Problem finding correct libjpeg

[Nexus]

When I tried to compile Thor with MinGW, I got linker errors in one of SFML's dependencies. Some symbols from libjpeg were not found.

Debugging showed me that during the CMake configuration step, a wrong libjpeg path is found:

find_package(SFML 2 COMPONENTS audio graphics window system)
message(STATUS "Dep: ${SFML_DEPENDENCIES}")

Dep: ... C:/Program Files (x86)/Java/jre7/bin/jpeg.dll ...

Why does it even find a .dll and not a .lib file? These arguments are supposed to be passed to target_link_libraries in order to be linked (not loaded at runtime like DLLs).

Investigating FindSFML.cmake shows that the call to find_library (through the macro find_sfml_dependency) already returns this wrong path... Which is strange since the library path appears first in the list, and I made sure libjpeg.a is there.

Debugging output used in FindSFML.cmake inside find_sfml_dependency:

message("\nFinding ${output} (${ARGN}) in ${FIND_SFML_PATHS}")
message(" -> ${${output}}")

Finding JPEG_LIBRARY (jpeg) in C:/C++Libs/mingw;~/Library/Frameworks;/Library/Frameworks;/usr/local;/usr;/sw;/opt/local;/opt/csw;/opt
 -> C:/Program Files (x86)/Java/jre7/bin/jpeg.dll

There is a file C:/C++Libs/mingw/lib/libjpeg.a, but somehow it's not recognized.

Strangely, the NMake toolchain works fine.

By the way, why does SFML not ship a FindJPEG.cmake module?

[Laurent]

Why does it even find a .dll and not a .lib file?

gcc on Windows can link directly to .dll files for C libraries. So you can expect them to be found as import libraries when trying to locate libraries.

By the way, why does SFML not ship a FindJPEG.cmake module?

Because there's one in CMake. But I guess your question is more "why don't we use find_package in FindSFML.cmake?", and... that is another story

Back to the problem: you should check the search order used by find_program in the CMake doc.

[Nexus]

Back to the problem: you should check the search order used by find_program in the CMake doc.

I assume you mean find_library, as this one is invoked by FindSFML.cmake.

I read the documentation, and environment variables (containing the JRE path in my example) are indeed looked up before the passed PATHS argument.

This can be disabled by passing NO_SYSTEM_ENVIRONMENT_PATH to find_library. It works like this. The question is, do we break other cases if we disable lookup in environment variables?

An option (described at the end of the doc) is to call find_library multiple times: first without taking environment variables into account, then -- only if nothing is found -- again with them. That might be unnecessary though.

[Laurent]

This can be disabled by passing NO_SYSTEM_ENVIRONMENT_PATH to find_library. It works like this.

That should be a safe fix.

[Nexus]

Ok, I'll propose a corresponding pull request.
[Edit] Here: #839

Thanks for the quick help!