qapi: Improve reporting of lexical errors

Show text up to next structural character, whitespace, or quote
character instead of just the first character.

Forgotten quotes now get reported like "Stray 'command'" instead of
"Stray 'c'".

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190914153506.2151-9-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

scripts/qapi/common.py

@@ -559,7 +559,11 @@ class QAPISchemaParser(object):
                 self.line += 1
                 self.line_pos = self.cursor
             elif not self.tok.isspace():
-                raise QAPIParseError(self, "Stray '%s'" % self.tok)
+                # Show up to next structural, whitespace or quote
+                # character
+                match = re.match('[^[\\]{}:,\\s\'"]+',
+                                 self.src[self.cursor-1:])
+                raise QAPIParseError(self, "Stray '%s'" % match.group(0))
 
     def get_members(self):
         expr = OrderedDict()

tests/qapi-schema/bad-type-int.err

@@ -1 +1 @@
-tests/qapi-schema/bad-type-int.json:3:13: Stray '1'
+tests/qapi-schema/bad-type-int.json:3:13: Stray '123'

tests/qapi-schema/funny-word.err

@@ -1 +1 @@
-tests/qapi-schema/funny-word.json:1:3: Stray 'c'
+tests/qapi-schema/funny-word.json:1:3: Stray 'command'