How to debug a pipelined PowerShell cmdlet in vscode?

I have come up with a workable solution. First, define your pipeline input parameter in your cmdlet to take an array rather than just a single object. In my case I am using an array of strings:

[CmdletBinding()]
param(
    [parameter(ValueFromPipeline=$true)]
    [string[]]$InputObject
)

(Side note: $InputObject is the customary name for pipelined input. Don't use $Input because that is an automatic variable.)

In the Process section of the script, add a foreach loop to operate on the array:

Process
{
    foreach ($object in $InputObject) {
        # Do stuff with $object
    }
}

To run the script in the vscode debugger, you can specify the arguments in your launch configuration (in launch.json) something like this:

"args": ["-InputObject (Get-Content /path/to/myFile.txt)"]

For reference, this is what my launch configuration looks like:

{
    "name": "PowerShell Launch Select-Blah.ps1",
    "type": "PowerShell",
    "request": "launch",
    "script": "${workspaceFolder}/Select-Blah.ps1",
    "cwd": "${cwd}",
    "args": ["-InputObject (Get-Content /path/to/myFile.txt)"]
}

You can select "PowerShell Launch Select-Blah.ps1" in the dropdown in the debugger, and hit f5 to launch it.

Edit, another possibility:

If you want to have a singular $InputObject:

[CmdletBinding()]
param(
    [parameter(ValueFromPipeline=$true)]
    [string]$InputObject
)

You can use the -Raw switch with Get-Content to get a single string:

"args": ["-InputObject (Get-Content -Raw /path/to/myFile.txt)"]