Track catalog & magic prereqs and diff for changes

If a new prerequisite for a catalog (or the compiled magic file) is
added, and it is newer than the last build, then the catalog (or
compiled magic file) will be rebuilt. However, formerly, the file would
not be rebuilt if the added file was older, or if a prerequisite was
removed instead of added, due to limitations in Make.

This commit tracks the list of prerequisites separately, and if it
changes, forces a rebuild of the file regardless of whether the
prerequisites are newer or older than the target.

diff --git a/GNUmakefile b/GNUmakefile
index a784f21e5d4717c052cd0a94cb878d8549834493..5f55e1aa5b0d418cbcf96f1f554fb6fddb6b9710 100644 (file)
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -214,6 +214,15 @@ override quote = '$(subst ','"'"',$1)'
 # Outputs an `@´ to silence rules, unless `VERBOSE´ is nonempty.
 override silent := $(if $(VERBOSE),,@)
 
+# (callable) Test to see if the prerequisites provided by the second argument matches the value in the file corresponding to the first argument in `$(BUILDDIR)/lastprereqs´.
+# If not, save the new value and then add FORCE.
+# Return them regardless.
+#
+# Calling this variable is useful when a given target should be updated whenever its list of prerequisites changes in addition to whenever there is a change to one of its prerequisites.
+#
+# ☡ This variable creates at least one subshell every time it is computed.
+override diffprereqs = $(if $(subst $(shell $(CAT) $(call quote,$(BUILDDIR)/lastprereqs/$1) 2> /dev/null || true),,$2),$2 FORCE$(and $(shell $(call ensuredirectory,$(BUILDDIR)/lastprereqs) && $(PRINTF) '%s\n' $(call quote,$2) > $(BUILDDIR)/lastprereqs/$1),),$2)
+
 # (callable) Escape special characters for use in sed regular expressions.
 override sedesc = $(subst /,[/],$(subst $$,\$$,$(subst *,\*,$(subst .,\.,$(subst [,\[,$(subst ^,\^,$(subst \,\\,$1)))))))
 
@@ -411,6 +420,9 @@ uninstall :
 $(call compiled,$(recursivefiles)) :
        @$(PRINTF) '%b\n' $(call quote,\0033[93;41mError:\0033[39;49m `$(call uncompiled,$@)´ has recursive dependencies:\n$(subst |, ,$(subst $(space),$(newline),$(foreach recursive,$(call recursives,$(call uncompiled,$@)),•|$(recursive))))) && false
 
+# Add as a prerequisite to treat the target as tho it were phony.
+FORCE : ;
+
 # ─ ¶ Special Targets ─────────────────────────────────────────────────
 
 # Perform secondary expansion; this enables pattern rules to determine their prerequisites based on the matched pattern.
@@ -420,7 +432,7 @@ $(call compiled,$(recursivefiles)) :
 .SUFFIXES : ;
 
 # Phony rules; always consider these out·of·date.
-.PHONY : all default clean gone info install list uninstall $(call compiled,$(recursivefiles)) ;
+.PHONY : FORCE all default clean gone info install list uninstall $(call compiled,$(recursivefiles)) ;
 
 ifneq ($(typeupdates)$(wildcard $(BUILDDIR)/dependencies)$(wildcard $(BUILDDIR)/destinations),)
 # Reload this make·file if the dependency graph or output destinations have changed.
@@ -464,8 +476,7 @@ $(call magicfile,$(MAGIC)) : $(BUILDDIR)/magic/% : $$(call magicsource,$$@)
 # Generate the compiled magic file from its sources.
 #
 # It must be updated if any of the files in the magic directory change.
-# It ⁜also⁜ should be updated if any of the files in the magic directory are deleted, but this isn’t tracked presently.
-$(BUILDDIR)/magic.mgc : $(call magicfile,$(MAGIC))
+$(BUILDDIR)/magic.mgc : $(call diffprereqs,magic,$(sort $(call magicfile,$(MAGIC))))
        $(foreach outdated,$(filter-out $^,$(wildcard $(BUILDDIR)/magic/*)),$(silent)$(RM) $(call quote,$(outdated))$(newline))
        @$(ECHO) "Compiling new magic…"
        $(silent)$(call ensuredirectory,$(dir $@))
@@ -473,7 +484,7 @@ $(BUILDDIR)/magic.mgc : $(call magicfile,$(MAGIC))
        $(silent)$(TOUCH) $(call quote,$(BUILDDIR)/.update-types)
 
 # Generate the main parser.
-$(BUILDDIR)/parser.catalog : $(PARSERS)
+$(BUILDDIR)/parser.catalog : $(call diffprereqs,parsers,$(sort $(PARSERS)))
        @$(ECHO) "Generating catalog of parsers…"
        $(silent)$(XMLCATALOG) --create --noout $(call quote,$@)
        $(foreach parser,$(PARSERS),$(silent)( $(call id,$(parser)) ) | $(XARGS) -I %% $(XMLCATALOG) --add uri %% $(call quote,$(call fileuri,$(parser))) --noout $(call quote,$@)$(newline))
@@ -494,7 +505,7 @@ $(call parsed,$(sourcefiles) $(sourceincludes)) : % : $$(call unparsed,$$@) $(BU
 # Generate a catalog of all parsed files, for use when processing includes.
 #
 # This does not depend on actually transforming the files.
-$(BUILDDIR)/catalog : $(sourcefiles) $(sourceincludes) $(typeupdates)
+$(BUILDDIR)/catalog : $(call diffprereqs,sources,$(sort $(sourcefiles) $(sourceincludes))) $(typeupdates)
        @$(ECHO) "Generating catalog of parsed files…"
        $(silent)$(XMLCATALOG) --create --noout $(call quote,$@)
        $(foreach source,$(sourcefiles) $(sourceincludes),$(silent)$(XMLCATALOG) --add uri $(call quote,$(call localuri,$(source))) $(call quote,$(call fileuri,$(call parsed,$(source)))#$(if $(filter $(source),$(assetfiles)),asset,xml)) --noout $(call quote,$@)$(newline))
@@ -513,7 +524,7 @@ $(BUILDDIR)/destinations : $(BUILDDIR)/catalog $(call parsed,$(filter-out $(asse
        $(silent)$(XSLTPROC) -o $(call quote,$@) $(call quote,$(THISDIR)/lib/catalog2destinations.xslt) $(call quote,$<)
 
 # Generate the main transform.
-$(BUILDDIR)/transform.catalog : $(TRANSFORMS)
+$(BUILDDIR)/transform.catalog : $(call diffprereqs,transforms,$(sort $(TRANSFORMS)))
        @$(ECHO) "Generating catalog of transforms…"
        $(silent)$(XMLCATALOG) --create --noout $(call quote,$@)
        $(foreach transform,$(TRANSFORMS),$(silent)( $(call id,$(transform)) ) | $(XARGS) -I %% $(XMLCATALOG) --add uri %% $(call quote,$(call fileuri,$(transform))) --noout $(call quote,$@)$(newline))