Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues.
• Refer to the FAQ.
• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

Consider this example:

function Verb-Noun
{
    Param
    (
        [Parameter(Position = 0)]
        [string]
        $Param1,
        [Parameter(Position = 1)]
        [System.Management.Automation.ActionPreference]
        $Param2
    )
}
Verb-Noun -Param1 Hello <Tab>

I would expect the tab completion to suggest values for Param2 because it's the first positional parameter that hasn't been bound to a named parameter and this is how the real parameter binder works. Unfortunately it doesn't work, it simply falls back to the file/directory suggestions.
The same issue occurs if you (presumably by mistake) try to start the positional parameters at 1 instead of 0:

function Verb-Noun
{
    Param
    (
        [Parameter(Position = 1)]
        [System.Management.Automation.ActionPreference]
        $Param1
    )
}
Verb-Noun <Tab>

As far as I can tell the issue is here: https://github.com/PowerShell/PowerShell/blob/master/src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs#L1596 where it looks if the position for the parameter matches exactly the position the cursor is at.

Expected behavior

Tab completion should find the right parameter to offer completions for.

Actual behavior

It falls back to the generic file/directory completion

Error details

No response

Environment data

PS C:\> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.3.0-preview.5
PSEdition                      Core
GitCommitId                    7.3.0-preview.5
OS                             Microsoft Windows 10.0.19044
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response