git-p4: better error reporting when p4 fails

Currently when p4 fails to run, git-p4 just crashes with an obscure
error message.

For example, if the P4 ticket has expired, you get:

  Error: Cannot locate perforce checkout of <path> in client view

This change checks whether git-p4 can talk to the Perforce server when
the first P4 operation is attempted, and tries to print a meaningful
error message if it fails.

Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9833-errors.sh

@@ -0,0 +1,78 @@
+#!/bin/sh
+
+test_description='git p4 errors'
+
+. ./lib-git-p4.sh
+
+test_expect_success 'start p4d' '
+	start_p4d
+'
+
+test_expect_success 'add p4 files' '
+	(
+		cd "$cli" &&
+		echo file1 >file1 &&
+		p4 add file1 &&
+		p4 submit -d "file1"
+	)
+'
+
+# after this test, the default user requires a password
+test_expect_success 'error handling' '
+	git p4 clone --dest="$git" //depot@all &&
+	(
+		cd "$git" &&
+		P4PORT=: test_must_fail git p4 submit 2>errmsg
+	) &&
+	p4 passwd -P newpassword &&
+	(
+		P4PASSWD=badpassword test_must_fail git p4 clone //depot/foo 2>errmsg &&
+		grep -q "failure accessing depot.*P4PASSWD" errmsg
+	)
+'
+
+test_expect_success 'ticket logged out' '
+	P4TICKETS="$cli/tickets" &&
+	echo "newpassword" | p4 login &&
+	(
+		cd "$git" &&
+		test_commit "ticket-auth-check" &&
+		p4 logout &&
+		test_must_fail git p4 submit 2>errmsg &&
+		grep -q "failure accessing depot" errmsg
+	)
+'
+
+test_expect_success 'create group with short ticket expiry' '
+	P4TICKETS="$cli/tickets" &&
+	echo "newpassword" | p4 login &&
+	p4_add_user short_expiry_user &&
+	p4 -u short_expiry_user passwd -P password &&
+	p4 group -i <<-EOF &&
+	Group: testgroup
+	Timeout: 3
+	Users: short_expiry_user
+	EOF
+
+	p4 users | grep short_expiry_user
+'
+
+test_expect_success 'git operation with expired ticket' '
+	P4TICKETS="$cli/tickets" &&
+	P4USER=short_expiry_user &&
+	echo "password" | p4 login &&
+	(
+		cd "$git" &&
+		git p4 sync &&
+		sleep 5 &&
+		test_must_fail git p4 sync 2>errmsg &&
+		grep "failure accessing depot" errmsg
+	)
+'
+
+test_expect_success 'kill p4d' '
+	kill_p4d
+'
+
+
+test_done