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build: per-file automatic dependencies (.deps), retire the Depend/sed machinery 

Replace the monolithic per-directory `Depend` file -- generated by a separate,
serial `make depend` pass (one `gcc -MM` over all sources) and post-processed by
sed -- with automake-style per-file dependency fragments produced as a side
effect of each compile.

rules.mak's %.o rule now adds, when the compiler supports it,
  -MMD -MP -MF .deps/<stem>.d
so every object records the (non-system) headers it used.  Those fragments are
`-include`d best-effort: absent on a first build, present and correct after.
Benefits:
  * self-maintaining -- no explicit depend step; deps refresh on every compile;
  * parallel -- generated during the (already parallel) compile, no barrier;
  * -MMD already drops system headers (what the sed did) and -MP tolerates a
    removed/renamed header, so the sed post-processing is gone;
  * fixes out-of-tree incremental header tracking: with an absolute srcdir the
    old sed stripped the now-absolute *local* header paths too, silently losing
    them; the .d files keep them.

configure probes `-MMD -MP` (AUTODEP_FLAGS; empty and best-effort-skipped if the
compiler cannot).  clean/distclean remove .deps (rm -r); .gitignore replaces the
obsolete */Depend with .deps/.  `make depend` is kept as a no-op for callers that
still invoke it (e.g. the WASM build script).

Verified out-of-tree (--disable-ccache): 324 .d files, 0 Depend files, a header
touch recompiles its dependents, no-op rebuild is idle, clean clears .deps.  (The
top-level depend phase still runs here as a no-op; removed next.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Darryl L. Miles 2026-07-23 14:47:29 +00:00 committed by R. Timothy Edwards
parent c27ef5fab1
commit 1bc8537b5d
5 changed files with 78 additions and 41 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
.gitignore vendored
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@ -70,8 +70,8 @@ doc/latexfiles/Makefile
*.o *.o
*.a *.a
*.so *.so
*/Depend # Per-file dependency fragments (in-tree they land in each source module dir;
*/Depend*.tmp # out-of-tree they are under the build dir). Replaces the old */Depend files.
.deps/ .deps/
database/database.h database/database.h
# autoconf config header, generated by ./configure (in-tree location; out-of-tree # autoconf config header, generated by ./configure (in-tree location; out-of-tree

45
rules.mak
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@ -2,31 +2,23 @@
module: lib${MODULE}.o module: lib${MODULE}.o
depend: ${DEPEND_FILE} # Dependencies are now generated automatically as a side effect of each compile
# (see the %.o rule below); "make depend" is a no-op kept only so scripts/habits
# New Depend file generating line (Tim Edwards, 1/25/06). This gets around # that still invoke it do not error.
# problems with gcc. The purpose of "make depend" is to generate a list of .PHONY: depend
# all local dependencies, but gcc insists that anything that is in, for depend:
# example, the /usr/X11R6 path should also be included. The sed scripts
# (respectively) do: 1) remove comment lines generated by gcc, 2) remove
# any header (.h) files with an absolute path (beginning with "/"), and
# 3) remove isolated backslash-returns just to clean things up a bit.
# The $$PPID allows this to be run on the same dir in parallel without
# corrupting the output, the final MV is transactional. If that is needed
# it indicates a missing dependency somewhere in a upstream/parent Makefile.
${DEPEND_FILE}: ${DEPSRCS}
${CC} ${CFLAGS} ${CPPFLAGS} ${DFLAGS} ${DEPEND_FLAG} $(addprefix $(srcdir)/,${DEPSRCS}) > ${DEPEND_FILE}$$PPID.tmp
${SED} -e "/#/D" -e "/ \//s/ \/.*\.h//" -e "/ \\\/D" -i ${DEPEND_FILE}$$PPID.tmp
${MV} -f ${DEPEND_FILE}$$PPID.tmp ${DEPEND_FILE}
# Original Depend file generating line:
# ${CC} ${CFLAGS} ${CPPFLAGS} ${DFLAGS} ${DEPEND_FLAG} ${SRCS} > ${DEPEND_FILE}
# Compile a source into an object. When the compiler supports it
# (AUTODEP_FLAGS = "-MMD -MP"), also write .deps/<stem>.d listing the non-system
# headers this object used -- generated as a side effect of the compile, so there
# is no separate serial "make depend" pass and it parallelises for free. -MMD
# already drops system headers (the job the old sed did), and -MP adds a phony
# target per header so a later removed/renamed header does not break the build.
%.o: %.c %.o: %.c
@echo --- compiling ${MODULE}/$*.o @echo --- compiling ${MODULE}/$*.o
@test -z "${AUTODEP_FLAGS}" || mkdir -p .deps
${RM} $*.o ${RM} $*.o
${CC} ${CFLAGS} ${CPPFLAGS} ${DFLAGS} -c $< -o $@ ${CC} ${CFLAGS} ${CPPFLAGS} ${DFLAGS} ${AUTODEP_FLAGS} $(if ${AUTODEP_FLAGS},-MF .deps/$*.d) -c $< -o $@
lib${MODULE}.o: ${OBJS} lib${MODULE}.o: ${OBJS}
@echo --- linking lib${MODULE}.o @echo --- linking lib${MODULE}.o
@ -53,12 +45,13 @@ ${DESTDIR}${BINDIR}/${MODULE}${EXEEXT}: ${MODULE}${EXEEXT}
.PHONY: clean .PHONY: clean
clean: clean:
${RM} ${CLEANS} ${RM} ${CLEANS}
${RM} -r .deps
tags: ${SRCS} ${LIB_SRCS} tags: ${SRCS} ${LIB_SRCS}
ctags $(addprefix $(srcdir)/,${SRCS} ${LIB_SRCS}) ctags $(addprefix $(srcdir)/,${SRCS} ${LIB_SRCS})
# Depends are a somewhat optional part of the build process that are only useful when incremental # Per-file dependency fragments written by the %.o rule above. Best effort: none
# building. If the file is here it's here, if not continue with build optimistically # exist on a first build (everything compiles anyway); on later builds they cause
ifneq (,$(wildcard ${DEPEND_FILE})) # a recompile when a used header changes. `-include` tolerates their absence and
include ${DEPEND_FILE} # the `-MP` phony header targets tolerate a removed/renamed header.
endif -include $(wildcard .deps/*.d)

35
scripts/configure vendored
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@ -636,7 +636,7 @@ MSED
MCPP MCPP
LD_RUN_PATH LD_RUN_PATH
SHLIB_CFLAGS SHLIB_CFLAGS
DEPEND_FLAG AUTODEP_FLAGS
gr_hprog gr_hprog
gr_hsrcs gr_hsrcs
gr_srcs gr_srcs
@ -6349,7 +6349,7 @@ extra_defs="$extra_defs -DCAD_DIR=\\\"\${LIBDIR}\\\" -DBIN_DIR=\\\"\${BINDIR}\\\
X_LIBS= X_LIBS=
X_CFLAGS= X_CFLAGS=
INC_SPECS= INC_SPECS=
DEPEND_FLAG= AUTODEP_FLAGS=
SHLIB_CFLAGS="" SHLIB_CFLAGS=""
LD_RUN_PATH="" LD_RUN_PATH=""
WISH_EXE="" WISH_EXE=""
@ -9435,9 +9435,36 @@ fi
fi fi
if test "$GCC" = "yes" ; then { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC generates dependencies with -MMD -MP" >&5
DEPEND_FLAG="-MM" $as_echo_n "checking whether $CC generates dependencies with -MMD -MP... " >&6; }
magic_save_cflags="$CFLAGS"
CFLAGS="$CFLAGS -MMD -MP -MF conftest.autodep.d"
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
int
main ()
{
;
return 0;
}
_ACEOF
if ac_fn_c_try_compile "$LINENO"; then :
if test -f conftest.autodep.d ; then
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
$as_echo "yes" >&6; }; AUTODEP_FLAGS="-MMD -MP"
else
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no (produced no .d)" >&5
$as_echo "no (produced no .d)" >&6; }
fi
else
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
$as_echo "no" >&6; }
fi fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
rm -f conftest.autodep.d
CFLAGS="$magic_save_cflags"

26
scripts/configure.in
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@ -370,7 +370,7 @@ extra_defs="$extra_defs -DCAD_DIR=\\\"\${LIBDIR}\\\" -DBIN_DIR=\\\"\${BINDIR}\\\
X_LIBS= X_LIBS=
X_CFLAGS= X_CFLAGS=
INC_SPECS= INC_SPECS=
DEPEND_FLAG= AUTODEP_FLAGS=
SHLIB_CFLAGS="" SHLIB_CFLAGS=""
LD_RUN_PATH="" LD_RUN_PATH=""
WISH_EXE="" WISH_EXE=""
@ -1987,9 +1987,25 @@ if test $usingTcl ; then
fi fi
if test "$GCC" = "yes" ; then dnl Automatic per-file dependency generation. Compilers that support -MMD -MP
DEPEND_FLAG="-MM" dnl write a .deps/<stem>.d listing the (non-system) headers a source used, as a
fi dnl side effect of compiling it -- replacing the old serial "make depend" pass
dnl and its sed post-processing, and parallelising with the compile. Best
dnl effort: empty if unsupported, and the build proceeds without incremental
dnl header tracking. Probed (not assumed from $GCC) so clang and others are
dnl covered only when they actually produce the file.
AC_MSG_CHECKING([whether $CC generates dependencies with -MMD -MP])
magic_save_cflags="$CFLAGS"
CFLAGS="$CFLAGS -MMD -MP -MF conftest.autodep.d"
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [])],
[if test -f conftest.autodep.d ; then
AC_MSG_RESULT([yes]); AUTODEP_FLAGS="-MMD -MP"
else
AC_MSG_RESULT([no (produced no .d)])
fi],
[AC_MSG_RESULT([no])])
rm -f conftest.autodep.d
CFLAGS="$magic_save_cflags"
dnl Substitute all variables dnl Substitute all variables
@ -2032,7 +2048,7 @@ AC_SUBST(CFLAGS)
AC_SUBST(CPPFLAGS) AC_SUBST(CPPFLAGS)
AC_SUBST(CXX) AC_SUBST(CXX)
AC_SUBST(CXXFLAGS) AC_SUBST(CXXFLAGS)
AC_SUBST(DEPEND_FLAG) AC_SUBST(AUTODEP_FLAGS)
AC_SUBST(SHLIB_CFLAGS) AC_SUBST(SHLIB_CFLAGS)
AC_SUBST(LDFLAGS) AC_SUBST(LDFLAGS)
AC_SUBST(LD_RUN_PATH) AC_SUBST(LD_RUN_PATH)

9
scripts/defs.mak.in
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@ -200,8 +200,10 @@ LDFLAGS = @LDFLAGS@
READLINE_DEFS = @rl_defs@ READLINE_DEFS = @rl_defs@
READLINE_LIBS = @rl_libs@ READLINE_LIBS = @rl_libs@
DEPEND_FILE = Depend # Per-file dependency flags ("-MMD -MP" when the compiler supports it, else
DEPEND_FLAG = @DEPEND_FLAG@ # empty); used by the %.o rule in rules.mak to write .deps/<stem>.d as a compile
# side effect. Replaces the old serial "make depend" / Depend-file machinery.
AUTODEP_FLAGS = @AUTODEP_FLAGS@
EXEEXT = @EXEEXT@ EXEEXT = @EXEEXT@
GR_CFLAGS = @X_CFLAGS@ @gr_cflags@ GR_CFLAGS = @X_CFLAGS@ @gr_cflags@
@ -214,12 +216,11 @@ GR_HELPER_PROG = @gr_hprog@
OA = @OA@ OA = @OA@
OA_LIBS = @OA_LIBS@ OA_LIBS = @OA_LIBS@
DEPSRCS = ${SRCS}
C_OBJS = ${SRCS:.c=.o} C_OBJS = ${SRCS:.c=.o}
CXX_OBJS = ${CXXSRCS:.cpp=.o} CXX_OBJS = ${CXXSRCS:.cpp=.o}
OBJS = ${CXX_OBJS} ${C_OBJS} OBJS = ${CXX_OBJS} ${C_OBJS}
LIB_OBJS = ${LIB_SRCS:.c=.o} LIB_OBJS = ${LIB_SRCS:.c=.o}
CLEANS = Depend ${OBJS} ${LIB_OBJS} lib${MODULE}.a lib${MODULE}.o ${MODULE} CLEANS = ${OBJS} ${LIB_OBJS} lib${MODULE}.a lib${MODULE}.o ${MODULE}
# allows Makefile to be selective # allows Makefile to be selective
MAKE_TCL = @MAKE_TCL@ MAKE_TCL = @MAKE_TCL@