Powershell: Support localization of custom error messages for parameter validation attributes

[mklement0]

Now that at least _some_ of the custom error messages for parameter validation attributes support custom error messages - see #3745, it should be possible to support _localization_ of these error messages - currently, only literal strings are supported.

Without this ability, localized scripts are effectively prevented from using such validation attributes.

What currently works:

function foo {
  param(
    [ValidatePattern('o', ErrorMessage = 'Must have an "o".')]
    $bar
  )
  $bar
}

foo -bar baz

This yields:

foo : Cannot validate argument on parameter 'bar'. Must have an "o".

What support for localization _might_ look like (not sure about feasibility; solely based on noticing that some attributes accept _script blocks_):

$stringTable = DATA {
  @{
    msg = 'Must have an "o".'
  }
}

function foo {
  param(
    [ValidatePattern('o', ErrorMessage = { $stringTable.msg })]
    $bar
  )
  $bar
}

foo -bar baz

Environment data

PowerShell Core v6.0.0-beta (v6.0.0-beta.1)

[iSazonov]

Related https://github.com/PowerShell/PowerShell/pull/2728#discussion_r91215074

if we go that route, we need localization support similar to HelpMessageBaseName and HelpMessageResourceId in ParameterAttribute

[mmsaffari]

Are HelpMessageBaseName and HelpMessageResourceId currently working?

[wbpluto]

Still waiting for this. Come on, Microsoft, your're a global company.

[iSazonov]

@wbpluto It is an open source project so you can pull PR.

[mklement0]

@iSazonov, I think @wbpluto's concern is localization support _in general_, which requires a concerted, sustained effort, not just individual user contributions - see #666

[iSazonov]

@mklement0 I only point that everybody can contribute and do not wait.
For the issue a solution was mentioned in https://github.com/PowerShell/PowerShell/issues/3765#issuecomment-301155358

[mklement0]

Thanks, @iSazonov - coming back here I'd forgotten that this issue is about enabling localization of a user-supplied message, not about localizing PowerShell's own messages (which is what #666 is about).