RFC Trap handle non terminating errors

1-Draft/RFCXXXX-Trap-Handle-Non-Terminating-Errors.md

@@ -0,0 +1,126 @@
+---
+RFC: RFC0XXX
+Author: Tyler Leonhardt
+Status: Draft
+Area: Traps
+Comments Due: 
+---
+
+# Trap should handle non-terminating errors
+
+This RFC proposes that we change the behavior of the Trap statement to also trap non-terminating exceptions.
+
+To do this,
+we will also add a property on ErrorRecord to determine if it was a terminating or non-terminating exception.
+
+With this change, the following code:
+
+```pwsh
+trap {
+    "hello"
+    continue
+}
+Get-Process IDontExist
+```
+
+will output the same as the following code that works today:
+
+```pwsh
+trap {
+    "hello"
+    continue
+}
+Get-Process IDontExist -ErrorAction Stop
+```
+
+If you wanted to handle both terminating and non-terminating errors in your
+`trap`
+you can use the
+`ErrorType`
+property:
+
+```pwsh
+trap {
+    if($_.ErrorType -eq "Terminating") {
+        "oh no!"
+    } else {
+        "this is ok"
+        continue
+    }
+}
+```
+
+## Motivation
+
+The Trap statement has fallen out of favor in recent years to it's error handling cousin -
+the try/catch block.
+
+This gives us an opportunity to revamp the Trap statement so that it can serve a purpose that the try/catch could not serve.
+
+The purpose would be to offer a
+*single solution*
+to handle both terminating and non-terminating issues.
+
+## Specification
+
+`ErrorRecord`
+will get an additional property called
+`ErrorType`
+this will come from an
+`enum`
+called
+`ErrorRecordType`
+which has 2 values:
+
+* `Terminating`
+* `NonTerminating`
+
+Traps will then also be passed non-terminating errors to be handled. 
+
+## Alternate Proposals and Considerations
+
+### Introduce a `trapall`
+
+Instead of changing the behavior of
+`trap`,
+we would add a
+`trapall`
+that does the above behavior.
+This might get tricky if a
+`trap`
+and a
+`trapall`
+were defined.
+This also means that code written using
+`trapall`
+would not run at all in older versions of PowerShell.
+
+### Add a -OnError parameter to every cmdlet
+
+The motivation of this RFC comes from the issue
+[PowerShell#6010](https://github.com/PowerShell/PowerShell/issues/6010).
+
+ The proposal there was a parameter that you pass a ScriptBlock to:
+
+ ```pwsh
+Stop-Process foo* -OnError {
+     Write-Host "Had an error."
+}
+```
+
+ This would then:
+
+* run for every non-terminating error
+* run once for the terminating error
+
+ However,
+it's a bit confusing how this plays well with the pipeline and is suggesting changing the meaning of
+`continue`
+and
+`break`
+statements by adding them to a new context.
+
+ The
+`OnError`
+proposal reminds me of a JavaScript callback which isn't really a well adopted pattern in the PowerShell world,
+which is why I chose against it.