addition of ast.Constant type makes astroid crash on import when using current CPython master (which will become 3.8)

[njsmith]

It looks like the merge of python/cpython#9445 broke astroid on CPython 3.8 pre-releases:

../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/trio/tests/test_exports.py:9: in <module>
    from pylint.lint import PyLinter
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/pylint/lint.py:75: in <module>
    import astroid
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/__init__.py:156: in <module>
    __import__(module[:-3])
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/brain/brain_builtin_inference.py:103: in <module>
    extend_builtins({'bytes': partial(_extend_str, rvalue="b''"),
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/brain/brain_builtin_inference.py:99: in extend_builtins
    transform(builtin_ast[class_name])
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/brain/brain_builtin_inference.py:84: in _extend_str
    fake = AstroidBuilder(MANAGER).string_build(code)['whatever']
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/builder.py:132: in string_build
    module = self._data_build(data, modname, path)
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/builder.py:173: in _data_build
    module = builder.visit_module(node, modname, node_file, package)
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:162: in visit_module
    newnode.postinit([self.visit(child, newnode) for child in node.body])
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:162: in <listcomp>
    newnode.postinit([self.visit(child, newnode) for child in node.body])
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:174: in visit
    return visit_method(node, parent)
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:954: in visit_classdef
    return super(TreeRebuilder3, self).visit_classdef(node, parent,
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:394: in visit_classdef
    [self.visit(child, newnode)
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:394: in <listcomp>
    [self.visit(child, newnode)
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:174: in visit
    return visit_method(node, parent)
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:576: in visit_functiondef
    return self._visit_functiondef(nodes.FunctionDef, node, parent)
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:566: in _visit_functiondef
    body=[self.visit(child, newnode) for child in node.body],
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:566: in <listcomp>
    body=[self.visit(child, newnode) for child in node.body],
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:174: in visit
    return visit_method(node, parent)
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:741: in visit_return
    newnode.postinit(self.visit(node.value, newnode))
../../../../virtualenv/python3.8-dev/lib/python3.8/site-packages/astroid/rebuilder.py:172: in visit
    visit_method = getattr(self, visit_name)
E   AttributeError: 'TreeRebuilder3' object has no attribute 'visit_constant'

(See: https://travis-ci.org/python-trio/trio/jobs/435176057)

[njsmith]

Looking more closely at bpo-32892, it looks like ast.Constant was actually added in 3.6, so it would be good to define visit_constant in any case. What changed in that PR is that the compiler now generates it in (many) more cases.

[serhiy-storchaka]

And #616 should fix this issue.

[PCManticore]

Should be fixed in master, going to create a dev release shortly. Thank you both for fixing this!