Searched a bunch, hope I didn't miss something obvious...
I have multiple book directories. Each has a single *.ditamap file (always named for the book) that references several dozen accompanying *.dita topic files:
makefile
book1/
book1.ditamap intro.dita topic1.dita topic2.dita glossary.dita
book2/
book2.ditamap about.dita topicA.dita topicB.dita appendix.dita
book3/
book3.ditamap cmd1.dita cmd2.dita cmd3.dita
The XHTML output (target) for a book depends on its single .ditamap file plus all the *.dita files in that book directory (prerequisites). The makefile is placed alongside the book directories.
Building XHTML for a book creates an output XHTML directory inside that book directory, with an index.html file that I use as the target:
book1/
book1.ditamap intro.dita topic1.dita topic2.dita glossary.dita
book1/book1_xhtml/
index.html ...more html and CSS files...
The following static pattern rule will rebuild the XHTML directory inside any book directory where the *.ditamap file has changed:
ditamap_files := $(wildcard */*.ditamap)
xhtml_files := $(patsubst %.ditamap,%_xhtml/index.html,${ditamap_files})
all: dita xhtml
dita: ${ditamap_files}
xhtml: ${xhtml_files}
${xhtml_files}: %_xhtml/index.html: %.ditamap
dita -i "${<}" -f xhtml -o "${*}_xhtml"
(Side note: make nicely handles building the path to the index.html target thanks to its clever directory-handling rules!)
However, I haven't found a way to extend this rule to be sensitive to the *.dita files too. Whenever .ditamap or .dita has changed inside the book directory, the book XHTML file must be rebuilt.
I tried stuff like
${xhtml_files}: %_xhtml/index.html: %.ditamap $(wildcard $(dir %)/*.dita)
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^
dita -i "${<}" -f xhtml -o "${*}_xhtml" 2>&1 | tee "${*}_xhtml.out"
but this completely fails to work because wildcards aren't supported in static pattern rules. Somehow I need to collect wildcarded files within the directory of the stem of each target, then make them prerequisites for that book.
Secondary expansion, maybe:
.SECONDEXPANSION:
$(xhtml_files): %_xhtml/index.html: %.ditamap $$(wildcard $$(dir $$*)/*.dita)
dita -i "$<" -f xhtml -o "$*_xhtml"
By the way, did you consider that dita files can change but also appear or disappear? Is this possible? If it is, what do you want to do? And do you know already how to detect this?