[swift-users] Can't get Error pattern matching to work cross framework and command line tool

[Ian Terrell]

Is this a naming collision? Do multiple modules defined a
Transaction.Error.NotFound?

For instance, in your passing case, is the Transaction.Error.NotFound that
is caught a Z.Transaction.Error.NotFound, or one in your local app module
(i.e. CLI.Transaction.Error.NotFound).

If your CLI module has that defined, then that is what you are looking for
in the catch statement. And since a Z.Transaction is not a CLI.Transaction
it fails to catch it appropriately.

Just a thought.

Ian

On Tue, May 31, 2016 at 12:44 AM, Joakim Hassila via swift-users <
swift-users at swift.org> wrote:

> Ok, I am stumped and wanted to see if anyone had any ideas on how to
> troubleshoot this.
>
> Short background:
> First off, I do have throwing/do/catch working perfectly fine in
> Playgrounds as well as in standalone apps as well as in an app that links
> with one of my own test frameworks, so I would hope this is not a simple
> user error.
>
> I’m testing this on OS X w. XCode 7.3.1 using Swift 2.2 all with Debug
> builds.
>
> I have a command line tool project "X" that links with two of my own Swift
> frameworks, “Y" and “Z". Z also links with a pure C-language library, “W”
> using a module map.
> All of this works fine, as X can use entities from both Y and Z perfectly
> fine, including indirect access of the C-library beneath.
>
> So the issue is when I am looking at throwing errors from Z, as X can’t
> properly pattern match the errors.
>
> Short snippet showing relevant code and output from a testrun:
>
> From the command line tool X:
> ——
> func localThrow () throws -> Void
> {
>     throw Transaction.Error.NotFound
> }
>
> do{
>     try localThrow() // try throwing from embedded local function
> } catch Transaction.Error.NotFound { // this matches as expectd
>     print("Transaction not found (local)")
> } catch  {
>     print("Unknown error (local)")
> }
>
> let transaction2 = Transaction()
>
> do {
>     try transaction2.errorNow() // try throwing from framework
> } catch Transaction.Error.NotFound { // this never matches!
>     print("Transaction not found (framework)")
> } catch {
>     print("Unknown error (framework)")
> }
> ——
>
> In the framework Z, we have:
> ——
> import W
>
> public class Transaction {
> // ...
> }
>
> public extension Transaction {
>
>     public final func errorNow() throws -> Void
>     {
>         throw Transaction.Error.NotFound
>     }
> }
> ——
>
> and the output when run is:
> ——
> Transaction not found (local)
> Unknown error (framework)
> ——
>
> Setting a breakpoint and inspecting ‘error’ shows the following when
> stepping over the call, and single stepping in the debugger shows that it
> throws properly, it is just the matching that seems to fail. The Xcode lldb
> inspector shows the error value as:
>
> error = (Z.Transaction.Error) NotFound
>
> When single-stepping the local call, ‘error’ does not seem to be populated
> properly but it matches as it should.
>
> I tried minimizing it with a simple app (not command line though) and
> framework, but there it works as expected of course…
>
> Anyone have any ideas what might be the problem?
>
> Cheers,
>
> Joakim
>
>
> _______________________________________________
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>
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