Introduce git_etc_gitconfig() that encapsulates access of ETC_GITCONFIG.

In a subsequent patch the path to the system-wide config file will be
computed. This is a preparation for that change. It turns all accesses
of ETC_GITCONFIG into function calls. There is no change in behavior.

As a consequence, config.c is the only file that needs the definition of
ETC_GITCONFIG. Hence, -DETC_GITCONFIG is removed from the CFLAGS and a
special build rule for config.c is introduced. As a side-effect, changing
the defintion of ETC_GITCONFIG (e.g. in config.mak) does not trigger a
complete rebuild anymore.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -754,7 +754,7 @@ TCLTK_PATH_SQ = $(subst ','\'',$(TCLTK_PATH))
 LIBS = $(GITLIBS) $(EXTLIBS)
 
 BASIC_CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER_SQ)' \
-	-DETC_GITCONFIG='"$(ETC_GITCONFIG_SQ)"' $(COMPAT_CFLAGS)
+	$(COMPAT_CFLAGS)
 LIB_OBJS += $(COMPAT_OBJS)
 
 ALL_CFLAGS += $(BASIC_CFLAGS)
@@ -903,6 +903,9 @@ exec_cmd.o: exec_cmd.c GIT-CFLAGS
 builtin-init-db.o: builtin-init-db.c GIT-CFLAGS
 	$(QUIET_CC)$(CC) -o $*.o -c $(ALL_CFLAGS) -DDEFAULT_GIT_TEMPLATE_DIR='"$(template_dir_SQ)"' $<
 
+config.o: config.c GIT-CFLAGS
+	$(QUIET_CC)$(CC) -o $*.o -c $(ALL_CFLAGS) -DETC_GITCONFIG='"$(ETC_GITCONFIG_SQ)"' $<
+
 http.o: http.c GIT-CFLAGS
 	$(QUIET_CC)$(CC) -o $*.o -c $(ALL_CFLAGS) -DGIT_USER_AGENT='"git/$(GIT_VERSION)"' $<
 

builtin-config.c

@@ -81,7 +81,7 @@ static int get_value(const char* key_, const char* regex_)
 			local = repo_config = xstrdup(git_path("config"));
 		if (home)
 			global = xstrdup(mkpath("%s/.gitconfig", home));
-		system_wide = ETC_GITCONFIG;
+		system_wide = git_etc_gitconfig();
 	}
 
 	key = xstrdup(key_);
@@ -191,7 +191,7 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 			}
 		}
 		else if (!strcmp(argv[1], "--system"))
-			setenv(CONFIG_ENVIRONMENT, ETC_GITCONFIG, 1);
+			setenv(CONFIG_ENVIRONMENT, git_etc_gitconfig(), 1);
 		else if (!strcmp(argv[1], "--file") || !strcmp(argv[1], "-f")) {
 			if (argc < 3)
 				usage(git_config_set_usage);

cache.h

@@ -557,6 +557,7 @@ extern int git_config_bool(const char *, const char *);
 extern int git_config_set(const char *, const char *);
 extern int git_config_set_multivar(const char *, const char *, const char *, int);
 extern int git_config_rename_section(const char *, const char *);
+extern const char *git_etc_gitconfig(void);
 extern int check_repository_format_version(const char *var, const char *value);
 
 #define MAX_GITNAME (1000)

config.c

@@ -459,6 +459,11 @@ int git_config_from_file(config_fn_t fn, const char *filename)
 	return ret;
 }
 
+const char *git_etc_gitconfig(void)
+{
+	return ETC_GITCONFIG;
+}
+
 int git_config(config_fn_t fn)
 {
 	int ret = 0;
@@ -471,8 +476,8 @@ int git_config(config_fn_t fn)
 	 * config file otherwise. */
 	filename = getenv(CONFIG_ENVIRONMENT);
 	if (!filename) {
-		if (!access(ETC_GITCONFIG, R_OK))
+		if (!access(git_etc_gitconfig(), R_OK))
-			ret += git_config_from_file(fn, ETC_GITCONFIG);
+			ret += git_config_from_file(fn, git_etc_gitconfig());
 		home = getenv("HOME");
 		filename = getenv(CONFIG_LOCAL_ENVIRONMENT);
 		if (!filename)