Crash running formatter on new, untitled document

[Jaykul]

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System Details

• Operating system name and version:
  Windows 10 AU
• VS Code version:
  1.9.0-Insider
• PowerShell extension version:
  0.9.0
• Output from $PSVersionTable:

Name                           Value
----                           -----
PSVersion                      5.1.14393.693
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.14393.693
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

Issue Description

Crash when calling format document on a new unsaved document.

Steps to repro

Create a New File
Set the Syntax to PowerShell
Write something in it, like

foreach($thing in $list){$result=Get-Thing $thing}

Then hit "Format Document" (e.g. alt+shift+f)

Attached Logs

1484856115-dfce8230-a989-4c8e-85bd-d9a055a6031d1484856005946.zip

[daviwil]

This is happening for new script files that haven't been saved yet, they are still marked as "Untitled". If you create a new file, paste in Joel's example script, click the file type selector in the status bar and turn it to PowerShell then hit Shift+Alt+F, you'll see the crash. Here's the exception from the logs:

System.IO.FileNotFoundException: Could not find file 'C:\Program Files (x86)\Microsoft VS Code Insiders\Untitled-1'

We basically just need to handle untitled files correctly.

/cc @kapilmb