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: https://github.com/dahlbyk/posh-git/blob/5dcdb9df9ffd9a10c65dd02c75352fee979ae019/src/GitPrompt.ps1#L112

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: https://github.com/dahlbyk/posh-git/blob/5dcdb9df9ffd9a10c65dd02c75352fee979ae019/src/posh-git.psm1#L55

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?

[dahlbyk]

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))

So the hypothesis is that some part of $ExecutionContext.SessionState.Path.CurrentLocation is returning $null, but only when called via ExpandString()? You can use $ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.SessionState.Path.CurrentLocation)') to narrow down what part is problematic. Does $ExecutionContext.SessionState.InvokeCommand.ExpandString('$(Get-Location)') work?

https://github.com/dahlbyk/posh-git/blob/5dcdb9df9ffd9a10c65dd02c75352fee979ae019/src/Utils.ps1#L282-L287

[rkeithhill]

FYI, you need to put that expression (that accesses properties) inside PowerShell sub-expression syntax e.g.:

$ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.SessionState.Path.CurrentLocation)')

[annahosanna]

@rkeithhill Sorry I must have miscommunicated something. 1) I no longer get the nullref using $ExecutionContext.SessionState.InvokeCommand.InvokeScript instead of $ExecutionContext.SessionState.InvokeCommand.ExpandString. 2) I understood that you were using ' to control when interpolation was done.

[annahosanna]

@dahlbyk No

PS>$ExecutionContext.SessionState.InvokeCommand.ExpandString('$(Get-Location)')
Object reference not set to an instance of an object.
    + CategoryInfo          : OperationStopped: (:) [], NullReferenceException
    + FullyQualifiedErrorId : System.NullReferenceException

[annahosanna]

@dahlbyk

PS>$ExecutionContext.SessionState.InvokeCommand.ExpandString('$ExecutionContext.SessionState.Path.CurrentLocation')
System.Management.Automation.EngineIntrinsics.SessionState.Path.CurrentLocation

[dahlbyk]

@annahosanna sorry, try this:

$ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.SessionState.Path.CurrentLocation)')

Or even this?

$ExecutionContext.SessionState.InvokeCommand.ExpandString('$pwd')

[annahosanna]

PS>$ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.SessionState.Path.CurrentLocation)')
Exception calling "ExpandString" with "1" argument(s): "Object reference not set to an
instance of an object."
At line:1 char:1
+ $ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.S ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : NullReferenceException

[dahlbyk]

$ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.SessionState)')

or

$ExecutionContext.SessionState.InvokeCommand.ExpandString('$pwd')

❓

[annahosanna]

PS>$ExecutionContext.SessionState.InvokeCommand.ExpandString('$pwd')
C:\Users\me\Documents\GitHub

[annahosanna]

PS>$ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.SessionState)')
Exception calling "ExpandString" with "1" argument(s): "Object reference not set to an
instance of an object."
At line:1 char:1
+ $ExecutionContext.SessionState.InvokeCommand.ExpandString('$($ExecutionContext.S ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : NullReferenceException

[annahosanna]

@rkeithhill , @dahlbyk

I'm happy to answer questions; however, this issue does not need to remain open since I can use the defaults with the solution I mentioned earlier.

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

[dahlbyk]

@annahosanna we appreciate your assistance troubleshooting!

@rkeithhill can you think of a reason not to switch to the InvokeScript(NewScriptBlock(...)) workaround instead of ExpandString() for v0.x, since that seems not to work as expected in PS 4.0?

[rkeithhill]

No but I would like to spin up a PS v4 VM to see if I can replicate this (later tonight). BTW we can cache the scriptblock that gets created. It doesn't need to be recreated each time. Strike-that - in v0 we have no good way update the scriptblock if the user changes the setting. :-(

[annahosanna]

Googling around, the examples I could find seem like this may be specific to certain versions of Windows (I'm using Windows 7 enterprise, but I've also seen mention of this with 2012/2012 R2) with PS 4.

[dahlbyk]

The other workaround would be to add:

if (-not $pathInfo) {
  $pathInfo = $pwd
}

[rkeithhill]

I was able to easily repro this on a Windows 7 VM updated to PS 4. It seems the parser chokes on any sub-expression passed to ExpandString():

Below you can see the full stack trace of where it chokes in our prompt function. Looks like it chokes reading a Line property on some InternalScriptPosition object.

Unfortunately the suggestion solution doesn't always work:

But it does work with the default case and can be made to work in the scenario above with an extra set of double quotes e.g.:

$GitPromptSettings.DefaultPromptPath.Text = '"MyPath is $(Get-PromptPath)"'

However, this change could break folks on PS >= 5 who have customized their DefaultPromptPath setting e.g.:

07-28 12:39:55 11> $GitPromptSettings.DefaultPromptPath.Text = 'MyPath is $(Get-PromptPath)'
07-28 12:41:16 12> $ExecutionContext.SessionState.InvokeCommand.InvokeScript($ExecutionContext.SessionState.InvokeCommand.NewScriptBlock($GitPromptSettings.DefaultPromptPath.Text))
Exception calling "InvokeScript" with "1" argument(s): "The term 'MyPath' is not recognized as the name of a cmdlet,
function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the
path is correct and try again."
At line:1 char:1
+ $ExecutionContext.SessionState.InvokeCommand.InvokeScript($ExecutionC ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : CommandNotFoundException

So I'm thinking we should conditionally apply this fix to PS <= v4. Thoughts? I suppose we should also verify the "fix" works on PS v3.

[dahlbyk]

How about a string wrapper inside NewScriptBlock? Roughly (on phone, untested):

$ExecutionContext.SessionState.InvokeCommand.InvokeScript(
  $ExecutionContext.SessionState.InvokeCommand.NewScriptBlock(
  "`"`$($($GitPromptSettings.DefaultPromptPath))`""
  ))

(Note this bug is for v0, so we don't want .Text)

[rkeithhill]

(Note this bug is for v0, so we don't want .Text)

Got that. But on my dev system (running V5 / V6.1) it is easier to test $ExecutionContext with my currently loaded posh-git v1 beta2. Ultimately, the text passed into NewScriptBlock is the same.

The string wrapper, as-is, still fails:

[dahlbyk]

Oh, I was overthinking it. This is what I meant:

$ExecutionContext.SessionState.InvokeCommand.InvokeScript(
  $ExecutionContext.SessionState.InvokeCommand.NewScriptBlock(
    "`"$($GitPromptSettings.DefaultPromptPath)`""
  ))

Which should resolve to:

$ExecutionContext.SessionState.InvokeCommand.InvokeScript(
  $ExecutionContext.SessionState.InvokeCommand.NewScriptBlock(
    "MyPath is $(Get-PromptPath)"
  ))

FWIW, I've been testing this by launching with -NoProfile and adding:

$GitPromptSettings = @{ DefaultPromptPath = 'MyPath is $(Get-Location)' }