Makefile: re-use Git's Makefile where possible

Git does quite a lot of platform-specific detection in its Makefile,
which can result in it defining preprocessor variables that are used in
its header files.  If CGit does not define the same variables it can
result in different sizes of some structures in different places in the
same application.

For example, on Solaris Git uses it's "compat" regex library which has a
different sized regex_t structure than that available in the platform
regex.h.  This has a knock-on effect on the size of "struct rev_info"
and leads to hard to diagnose runtime issues.

In order to avoid all of this, introduce a "cgit.mk" file that includes
Git's Makefile and make all of the existing logic apply to CGit's
objects as well.  This is slightly complicated because Git's Makefile
must run in Git's directory, so all references to CGit files need to be
prefixed with "../".

In addition, OBJECTS is a simply expanded variable in Git's Makefile so
we cannot just add our objects to it.  Instead we must copy the two
applicable rules into "cgit.mk".  This has the advantage that we can
split CGit-specific CFLAGS from Git's CFLAGS and hence avoid rebuilding
all of Git whenever a CGit-specific value changes.

Signed-off-by: John Keeping <john@keeping.me.uk>
Acked-by: Jamie Couture <jamie.couture@gmail.com>

3 files changed, 80 insertions, 119 deletions

diff --git a/.gitignore b/.gitignore
index 487728b..8011b39 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 # Files I don't care to see in git-status/commit
 cgit
 cgit.conf
+CGIT-CFLAGS
 VERSION
 cgitrc.5
 cgitrc.5.fo
diff --git a/Makefile b/Makefile
index 1127961..8c00190 100644
--- a/Makefile
+++ b/Makefile
@@ -23,13 +23,6 @@ DOC_MAN5 = $(patsubst %.txt,%,$(MAN5_TXT))
 DOC_HTML = $(patsubst %.txt,%.html,$(MAN_TXT))
 DOC_PDF  = $(patsubst %.txt,%.pdf,$(MAN_TXT))
 
-# Define NO_STRCASESTR if you don't have strcasestr.
-#
-# Define NO_OPENSSL to disable linking with OpenSSL and use bundled SHA1
-# implementation (slower).
-#
-# Define NEEDS_LIBICONV if linking with libc is not enough (eg. Darwin).
-#
 # Define NO_C99_FORMAT if your formatted IO functions (printf/scanf et.al.)
 # do not support the 'size specifiers' introduced by C99, namely ll, hh,
 # j, z, t. (representing long long int, char, intmax_t, size_t, ptrdiff_t).
@@ -39,22 +32,12 @@ DOC_PDF  = $(patsubst %.txt,%.pdf,$(MAN_TXT))
 #-include config.mak
 
 #
-# Platform specific tweaks
-#
-
-VERSION: force-version
-	@./gen-version.sh "$(CGIT_VERSION)"
--include VERSION
-
-uname_S := $(shell sh -c 'uname -s 2>/dev/null || echo not')
-uname_O := $(shell sh -c 'uname -o 2>/dev/null || echo not')
-uname_R := $(shell sh -c 'uname -r 2>/dev/null || echo not')
-
-#
 # Let the user override the above settings.
 #
 -include cgit.conf
 
+export CGIT_SCRIPT_NAME CGIT_SCRIPT_PATH CGIT_DATA_PATH CGIT_CONFIG CACHE_ROOT
+
 #
 # Define a way to invoke make in subdirs quietly, shamelessly ripped
 # from git.git
@@ -69,8 +52,6 @@ NO_SUBDIR = :
 endif
 
 ifndef V
-	QUIET_CC       = @echo '   ' CC $@;
-	QUIET_LINK     = @echo '   ' LINK $@;
 	QUIET_SUBDIR0  = +@subdir=
 	QUIET_SUBDIR1  = ;$(NO_SUBDIR) echo '   ' SUBDIR $$subdir; \
 			 $(MAKE) $(PRINT_DIR) -C $$subdir
@@ -78,107 +59,12 @@ ifndef V
 	export V
 endif
 
-LDFLAGS ?=
-CFLAGS ?= -g -Wall
-CFLAGS += -Igit
-CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER)'
-CFLAGS += -DCGIT_VERSION='"$(CGIT_VERSION)"'
-CFLAGS += -DCGIT_CONFIG='"$(CGIT_CONFIG)"'
-CFLAGS += -DCGIT_SCRIPT_NAME='"$(CGIT_SCRIPT_NAME)"'
-CFLAGS += -DCGIT_CACHE_ROOT='"$(CACHE_ROOT)"'
-
-ifeq ($(uname_O),Cygwin)
-	NO_STRCASESTR = YesPlease
-	NEEDS_LIBICONV = YesPlease
-endif
-
-ifeq ($(uname_S),$(filter $(uname_S),FreeBSD OpenBSD))
-	# Apparantly libiconv is installed in /usr/local on BSD
-	LDFLAGS += -L/usr/local/lib
-	CFLAGS += -I/usr/local/include
-	NEEDS_LIBICONV = yes
-endif
-
-GIT_OPTIONS = prefix=/usr NO_GETTEXT=1
-OBJECTS =
-
-ifdef NO_ICONV
-	CFLAGS += -DNO_ICONV
-endif
-ifdef NO_STRCASESTR
-	CFLAGS += -DNO_STRCASESTR
-endif
-ifdef NO_C99_FORMAT
-	CFLAGS += -DNO_C99_FORMAT
-endif
-ifdef NO_OPENSSL
-	CFLAGS += -DNO_OPENSSL
-	GIT_OPTIONS += NO_OPENSSL=1
-else
-	LDLIBS += -lcrypto
-endif
-
-ifdef NEEDS_LIBICONV
-	LDLIBS += -liconv
-endif
-
-LDLIBS += git/libgit.a git/xdiff/lib.a -lz -lpthread
-
-OBJECTS += cgit.o
-OBJECTS += cache.o
-OBJECTS += cmd.o
-OBJECTS += configfile.o
-OBJECTS += html.o
-OBJECTS += parsing.o
-OBJECTS += scan-tree.o
-OBJECTS += shared.o
-OBJECTS += ui-atom.o
-OBJECTS += ui-blob.o
-OBJECTS += ui-clone.o
-OBJECTS += ui-commit.o
-OBJECTS += ui-diff.o
-OBJECTS += ui-log.o
-OBJECTS += ui-patch.o
-OBJECTS += ui-plain.o
-OBJECTS += ui-refs.o
-OBJECTS += ui-repolist.o
-OBJECTS += ui-shared.o
-OBJECTS += ui-snapshot.o
-OBJECTS += ui-ssdiff.o
-OBJECTS += ui-stats.o
-OBJECTS += ui-summary.o
-OBJECTS += ui-tag.o
-OBJECTS += ui-tree.o
-OBJECTS += vector.o
-
-dep_files := $(foreach f,$(OBJECTS),$(dir $f).deps/$(notdir $f).d)
-dep_dirs := $(addsuffix .deps,$(sort $(dir $OBJECTS)))
-
-$(dep_dirs):
-	@mkdir -p $@
-
-missing_dep_dirs := $(filter-out $(wildcard $(dep_dirs)),$(dep_dirs))
-dep_file = $(dir $@).deps/$(notdir $@).d
-dep_args = -MF $(dep_file) -MMD -MP
-
 .SUFFIXES:
 
-$(OBJECTS): %.o: %.c $(missing_dep_dirs)
-	$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(CFLAGS) $<
-
-dep_files_present := $(wildcard $(dep_files))
-ifneq ($(dep_files_present),)
-include $(dep_files_present)
-endif
-
 all:: cgit
 
-cgit: VERSION $(OBJECTS) libgit
-	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(OBJECTS) $(LDLIBS)
-
-libgit:
-	$(QUIET_SUBDIR0)git $(QUIET_SUBDIR1) NO_CURL=1 $(GIT_OPTIONS) libgit.a
-	$(QUIET_SUBDIR0)git $(QUIET_SUBDIR1) NO_CURL=1 $(GIT_OPTIONS) xdiff/lib.a
+cgit:
+	$(QUIET_SUBDIR0)git $(QUIET_SUBDIR1) -f ../cgit.mk ../cgit NO_CURL=1
 
 test: all
 	$(QUIET_SUBDIR0)tests $(QUIET_SUBDIR1) all
@@ -259,7 +145,7 @@ get-git:
 tags:
 	$(QUIET_TAGS)find . -name '*.[ch]' | xargs ctags
 
-.PHONY: all cgit get-git libgit force-version
+.PHONY: all cgit get-git
 .PHONY: clean clean-doc cleanall
 .PHONY: doc doc-html doc-man doc-pdf
 .PHONY: install install-doc install-html install-man install-pdf
diff --git a/cgit.mk b/cgit.mk
new file mode 100644
index 0000000..4869c55
--- /dev/null
+++ b/cgit.mk
@@ -0,0 +1,74 @@
+# This Makefile is run in the "git" directory in order to re-use Git's
+# build variables and operating system detection.  Hence all files in
+# CGit's directory must be prefixed with "../".
+include Makefile
+
+CGIT_PREFIX = ../
+
+# The CGIT_* variables are inherited when this file is called from the
+# main Makefile - they are defined there.
+
+$(CGIT_PREFIX)VERSION: force-version
+	@cd $(CGIT_PREFIX) && ./gen-version.sh "$(CGIT_VERSION)"
+-include $(CGIT_PREFIX)VERSION
+.PHONY: force-version
+
+# CGIT_CFLAGS is a separate variable so that we can track it separately
+# and avoid rebuilding all of Git when these variables change.
+CGIT_CFLAGS += -DCGIT_VERSION='"$(CGIT_VERSION)"'
+CGIT_CFLAGS += -DCGIT_CONFIG='"$(CGIT_CONFIG)"'
+CGIT_CFLAGS += -DCGIT_SCRIPT_NAME='"$(CGIT_SCRIPT_NAME)"'
+CGIT_CFLAGS += -DCGIT_CACHE_ROOT='"$(CACHE_ROOT)"'
+
+ifdef NO_C99_FORMAT
+	CFLAGS += -DNO_C99_FORMAT
+endif
+
+CGIT_OBJ_NAMES += cgit.o
+CGIT_OBJ_NAMES += cache.o
+CGIT_OBJ_NAMES += cmd.o
+CGIT_OBJ_NAMES += configfile.o
+CGIT_OBJ_NAMES += html.o
+CGIT_OBJ_NAMES += parsing.o
+CGIT_OBJ_NAMES += scan-tree.o
+CGIT_OBJ_NAMES += shared.o
+CGIT_OBJ_NAMES += ui-atom.o
+CGIT_OBJ_NAMES += ui-blob.o
+CGIT_OBJ_NAMES += ui-clone.o
+CGIT_OBJ_NAMES += ui-commit.o
+CGIT_OBJ_NAMES += ui-diff.o
+CGIT_OBJ_NAMES += ui-log.o
+CGIT_OBJ_NAMES += ui-patch.o
+CGIT_OBJ_NAMES += ui-plain.o
+CGIT_OBJ_NAMES += ui-refs.o
+CGIT_OBJ_NAMES += ui-repolist.o
+CGIT_OBJ_NAMES += ui-shared.o
+CGIT_OBJ_NAMES += ui-snapshot.o
+CGIT_OBJ_NAMES += ui-ssdiff.o
+CGIT_OBJ_NAMES += ui-stats.o
+CGIT_OBJ_NAMES += ui-summary.o
+CGIT_OBJ_NAMES += ui-tag.o
+CGIT_OBJ_NAMES += ui-tree.o
+CGIT_OBJ_NAMES += vector.o
+
+CGIT_OBJS := $(addprefix $(CGIT_PREFIX),$(CGIT_OBJ_NAMES))
+
+ifeq ($(wildcard $(CGIT_PREFIX).depend),)
+missing_dep_dirs += $(CGIT_PREFIX).depend
+endif
+
+$(CGIT_PREFIX).depend:
+	@mkdir -p $@
+
+$(CGIT_PREFIX)CGIT-CFLAGS: FORCE
+	@FLAGS='$(subst ','\'',$(CGIT_CFLAGS))'; \
+	    if test x"$$FLAGS" != x"`cat ../CGIT-CFLAGS 2>/dev/null`" ; then \
+		echo 1>&2 "    * new CGit build flags"; \
+		echo "$$FLAGS" >$(CGIT_PREFIX)CGIT-CFLAGS; \
+            fi
+
+$(CGIT_OBJS): %.o: %.c GIT-CFLAGS $(CGIT_PREFIX)CGIT-CFLAGS $(missing_dep_dirs)
+	$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $(CGIT_CFLAGS) $<
+
+$(CGIT_PREFIX)cgit: $(CGIT_OBJS) GIT-LDFLAGS $(GITLIBS)
+	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) $(LIBS)