Fix the filelock test under Mac

[ndmitchell]

Currently it goes a bit weird:

## FINISHED TESTING errors
## BUILD filelock test
## TESTING filelock
(5.466000000000001e-6,"before onceFork")
(7.8909e-5,"after onceFork")
(1.41555e-4,"a1")
## BUILD filelock -VVV
(1.72613e-4,"b1")
## BUILD filelock -VVV
% Starting run
% Starting run 2
% Starting run 3
% Before withLockFile on ./.shake.lock
% Inside withLockFile
% Starting run
% Starting run 2
% Starting run 3
% Before withLockFile on ./.shake.lock
% Inside withLockFile
./.shake.database: openFile: resource busy (file is locked)
% Missing -> Waiting, filelock
# filelock
% Waiting -> Error, filelock
% result filelock = error
Error when running Shake build system:
* filelock
Error, file does not exist and no rule available:
  filelock
CallStack (from HasCallStack):
  error, called at src/Development/Shake/Internal/Rules/File.hs:180:58 in main:Development.Shake.Internal.Rules.File
(4.925253e-3,"after try a")
(5.0741070000000004e-3,"after try b")
TESTS FAILED
shake-test: user error (Expected one success and one failure, got [Left (ExitFailure 1),Left (ExitFailure 1)])
Test suite shake-test: FAIL
Test suite logged to: dist/test/shake-0.16-shake-test.log
0 of 1 test suites (0 of 1 test cases) passed.
neil: Failed when running system command: cabal test --show-details=streaming
CallStack (from HasCallStack):
  error, called at src/System/Process/Extra.hs:34:9 in extra-1.6.2-H6ipqC4P0F96PdmnLHr5qr:System.Process.Extra
  system_, called at src/Cabal.hs:197:24 in main:Cabal

For now I've disabled it with an isMac test.

[dwijnand]

Removing the isMac and running with cabal v2-run -O0 shake-test -- filelock it seemed to pass for me:

09:42:54 $ cabal v2-run -O0 shake-test -- filelock
Resolving dependencies...
Up to date
Longest file modification time lag was 2ms
## BUILD filelock
Starting sleep
Finished sleep
Build completed in 5.01s


09:44:48 $

Perhaps that's because I upgraded from HFS+ which has 1s time granularity to APFS (Apple File System) which has 1ns? Looks like Travis CI still uses HFS+: https://docs.travis-ci.com/user/reference/osx/#file-system.

[ndmitchell]

That could well be it - glad to hear it works somewhere - that means it probably works fine for users even if I still have to disable it on CI.

[ndmitchell]

Having tried on the branch 560-ismac I can confirm it still fails on CI. Not sure if it's the 1s vs 1ns difference (there's no timing aspects in the code), but I can imagine the file locking on HFS+ has some kind of issues.

[ndmitchell]

Given it works locally on modern systems (thanks for testing!), and the lock isn't essential for correct operation in normal usage, I'm going to close this issue.