[CMake] CMAKE 2.6.0: Wrong dependencies when CMake<LANG>Information.cmake is missing

[Wojciech Migda]

Hi,

I did have a problem with cmake regenerating the whole build tree 
everytime I executed make. As it turned out the rebuild was done due to 
the dependency check made in 
cmGlobalUnixMakefileGenerator3::WriteMainCMakefile. It came out that the 
CMAKE_MAKEFILE_DEPENDS list in Makefile.cmake contained the current 
directory (".") entry, which appeared to be always more recent than the 
newest output - CMakeFiles/cmake.check_cache. It was enough to remove 
the "." entry to get rid of the rebuild. Anyway I kept investigating.

As it appeared the "." entry was present due to me using user-defined 
assembler compiler for the build. Commenting out the relevant 
ENABLE_LANGUAGE command in CMakeLists.txt led to proper behaviour. But 
why ? I looked at the cmGlobalGenerator::EnableLanguage function and 
after debugging I noticed that when a check for 
CMake<LANG>Information.cmake was made, a file which was missing - I did 
put all assembly compiler definitions into CMake<LANG>Compiler.cmake, a 
call to GetModulesFile returned an empty string. ReadListFile executed 
with that empty string did not fail, and that probably led to the "." 
directory being present in the CMAKE_MAKEFILE_DEPENDS list.

I confirmed that by setting the CMAKE_<LANG>_INFORMATION_LOADED variable 
before execution of ENABLE_LANGUAGE - the dependencies were correct. 
Nonetheless I'd expect that a fix with additional check for ifpath being 
empty is introduced in 
cmGlobalGenerator.cxx/cmGlobalGenerator::EnableLanguage.

I've prepared a patch against the 2.6.0 version. Unfortunately I could 
not find the patch format instructions for cmake, so I took those for 
linux kernel (diff -up).

--- cmake-2.6.0/Source/cmGlobalGenerator.cxx.orig    2008-05-05 
18:25:54.000000000 +0000
+++ cmake-2.6.0/Source/cmGlobalGenerator.cxx    2008-06-08 
15:28:43.986483015 +0000
@@ -415,10 +415,10 @@ cmGlobalGenerator::EnableLanguage(std::v
       fpath +=  lang;
       fpath += "Information.cmake";
       fpath = mf->GetModulesFile(fpath.c_str());
-      if(!mf->ReadListFile(0,fpath.c_str()))
+      if(!mf->ReadListFile(0,fpath.c_str()) || fpath.empty())
         {
         cmSystemTools::Error("Could not find cmake module file:",
-                             fpath.c_str());
+                            "CMake", lang, "Information.cmake");
         }
       }
     if (needSetLanguageEnabledMaps[lang])

The latest HEAD version 1.233 appears to have the same problem.

With best regards,

Wojciech Migda


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