push: make non-fast-forward help message configurable

This message is designed to help new users understand what
has happened when refs fail to push. However, it does not
help experienced users at all, and significantly clutters
the output, frequently dwarfing the regular status table and
making it harder to see.

This patch introduces a general configuration mechanism for
optional messages, with this push message as the first
example.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -113,6 +113,17 @@ For command-specific variables, you will find a more detailed description
 in the appropriate manual page. You will find a description of non-core
 porcelain configuration variables in the respective porcelain documentation.
 
+advice.*::
+	When set to 'true', display the given optional help message.
+	When set to 'false', do not display. The configuration variables
+	are:
++
+--
+	pushNonFastForward::
+		Advice shown when linkgit:git-push[1] refuses
+		non-fast-forward refs. Default: true.
+--
+
 core.fileMode::
 	If false, the executable bit differences between the index and
 	the working copy are ignored; useful on broken filesystems like FAT.

Makefile

@@ -397,6 +397,7 @@ export PERL_PATH
 LIB_FILE=libgit.a
 XDIFF_LIB=xdiff/lib.a
 
+LIB_H += advice.h
 LIB_H += archive.h
 LIB_H += attr.h
 LIB_H += blob.h
@@ -454,6 +455,7 @@ LIB_H += utf8.h
 LIB_H += wt-status.h
 
 LIB_OBJS += abspath.o
+LIB_OBJS += advice.o
 LIB_OBJS += alias.o
 LIB_OBJS += alloc.o
 LIB_OBJS += archive.o

advice.c

@@ -0,0 +1,25 @@
+#include "cache.h"
+
+int advice_push_nonfastforward = 1;
+
+static struct {
+	const char *name;
+	int *preference;
+} advice_config[] = {
+	{ "pushnonfastforward", &advice_push_nonfastforward },
+};
+
+int git_default_advice_config(const char *var, const char *value)
+{
+	const char *k = skip_prefix(var, "advice.");
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(advice_config); i++) {
+		if (strcmp(k, advice_config[i].name))
+			continue;
+		*advice_config[i].preference = git_config_bool(var, value);
+		return 0;
+	}
+
+	return 0;
+}

advice.h

@@ -0,0 +1,8 @@
+#ifndef ADVICE_H
+#define ADVICE_H
+
+extern int advice_push_nonfastforward;
+
+int git_default_advice_config(const char *var, const char *value);
+
+#endif /* ADVICE_H */

builtin-push.c

@@ -157,7 +157,7 @@ static int do_push(const char *repo, int flags)
 			continue;
 
 		error("failed to push some refs to '%s'", url[i]);
-		if (nonfastforward) {
+		if (nonfastforward && advice_push_nonfastforward) {
 			printf("To prevent you from losing history, non-fast-forward updates were rejected\n"
 			       "Merge the remote changes before pushing again.  See the 'non-fast forward'\n"
 			       "section of 'git push --help' for details.\n");

cache.h

@@ -4,6 +4,7 @@
 #include "git-compat-util.h"
 #include "strbuf.h"
 #include "hash.h"
+#include "advice.h"
 
 #include SHA1_HEADER
 #ifndef git_SHA_CTX

config.c

@@ -627,6 +627,9 @@ int git_default_config(const char *var, const char *value, void *dummy)
 	if (!prefixcmp(var, "mailmap."))
 		return git_default_mailmap_config(var, value);
 
+	if (!prefixcmp(var, "advice."))
+		return git_default_advice_config(var, value);
+
 	if (!strcmp(var, "pager.color") || !strcmp(var, "color.pager")) {
 		pager_use_color = git_config_bool(var,value);
 		return 0;