stringutil: add isauthorwellformed function

The regular expression for this function formerly lived at
https://hg.mozilla.org/hgcustom/version-control-tools/file/tip/hghooks/mozhghooks/author_format.py#l13

Differential Revision: https://phab.mercurial-scm.org/D2959

mercurial/utils/stringutil.py

@@ -131,6 +131,29 b' def email(author):'
         r = None
     return author[author.find('<') + 1:r]
 
+_correctauthorformat = remod.compile(br'^[^<]+\s\<[^<>]+@[^<>]+\>$')
+
+def isauthorwellformed(author):
+    '''Return True if the author field is well formed
+    (ie "Contributor Name <[e-mail]>")
+
+    >>> isauthorwellformed(b'Good Author <[e-mail]>')
+    True
+    >>> isauthorwellformed(b'Author <[e-mail]>')
+    True
+    >>> isauthorwellformed(b'Bad Author')
+    False
+    >>> isauthorwellformed(b'Bad Author <[e-mail]')
+    False
+    >>> isauthorwellformed(b'Bad Author [e-mail]')
+    False
+    >>> isauthorwellformed(b'<[e-mail]>')
+    False
+    >>> isauthorwellformed(b'Bad Author <author>')
+    False
+    '''
+    return _correctauthorformat.match(author) is not None
+
 def ellipsis(text, maxlength=400):
     """Trim string to at most maxlength (default: 400) columns in display."""
     return encoding.trim(text, maxlength, ellipsis='...')