GNU Make how to make a static pattern rule for files that are not in the same directory?

Question

I want to use make and create a static pattern rule that has the target in a output directory, and the prerequisite files are in the preceeding directory, and it has to work recursively.

I have a minimal example here:

.
├── anotherdir
│   ├── output
│   │   ├── source3.md
│   │   └── source4.md
│   ├── source3.json
│   └── source4.json
├── output
│   ├── source1.md
│   └── source2.md
├── source1.json
└── source2.json

I want to generate the output directories if they do not exist, and I want to generate *.md files from the *.json using make if they do not exist, or *.json is updated.

So far, I have the following Makefile:

SOURCE_FILES := $(shell find ./ -name "*.json")
OUTPUT_FILES := $(join $(addsuffix output/,$(dir $(SOURCE_FILES))), $(addsuffix .md,$(basename $(notdir $(SOURCE_FILES)))))

.PHONY: all
all: $(OUTPUT_FILES)

$(OUTPUT_FILES): %.md: %.json
    mkdir -p $(dir $@)
    # Command to create MD file from json file into the output directory here

The actual command to create the MD file from the json file doesn't matter here, because I have a script that I will call that will do this for me. The problem here, is that when I try to even run this at all, I get the following output:

> make all
make: *** No rule to make target 'anotherdir/output/source4.json', needed by 'anotherdir/output/source4.md'.  Stop.

Obviously, source4.json is not in anotherdir/output, but rather, it's in the preceeding directory, which is just anotherdir. I don't know how to make it so that the pattern $(OUTPUT_FILES): %.md: %.json will match it properly.

Or is a static pattern rule not good here? I'm not sure what to do to fit my scenario.

EDIT: I tried to do something like this:

$(OUTPUT_FILES): %.md: $(join $(subst output,,$(dir %)), $(addsuffix .json,$(basename $(notdir %))))

and this doesn't work, I still get:

> make all
make: *** No rule to make target 'anotherdir/output/source4.json', needed by 'anotherdir/output/source4.md'.  Stop.

Edit 2: to clarify, i start with the following files

.
├── anotherdir
│   ├── source3.json
│   └── source4.json
├── source1.json
└── source2.json

And then when i run make, i want it to generate the output folders like this

.
├── anotherdir
│   ├── output
│   │   ├── source3.md
│   │   └── source4.md
│   ├── source3.json
│   └── source4.json
├── output
│   ├── source1.md
│   └── source2.md
├── source1.json
└── source2.json

I want to use some kind of smart makefile syntax to pick up these files names without me hard coding it in myself. Hence, i looked at the documentation and saw that static pattern rules might be the solution that i want, except that i can't get the right prerequisite pattern down.

Answer 1

I would do it this way:

First, find the source files just as you did (with a small change to prevent the unsightly double-slash):

SOURCE_FILES := $(shell find . -name "*.json")

A pattern file would be nice, if we could use two wildcards at once, but Make can't quite do that. So I recommend using a template:

define template
TDIR := $(dir $(1))output
TARG := $$(TDIR)/$(notdir $(basename $(1))).md
$$(TARG): $(1)
    mkdir -p $$@
    @echo building $$@ from $$<
    # Command to create MD file from json file into the output directory here
endef

$(foreach SOURCE,$(SOURCE_FILES),$(eval $(call template,$(SOURCE))))

If this works, all that's left is to construct a list of output files, and a default rule that has all of them as prerequisites:

define template
TDIR := $(dir $(1))output
TARG := $$(TDIR)/$(notdir $(basename $(1))).md
OUTPUT_FILES += $$(TARG)
$$(TARG): $(1)
    mkdir -p $$@
    @echo building $$@ from $$<
    # Command to create MD file from json file into the output directory here
endef

all:

$(foreach SOURCE,$(SOURCE_FILES),$(eval $(call template,$(SOURCE))))

all: $(OUTPUT_FILES)

It isn't pretty, but it seems to work.