View Issue Details [ Jump to Notes ] [ Print ]
IDProjectCategoryView StatusDate SubmittedLast Update
0014022CMakeCMakepublic2013-03-18 10:402016-06-10 14:31
ReporterPetr Kmoch 
Assigned ToKitware Robot 
PrioritynormalSeverityminorReproducibilityalways
StatusclosedResolutionmoved 
PlatformUnixOSOS Version
Product VersionCMake 2.8.9 
Target VersionFixed in Version 
Summary0014022: if(EXISTS) returns false for broken symlinks
Description'if(EXISTS arg)' evaluates to false if 'arg' is a symlink pointing to a non-existent file. To me, this feels like incorrect behaviour - arg itself exists, so the test should pass.

If the current behaviour is actually intended, I believe it should at least be documented.

With Windows symlinks, this does not happen; 'if(EXISTS arg)' evaluates to true if 'arg' is a broken link created with 'mklink'.
Steps To Reproduce$ ln -s target link
$ cmake -P test_link.cmake (attached)
$ touch target
$ cmake -P test_link.cmake

'link' exists in both cases, but first run reports 'link does not exist'
TagsNo tags attached.
Attached Files? file icon test_link.cmake [^] (114 bytes) 2013-03-18 10:40

 Relationships
related to 0010468closedBrad King find_program() doesn't find not readable programs on *nix 

  Notes
(0032656)
Brad King (manager)
2013-03-18 11:05

 This is because the SystemTools::FileExists method:

 http://cmake.org/gitweb?p=cmake.git;a=blob;f=Source/kwsys/SystemTools.cxx;hb=v2.8.10.2#l1080 [^]

uses "access" instead of "lstat" because someone once thought it was faster and so that find_* commands would only find readable files:

 http://public.kitware.com/gitweb?p=KWSys.git;a=commitdiff;h=4b0eccba [^]
 http://public.kitware.com/gitweb?p=KWSys.git;a=commitdiff;h=9fa7573f [^]

However, "access" should not be used for this purpose. Unfortunately it is hard to change now because many uses of FileExists have been introduced that assume its current behavior. Fixing this will require FileExists and all calls to it to be refactored into multiple functions that cover the actual needs of each call site. There are *many* such calls.
(0032702)
Brad King (manager)
2013-03-26 08:27

 At least some code relies on if(EXISTS) returning false for a broken symlink:

 http://cmake.org/gitweb?p=cmake.git;a=blob;f=Tests/CMakeLists.txt;hb=v2.8.10.2#l2195 [^]
 http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=46c0a583 [^]

Due to the historic "access()" implementation the if(EXISTS) check tests whether a file is readable. Any fix to this will have to preserve that, at least with a policy.
(0035496)
Ben Boeckel (developer)
2014-03-24 18:05

 Would a policy or a new keyword (FILENAME_EXISTS) be better?
(0035529)
Brad King (manager)
2014-03-26 11:02

 Re 0014022:0035496: I think a policy would be better. It will avoid carrying two almost identical interfaces and having to document the subtle difference.
(0042253)
Kitware Robot (administrator)
2016-06-10 14:28

 Resolving issue as `moved`.

This issue tracker is no longer used. Further discussion of this issue may take place in the current CMake Issues page linked in the banner at the top of this page.

 Issue History
Date Modified Username Field Change
2013-03-18 10:40 Petr Kmoch New Issue
2013-03-18 10:40 Petr Kmoch File Added: test_link.cmake
2013-03-18 10:57 Brad King Relationship added related to 0010468
2013-03-18 11:05 Brad King Note Added: 0032656
2013-03-18 11:05 Brad King Status new => backlog
2013-03-26 08:27 Brad King Note Added: 0032702
2014-03-24 18:05 Ben Boeckel Note Added: 0035496
2014-03-26 11:02 Brad King Note Added: 0035529
2016-06-10 14:28 Kitware Robot Note Added: 0042253
2016-06-10 14:28 Kitware Robot Status backlog => resolved
2016-06-10 14:28 Kitware Robot Resolution open => moved
2016-06-10 14:28 Kitware Robot Assigned To => Kitware Robot
2016-06-10 14:31 Kitware Robot Status resolved => closed

Copyright © 2000 - 2018 MantisBT Team