* depend2.am (%.o): Handle deleted header file problem.

[platform/upstream/automake.git] / lib / am / depend2.am

diff --git a/lib/am/depend2.am b/lib/am/depend2.am
index 97fe1c9..7e4c6a3 100644 (file)
--- a/lib/am/depend2.am
+++ b/lib/am/depend2.am
@@ -1,5 +1,5 @@
 ## automake - create Makefile.in from Makefile.am
-## Copyright (C) 1994, 1995, 1996 Free Software Foundation, Inc.
+## Copyright (C) 1994, 1995, 1996, 1997, 1998 Free Software Foundation, Inc.
 
 ## This program is free software; you can redistribute it and/or modify
 ## it under the terms of the GNU General Public License as published by
@@ -15,8 +15,41 @@
 ## along with this program; if not, write to the Free Software
 ## Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
 ## 02111-1307, USA.
-.deps/%.P: $(srcdir)/%@EXT@
-       @echo "Computing dependencies for $<..."
-       @o='o';                         \
-ONLYC  test -n "$o" && o='$$o';        \
-       $(@MKDEP@) $< | sed "s/^\(.*\)\.o:/\1.$$o \1.l$$o:/" > $@
+%.o: %@EXT@
+       @echo '$(@PFX@COMPILE) -c $<'; \
+## There are various ways to get dependency output from gcc.  Here's
+## why we pick this rather obscure method:
+## - Don't want to use -MD because we'd like the dependencies to end
+##   up in a subdir.  Having to rename by hand is ugly.
+##   (We might end up doing this anyway to support other compilers.)
+## - The DEPENDENCIES_OUTPUT environment variable makes gcc act like
+##   -MM, not -M (despite what the docs say).
+## - Using -M directly means running the compiler twice (even worse
+##   than renaming).
+       $(@PFX@COMPILE) -Wp,-MD,.deps/$(*F).p -c $<
+## This next piece of magic avoids the `deleted header file' problem.
+## The problem is that when a header file which appears in a .P file
+## is deleted, the dependency causes make to die (because there is
+## typically no way to rebuild the header).  We avoid this by adding
+## dummy dependencies for each header file.  Too bad gcc doesn't do
+## this for us directly.
+       @-tr '\\ ' '\n\n' < .deps/$(*F).p \
+## The very first nondeleted line is always the primary source file.
+## No need for that, so we remove it too via `1d'.
+         | sed -e '/^$$/ d' -e '/:$$/ d' -e 1d -e 's/$$/:/' > .deps/$(*F).P; \
+       rm .deps/$(*F).p
+
+%.lo: %@EXT@
+       @echo '$(LT@PFX@COMPILE) -c $<'; \
+## See above to understand implementation weirdness.
+       $(LT@PFX@COMPILE) -Wp,-MD,.deps/$(*F).p -c $<
+       @-sed -e 's/^\([^:]*\)\.o:/\1.lo \1.o:/' \
+         < .deps/$(*F).p > .deps/$(*F).P; \
+## See above to understand deleted header file trick.
+       tr '\\ ' '\n\n' < .deps/$(*F).p \
+## The very first nondeleted line is always the primary source file.
+## No need for that, so we remove it too via `1d'.
+         | sed -e '/^$$/ d' -e '/:$$/ d' -e 1d -e 's/$$/:/' \
+## Note subtle difference: here we append to the .P file.
+           >> .deps/$(*F).P; \
+       rm -f .deps/$(*F).p