Omit module-internal lines from stack trace when resource throws exception

[alx9r]

This code

$document = {
    Get-DscResource TestStub | Import-DscResource

    TestStub a @{
        Key = 'a'
        ThrowOnSet = 'always'
    }
}

Describe 'resource stack trace' {
    $h = @{}

    It 'create instructions' {
        $h.Instructions = ConfigInstructions Name $document
    }
    foreach ( $step in $h.Instructions )
    {
        It $step.Message {
            $step | Invoke-ConfigStep
        }
    }
}

outputs

Describing resource stack trace
 [+] create instructions 14.46s
 [+] Pretest: Test resource [TestStub]a 1.28s
 [-] Configure: Set resource [TestStub]a 162ms
   RuntimeException: TestStub forced exception because ThrowOnSet=always
   at Set-TargetResource<Process>, C:\Users\un1\Documents\WindowsPowerShell\Modu
les\ZeroDSC\DSCResources\TestStub\TestStub.psm1: line 56
   at Invoke-MofResourceCommand<Process>, C:\Users\un1\Documents\WindowsPowerShe
ll\Modules\ZeroDSC\Functions\mofResourceInvokerType.ps1: line 105
   at _Invoke, C:\Users\un1\Documents\WindowsPowerShell\Modules\ZeroDSC\Function
s\mofResourceInvokerType.ps1: line 21
   at Invoke-ResourceCommand<Process>, C:\Users\un1\Documents\WindowsPowerShell\
Modules\ZeroDSC\Functions\resourceInvokerType.ps1: line 88
   at Invoke, C:\Users\un1\Documents\WindowsPowerShell\Modules\ZeroDSC\Functions
\resourceInvokerType.ps1: line 33
   at Invoke, C:\Users\un1\Documents\WindowsPowerShell\Modules\ZeroDSC\Functions
\boundResourceType.ps1: line 14
   at <ScriptBlock>, C:\Users\un1\Documents\WindowsPowerShell\Modules\ZeroDSC\Fu
nctions\configInstructionsType.ps1: line 285
   at Invoke-ConfigStep<Process>, C:\Users\un1\Documents\WindowsPowerShell\Modul
es\ZeroDSC\Functions\configInstructionsType.ps1: line 335
   at <ScriptBlock>, <No file>: line 19
 [+] Configure: Test resource [TestStub]a 320ms

Most of those lines are uninformative because they are just a record of the stack unwinding inside the ZeroDSC module. They should probably be omitted from the stack trace so that Pester shows only the helpful lines.

[alx9r]

Implementation ideas:

1. Rewrite the .ScriptStackTrace property with a string that omits a bunch of the stack trace.
2. Catch the exception at lowest point in the call stack that is inside ZeroDSC, and somehow re-throw that same exception at the highest point in the call stack.
3. Change the way [ConfigStep] objects are set up such that the call stack between Invoke-ConfigStep and the underlying resource is minimized.

[alx9r]

(1) is complicated by .ScriptStackTrace being a read-only property.

try
{
    throw
}
catch
{
    $_.ScriptStackTrace = 'new trace'
}

results in

'ScriptStackTrace' is a ReadOnly property.
At C:\Users\un1\Desktop\test.ps1:7 char:5
+     $_.ScriptStackTrace = 'new trace'
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : PropertyAssignmentException

[alx9r]

It doesn't seem like (2) would work because .ScriptStackTrace is populated when the exception is first thrown. So catching and re-throwing doesn't change its contents. For example,

function f1 { throw 'exception in f1' }
function f2 { try { f1 } catch { return $_ } }
function f3 { $e = f2; return $e }
function f4 { $e = f3; throw $e }

Describe 'delayed re-throw' {
    It 'test' {
        f4
    }
}

results in

Describing delayed re-throw
 [-] test 18ms
   RuntimeException: exception in f1
   at f1, C:\Users\un1\Desktop\test.ps1: line 1
   at f2, C:\Users\un1\Desktop\test.ps1: line 2
   at f3, C:\Users\un1\Desktop\test.ps1: line 3
   at f4, C:\Users\un1\Desktop\test.ps1: line 4
   at <ScriptBlock>, C:\Users\un1\Desktop\test.ps1: line 8