[cmake-developers] [CMake 0015795]: pkg_check_modules produces incorrect results depending on contents of CMakeCache.txt

[Mantis Bug Tracker]

The following issue has been SUBMITTED. 
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https://cmake.org/Bug/view.php?id=15795 
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Reported By:                Sam Thursfield
Assigned To:                
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Project:                    CMake
Issue ID:                   15795
Category:                   Modules
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
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Date Submitted:             2015-10-16 10:41 EDT
Last Modified:              2015-10-16 10:41 EDT
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Summary:                    pkg_check_modules produces incorrect results
depending on contents of CMakeCache.txt
Description: 
I got bitten by a bug involving pkg_check_modules.

If I run cmake, then edit my CMakeLists.txt to change the parameters passed to
pkg_check_modules, and rerun cmake, it ignores the change that I made to
CMakeLists.txt. I needed to delete the CMakeCache.txt file to get the right
results.

This seems like a cache invalidation bug to me -- a change in the parameters
passed to to pkg_check_modules() should cause the cached values to be
invalidated.

I've attached a small script that reproduces the issue.

Steps to Reproduce: 
Use attached script. It uses the 'avahi' library as an example, so needs the
avahi-devel or libavahi-dev package (or whatever else your distro calls it) to
be installed. Any two pkg-config modules will trigger the same error.

Output on my machine:

Creating initial CMakeLists.txt
Avahi libs should be: avahi-gobject
AVAHI LIBS: avahi-gobject;avahi-common;avahi-client;avahi-glib;glib-2.0

Updating pkg_check_modules call
Avahi libs should be:
avahi-gobject;avahi-common;avahi-client;avahi-glib;glib-2.0
AVAHI LIBS: avahi-gobject;avahi-common;avahi-client;avahi-glib;glib-2.0

Removing cache and trying again
Avahi libs should be:
avahi-gobject;avahi-common;avahi-client;avahi-glib;glib-2.0
AVAHI LIBS: avahi-gobject;avahi-common;avahi-client;avahi-glib;glib-2.0

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Issue History 
Date Modified    Username       Field                    Change               
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2015-10-16 10:41 Sam Thursfield New Issue                                    
2015-10-16 10:41 Sam Thursfield File Added: testcase.sh                      
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