[cmake-developers] [CMake 0014619]: Windows: Regression affecting CMAKE_FIND_ROOT_PATH interaction with FIND_* commands, introduced since 2.8.11

Tue Dec 3 02:43:06 EST 2013

The following issue has been SUBMITTED. 
====================================================================== 
http://www.cmake.org/Bug/view.php?id=14619 
====================================================================== 
Reported By:                nOOb3167
Assigned To:                
====================================================================== 
Project:                    CMake
Issue ID:                   14619
Category:                   CMake
Reproducibility:            always
Severity:                   major
Priority:                   normal
Status:                     new
====================================================================== 
Date Submitted:             2013-12-03 08:43 CET
Last Modified:              2013-12-03 08:43 CET
====================================================================== 
Summary:                    Windows: Regression affecting CMAKE_FIND_ROOT_PATH
interaction with FIND_* commands, introduced since 2.8.11
Description: 
Due to an unrelated fix of issue http://www.cmake.org/Bug/view.php?id=10994,
commit f9eee7f1, regarding drive letter paths on Windows, CMAKE_FIND_ROOT_PATH
scenarios break on Windows hosts.

The correct operation of find_file and other find_* command calls in
CMAKE_FIND_ROOT_PATH scenarios on Windows might be possible to restore, while
still keeping the rest of the issue http://www.cmake.org/Bug/view.php?id=10994
fix.

Steps to Reproduce: 
Unpack uploaded test example.

= Contents =
CMakeLists.txt             : CMakeLists file to be used.
testToolChain.toolchain    : Toolchain file demonstrating a workaround.
root/                      : Directory to be used as CMAKE_FIND_ROOT_PATH.
root/include/dummyFile.txt : File to be searched for by FIND_FILE.
Build/                     : Out-of-source build directory.
                             Used to get a clean state between the multiple
                             cmake invocations that will be performed.
= Reproducing =
The CMakeLists.txt will be Configured by CMake versions 2.8.11 and 2.8.12.
The results will differ.

== Steps ==

=== 2.8.11 ===
1. Use CMake version 2.8.11
2. Invoke from Build/ :
    cmake ..

The variable TEST_NOROOT is set to path of dummyFile.txt.

=== 2.8.12 ===
1. Use CMake version 2.8.12
2. Invoke from Build/ :
    cmake ..

The variable TEST_NOROOT is not set to path of dummyFile.txt - Its value is
TEST_NOROOT-NOTFOUND.
This result differs from 2.8.11 and is therefore a regression.

Additional Information: 
Observing the changelog (http://www.cmake.org/Wiki/CMake/ChangeLog), shows the
following line in the 'Changes in CMake 2.8.12-rc1 (since 2.8.11.2)' entry:
  "Windows: Search '/' prefix only when cross compiling
(http://www.cmake.org/Bug/view.php?id=10994)"

A developer comment on issue http://www.cmake.org/Bug/view.php?id=10994
(http://www.cmake.org/Bug/view.php?id=10994#c32940), links to the attempted fix
commit f9eee7f1 (http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=f9eee7f1).

According to the f9eee7f1 commit message:
 "Fix WindowsPaths.cmake to add '/' to CMAKE_SYSTEM_PREFIX_PATH only when
  cross-compiling to Windows from a non-Windows host."
The root ('/') path is made to be omitted from CMAKE_SYSTEM_PREFIX_PATH on
Windows hosts, as a change from 2.8.11 to 2.8.12.

I claim this omission breaks CMAKE_FIND_ROOT_PATH on Windows hosts.
As demonstrated by the uploaded test example, a command call of the form:
 "find_file(<VAR> NAMES <NAMES> PATH_SUFFIXES <SUFFIXES>)"
Will no longer function in presence of CMAKE_FIND_ROOT_PATH.

As many Find* Modules included with CMake use find_file command calls of the
above form, these Modules therefore become unable to function in a
CMAKE_FIND_ROOT_PATH scenario.

The uploaded test example also contains a toolchain file.
The toolchain file appends '/' to CMAKE_SYSTEM_PREFIX_PATH.
The addition of '/' allows the command call to succeed.
This indicates the ab-or-pre-sence of '/' has a breaking effect on find_file.

The uploaded test example also attempts a command call of the form:
 "find_file(<VAR> NAMES <NAMES> PATHS / PATH_SUFFIXES <SUFFIXES>)"
Here a 'PATHS /' parameter is added with respect to the previous failing call.
The addition of '/' in PATHS also allows the command call to succeed.

Commit f9eee7f1, already mentioned and linked in a section above,
describes the reason for '/' omission as:
 "This will avoid searching and finding local paths without a drive letter on
Windows."

In a CMAKE_FIND_ROOT_PATH scenario with CMAKE_SYSTEM_PREFIX_PATH containing '/',
a drive-less path will never be formed by find_file. The operation of find_file,
relevant to this scenario, is described next.

Assuming values of:
 CMAKE_FIND_ROOT_PATH = F:\root
 CMAKE_SYSTEM_PREFIX_PATH = '/'     # (Or just containing '/' among other items)
A find_file command call will prefix F:\root to '/', getting 'F:\root\'.
This path will then be considered for the search.
(The find_file command documentation
(http://www.cmake.org/cmake/help/v2.8.12/cmake.html), describes
CMAKE_SYSTEM_PREFIX_PATH as used during the '5.' step of the search process. The
search path prefixing effect of CMAKE_FIND_ROOT_PATH is described towards the
end of find_file documentation.)

Using find_file in a CMAKE_FIND_ROOT_PATH scenario, the 'paths without a drive
letter' issue does not occur, as '/' is used just to form a longer path by
concatenation of CMAKE_FIND_ROOT_PATH with CMAKE_SYSTEM_PREFIX_PATH.

Commit f9eee7f1 has therefore introduced a new bug (A regression), while
attempting to fix an unrelated case.

====================================================================== 

Issue History 
Date Modified    Username       Field                    Change               
====================================================================== 
2013-12-03 08:43 nOOb3167       New Issue                                    
2013-12-03 08:43 nOOb3167       File Added: DummyProj.zip                    
======================================================================