git-p4: raise exceptions from p4CmdList based on error from p4 server

This change lays some groundwork for better handling of rowcount errors
from the server, where it fails to send us results because we requested
too many.

It adds an option to p4CmdList() to return errors as a Python exception.

The exceptions are derived from P4Exception (something went wrong),
P4ServerException (the server sent us an error code) and
P4RequestSizeException (we requested too many rows/results from the
server database).

This makes the code that handles the errors a bit easier.

The default behavior is unchanged; the new code is enabled with a flag.

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

git-p4.py

@@ -561,10 +561,30 @@ def isModeExec(mode):
     # otherwise False.
     return mode[-3:] == "755"
 
+class P4Exception(Exception):
+    """ Base class for exceptions from the p4 client """
+    def __init__(self, exit_code):
+        self.p4ExitCode = exit_code
+
+class P4ServerException(P4Exception):
+    """ Base class for exceptions where we get some kind of marshalled up result from the server """
+    def __init__(self, exit_code, p4_result):
+        super(P4ServerException, self).__init__(exit_code)
+        self.p4_result = p4_result
+        self.code = p4_result[0]['code']
+        self.data = p4_result[0]['data']
+
+class P4RequestSizeException(P4ServerException):
+    """ One of the maxresults or maxscanrows errors """
+    def __init__(self, exit_code, p4_result, limit):
+        super(P4RequestSizeException, self).__init__(exit_code, p4_result)
+        self.limit = limit
+
 def isModeExecChanged(src_mode, dst_mode):
     return isModeExec(src_mode) != isModeExec(dst_mode)
 
-def p4CmdList(cmd, stdin=None, stdin_mode='w+b', cb=None, skip_info=False):
+def p4CmdList(cmd, stdin=None, stdin_mode='w+b', cb=None, skip_info=False,
+        errors_as_exceptions=False):
 
     if isinstance(cmd,basestring):
         cmd = "-G " + cmd
@@ -611,9 +631,25 @@ def p4CmdList(cmd, stdin=None, stdin_mode='w+b', cb=None, skip_info=False):
         pass
     exitCode = p4.wait()
     if exitCode != 0:
-        entry = {}
-        entry["p4ExitCode"] = exitCode
-        result.append(entry)
+        if errors_as_exceptions:
+            if len(result) > 0:
+                data = result[0].get('data')
+                if data:
+                    m = re.search('Too many rows scanned \(over (\d+)\)', data)
+                    if not m:
+                        m = re.search('Request too large \(over (\d+)\)', data)
+
+                    if m:
+                        limit = int(m.group(1))
+                        raise P4RequestSizeException(exitCode, result, limit)
+
+                raise P4ServerException(exitCode, result)
+            else:
+                raise P4Exception(exitCode)
+        else:
+            entry = {}
+            entry["p4ExitCode"] = exitCode
+            result.append(entry)
 
     return result