Update-MarkdownCommandHelp does not handle old format

[MartinGC94]

Prerequisites

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Steps to reproduce

I have markdown files built with/for the old platyPS module version 0.14.2. I tried using Update-MarkdownCommandHelp from Microsoft.PowerShell.PlatyPS version 1.0.1 to update them to the new format and it ended up duplicating the parameter help text.
I don't know if it's supposed to be possible to migrate from the old to new format like this, but if it's not supposed to work maybe it should throw an error or write a warning instead of pretending it's all good?

Here's a snippet of the diff output I'm seeing:

Expected behavior

Either correctly update the format, or notify the user (via warning or error) that the markdown is invalid.

Actual behavior

The command silently completes just like it would on a successful run.

Error details

Environment data

Name                           Value
----                           -----
PSVersion                      7.6.0-preview.4
PSEdition                      Core
GitCommitId                    7.6.0-preview.4
OS                             Microsoft Windows 10.0.26100
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Version

1.0.1

Visuals

No response

[MartinGC94]

This might have been because the module was imported into the session and that it had an XML help file loaded. Anyway, as a workaround I just deleted the docs folder and created it from scratch with New-MarkdownCommandHelp which populated all the fields based on the XML help file so it was pretty easy to migrate.

[sdwheeler]

This is by design. The new PlatyPS can read the old format markdown but only writes the new format.