PShell helper commands do not throw exceptions (errors)

[Joe Caverly]

The following helper function/alias for PShell do not throw an execption on an error.

Invoke-TccCommand / tcc
Expand-TccValue / tccx
Get-TccVariable / tccvar

I have created a suggestion to have this addressed.

Ref: Allow PowerShell 5.1 to catch PShell helper command exceptions

Joe

 

[rconn]

They already do. The PowerShell functions are thin wrappers; the throwing happens inside the .NET static methods they call.

So any non-zero host result or any error text from the TCC side raises InvalidOperationException, which surfaces in PowerShell as a terminating error.

Things that legitimately would not throw today (and arguably are correct):

• TCC 'echo hi' when echo hi writes to stderr but returns 0 — nResult == 0 and no errortext, so no throw. That matches TCC's normal "stderr is just output" behavior.
• A TCC command that returns a non-zero exit code via EXIT n — that does throw, because nResult carries the command's return value. If you'd rather have $LASTEXITCODE-style semantics there, that's a deliberate design decision worth revisiting, but it isn't a bug.

So the only real gap I see is the third helper: Get-TccVariable already throws on a null/empty name, but it does not throw when the variable is undefined — ExpandValue("%nosuchvar") will typically return the literal %nosuchvar (TCC's default behavior) with nResult == 0. If you want "undefined variable ⇒ throw" semantics, that would need to be added explicitly in Get-TccVariable (compare the result to the input, or check via %@if[isdef…] first), since the host callback won't flag it.

 

[Joe Caverly]

Thanks Rex.

try {
    $result = [TakeCommand.PowerShellHost]::InvokeCommand("which ech")

    "Output: $result"
}
catch {
    "Caught TCC error: $($_.Exception.Message)"
}

Write-Host --------------------------------------------

try {
    $result = [TakeCommand.PowerShellHost]::InvokeCommand("which echo")

    "Output: $result"
}
catch {
    "Caught TCC error: $($_.Exception.Message)"
}

Proof:

R:\>pshell test.ps1
Caught TCC error: Exception calling "InvokeCommand" with "1" argument(s): "ech is an unknown command"
--------------------------------------------
Output: echo is an internal command

R:\>

Joe