build: accept @srcdir@-substituted subdir Makefiles

Enabler for the Makefile -> Makefile.in migration.  No module is
converted yet; behaviour is identical.

* scripts/defs.mak.in: dual-mode.  A module converted to Makefile.in will
  set `srcdir` (and VPATH) from @srcdir@ before including defs.mak; only
  derive them (the $(abspath)/$(patsubst) srcdir computation) when it
  did not -- `ifeq ($(origin srcdir),undefined)`.  BUILD_TOP (needed by
  GENINC) is computed either way.

* Makefile.in: route every subdir recursion through a single helper,
      $(call submake,<dir>,<goal>)
  which uses the generated build Makefile if config.status made one there
  (a converted Makefile.in) and otherwise falls back to the source
  Makefile with -f.  Today nothing is converted, so out-of-tree always
  takes the -f path and in-tree uses the (identical) static Makefile
  natively.  clean/ keeps its own no-mkdir variant.  readline/ is
  intentionally never converted and always takes -f.

* .gitignore: document the migration policy -- each converted module adds
  its generated "<dir>/Makefile" here in the same commit so an in-tree
  build can never commit a generated Makefile.  (None converted yet.)

Verified in-tree and out-of-tree: `configure && make && make install`
each produce 376 files with the header in the right place (database/
database.h in-tree, include/database/database.h relocated), 27/28 docs,
source tree clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -14,6 +14,13 @@ install.log
 make.log
 reconfigure.sh
 
+# Generated per-directory Makefiles (Makefile.in migration).  POLICY: whenever a
+# module's Makefile becomes a configure-generated Makefile.in, add its
+# "<dir>/Makefile" here in the *same commit*, so an in-tree build never lets a
+# generated Makefile be committed.  (Top-level /Makefile is handled above;
+# readline/ is intentionally NOT converted and keeps its tracked static Makefile.)
+# --- converted dirs below (none yet) ---
+
 # Compiled objects / libraries
 *.o
 *.a

Makefile.in

@@ -4,9 +4,8 @@
 
 MAGICDIR   = .
 # Absolute path to the source tree (config.status substitutes @abs_top_srcdir@).
-# For an in-tree build this is the same directory as the build top.  Every
-# recursion below drives a build subdirectory (created on demand) using the
-# module Makefile from the source tree: -C <builddir> -f ${MAGICSRC}/<dir>/Makefile.
+# For an in-tree build this is the same directory as the build top.  Recursion
+# into subdirectories goes through $(submake) (defined below).
 MAGICSRC   = @abs_top_srcdir@
 PROGRAMS   = magic
 TECHS      = scmos
@@ -27,6 +26,16 @@ INSTALL_CAD_DIRS = windows doc ${TECHS}
 # the build tree), empty otherwise (the pre-built PostScript is installed as-is).
 DOCS_TARGET = @DOCS_TARGET@
 
+# $(call submake,<dir>,<goal>) -- recurse into a build subdirectory.
+# Use the generated build Makefile if config.status created one there (a module
+# converted to Makefile.in); otherwise fall back to the source Makefile
+# with -f.  The build subdir is created on demand.  During the
+# Makefile.in migration both kinds coexist; readline/ is intentionally never
+# converted, so it always takes the -f path.
+define submake
+mkdir -p $(1) && if test -f $(1)/Makefile; then $(MAKE) -C $(1) $(2); else $(MAKE) -C $(1) -f $(MAGICSRC)/$(1)/Makefile $(2); fi
+endef
+
 all:	$(ALL_TARGET) techs $(DOCS_TARGET)
 
 standard: mains
@@ -47,12 +56,12 @@ config:
 tcllibrary: ${DATABASE_H} modules
 	@echo --- making Tcl shared libraries
 	for dir in ${PROGRAMS}; do \
-		mkdir -p $$dir && ${MAKE} -C $$dir -f ${MAGICSRC}/$$dir/Makefile tcl-main || exit 1; done
+		$(call submake,$$dir,tcl-main) || exit 1; done
 
 mains: ${DATABASE_H} modules libs
 	@echo --- making main programs
 	for dir in ${PROGRAMS}; do \
-		mkdir -p $$dir && ${MAKE} -C $$dir -f ${MAGICSRC}/$$dir/Makefile main || exit 1; done
+		$(call submake,$$dir,main) || exit 1; done
 
 # makedbh is the one generated helper script; it lives in the *build* tree.
 # ${DATABASE_H} is $(builddir)/database/database.h in-tree, or
@@ -77,13 +86,13 @@ LIBS_SUBDIR := $(shell for i in ${MODULES}; do echo "$${i}/lib$${i}.a"; done)
 
 .PHONY: FORCE
 ${MODULES_SUBDIR}: FORCE
-	@d=$(dir $@); mkdir -p $$d && ${MAKE} -C $$d -f ${MAGICSRC}/$${d}Makefile module
+	@$(call submake,$(patsubst %/,%,$(dir $@)),module)
 
 .PHONY: modules
 modules: ${DATABASE_H} depend ${MODULES_SUBDIR}
 
 ${LIBS_SUBDIR}: FORCE
-	@d=$(dir $@); mkdir -p $$d && ${MAKE} -C $$d -f ${MAGICSRC}/$${d}Makefile lib
+	@$(call submake,$(patsubst %/,%,$(dir $@)),lib)
 
 # Force the tiles/utils modules to exist first for libdatabase.a
 .PHONY: libs
@@ -106,7 +115,7 @@ SUBDIRS_DEPEND = $(addsuffix /Depend, ${SUBDIRS_FILTERED})
 
 ${SUBDIRS_DEPEND}: ${DATABASE_H}
 	@echo --- making dependencies
-	@d=$(dir $@); mkdir -p $$d && ${MAKE} -C $$d -f ${MAGICSRC}/$${d}Makefile depend
+	@$(call submake,$(patsubst %/,%,$(dir $@)),depend)
 
 .PHONY: depend
 depend: defs.mak ${SUBDIRS_DEPEND}
@@ -115,7 +124,7 @@ depend: defs.mak ${SUBDIRS_DEPEND}
 techs: depend
 	@echo --- making techs
 	for dir in ${TECHS}; do \
-		mkdir -p $$dir && ${MAKE} -C $$dir -f ${MAGICSRC}/$$dir/Makefile all || exit 1; done
+		$(call submake,$$dir,all) || exit 1; done
 
 # Regenerate the PostScript documentation from its .tex sources (only reached
 # from "all" when configure found latex+dvips; see DOCS_TARGET).
@@ -135,9 +144,9 @@ install-magic:
 
 install-real: install-dirs
 	for dir in ${INSTALL_CAD_DIRS}; do \
-		mkdir -p $$dir && ${MAKE} -C $$dir -f ${MAGICSRC}/$$dir/Makefile install; done
+		$(call submake,$$dir,install); done
 	for dir in ${PROGRAMS}; do \
-		mkdir -p $$dir && ${MAKE} -C $$dir -f ${MAGICSRC}/$$dir/Makefile install; done
+		$(call submake,$$dir,install); done
 
 install-tcl-dirs:
 	${SCRIPTS}/mkdirs $(DESTDIR)${INSTALL_BINDIR} \
@@ -156,11 +165,15 @@ install-tcl:
 
 install-tcl-real: install-tcl-dirs
 	for dir in ${INSTALL_CAD_DIRS} ${PROGRAMS}; do \
-		mkdir -p $$dir && ${MAKE} -C $$dir -f ${MAGICSRC}/$$dir/Makefile install-tcl; done
+		$(call submake,$$dir,install-tcl); done
 
 clean:
+	@# clean must not create dirs: skip absent ones, and use the generated build
+	@# Makefile if present else the source one (mirrors $(submake) without mkdir).
 	for dir in ${SUBDIRS_FILTERED} ${TECHS} ${BUNDLED_MODULES}; do \
-		test -d $$dir && ${MAKE} -C $$dir -f ${MAGICSRC}/$$dir/Makefile clean || true; done
+		test -d $$dir || continue; \
+		if test -f $$dir/Makefile; then ${MAKE} -C $$dir clean; \
+		else ${MAKE} -C $$dir -f ${MAGICSRC}/$$dir/Makefile clean; fi || true; done
 	${RM} *.tmp */*.tmp *.sav */*.sav *.log TAGS tags
 
 distclean:

scripts/defs.mak.in

@@ -21,6 +21,11 @@ MAGICSRC               = @abs_top_srcdir@
 #   subpath    = "/tiles", or "" at the top
 #   srcdir     = $(MAGICSRC)$(subpath)
 BUILD_TOP              := $(abspath $(MAGICDIR))
+# Dual mode: a module converted to Makefile.in sets `srcdir` (and VPATH) from
+# @srcdir@ *before* including this file, so we only derive them when it did not.
+# This lets the two kinds of Makefile coexist during the migration.  BUILD_TOP
+# (needed by GENINC below) is computed either way.
+ifeq ($(origin srcdir),undefined)
 # Anchored prefix strip (patsubst matches the whole word, so BUILD_TOP must be a
 # leading prefix): "" at the build top, "/tiles" in a subdir.  Unlike $(subst …)
 # this cannot mis-fire if BUILD_TOP happens to recur later in the path.
@@ -32,6 +37,7 @@ srcdir                 := $(MAGICSRC)$(MODULE_SUBPATH)
 ifneq ($(MODULE_SUBPATH),)
 VPATH                  := $(srcdir)
 endif
+endif
 
 # Generated headers (currently just database/database.h) are exposed through a
 # single include directory, ${GENINC}: