Finds VB6 procedures that have `On Error GoTo 0` but do NOT have a real error handler

Find-DanglingOnErrorGoto0.ps1

# Find-DanglingOnErrorGoto0.ps1

param(
    [string]$Path
)

# Finds VB6 procedures that have `On Error GoTo 0` but do NOT have a real
# error handler (neither `On Error GoTo <label>` nor `On Error Resume Next`).

if (-not $Path) {
    @"
Find-DanglingOnErrorGoto0.ps1 - Find VB6 procedures with a dangling 'On Error GoTo 0'.

Reports procedures that contain 'On Error GoTo 0' but never install a real error
handler ('On Error GoTo <label>' or 'On Error Resume Next') before it.

Usage:
    .\Find-DanglingOnErrorGoto0.ps1 -Path <folder-or-file>

Parameters:
    -Path   Folder (searched recursively) or file to scan. Scans *.bas, *.cls,
            *.frm and *.ctl files.

Example:
    .\Find-DanglingOnErrorGoto0.ps1 -Path C:\Projects\MyVB6App
"@ | Write-Output
    return
}

$reProcStart = '^\s*(?:(?:Public|Private|Friend|Static)\s+)*(?:Sub|Function|Property\s+(?:Get|Let|Set))\s+(\w+)'
$reProcEnd   = '^\s*End\s+(?:Sub|Function|Property)\b'
$reGoto0     = '^\s*On\s+Error\s+GoTo\s+0\s*$'
$reResume    = '^\s*On\s+Error\s+Resume\s+Next\b'
$reGotoLabel = '^\s*On\s+Error\s+GoTo\s+(?!0\s*$)\S+'

$files = Get-ChildItem -Path $Path -Recurse -Include *.bas, *.cls, *.frm, *.ctl -File
$results = foreach ($f in $files) {
    $lines = Get-Content -LiteralPath $f.FullName
    $inProc = $false
    $procName = ''
    $procStartLine = 0
    $handlerInstalled = $false   # is a handler active AT THIS POINT
    $danglingLines = @()         # On Error GoTo 0 with no active handler before it

    for ($i = 0; $i -lt $lines.Count; $i++) {
        $line = $lines[$i]
        $lineNo = $i + 1

        if (-not $inProc) {
            $m = [regex]::Match($line, $reProcStart, 'IgnoreCase')
            if ($m.Success) {
                $inProc = $true
                $procName = $m.Groups[1].Value
                $procStartLine = $lineNo
                $handlerInstalled = $false
                $danglingLines = @()
            }
            continue
        }

        if ($line -imatch $reProcEnd) {
            if ($danglingLines.Count -gt 0) {
                [pscustomobject]@{
                    File      = $f.FullName
                    Procedure = $procName
                    ProcLine  = $procStartLine
                    Goto0At   = ($danglingLines -join ',')
                }
            }
            $inProc = $false
            continue
        }

        if ($line -imatch $reResume -or $line -imatch $reGotoLabel) {
            $handlerInstalled = $true       # installs a handler for the rest of the procedure
        } elseif ($line -imatch $reGoto0) {
            # flag only if NO handler was installed anywhere earlier in the procedure;
            # sticky flag, because due to branching (each GoTo 0 sits in a separate branch,
            # followed by Err.Raise/Exit) the top-level handler is actually active on the path
            if (-not $handlerInstalled) { $danglingLines += $lineNo }
        }
    }
}

$results = @($results)
if ($results.Count -gt 0) {
    $results | Sort-Object File, ProcLine | Format-Table -AutoSize
    "Total: $($results.Count) procedure(s) with dangling 'On Error GoTo 0'." | Write-Output
} else {
    "None found." | Write-Output
}