stringutil: improve check for failed mailmap line parsing

The existing check for a bad mailmap file entry fails with inputs
like b'>@<'. This commit adds a function to check if a sufficient
amount of information has been parsed from a mailmap file entry.

At minimum, one email must be found (assumed to be the commit email).
If email is not empty and no names are found, then there must be
two emails. If there are at least one email and name, the mapping
is valid.

Differential Revision: https://phab.mercurial-scm.org/D3003

mercurial/utils/stringutil.py

@@ -166,6 +166,30 b' class mailmapping(object):'
     email = attr.ib()
     name = attr.ib(default=None)
 
+def _ismailmaplineinvalid(names, emails):
+    '''Returns True if the parsed names and emails
+    in a mailmap entry are invalid.
+
+    >>> # No names or emails fails
+    >>> names, emails = [], []
+    >>> _ismailmaplineinvalid(names, emails)
+    True
+    >>> # Only one email fails
+    >>> emails = [b'[e-mail]']
+    >>> _ismailmaplineinvalid(names, emails)
+    True
+    >>> # One email and one name passes
+    >>> names = [b'Test Name']
+    >>> _ismailmaplineinvalid(names, emails)
+    False
+    >>> # No names but two emails passes
+    >>> names = []
+    >>> emails = [b'[e-mail]', b'[e-mail]']
+    >>> _ismailmaplineinvalid(names, emails)
+    False
+    '''
+    return not emails or not names and len(emails) < 2
+
 def parsemailmap(mailmapcontent):
     """Parses data in the .mailmap format
 
@@ -199,7 +223,7 b' def parsemailmap(mailmapcontent):'
 
         # Don't bother checking the line if it is a comment or
         # is an improperly formed author field
-        if line.lstrip().startswith('#') or any(c not in line for c in '<>@'):
+        if line.lstrip().startswith('#'):
             continue
 
         # names, emails hold the parsed emails and names for each line
@@ -230,6 +254,12 b' def parsemailmap(mailmapcontent):'
                 # We have found another word in the committers name
                 namebuilder.append(element)
 
+        # Check to see if we have parsed the line into a valid form
+        # We require at least one email, and either at least one
+        # name or a second email
+        if _ismailmaplineinvalid(names, emails):
+            continue
+
         mailmapkey = mailmapping(
             email=emails[-1],
             name=names[-1] if len(names) == 2 else None,