[PATCH 1/6] qapi/error.py: refactor error classes

[John Snow]

Create a ubiquitous, context-free base error class that all exceptions
in the qapi package should inherit from.

Move the QAPISourceInfo relevant fields up into QAPIErrorLocation;
making sure the order of arguments is consistent between
QAPIErrorLocation and QAPISemError.

---

The order of arguments for QAPIParseError is inconsistent, but handled
explicitly in the __init__ method; this will be addressed in forthcoming
patches, but it works correctly here.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 scripts/qapi/error.py  | 35 +++++++++++++++++++++++------------
 scripts/qapi/main.py   |  2 +-
 scripts/qapi/schema.py |  4 ++--
 3 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/scripts/qapi/error.py b/scripts/qapi/error.py
index ae60d9e2fe..47f266f33d 100644
--- a/scripts/qapi/error.py
+++ b/scripts/qapi/error.py
@@ -11,23 +11,35 @@
 # This work is licensed under the terms of the GNU GPL, version 2.
 # See the COPYING file in the top-level directory.
 
+from typing import Optional
+
+from .source import QAPISourceInfo
+
 
 class QAPIError(Exception):
-    def __init__(self, info, col, msg):
-        Exception.__init__(self)
+    """Base class for all exceptions from the QAPI module."""
+
+
+class QAPISourceError(QAPIError):
+    """Error class for all exceptions identifying a source location."""
+    def __init__(self,
+                 info: QAPISourceInfo,
+                 msg: str,
+                 col: Optional[int] = None):
+        super().__init__()
         self.info = info
-        self.col = col
         self.msg = msg
+        self.col = col
 
-    def __str__(self):
+    def __str__(self) -> str:
         loc = str(self.info)
         if self.col is not None:
-            assert self.info.line is not None
-            loc += ':%s' % self.col
-        return loc + ': ' + self.msg
+            loc += f":{self.col}"
+        return f"{loc}: {self.msg}"
 
 
-class QAPIParseError(QAPIError):
+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]:
@@ -35,9 +47,8 @@ def __init__(self, parser, msg):
                 col = (col + 7) % 8 + 1
             else:
                 col += 1
-        super().__init__(parser.info, col, msg)
+        super().__init__(parser.info, msg, col)
 
 
-class QAPISemError(QAPIError):
-    def __init__(self, info, msg):
-        super().__init__(info, None, msg)
+class QAPISemError(QAPISourceError):
+    """Error class for semantic QAPI errors."""
diff --git a/scripts/qapi/main.py b/scripts/qapi/main.py
index 3f8338ade8..302b9eee81 100644
--- a/scripts/qapi/main.py
+++ b/scripts/qapi/main.py
@@ -45,7 +45,7 @@ def generate(schema_file: str,
     if match and match.end() != len(prefix):
         msg = "funny character '{:s}' in prefix '{:s}'".format(
             prefix[match.end()], prefix)
-        raise QAPIError('', None, msg)
+        raise QAPIError(msg)
 
     schema = QAPISchema(schema_file)
     gen_types(schema, output_dir, prefix, builtins)
diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index 3023bab44b..121d8488d2 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -20,7 +20,7 @@
 from typing import Optional
 
 from .common import c_name, POINTER_SUFFIX
-from .error import QAPIError, QAPISemError
+from .error import QAPISourceError, QAPISemError
 from .expr import check_exprs
 from .parser import QAPISchemaParser
 
@@ -841,7 +841,7 @@ def _def_entity(self, ent):
         other_ent = self._entity_dict.get(ent.name)
         if other_ent:
             if other_ent.info:
-                where = QAPIError(other_ent.info, None, "previous definition")
+                where = QAPISourceError(other_ent.info, "previous definition")
                 raise QAPISemError(
                     ent.info,
                     "'%s' is already defined\n%s" % (ent.name, where))
-- 
2.26.2