lxml parsing with validation and target?

[Robin Becker]

I'm having a problem using lxml.etree to make a treebuilding parser that validates; I have test code where invalid xml 
is detected and an error raised when the line below target=ET.TreeBuilder(), is commented out.

The validation error looks as expected >  python tlxml.py invalid.rml
> re.compile('^.*(?:\\W|\\b)(?P<fn>dynamic_rml\\.dtd|rml\\.dtd|rml_0_2\\.dtd|rml_0_3\\.dtd|rml_1_0\\.dtd)$', re.MULTILINE)
> Resolving url='../rml.dtd' context=<lxml.etree._ParserContext object at 0x7f66103273c0> dtdPath='rml.dtd'
> Traceback (most recent call last):
>   File "/home/robin/devel/reportlab/REPOS/rlextra/tmp/tlxml.py", line 78, in <module>
>     tree = ET.parse(sys.argv[1],parser)
>   File "src/lxml/etree.pyx", line 3521, in lxml.etree.parse
>   File "src/lxml/parser.pxi", line 1859, in lxml.etree._parseDocument
>   File "src/lxml/parser.pxi", line 1885, in lxml.etree._parseDocumentFromURL
>   File "src/lxml/parser.pxi", line 1789, in lxml.etree._parseDocFromFile
>   File "src/lxml/parser.pxi", line 1177, in lxml.etree._BaseParser._parseDocFromFile
>   File "src/lxml/parser.pxi", line 615, in lxml.etree._ParserContext._handleParseResultDoc
>   File "src/lxml/parser.pxi", line 725, in lxml.etree._handleParseResult
>   File "src/lxml/parser.pxi", line 654, in lxml.etree._raiseParseError
>   File "invalid.rml", line 23
> lxml.etree.XMLSyntaxError: No declaration for attribute x of element place1, line 23, column 55

when I have the target=etree.TreeBuilder() active the validation does not work and the tree is formed and passed to the 
primitive tuple tree builder so the output looks like
> $ python tlxml.py invalid.rml 
> Resolving url='../rml.dtd' context=<lxml.etree._TargetParserContext object at 0x7f73d7b159c0> dtdPath='rml.dtd'
> ('document',
>  {'filename': 'test_000_simple.pdf', 'invariant': '1'},
>  ['\n\n',
>   ('stylesheet',
 > ........
>        None,
>        44),
>       '\n    \t\t\n    \t\t'],
>      40),
>     '\n'],
>    35),
>   '\n\n'],
>  2)

If I use the standard example EchoTarget the validation also fails. So I assume that the target argument makes the 
validation fail. Is there a way to get validation to work with a target?

The code is
######################################################################################################
from pprint import pprint
from lxml import etree as ET
import sys, os, re
from rlextra.rml2pdf.rml2pdf import CompatibleDTDNames as rmlDTDPat
rmlDTDPat = re.compile('^.*(?:\\W|\\b)(?P<fn>%s)$' % '|'.join((re.escape(_) for _ in rmlDTDPat)),re.M)

class TT:
     def __init__(self):
         pass

     def __call__(self,e):
         return (e.tag,e.attrib or None,self.content(e),e.sourceline)

     def content(self,e):
         t = e.text
         if len(e)==0 and t is None:
             return t
         else:
             r = [].append
             if t is not None: r(t)
             for c in e:
                 r(self(c))
                 t = c.tail
                 if t is not None:
                     r(t)
             return r.__self__

class RMLDTDResolver(ET.Resolver):
     __dtds = None
     def resolve(self, url, id, context):
         m = rmlDTDPat.match(url)
         if m:
             if self.__dtds is None:
                 from rlextra import rml2pdf
                 self.__dtds = {}
                 for fn in ('rml.dtd','dynamic_rml.dtd'):
                     with open(os.path.join(os.path.dirname(rml2pdf.__file__),fn),'r') as _:
                         self.__dtds[fn] = _.read()
             fn = m.group('fn')
             dtdPath = 'rml.dtd' if fn.startswith('rml') else 'dynamic.dtd'
             print(f"Resolving url={url!r} context={context!r} {dtdPath=}")
             return self.resolve_string(
                     self.__dtds[dtdPath],
                     context,
                     )
         else:
             return None

parser = ET.XMLParser(
                     load_dtd=True,
                     dtd_validation=True,
                     attribute_defaults=True,
                     no_network=True,
                     remove_comments=True,
                     remove_pis=True,
                     strip_cdata=True,
                     resolve_entities=True,
                     target=ET.TreeBuilder(),   #if commented the parser validates
                     )
parser.resolvers.add(RMLDTDResolver())
tree = ET.parse(sys.argv[1],parser)
pprint(TT()(tree))
######################################################################################################