hgfixes: added a fixer to convert changes in the email package

This patch adds a fixer that accounts for changes in python packages, as the
framework provided by lib2to3 is only able to track changes in module names.
This fixer (hopefully) can fix any change in one-level hierarchies.

To exemplify, this fixer can successfully change an import from
"email.MIMEMultipart" to "email.mime.multipart".

contrib/hgfixes/fix_leftover_imports.py

@@ -0,0 +1,108
+"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 + ' )'
+    bare_names = alternates(mapping.keys())
+
+    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(''))
+