[PATCH] ssh: add 'ssh.keyfile' option

["Raymond E. Pasco" <ray@ameretat.dev>]

When a specific private key needs to be used with a repository, manually
specifying it via 'core.sshCommand' is not ideal. This option allows a
keyfile to be specified in the local configuration. If a keyfile is
specified, SSH agents are disabled for the command.

Signed-off-by: Raymond E. Pasco <ray@ameretat.dev>
---
I've encountered the need to specify a specific SSH key to be used with
a repository, and overriding the whole ssh command isn't great. I have
only tested this with OpenSSH.

 connect.c | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/connect.c b/connect.c
index 23013c6344..dc7c75ead3 100644
--- a/connect.c
+++ b/connect.c
@@ -1104,8 +1104,9 @@ static struct child_process *git_connect_git(int fd[2], char *hostandport,
  * `args` for running ssh in Git's SSH-tunneled transport.
  */
 static void push_ssh_options(struct argv_array *args, struct argv_array *env,
-			     enum ssh_variant variant, const char *port,
-			     enum protocol_version version, int flags)
+			     enum ssh_variant variant, const char *keyfile,
+			     const char *port, enum protocol_version version,
+			     int flags)
 {
 	if (variant == VARIANT_SSH &&
 	    version > 0) {
@@ -1144,6 +1145,26 @@ static void push_ssh_options(struct argv_array *args, struct argv_array *env,
 	if (variant == VARIANT_TORTOISEPLINK)
 		argv_array_push(args, "-batch");
 
+	if (keyfile) {
+		switch (variant) {
+		case VARIANT_AUTO:
+			BUG("VARIANT_AUTO passed to push_ssh_options");
+		case VARIANT_SIMPLE:
+			die(_("ssh variant 'simple' does not support setting keyfiles"));
+		case VARIANT_SSH:
+			argv_array_push(args, "-a");
+			argv_array_push(args, "-i");
+			argv_array_push(args, keyfile);
+			break;
+		case VARIANT_PLINK:
+		case VARIANT_PUTTY:
+		case VARIANT_TORTOISEPLINK:
+			argv_array_push(args, "-noagent");
+			argv_array_push(args, "-i");
+			argv_array_push(args, keyfile);
+		}
+	}
+
 	if (port) {
 		switch (variant) {
 		case VARIANT_AUTO:
@@ -1169,6 +1190,7 @@ static void fill_ssh_args(struct child_process *conn, const char *ssh_host,
 			  int flags)
 {
 	const char *ssh;
+	const char *keyfile;
 	enum ssh_variant variant;
 
 	if (looks_like_command_line_option(ssh_host))
@@ -1200,14 +1222,16 @@ static void fill_ssh_args(struct child_process *conn, const char *ssh_host,
 		argv_array_push(&detect.args, ssh);
 		argv_array_push(&detect.args, "-G");
 		push_ssh_options(&detect.args, &detect.env_array,
-				 VARIANT_SSH, port, version, flags);
+				 VARIANT_SSH, keyfile, port, version, flags);
 		argv_array_push(&detect.args, ssh_host);
 
 		variant = run_command(&detect) ? VARIANT_SIMPLE : VARIANT_SSH;
 	}
 
+	git_config_get_string_const("ssh.keyfile", &keyfile);
+
 	argv_array_push(&conn->args, ssh);
-	push_ssh_options(&conn->args, &conn->env_array, variant, port, version, flags);
+	push_ssh_options(&conn->args, &conn->env_array, variant, keyfile, port, version, flags);
 	argv_array_push(&conn->args, ssh_host);
 }
 
-- 
2.26.1