Make file with multiple potential dependencies

Question

I'm trying to make a make file for a static page generator, and I'm using jinja and pandoc so far, and the idea is to have a file structure as such

.
|-content
|-public
|-templates
|-Makefile

VPATH=public
TARGETS=$(find content -regex ".*(htm|md)" | sed -e "s/md$/htm/g;s/^content/public/g")
all: $(TARGETS)
 @echo fullbuild
public/%: content/%
content/%.md:
 # Pandoc script 
 pandoc -i $@ -o ${${@:.md=.htm}:content=public}
content/%.htm:
 # Jinja Script

The problem I'm having (At least I think that's it) is that according to me the syntax is

# For a final result
target: dependency
 commands
# A rule for dependency
dependency: 
 commands

My dependencies are in the content dir and my targets are in the public dir that may or may not exist yet, and almost all the files I generate will be htm files, and in that case if the target is public/some/route/to/file.htm the dependency will be any of this two content/some/route/to/file.(htm|md).

I can easily generate by walking the content dir, and changing extensions.

How should I write the rules properly, so - Make knows where to "watch" for changes every time I do a make, because right now it points that every file is up to date - How do I indicate properly the dependency of a file to it's content file.

Answer 1

This rule:

public/%: content/%

does nothing because pattern rules without recipes delete existing pattern rules, they don't define new pattern rules.

It's very simple, you should write two rules like this:

public/%.htm: content/%.md:
 # Pandoc script 
 pandoc -i $< -o $@
public/%.htm: content/%.htm
 # Jinja Script

Here's a hint: whenever you're writing a makefile recipe and you discover that you need to create a target which is different than exactly $@, unmodified, immediately stop what you're doing and back up: you've taken a wrong turn.