CLI: -File-based / shebang-based invocations break with the end-of-parameters token, -- #20208

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

--, the (somewhat confusingly named) end-of-parameters token, signals the end of named arguments and treats all remaining token as positional arguments.

This mechanism is broken when calling via pwsh -File, which also happens implicitly when you call a shebang line-based PowerShells script (that doesn't have a .ps1 extension).

The -- is mistakenly interpreted as a parameter without a name.

# On Unix:
# Create a simple shebang-based script.
@'
#!/usr/bin/env pwsh
[CmdletBinding()]
param(
  $a,
  [Parameter(ValueFromRemainingArguments)] $rest
)
"`$a: $a"
"`$rest: $rest"
'@ > tmpscript
chmod a+x tmpscript

# Invoke as stand-alone executable via the shebang line
./tmpscript -a one -- -a other stuff

# Invoke explicitly via pwsh -File
pwsh -File ./tmpscript -a one -- -a other stuff

Expected behavior

$a: one
$rest: -a other stuff

That is, only one should bind to -a, with all arguments following -- binding to -rest, and the -- itself should be removed.

Actual behavior

Both calls fail with:

: Parameter cannot be processed because the parameter name '' is ambiguous. [...]

That is, -- was misinterpreted as a reference to a parameter without a name.

If you were to rename tmpscript to tmpscript.ps1 and invoke it in-process, the behavior would be as expected.

Error details

No response

Environment data

PowerShell 7.4.0-preview.5 on Unix-like platforms.

Visuals

No response