I have Makefiles for several custom domain specific languages. One of them require weird paths for the input/output files passed to the compiler, So I had to use some gnumake tricks. Now they are not playing nice with variable overloading, even using the always-re-parse-variable (=).

# Makefile.main
SOURCE_FILES=forgot_to_set_source_files.ksp

# Paths
SRCDIR=src
OBJDIR=Resources/scripts

.SUFFIXES:            # Delete the default suffixes
.SUFFIXES: .txt .ksp  # Define our suffix list
VPATH =
VPATH = $(SRCDIR)
OBJECT_FILES = $(addprefix $(OBJDIR)/, $(SOURCE_FILES:.ksp=.txt))

# src/abc.ksp -> Resources/script/abc.txt
$(OBJECT_FILES): $(OBJDIR)/%.txt: %.ksp
    $(info Compiling $<)
    @mkdir -p $(@D)
    "$(CC)" $(CC_FLAGS) $< $@


build: $(VMPID) $(OBJECT_FILES)
    $(info $(OBJECT_FILES))
    $(info $(SOURCE_FILES))

Now each project have:

# projA/Makefile
include ../Makefile.main

SOURCE_FILES=
    one.ksp 
    two.ksp

Now when i try to make:

 $ make
make: *** No rule to make target 'forgot_to_set_source_files.ksp', needed by 'Resources/scripts/forgot_to_set_source_files.txt'.  Stop.

tried to remove the default value

$ git diff ../Makefile.main
- SOURCE_FILES=forgot_to_set_source_files.ksp
+ #SOURCE_FILES

$ make
Resources/scripts/one.txt Resources/scripts/two.txt
one.ksp two.ksp
make: Nothing to be done for 'default'.

From the output of the two $(info ...) we confirm make “sees” an empty variable for the rules targets, but see the correct value inside the rule.

I then tried to reset all values that are used to construct the rule target into the project Makefile, and added some exports for good measure.

# projA/Makefile
include ../Makefile.main

export SOURCE_FILES=
    one.ksp 
    two.ksp

export OBJECT_FILES=$(addprefix $(OBJDIR)/, $(SOURCE_FILES:.ksp=.txt))

export

No change. Still exact same failures.

I tried to re-declare the sulfix rule ($(OBJECT_FILES): $(OBJDIR)/%.txt: %.ksp) in the project makefile. Still fails!

I tried to use ?= on the main makefile’s assignment of SOURCE_FILES, and I still get No rule to make target 'forgot_to_set_source_files.ksp'...

What is preventing that rule from getting the updated value of SOURCE_FILES? Is there anything special about $(addprefix ...)?