[BUG] [Powershell] Array context not maintained when converting a parameter to JSON

[condorcorde]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Consider the function Invoke-PS123TestSpecialTags of PSPetstore. It has a parameter $Client of type [PSCustomObject]:

        [Parameter(Position = 0, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true, Mandatory = $false)]
        [PSCustomObject]
        ${Client},

which is correctly translated into JSON by the line

$LocalVarBodyParameter = $Client | ConvertTo-Json -Depth 100

Now suppose that $Client is defined as being an array [PSCustomObject[]]. The conversion to JSON is done in the same way, but the JSON output changes depending on whether $Client is an array of one or multiple elements, because the parameter type declaration does not force an array context when the array contains a single element.

openapi-generator version

Up to 7.5

OpenAPI declaration file content or url

The issue was first noticed using a PowerShell client generated from Connectwise PSA API specs. The specs are too complex (over 4K endpoints) to be used for an example.

Generation Details

openapi-generator generate --input-spec SPECS/2022.2/All.json --generator-name powershell --output PSClient --additional-properties=packageName=CWPSA,packageVersion=2022.2,apiNamePrefix=PSA --skip-validate-spec

Steps to reproduce

Reproducing the issue requires changing AnotherFakeApi specs, but the same behaviour can be seen from the console:

PS /> $Client = [PSCustomObject]@{client = 'X'}
# Array of two elements
PS /> $c = @($Client, $Client)                                                                                                                          
PS /> $c | ConvertTo-Json
[
  {
    "client": "X"
  },
  {
    "client": "X"
  }
]
# Array of one element
PS /> $c = @($Client)
PS /> $c | ConvertTo-Json
{
  "client": "X"
}
# Array of one element forcing array context
PS /> ,$c | ConvertTo-Json
[
  {
    "client": "X"
  }
]

Related issues/PRs

None found

Suggest a fix

The optimal solution would be to force an array context when the parameter is declared as being an array, as in:

$LocalVarBodyParameter = ,$Client | ConvertTo-Json -Depth 100

I would not know what changes to the mustache files are required to obtain this result.