ident: add user.useConfigOnly boolean for when ident shouldn't be guessed

It used to be that:

   git config --global user.email "(none)"

was a viable way for people to force themselves to set user.email in
each repository.  This was helpful for people with more than one
email address, targeting different email addresses for different
clones, as it barred git from creating a commit unless the user.email
config was set in the per-repo config to the correct email address.

A recent change, 19ce497 (ident: keep a flag for bogus
default_email, 2015-12-10), however, declared that an explicitly
configured user.email is not bogus, no matter what its value is, so
this hack no longer works.

Provide the same functionality by adding a new configuration
variable user.useConfigOnly; when this variable is set, the
user must explicitly set user.email configuration.

Signed-off-by: Junio C Hamano <[email protected]>
Helped-by: Eric Sunshine <[email protected]>
Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Dan Aloni <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: da-x

Documentation/config.txt

@@ -2775,6 +2775,16 @@ user.name::
 	Can be overridden by the 'GIT_AUTHOR_NAME' and 'GIT_COMMITTER_NAME'
 	environment variables.  See linkgit:git-commit-tree[1].
 
+user.useConfigOnly::
+	Instruct Git to avoid trying to guess defaults for 'user.email'
+	and 'user.name', and instead retrieve the values only from the
+	configuration. For example, if you have multiple email addresses
+	and would like to use a different one for each repository, then
+	with this configuration option set to `true` in the global config
+	along with a name, Git will prompt you to set up an email before
+	making new commits in a newly cloned repository.
+	Defaults to `false`.
+
 user.signingKey::
 	If linkgit:git-tag[1] or linkgit:git-commit[1] is not selecting the
 	key you want it to automatically when creating a signed tag or

ident.c

@@ -13,11 +13,14 @@ static struct strbuf git_default_date = STRBUF_INIT;
 static int default_email_is_bogus;
 static int default_name_is_bogus;
 
+static int ident_use_config_only;
+
 #define IDENT_NAME_GIVEN 01
 #define IDENT_MAIL_GIVEN 02
 #define IDENT_ALL_GIVEN (IDENT_NAME_GIVEN|IDENT_MAIL_GIVEN)
 static int committer_ident_explicitly_given;
 static int author_ident_explicitly_given;
+static int ident_config_given;
 
 #ifdef NO_GECOS_IN_PWENT
 #define get_gecos(ignored) "&"
@@ -354,6 +357,9 @@ const char *fmt_ident(const char *name, const char *email,
 				fputs(env_hint, stderr);
 				die("unable to auto-detect name (got '%s')", name);
 			}
+			if (strict && ident_use_config_only
+			    && !(ident_config_given & IDENT_NAME_GIVEN))
+				die("user.useConfigOnly set but no name given");
 		}
 		if (!*name) {
 			struct passwd *pw;
@@ -373,6 +379,9 @@ const char *fmt_ident(const char *name, const char *email,
 			fputs(env_hint, stderr);
 			die("unable to auto-detect email address (got '%s')", email);
 		}
+		if (strict && ident_use_config_only
+		    && !(ident_config_given & IDENT_MAIL_GIVEN))
+			die("user.useConfigOnly set but no mail given");
 	}
 
 	strbuf_reset(&ident);
@@ -446,13 +455,19 @@ int author_ident_sufficiently_given(void)
 
 int git_ident_config(const char *var, const char *value, void *data)
 {
+	if (!strcmp(var, "user.useconfigonly")) {
+		ident_use_config_only = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "user.name")) {
 		if (!value)
 			return config_error_nonbool(var);
 		strbuf_reset(&git_default_name);
 		strbuf_addstr(&git_default_name, value);
 		committer_ident_explicitly_given |= IDENT_NAME_GIVEN;
 		author_ident_explicitly_given |= IDENT_NAME_GIVEN;
+		ident_config_given |= IDENT_NAME_GIVEN;
 		return 0;
 	}
 
@@ -463,6 +478,7 @@ int git_ident_config(const char *var, const char *value, void *data)
 		strbuf_addstr(&git_default_email, value);
 		committer_ident_explicitly_given |= IDENT_MAIL_GIVEN;
 		author_ident_explicitly_given |= IDENT_MAIL_GIVEN;
+		ident_config_given |= IDENT_MAIL_GIVEN;
 		return 0;
 	}
 

t/t7517-per-repo-email.sh

@@ -0,0 +1,39 @@
+#!/bin/sh
+#
+# Copyright (c) 2016 Dan Aloni
+# Copyright (c) 2016 Jeff King
+#
+
+test_description='per-repo forced setting of email address'
+
+. ./test-lib.sh
+
+test_expect_success 'setup a likely user.useConfigOnly use case' '
+	# we want to make sure a reflog is written, since that needs
+	# a non-strict ident. So be sure we have an actual commit.
+	test_commit foo &&
+
+	sane_unset GIT_AUTHOR_NAME GIT_AUTHOR_EMAIL &&
+	sane_unset GIT_COMMITTER_NAME GIT_COMMITTER_EMAIL &&
+	git config user.name "test" &&
+	git config --global user.useConfigOnly true
+'
+
+test_expect_success 'fails committing if clone email is not set' '
+	test_must_fail git commit --allow-empty -m msg
+'
+
+test_expect_success 'fails committing if clone email is not set, but EMAIL set' '
+	test_must_fail env [email protected] git commit --allow-empty -m msg
+'
+
+test_expect_success 'succeeds committing if clone email is set' '
+	test_config user.email "[email protected]" &&
+	git commit --allow-empty -m msg
+'
+
+test_expect_success 'succeeds cloning if global email is not set' '
+	git clone . clone
+'
+
+test_done