Ensure external help file from metadata is used for generating the MAML file name (#779)

Author: adityapatwardhan

src/Command/ExportMamlCommandHelp.cs

@@ -70,11 +70,12 @@ protected override void EndProcessing()
             }
 
             // emit a MAML file for each group of CommandHelp objects
-            var helpGroup = _commandHelps.GroupBy(c => c.ModuleName);
+            var helpGroup = _commandHelps.GroupBy(c => c?.ExternalHelpFile ?? c?.ModuleName)
+                                         .OrderBy(g => g.Key);
             foreach(var group in helpGroup)
             {
                 string moduleName = group.First().ModuleName;
-                string helpFileName = $"{moduleName}-Help.xml";
+                string helpFileName = group.First().ExternalHelpFile ?? $"{moduleName}-Help.xml";
 
                 if (!ShouldProcess(helpFileName))
                 {

src/Common/MergeUtils.cs

@@ -29,6 +29,9 @@ internal static CommandHelp MergeCommandHelp(CommandHelp fromMarkdown, CommandHe
             // We will update this copy with new information from the cmdlet.
             CommandHelp helpCopy = new (fromMarkdown);
 
+            // Copy the ExternalHelpFile from markdown on cmletinfo
+            helpCopy.ExternalHelpFile = fromMarkdown.ExternalHelpFile ?? fromCmdlet.ExternalHelpFile;
+
             // The following are not available in the cmdlet, so we will just use what was in the help.
             // - Synopsis
             // - Description

src/Common/MetadataUtils.cs

@@ -60,6 +60,7 @@ public static OrderedDictionary GetCommandHelpBaseMetadataFromCommandInfo(Comman
 
         private static string GetHelpFileFromCommandInfo(CommandInfo commandInfo)
         {
+            // We are chosing upper case for the "Help.xml" file name to avoid issues with non-Windows platforms.
             string helpFileName;
             if (commandInfo is CmdletInfo cmdlet && ! string.IsNullOrEmpty(cmdlet.HelpFile))
             {

src/Transform/TransformBase.cs

@@ -57,6 +57,7 @@ protected CommandHelp ConvertCmdletInfo(CommandInfo? commandInfo)
 
             CommandHelp cmdHelp = new(commandInfo.Name, commandInfo.ModuleName, Settings.Locale);
             cmdHelp.Metadata = MetadataUtils.GetCommandHelpBaseMetadataFromCommandInfo(commandInfo);
+            cmdHelp.ExternalHelpFile = cmdHelp.Metadata["external help file"].ToString() ?? string.Empty;
             cmdHelp.OnlineVersionUrl = Settings.OnlineVersionUrl;
             cmdHelp.Synopsis = GetSynopsis(helpItem, addDefaultStrings);
             cmdHelp.AddSyntaxItemRange(GetSyntaxItem(commandInfo, helpItem));