internal static bool NoPromptForPassword;
         internal static bool ForceFormatListFixedLabelWidth;
 
+        // Update-Help tests
+        internal static bool ThrowHelpCultureNotSupported;
+        internal static CultureInfo CurrentUICulture;
+
         // Stop/Restart/Rename Computer tests
         internal static bool TestStopComputer;
         internal static bool TestWaitStopComputer;

@@ -550,7 +550,8 @@ private void ProcessModule(UpdatableHelpModuleInfo module)
 #endif
                 catch (UpdatableHelpSystemException e)
                 {
-                    if (e.FullyQualifiedErrorId == "HelpCultureNotSupported")
+                    if (e.FullyQualifiedErrorId == "HelpCultureNotSupported"
+                            || e.FullyQualifiedErrorId == "UnableToRetrieveHelpInfoXml")
                     {
                         installed = false;
 
@@ -665,7 +666,7 @@ internal bool IsUpdateNecessary(UpdatableHelpModuleInfo module, UpdatableHelpInf
             }
 
             // Culture check
-            if (!newHelpInfo.IsCultureSupported(culture))
+            if (!newHelpInfo.IsCultureSupported(culture.Name))
             {
                 throw new UpdatableHelpSystemException("HelpCultureNotSupported",
                     StringUtil.Format(HelpDisplayStrings.HelpCultureNotSupported,

@@ -1,9 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Diagnostics;
 using System.Globalization;
+using System.Linq;
 using System.Management.Automation.Internal;
 using System.Text;
 
@@ -37,6 +39,44 @@ internal CultureSpecificUpdatableHelp(CultureInfo culture, Version version)
         /// Supported culture.
         /// </summary>
         internal CultureInfo Culture { get; set; }
+
+        /// <summary>
+        /// Enumerates fallback chain (parents) of the culture, including itself.
+        /// </summary>
+        /// <param name="culture">Culture to enumerate</param>
+        /// <example>
+        /// Examples:
+        /// en-GB => { en-GB, en }
+        /// zh-Hans-CN => { zh-Hans-CN, zh-Hans, zh }.
+        /// </example>
+        /// <returns>An enumerable list of culture names.</returns>
+        internal static IEnumerable<string> GetCultureFallbackChain(CultureInfo culture)
+        {
+            // We use just names instead because comparing two CultureInfo objects
+            // can fail if they are created using different means
+            while (culture != null)
+            {
+                if (string.IsNullOrEmpty(culture.Name))
+                {
+                    yield break;
+                }
+
+                yield return culture.Name;
+
+                culture = culture.Parent;
+            }
+        }
+
+        /// <summary>
+        /// Checks if a culture is supported.
+        /// </summary>
+        /// <param name="cultureName">Name of the culture to check.</param>
+        /// <returns>True if supported, false if not.</returns>
+        internal bool IsCultureSupported(string cultureName)
+        {
+            Debug.Assert(cultureName != null, $"{nameof(cultureName)} may not be null");
+            return GetCultureFallbackChain(Culture).Any(fallback => fallback == cultureName);
+        }
     }
 
     /// <summary>
@@ -99,22 +139,12 @@ internal bool IsNewerVersion(UpdatableHelpInfo helpInfo, CultureInfo culture)
         /// <summary>
         /// Checks if a culture is supported.
         /// </summary>
-        /// <param name="culture">Culture to check.</param>
+        /// <param name="cultureName">Name of the culture to check.</param>
         /// <returns>True if supported, false if not.</returns>
-        internal bool IsCultureSupported(CultureInfo culture)
+        internal bool IsCultureSupported(string cultureName)
         {
-            Debug.Assert(culture != null);
-
-            foreach (CultureSpecificUpdatableHelp updatableHelpItem in UpdatableHelpItems)
-            {
-                if (string.Equals(updatableHelpItem.Culture.Name, culture.Name,
-                    StringComparison.OrdinalIgnoreCase))
-                {
-                    return true;
-                }
-            }
-
-            return false;
+            Debug.Assert(cultureName != null, $"{nameof(cultureName)} may not be null");
+            return UpdatableHelpItems.Any(item => item.IsCultureSupported(cultureName));
         }
 
         /// <summary>

@@ -294,19 +294,13 @@ internal IEnumerable<string> GetCurrentUICulture()
         {
             CultureInfo culture = CultureInfo.CurrentUICulture;
 
-            while (culture != null)
+            // Allow tests to override system culture
+            if (InternalTestHooks.CurrentUICulture != null)
             {
-                if (string.IsNullOrEmpty(culture.Name))
-                {
-                    yield break;
-                }
-
-                yield return culture.Name;
-
-                culture = culture.Parent;
+                culture = InternalTestHooks.CurrentUICulture;
             }
 
-            yield break;
+            return CultureSpecificUpdatableHelp.GetCultureFallbackChain(culture);
         }
 
         #region Help Metadata Retrieval
@@ -591,13 +585,9 @@ internal UpdatableHelpInfo CreateHelpInfo(string xml, string moduleName, Guid mo
 
             if (!string.IsNullOrEmpty(currentCulture))
             {
-                IEnumerable<WildcardPattern> patternList = SessionStateUtilities.CreateWildcardsFromStrings(
-                    globPatterns: new[] { currentCulture },
-                    options: WildcardOptions.IgnoreCase | WildcardOptions.CultureInvariant);
-
                 for (int i = 0; i < updatableHelpItem.Length; i++)
                 {
-                    if (SessionStateUtilities.MatchesAnyWildcardPattern(updatableHelpItem[i].Culture.Name, patternList, true))
+                    if (updatableHelpItem[i].IsCultureSupported(currentCulture))
                     {
                         helpInfo.HelpContentUriCollection.Add(new UpdatableHelpUri(moduleName, moduleGuid, updatableHelpItem[i].Culture, uri));
                     }

diff --git a/test/powershell/engine/Help/HelpSystem.Tests.ps1 b/test/powershell/engine/Help/HelpSystem.Tests.ps1
@@ -30,7 +30,7 @@ function UpdateHelpFromLocalContentPath {
         throw "Unable to find help content at '$helpContentPath'"
     }
 
-    # Test files are 'en-US', set explicit culture so test does not help on non-US systems
+    # Test files are 'en-US', set explicit culture so test does not fail on non-US systems
     Update-Help -Module $ModuleName -SourcePath $helpContentPath -UICulture 'en-US' -Force -ErrorAction Stop -Scope $Scope
 }
 
@@ -613,3 +613,54 @@ Describe 'help renders when using a PAGER with a space in the path' -Tags 'CI' {
         help Get-Command | Should -Be "R2V0LUNvbW1hbmQ="
     }
 }
+
+Describe 'Update-Help allows partial culture matches' -Tags 'CI' {
+    BeforeAll {
+        function Test-UpdateHelpAux($UICulture, $Pass)
+        {
+            # If null (in system culture tests), omit entirely
+            $CultureArg = $UICulture ? @{ UICulture = $UICulture } : @{}
+            $Args = @{
+                Module = 'Microsoft.PowerShell.Core'
+                SourcePath = Join-Path $PSScriptRoot 'assets'
+                Force = $true
+                ErrorAction = $Pass ? 'Stop' : 'SilentlyContinue'
+                ErrorVariable = 'ErrorVariable'
+            }
+
+            Update-Help @Args @CultureArg
+
+            if (-not $Pass) {
+                $ErrorVariable | Should -Match 'Failed to update Help for the module.*'
+            }
+        }
+    }
+
+    AfterEach {
+        [System.Management.Automation.Internal.InternalTestHooks]::SetTestHook('CurrentUICulture', $null)
+    }
+
+    It 'Checks culture match against en-US: <UICulture>' -TestCases @(
+        @{ UICulture = 'en-US' }
+        @{ UICulture = 'en' }
+        @{ UICulture = 'en-GB'; Pass = $false }
+        @{ UICulture = 'de-DE'; Pass = $false }
+    ) {
+        param($UICulture, $Pass = $true)
+
+        Test-UpdateHelpAux $UICulture $Pass
+    }
+
+    # When using system culture, "en-GB" will use "en" as fallback, so passes
+    It 'Checks system culture match against en-US: <UICulture>' -TestCases @(
+        @{ UICulture = 'en-US' }
+        @{ UICulture = 'en' }
+        @{ UICulture = 'en-GB' }
+        @{ UICulture = 'de-DE'; Pass = $false }
+    ) {
+        param($UICulture, $Pass = $true)
+
+        [System.Management.Automation.Internal.InternalTestHooks]::SetTestHook('CurrentUICulture', [System.Globalization.CultureInfo]::new($UICulture))
+        Test-UpdateHelpAux $null $Pass
+    }
+}