view contrib/hgfixes/fix_leftover_imports.py @ 27142:060f83d219b9

extensions: refuse to load extensions if minimum hg version not met

As the author of several 3rd party extensions, I frequently see bug
reports from users attempting to run my extension with an old version
of Mercurial that I no longer support in my extension. Oftentimes, the
extension will import just fine. But as soon as we run extsetup(),
reposetup(), or get into the guts of a wrapped function, we encounter
an exception and abort. Today, Mercurial will print a message about
extensions that don't have a "testedwith" declaring explicit
compatibility with the current version.

The existing mechanism is a good start. But it isn't as robust as I
would like. Specifically, Mercurial assumes compatibility by default.
This means extension authors must perform compatibility checking in
their extsetup() or we wait and see if we encounter an abort at
runtime. And, compatibility checking can involve a lot of code and
lots of error checking. It's a lot of effort for extension authors.

Oftentimes, extension authors know which versions of Mercurial there
extension works on and more importantly where it is broken.

This patch introduces a magic "minimumhgversion" attribute in
extensions. When found, the extension loading mechanism will compare
the declared version against the current Mercurial version. If the
extension explicitly states we require a newer Mercurial version, a
warning is printed and the extension isn't loaded beyond importing
the Python module. This causes a graceful failure while alerting
the user of the compatibility issue.

I would be receptive to the idea of making the failure more fatal.
However, care would need to be taken to not criple every hg command.
e.g. the user may use `hg config` to fix the hgrc and if we aborted
trying to run that, the user would effectively be locked out of `hg`!

A potential future improvement to this functionality would be to catch
ImportError for the extension/module and parse the source code for
"minimumhgversion = 'XXX'" and do similar checking. This way we could
give more information about why the extension failed to load.

"Fixer that translates some APIs ignored by the default 2to3 fixers."

# FIXME: This fixer has some ugly hacks. Its main design is based on that of
# fix_imports, from lib2to3. Unfortunately, the fix_imports framework only
# changes module names "without dots", meaning it won't work for some changes
# in the email module/package. Thus this fixer was born. I believe that with a
# bit more thinking, a more generic fixer can be implemented, but I'll leave
# that as future work.

from lib2to3.fixer_util import Name
from lib2to3.fixes import fix_imports

# This maps the old names to the new names. Note that a drawback of the current
# design is that the dictionary keys MUST have EXACTLY one dot (.) in them,
# otherwise things will break. (If you don't need a module hierarchy, you're
# better of just inherit from fix_imports and overriding the MAPPING dict.)

MAPPING = {'email.Utils': 'email.utils',
           'email.Errors': 'email.errors',
           'email.Header': 'email.header',
           'email.Parser': 'email.parser',
           'email.Encoders': 'email.encoders',
           'email.MIMEText': 'email.mime.text',
           'email.MIMEBase': 'email.mime.base',
           'email.Generator': 'email.generator',
           'email.MIMEMultipart': 'email.mime.multipart',
}

def alternates(members):
    return "(" + "|".join(map(repr, members)) + ")"

def build_pattern(mapping=MAPPING):
    packages = {}
    for key in mapping:
        # What we are doing here is the following: with dotted names, we'll
        # have something like package_name <trailer '.' module>. Then, we are
        # making a dictionary to copy this structure. For example, if
        # mapping={'A.B': 'a.b', 'A.C': 'a.c'}, it will generate the dictionary
        # {'A': ['b', 'c']} to, then, generate something like "A <trailer '.'
        # ('b' | 'c')".
        name = key.split('.')
        prefix = name[0]
        if prefix in packages:
            packages[prefix].append(name[1:][0])
        else:
            packages[prefix] = name[1:]

    mod_list = ' | '.join(["'%s' '.' ('%s')" %
        (key, "' | '".join(packages[key])) for key in packages])
    mod_list = '(' + mod_list + ' )'

    yield """name_import=import_name< 'import' module_name=dotted_name< %s > >
          """ % mod_list

    yield """name_import=import_name< 'import'
            multiple_imports=dotted_as_names< any*
            module_name=dotted_name< %s >
            any* >
            >""" % mod_list

    packs = ' | '.join(["'%s' trailer<'.' ('%s')>" % (key,
               "' | '".join(packages[key])) for key in packages])

    yield "power< package=(%s) trailer<'.' any > any* >" % packs

class FixLeftoverImports(fix_imports.FixImports):
    # We want to run this fixer after fix_import has run (this shouldn't matter
    # for hg, though, as setup3k prefers to run the default fixers first)
    mapping = MAPPING

    def build_pattern(self):
        return "|".join(build_pattern(self.mapping))

    def transform(self, node, results):
        # Mostly copied from fix_imports.py
        import_mod = results.get("module_name")
        if import_mod:
            try:
                mod_name = import_mod.value
            except AttributeError:
                # XXX: A hack to remove whitespace prefixes and suffixes
                mod_name = str(import_mod).strip()
            new_name = self.mapping[mod_name]
            import_mod.replace(Name(new_name, prefix=import_mod.prefix))
            if "name_import" in results:
                # If it's not a "from x import x, y" or "import x as y" import,
                # marked its usage to be replaced.
                self.replace[mod_name] = new_name
            if "multiple_imports" in results:
                # This is a nasty hack to fix multiple imports on a line (e.g.,
                # "import StringIO, urlparse"). The problem is that I can't
                # figure out an easy way to make a pattern recognize the keys of
                # MAPPING randomly sprinkled in an import statement.
                results = self.match(node)
                if results:
                    self.transform(node, results)
        else:
            # Replace usage of the module.
            # Now this is, mostly, a hack
            bare_name = results["package"][0]
            bare_name_text = ''.join(map(str, results['package'])).strip()
            new_name = self.replace.get(bare_name_text)
            prefix = results['package'][0].prefix
            if new_name:
                bare_name.replace(Name(new_name, prefix=prefix))
                results["package"][1].replace(Name(''))