[swift-corelibs-dev] NSTask and try!

Sat May 14 04:05:08 CDT 2016

This does seem to keep more inline with the current Darwin implementation. 

Please excuse my ignorance, I have looked into the POSIX calls, but am I right in assuming that the EBADF is due to the test calling to a file that doesn't exist and that is just how OSX handles this case?

Cheers for the clarification

James

Sent from my iPhone

> On 14 May 2016, at 09:33, Bouke Haarsma via swift-corelibs-dev <swift-corelibs-dev at swift.org> wrote:
> 
> The failing testcase is TestNSTask.test_pipe_stdout_and_stderr_same_pipe. The call to posix_spawn returns an error code 9 (EBADF). 
> 
> 
> 
> In order to avoid code repetition I've wrapped all posix calls with a throwing status code check;
> 
> 
> 
> private func posix(_ code: Int32) throws {
> 
>     switch code {
> 
>     case 0: return
> 
>     default: throw NSError(domain: NSPOSIXErrorDomain, code: Int(code), userInfo: nil)
> 
>     }
> 
> }
> 
> 
> 
> However this produces the not-so-helpful error dump on OSX:
> 
> 
> 
> Test Case 'TestNSTask.test_pipe_stdout_and_stderr_same_pipe' started at 10:20:59.741
> 
> fatal error: 'try!' expression unexpectedly raised an error: <NSError: 0x0000600000067c40>: file /Users/buildnode/jenkins/workspace/oss-swift-package-osx/swift/stdlib/public/core/ErrorType.swift, line 53
> 
> 
> 
> 
> 
> 
> 
> On 2016-05-13 21:07:59 +0000, Tony Parker via swift-corelibs-dev said:
> 
> 
> 
> 
> 
> On May 13, 2016, at 1:05 PM, James Lee <james at jelee.co.uk> wrote:
> 
> 
> 
> Cheers for the clarification. I started assuming there may be a reason when changing the guard let on the launch args to use the InvalidArgumentException.
> 
> 
> 
> Could this be a position where we may need os checking to cover the regression for the moment. It seems odd that the test would pass in CI when an error is thrown with a try! but fail on OSX
> 
> Task is certainly one of the cases where the underlying stuff that we’re abstracting is significantly different, so I’m not too surprised.
> 
> 
> 
> We should try to get something in place so we’re not failing on OS X in the short term for sure.
> 
> 
> 
> - Tony
> 
> 
> 
> Sent from my iPhone
> 
> 
> 
> On 13 May 2016, at 20:48, Tony Parker <anthony.parker at apple.com> wrote:
> 
> 
> 
> Hi James,
> 
> 
> 
> On May 13, 2016, at 12:25 PM, James Lee via swift-corelibs-dev <swift-corelibs-dev at swift.org> wrote:
> 
> 
> 
> Following on from a previous discussion with Tests failing on OSX. I have been looking into the failures. It seems that one of the earliest failures is due to an error from a try! within NSTask.launch(). This came in with this commit: https://github.com/apple/swift-corelibs-foundation/commit/4c6f04cfcad3d4b06688558021595d06751fc66a
> 
> 
> 
> Going by the docs for Foundation - The launch function apparently "Raises an NSInvalidArgumentException if the launch path has not been set or is invalid or if it fails to create a process."
> 
> 
> 
> https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSTask_Class/#//apple_ref/occ/instm/NSTask/launch
> 
> 
> 
> My question is, should this be built into the Swift Foundation API? The documentation for Swift doesn't state that the launch function throws.
> 
> 
> 
> With the test that is failing expecting an error, it feels more Swift-y to have any errors throw explicitly, rather than looking at what the lower level fills the data with.
> 
> 
> 
> But before jumping into doing this, I would rather put it out there and see what the community feels about this?
> 
> 
> 
> Unfortunately the ‘throws’ syntax in Swift often causes a mixup between two different things, because it flipped the terminology from what all of our documentation and header comments use.
> 
> 
> 
> 1. Cocoa uses exceptions (@throw in ObjC) to indicate programmer errors and they are generally not intended to be recoverable.  Example: passing nil where not expected, passing an invalid argument, failing to meet a precondition of an API.
> 
> 2. Cocoa uses NSError ** to indicate runtime errors that are recoverable or at least presentable to user. Example: out of disk space, name of file already exists.
> 
> 
> 
> The ‘throws’ syntax in Swift is actually for case #2, not #1. In Swift, #1 is fatalError or preconditionFailure. #2 is ‘throw Error’.
> 
> 
> 
> While API compatibility should be the fore-most goal here, I feel like there's room for improvement here for the API overlays. While in ObjC one has the ability to recover from NSInvalidArgumentException, on Swift this would trap.
> 
> 
> 
> 
> 
> In the case of NSTask, when the documentation says “raises an NSInvalidArgumentException” (#1) then in Swift, that should translate to fatalError or preconditionFailure.
> 
> 
> 
> As a resort; I propose to change the error wrapper (see https://github.com/apple/swift-corelibs-foundation/pull/362):
> 
> 
> 
> private func posix(_ code: Int32) {
> 
>     switch code {
> 
>     case 0: return
> 
>     case EBADF: fatalError("POSIX command failed with error: \(code) -- EBADF")
> 
>     default: fatalError("POSIX command failed with error: \(code)")
> 
>     }
> 
> }
> 
> 
> 
> Which would produce the following –more helpful– error on OSX:
> 
> 
> 
> Test Case 'TestNSTask.test_pipe_stdout_and_stderr_same_pipe' started at 10:13:55.584
> 
> fatal error: POSIX command failed with error: 9 -- EBADF: file <somedir>/swift-corelibs-foundation/Foundation/NSTask.swift, line 424
> 
> 
> 
> 
> 
> 
> 
> Hope this helps,
> 
> - Tony
> 
> 
> 
> Cheers
> 
> 
> 
> James
> 
> _______________________________________________
> 
> swift-corelibs-dev mailing list
> 
> swift-corelibs-dev at swift.org
> 
> https://lists.swift.org/mailman/listinfo/swift-corelibs-dev
> 
> 
> 
> 
> 
> 
> 
> _______________________________________________
> 
> swift-corelibs-dev mailing list
> 
> swift-corelibs-dev at swift.org
> 
> https://lists.swift.org/mailman/listinfo/swift-corelibs-dev
> 
> 
> 
> _______________________________________________
> swift-corelibs-dev mailing list
> swift-corelibs-dev at swift.org
> https://lists.swift.org/mailman/listinfo/swift-corelibs-dev
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-corelibs-dev/attachments/20160514/717a2c20/attachment.html>