From 6d6279f690d63fcd2ad6425d3d98608dc6e35c4d Mon Sep 17 00:00:00 2001
From: wolf <wolf@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Wed, 24 Feb 1999 12:56:20 +0000
Subject: [PATCH] Make forward declarations work much better than before.

git-svn-id: https://svn.dealii.org/trunk@890 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/deal.II/Makefile        |  2 +-
 deal.II/deal.II/source/Makefile | 45 ++++++++++++++++++++++++++++++---
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/deal.II/deal.II/Makefile b/deal.II/deal.II/Makefile
index 568f6fe47a..e277543fe0 100644
--- a/deal.II/deal.II/Makefile
+++ b/deal.II/deal.II/Makefile
@@ -14,7 +14,7 @@ examples:
 	cd examples ; make
 
 lib-clean:
-	-rm -f *~ include/*~ include/*/*~
+	-rm -f *~ include/*~ include/*/*~ include/basic/forward-declarations.h*
 	cd lib ; make clean
 
 examples-clean:
diff --git a/deal.II/deal.II/source/Makefile b/deal.II/deal.II/source/Makefile
index 2ddec2e403..607304eb6f 100644
--- a/deal.II/deal.II/source/Makefile
+++ b/deal.II/deal.II/source/Makefile
@@ -17,6 +17,8 @@ include $D/deal.II/Make.global_options
 cc-files = $(wildcard */*.cc)
 h-files  = $(wildcard ../include/*/*.h)
 
+forward-declarations = ../include/basic/forward-declarations.h
+
 # strip subdirectories from cc file names, preprend a "../lib/[g]o"
 # and change the suffix. We place the object files with or without
 # debug info in different directories, since we want to use the
@@ -46,9 +48,46 @@ all: 1d 2d 3d
 
 
 # rule how to make the file containing all the forward declarations
-../include/basic/forward-declarations.h: $(filter-out %forward-declarations.h,$(h-files))
+# this rule is rather complicated, it works as follows:
+#
+# - if this is the outermost 'make', then create a file $@.old.
+#   if the forward declaration file $@ already exists, then copy
+#   it over, otherwise leave it empty. this way, we always have
+#   a file to run diff on
+# - write the forward declarations for the presently available
+#   header files to $@.new
+# - we would like to compare the output of the script generating
+#   the forward declarations with the old file, or the empty
+#   string if there is no such file; this is why we created $@.old
+# - if the files differ, we would like to copy over the old file.
+# - this can either be done using shell programming using 'if [...]'
+#   or using conditionals inside 'make'. the first way is not 
+#   portable over different shells, however, and I also do not know
+#   how to write it. the second way has a problem also: conditionals
+#   are evaluated at the time the Makefile is read first, so we
+#   can't compare against $@.old, since this file does not exist at
+#   that time.
+# - we therefore invoke a second 'make', which can compare the two
+#   files against each other in a preconditional clause and
+#   copy over the file if necessary.
+# - delete the two temporary files
+$(forward-declarations): $(filter-out $(forward-declarations),$(h-files))
+ifeq (0,${MAKELEVEL})
+	@echo ============================ Checking $@
+	@touch $@.old
+	-@cp $@ $@.old
+	@perl ../Make_forward_declarations $(filter-out $(forward-declarations),$(h-files)) > $@.new
+	@make --silent $@
+	@rm $@.old $@.new
+else
+  ifneq (,$(shell diff $(forward-declarations).old $(forward-declarations).new))
 	@echo ============================ Generating $@
-	@perl ../Make_forward_declarations $(filter-out %forward-declarations.h,$(h-files)) > $@
+	@cp $@.new $@
+  else
+	@echo "============================          $@ needs no change"
+  endif
+endif
+
 
 
 
@@ -141,7 +180,7 @@ clean:
 #programs which use the 2d *and* the 3d library;
 #if the files within these libraries had the same names,
 #we may get into trouble.
-../lib/Makefile.dep: $(cc-files) $(h-files) Makefile ../Make.global_options
+../lib/Makefile.dep: $(cc-files) $(filter-out $(forward-declarations),$(h-files)) Makefile ../Make.global_options
 	@echo ============================ Remaking Makefile
 	@echo "# This Makefile was automatically generated by ../source/Makefile" \
 		> ../lib/Makefile.dep
-- 
2.39.5