qapi/error.py: move QAPIParseError to parser.py

Keeping it in error.py will create some cyclic import problems when we
add types to the QAPISchemaParser. Callers don't need to know the
details of QAPIParseError unless they are parsing or dealing directly
with the parser, so this won't create any harsh new requirements for
callers in the general case.

Update error.py with a little docstring that gives a nod to where the
error may now be found.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210421192233.3542904-6-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/error.py

@@ -1,7 +1,5 @@
 # -*- coding: utf-8 -*-
 #
-# QAPI error classes
-#
 # Copyright (c) 2017-2019 Red Hat Inc.
 #
 # Authors:
@@ -11,6 +9,14 @@
 # This work is licensed under the terms of the GNU GPL, version 2.
 # See the COPYING file in the top-level directory.
 
+"""
+QAPI error classes
+
+Common error classes used throughout the package.  Additional errors may
+be defined in other modules.  At present, `QAPIParseError` is defined in
+parser.py.
+"""
+
 
 class QAPIError(Exception):
     """Base class for all exceptions from the QAPI package."""
@@ -33,17 +39,5 @@ class QAPISourceError(QAPIError):
         return loc + ': ' + self.msg
 
 
-class QAPIParseError(QAPISourceError):
-    """Error class for all QAPI schema parsing errors."""
-    def __init__(self, parser, msg):
-        col = 1
-        for ch in parser.src[parser.line_pos:parser.pos]:
-            if ch == '\t':
-                col = (col + 7) % 8 + 1
-            else:
-                col += 1
-        super().__init__(parser.info, msg, col)
-
-
 class QAPISemError(QAPISourceError):
     """Error class for semantic QAPI errors."""

scripts/qapi/parser.py

@@ -18,10 +18,22 @@ from collections import OrderedDict
 import os
 import re
 
-from .error import QAPIParseError, QAPISemError
+from .error import QAPISemError, QAPISourceError
 from .source import QAPISourceInfo
 
 
+class QAPIParseError(QAPISourceError):
+    """Error class for all QAPI schema parsing errors."""
+    def __init__(self, parser, msg):
+        col = 1
+        for ch in parser.src[parser.line_pos:parser.pos]:
+            if ch == '\t':
+                col = (col + 7) % 8 + 1
+            else:
+                col += 1
+        super().__init__(parser.info, msg, col)
+
+
 class QAPISchemaParser:
 
     def __init__(self, fname, previously_included=None, incl_info=None):