qapi: New QAPISourceInfo, replacing dict

We track source locations with a dict of the form

    {'file': FNAME, 'line': LINENO, 'parent': PARENT}

where PARENT is None for the main file, and the include directive's
source location for included files.

This is serviceable enough, but the next commit will add information,
and that's going to come out cleaner if we turn this into a class.  So
do that.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190927134639.4284-4-armbru@redhat.com>

scripts/qapi/common.py

@@ -13,6 +13,7 @@
 
 from __future__ import print_function
 from contextlib import contextmanager
+import copy
 import errno
 import os
 import re
@@ -53,34 +54,50 @@ struct_types = {}
 union_types = {}
 all_names = {}
 
+
 #
 # Parsing the schema into expressions
 #
 
+class QAPISourceInfo(object):
+    def __init__(self, fname, line, parent):
+        self.fname = fname
+        self.line = line
+        self.parent = parent
 
-def error_path(parent):
-    res = ''
-    while parent:
-        res = ('In file included from %s:%d:\n' % (parent['file'],
-                                                   parent['line'])) + res
-        parent = parent['parent']
-    return res
+    def next_line(self):
+        info = copy.copy(self)
+        info.line += 1
+        return info
+
+    def loc(self):
+        return '%s:%d' % (self.fname, self.line)
+
+    def include_path(self):
+        ret = ''
+        parent = self.parent
+        while parent:
+            ret = 'In file included from %s:\n' % parent.loc() + ret
+            parent = parent.parent
+        return ret
+
+    def __str__(self):
+        return self.include_path() + self.loc()
 
 
 class QAPIError(Exception):
-    def __init__(self, fname, line, col, incl_info, msg):
+    def __init__(self, info, col, msg):
         Exception.__init__(self)
-        self.fname = fname
-        self.line = line
+        self.info = info
         self.col = col
-        self.info = incl_info
         self.msg = msg
 
     def __str__(self):
-        loc = '%s:%d' % (self.fname, self.line)
+        loc = str(self.info)
         if self.col is not None:
+            assert self.info.line is not None
             loc += ':%s' % self.col
-        return error_path(self.info) + '%s: %s' % (loc, self.msg)
+        return loc + ': ' + self.msg
 
 
 class QAPIParseError(QAPIError):
@@ -91,14 +108,12 @@ class QAPIParseError(QAPIError):
                 col = (col + 7) % 8 + 1
             else:
                 col += 1
-        QAPIError.__init__(self, parser.fname, parser.line, col,
-                           parser.incl_info, msg)
+        QAPIError.__init__(self, parser.info, col, msg)
 
 
 class QAPISemError(QAPIError):
     def __init__(self, info, msg):
-        QAPIError.__init__(self, info['file'], info['line'], None,
-                           info['parent'], msg)
+        QAPIError.__init__(self, info, None, msg)
 
 
 class QAPIDoc(object):
@@ -382,12 +397,11 @@ class QAPISchemaParser(object):
     def __init__(self, fp, previously_included=[], incl_info=None):
         self.fname = fp.name
         previously_included.append(os.path.abspath(fp.name))
-        self.incl_info = incl_info
         self.src = fp.read()
         if self.src == '' or self.src[-1] != '\n':
             self.src += '\n'
         self.cursor = 0
-        self.line = 1
+        self.info = QAPISourceInfo(self.fname, 1, incl_info)
         self.line_pos = 0
         self.exprs = []
         self.docs = []
@@ -395,8 +409,7 @@ class QAPISchemaParser(object):
         cur_doc = None
 
         while self.tok is not None:
-            info = {'file': self.fname, 'line': self.line,
-                    'parent': self.incl_info}
+            info = self.info
             if self.tok == '#':
                 self.reject_expr_doc(cur_doc)
                 cur_doc = self.get_doc(info)
@@ -456,9 +469,9 @@ class QAPISchemaParser(object):
         # catch inclusion cycle
         inf = info
         while inf:
-            if incl_abs_fname == os.path.abspath(inf['file']):
+            if incl_abs_fname == os.path.abspath(inf.fname):
                 raise QAPISemError(info, "Inclusion loop for %s" % include)
-            inf = inf['parent']
+            inf = inf.parent
 
         # skip multiple include of the same file
         if incl_abs_fname in previously_included:
@@ -552,7 +565,7 @@ class QAPISchemaParser(object):
                 if self.cursor == len(self.src):
                     self.tok = None
                     return
-                self.line += 1
+                self.info = self.info.next_line()
                 self.line_pos = self.cursor
             elif not self.tok.isspace():
                 # Show up to next structural, whitespace or quote
@@ -1172,7 +1185,7 @@ class QAPISchemaEntity(object):
     def check(self, schema):
         assert not self._checked
         if self.info:
-            self._module = os.path.relpath(self.info['file'],
+            self._module = os.path.relpath(self.info.fname,
                                            os.path.dirname(schema.fname))
         self._checked = True
 
@@ -1781,9 +1794,9 @@ class QAPISchema(object):
         include = expr['include']
         assert doc is None
         main_info = info
-        while main_info['parent']:
-            main_info = main_info['parent']
-        fname = os.path.relpath(include, os.path.dirname(main_info['file']))
+        while main_info.parent:
+            main_info = main_info.parent
+        fname = os.path.relpath(include, os.path.dirname(main_info.fname))
         self._def_entity(QAPISchemaInclude(fname, info))
 
     def _def_builtin_type(self, name, json_type, c_type):