commit: allow suppression of implicit identity advice

We now nag the user with a giant warning when their identity
was pulled from the username, hostname, and gecos
information, in case it is not correct. Most users will
suppress this by simply setting up their information
correctly.

However, there may be some users who consciously want to use
that information, because having the value change from host
to host contains useful information. These users can now set
advice.implicitidentity to false to suppress the message.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/config.txt b/Documentation/config.txt
index a1e36d7..6f70cc9 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -130,6 +130,10 @@
 		Advice shown when linkgit:git-merge[1] refuses to
 		merge to avoid overwritting local changes.
 		Default: true.
+	implicitIdentity::
+		Advice on how to set your identity configuration when
+		your information is guessed from the system username and
+		domain name. Default: true.
 --
 
 core.fileMode::
diff --git a/advice.c b/advice.c
index cb666ac..8f7de0e 100644
--- a/advice.c
+++ b/advice.c
@@ -3,6 +3,7 @@
 int advice_push_nonfastforward = 1;
 int advice_status_hints = 1;
 int advice_commit_before_merge = 1;
+int advice_implicit_identity = 1;
 
 static struct {
 	const char *name;
@@ -11,6 +12,7 @@
 	{ "pushnonfastforward", &advice_push_nonfastforward },
 	{ "statushints", &advice_status_hints },
 	{ "commitbeforemerge", &advice_commit_before_merge },
+	{ "implicitidentity", &advice_implicit_identity },
 };
 
 int git_default_advice_config(const char *var, const char *value)
diff --git a/advice.h b/advice.h
index 3de5000..728ab90 100644
--- a/advice.h
+++ b/advice.h
@@ -4,6 +4,7 @@
 extern int advice_push_nonfastforward;
 extern int advice_status_hints;
 extern int advice_commit_before_merge;
+extern int advice_implicit_identity;
 
 int git_default_advice_config(const char *var, const char *value);
 
diff --git a/builtin-commit.c b/builtin-commit.c
index b923038..a73a532 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -994,8 +994,10 @@
 	if (!user_ident_explicitly_given) {
 		strbuf_addstr(&format, "\n Committer: ");
 		strbuf_addbuf_percentquote(&format, &committer_ident);
-		strbuf_addch(&format, '\n');
-		strbuf_addstr(&format, implicit_ident_advice);
+		if (advice_implicit_identity) {
+			strbuf_addch(&format, '\n');
+			strbuf_addstr(&format, implicit_ident_advice);
+		}
 	}
 	strbuf_release(&author_ident);
 	strbuf_release(&committer_ident);