Jam - Separate Release/Debug Target Directories

By default, AppWizard-generated applications use separate directories for the output of the different debug and release builds. We’d like to replicate that functionality.

This is controlled by the LOCATE_TARGET variable. It’s initialised by the SubDir rule to be the same as the SEARCH_SOURCE variable, unless ALL_LOCATE_TARGET is set.

However, if we set ALL_LOCATE_TARGET to, e.g. Debug in our Jamrules file, or using the -s switch to jam, the object files and targets are all built in exactly the same directory. It’s not relative to the subdirectory. This could cause confusion if directories generate object files with the same names.

The comments in Jambase state that the LOCATE_TARGET variable should be set after invoking the SubDir rule, if required. This is a pain. We much prefer the following change to the SubDir rule:

       # directory should not hold object files, LOCATE_TARGET can
       # subsequently be redefined.

       **local path = [ FDirName $(SUBDIR) $(TARGET_PREFIX) ] ;

       SEARCH_SOURCE = $(SUBDIR) ;
       LOCATE_SOURCE = $(ALL_LOCATE_TARGET) $(path) ;
       LOCATE_TARGET = $(ALL_LOCATE_TARGET) $(path) ;
       SOURCE_GRIST = $(path) ;**

       # Reset per-directory ccflags, hdrs

This allows us to place a rule like the following in our Jamrules file:

if ! $(DEBUG) {
	ECHO Assuming DEBUG=1 ;
	DEBUG = 1 ;
}

if $(DEBUG) = 0 {
	TARGET_PREFIX = Release ;
}
else {
	TARGET_PREFIX = Debug ;
}