Prompt script block System.NullReferenceException

[annahosanna]

• posh-git version/path: 0.7.3.1 C:\tools\poshgit\dahlbyk-posh-git-9bda399\src
• PowerShell version: 4.0
• git version 2.18.0.windows.1
• OS: Microsoft Windows NT 6.1.7601 Service Pack 1

Posh-git installed via Chocolatey

After posh-git install Powershell prompt appeared as:
PS>

It seems that there was an issue setting currentPath within the prompt script block:
$currentPath = $ExecutionContext.SessionState.InvokeCommand.ExpandString($GitPromptSettings.DefaultPromptPath);

Object reference not set to an instance of an object.
+ CategoryInfo : OperationStopped: (:) [], NullReferenceException
+ FullyQualifiedErrorId : System.NullReferenceException

However DefaultPromptPath seems to be defined:
write-host $global:GitPromptSettings.DefaultPromptPath
$(Get-PromptPath)

To resolve the issue I was able to redefine the prompt function with an updated prompt script block in the profile, after importing the posh-git module, by updating this single line:
$currentPath = $(Get-PromptPath)

Is there a better way to resolve this?

Thank you

[dahlbyk]

Are you able to get a full stack trace? Try setting $GitPromptSettings.Debug = $true.

[dahlbyk]

If you restore posh-git back to the original code, do you get the same error if you set $GitPromptSettings.DefaultPromptPath = '$pwd'?

[annahosanna]

Updating GitPrompt.ps1 to set GitPromptSettings.Debug to $true had no effect (prompt was still "PS>" )

[annahosanna]

Your second suggestion worked:

PS>cd .\myrepo
PS>$GitPromptSettings.DefaultPromptPath = '$pwd'
C:\Users\me\Documents\GitHub\myrepo [master ≡]>

[dahlbyk]

Is calling Get-PromptPath directly successful as well? I'm struggling to reconcile that '$pwd' can be expanded but '$(Get-PromptPath)' can't be.

[annahosanna]

PS>$(Get-PromptPath)
C:\Users\me\Documents\GitHub\myrepo
PS>
PS>$GitPromptSettings.DefaultPromptPath = $(Get-PromptPath)
C:\Users\me\Documents\GitHub\myrepo [master ≡]>

[annahosanna]

Seems like it is using the literal value "$(Get-PromptPath)" rather than the result from evaluating that function.

PS>write-host $Global:GitPromptSettings.DefaultPromptPath
$(Get-PromptPath)

PS>$GitPromptSettings.DefaultPromptPath = $(Get-PromptPath)
C:\Users\me\Documents\GitHub\myrepo [master ≡]> write-host $Global:GitPromptSettings.DefaultPromptPath
C:\Users\me\Documents\GitHub\myrepo

[annahosanna]

I think it is from GitPrompt.ps1. (in this version). DefaultPromptPath should be using quotes not ticks.

DefaultPromptPath = '$(Get-PromptPath)'
should be:
DefaultPromptPath = "$(Get-PromptPath)"

[rkeithhill]

Indeed, you have to use single quotes when setting the value. I think we should update that to make it also handle a scriptblock. This would be less susceptible to error:

# NOT SUPPORTED YET
$GitPromptSettings.DefaultPromptPath = { Get-PromptPath }

[dahlbyk]

Handling a ScriptBlock would be neat.

I still don't know what the nullref is from, though.

[annahosanna]

I'm guessing it is because $ExecutionContext.SessionState is not defined/null when expanded from a string, but defined when it is called as part of a script/script block.

This does not work for me either:

$Global:GitPromptSettings.DefaultPromptPath='$($ExecutionContext.SessionState.Path.CurrentLocation.Path)'

Nor this:

C:\Users\me\Documents\GitHub\myrepo [master ≡]> $ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.SessionState.Path.CurrentLocation.Path)')
Exception calling "ExpandString" with "1" argument(s): "Object reference not set to aninstance of an object."
At line:1 char:1
+ $ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.S ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : NullReferenceException

[annahosanna]

But this works:

C:\Users\me\Documents\GitHub\myrepo [master ≡]> $ExecutionContext.SessionState.InvokeCommand.InvokeScript($ExecutionContext.SessionState.InvokeCommand.NewScriptBlock('$($ExecutionContext.SessionState.Path.CurrentLocation.Path)'))

This works too:

PS>$Global:GitPromptSettings.DefaultPromptPath='$(Get-PromptPath)'
PS>$ExecutionContext.SessionState.InvokeCommand.InvokeScript($ExecutionContext.SessionState.InvokeCommand.NewScriptBlock($Global:GitPromptSettings.DefaultPromptPath))
C:\Users\me\Documents\GitHub\myrepo

This works in the GitPromptScritpBlock
replacing:

$currentPath = $ExecutionContext.SessionState.InvokeCommand.ExpandString($GitPromptSettings.DefaultPromptPath)

With:

$currentPath = $ExecutionContext.SessionState.InvokeCommand.InvokeScript($ExecutionContext.SessionState.InvokeCommand.NewScriptBlock($GitPromptSettings.DefaultPromptPath))

[rkeithhill]

This:

$Global:GitPromptSettings.DefaultPromptPath='$(Get-PromptPath)'

Is what we expect folks to use and is how it is set by default:

posh-git/src/GitPrompt.ps1

Line 112 in 5dcdb9d

DefaultPromptPath = '$(Get-PromptPath)'

The single quotes defers interpolation until we call ExpandString in the posh-git provided prompt function. And this is what we do in our prompt function:

posh-git/src/posh-git.psm1

Line 55 in 5dcdb9d

$currentPath = $ExecutionContext.SessionState.InvokeCommand.ExpandString($GitPromptSettings.DefaultPromptPath)

So, when you have the property set like this do you still the get NullRefEx?

[annahosanna]

It works with single quotes, and performs dynamic expansion. It creates a script block from the text in single quotes, and then evaluates the script block. However, because this is a script block plain strings need extra quotes now. Roughly '"test"' becomes { "test" } whereas "test" becomes { test } (which is an error because the variable named test is undefined). So these work:

$Global:GitPromptSettings.DefaultPromptPath='"test"'
$Global:GitPromptSettings.DefaultPromptPath='$(Get-PromptPath)'

and this does not:
$Global:GitPromptSettings.DefaultPromptPath="$(Get-PromptPath)"

[rkeithhill]

It creates a script block from the text in single quotes

That's not correct. By using single quotes, you're telling PowerShell not to do interpolation. When you use double quotes, PowerShell interpolates first and then assigns the result of the interpolation to the setting e.g.:

$Global:GitPromptSettings.DefaultPromptPath='$(Get-PromptPath)'
$Global:GitPromptSettings.DefaultPromptPath
'$(Get-PromptPath)'

$Global:GitPromptSettings.DefaultPromptPath="$(Get-PromptPath)" # Currently in C:\Users\hillr
$Global:GitPromptSettings.DefaultPromptPath
C:\User\hillr

The point of calling $ExecutionContext.SessionState.InvokeCommand.ExpandString() is that it will do the interpolation for us at the point in time we call it.

Try this:

$foo = '$(2+2)'
$foo
$(2+2)

$ExecutionContext.SessionState.InvokeCommand.ExpandString($foo)
4

But let me ask this again, when you have the property set like this (in single quotes) do you still the get NullRefEx?