Description Alex Freidin 2011-01-24 06:32:08 EST

Build Identifier: 20100917-0705

A project may include the same files names but with different extensions, e.g. .c, .cpp, .s. The case when more than one file is being compiled is described in bug 185671. 
This case is when only one of the files is "active" and another is excluded from build. For example, code that started as C and then enhanced to C++ or optimized into assembly. It is common to keep the original C source in the project as reference and exclude it from build. In such project, if the Internal Builder is used, the build is done correctly. If the makefile builder is used, then sometimes an excluded file is built instead of the "active" one.

Steps to reproduce (reproducible in CDT 7.0.1):
1. Create Hello World C++ template project named HelloCPP
2. Add file.cpp and file.c
3. Exclude file.cpp from build
4. Make sure "External Builder" is selected at Project>Properties>C/C++ Build>Builder Settings>Builder type.
5. Build the project, observe that file.cpp is built instead of file.c

The reason for the bug is in the makefile generation. The subdir.mk has a list of objects in $(OBJECTS) variable. It then matches them with the rules:

src/%.o: ../src/%.cpp

src/%.o: ../src/%.c

If the CPP rule appears first in the makefile, then for file.o, the makefile matches file.cpp, even if it is excluded from build. So, the correct file.c is never compiled. Note that the rules order is undefined and changes depending on the file names in the source directory. That's why sometimes everything works OK and sometimes it doesn't.

To build projects properly, the rules should be enhanced to relate to the relevant objects, e.g. 

$(C_OBJS): src/%.o: ../src/%.c
$(CPP_OBJS): src/%.o: ../src/%.cpp

The variables C_OBJS and CPP_OBJS can be initialized directly like $(OBJECTS) or be derived i.e.: C_OBJS = $(C_SRCS:../src/%.c=src/%.o)

Reproducible: Always