PowerShell 3.0 stuck in infinite loop resolving members internally (is this a PS bug??)

Question

Sorry for long post... I have this scenario:
- Issue is on PS3, PS2 works fine
- I create a new object via "$myObj = New-Object PSObject"
- I append a number of PSMembers to it via something similar to:
"if (-not (Get-Member -InputObject $myObj -Name MyProperty))
 Add-Member -InputObject $myObj -MemberType ScriptProperty -Name MyProperty -Value { return MyFunction }
I am seeing situations where what I believe is the call to "Get-Member" causes a huge number of invocations that appear to be calling the equivalent of the "MyFunction" in the above sample. I have debug statements in the MyFunction
function and nested functions and can see they are called by what appears to be the PS framework itself. Even running a "Get-PSCallstack" call from one of these functions seems to also trigger the debug statements to be hit (midway through the callstack
output??!) - bit confused by that but it's like PS is invoking the member in order to reflect it or something.
I used Trace-Command and could see that the "MemberResolution" trace source is repeatedly/infinitely called with the output:
MemberResolution Information: 0 :         Matching "*"
MemberResolution Information: 0 :             Generating the total list of members
MemberResolution Information: 0 :                 Type table members: 0.
MemberResolution Information: 0 :                 Adapted members: 0.
MemberResolution Information: 0 :             21 total matches.
This appears to be in an infinite loop. Therefore I added "-ListenerOption Callstack" to the Trace-Command call and captured the following and more (notice the call to PSObject.ToStringEmptyBaseObject()):
at System.Management.Automation.PSObject.AdapterGetMembersDelegate[T](PSObject msjObj)
   at System.Management.Automation.PSMemberInfoIntegratingCollection`1.GetIntegratedMembers(MshMemberMatchOptions matchOptions)
   at System.Management.Automation.PSMemberInfoIntegratingCollection`1.Match(String name, PSMemberTypes memberTypes, MshMemberMatchOptions matchOptions)
   at System.Management.Automation.PSObject.ToStringEmptyBaseObject(ExecutionContext context, PSObject mshObj, String separator, String format, IFormatProvider formatProvider)
   at System.Management.Automation.PSObject.ToString(ExecutionContext context, Object obj, String separator, String format, IFormatProvider formatProvider, Boolean recurse, Boolean unravelEnumeratorOnRecurse)
   at System.Management.Automation.PSObject.ToString()
   at System.String.Join(String separator, Object[] values)
   at System.Management.Automation.ParameterBinderBase.BindParameter(CommandParameterInternal parameter, CompiledCommandParameter parameterMetadata, ParameterBindingFlags flags)
I then disassembled the relevant code in Reflector and could see that the ToString() method of PSObject has a check for "if obj.immediateBaseObjectIsEmpty" then to call the ToStringEmptyBaseObject() function. I could also see that the immediateBaseObjectIsEmpty
field is set in the CommonInitialization internal method if "obj is PSCustomObject" (which is the actual object type you get when you New-Object PSObject).
I then updated my code to create "$myObj = New-Object Object" (i.e. System.Object instead) and the issue goes away.
Can anyone explain what I may have done wrong here or is this looking like a bug in PowerShell?
Cheers!

Answer 1

Hi Matt,
I'm not sure if we are on the same page? Getting the list of (i.e. metadata of) the members shouldn't invoke the member.  I have used this technique in many places and it's never been an issue whereby you "wrap" a utility function with
a ScriptProperty or ScriptMethod to provide OO semantics on a PS object. The member isn't invoked by Get-Member, only when it's called explicitly.
Here's a small example:
function TestFunction
 Write-Host "TestFunction called"
 return "TestFunction return value"
$myObj = New-Object PSObject
Add-Member -InputObject $myObj -MemberType ScriptProperty -Name TestScriptProperty -Value `
 Write-Host "TestScriptProperty called"
 return TestFunction
Write-Host "Getting members"
Get-Member -InputObject $myObj -Name TestScriptProperty | Select *
Write-Host "Invoking property"
$myObj.TestScriptProperty
Here's the output (Get-Member output a bit mangled due to the text wrapping):
Getting members
TypeName                                   Name                                                                      
MemberType Definition                               
System.Management.Automation.PSCustomOb... TestScriptProperty                                                    
ScriptProperty System.Object TestScriptProperty {get=...
Invoking property
TestScriptProperty called
TestFunction called
TestFunction return value
Yup I see your point, but when you run your original code with this example object you can see there is no loop. There must either be a loop in the function or in the body of the script itself. This is very tough to troubleshoot without seeing the code you
are actually running.
You said you are adding several members to the custom object. Is this done in a loop?