check-commit: try to curb bad commit summary keywords

The goal of commit summary keywords is to help us sort, categorize,
and filter our voluminous commits for our release notes in a way
that's helpful and meaningful to end users. Lately, there have been a
huge number of "keywords" that are neither words nor particularly key.

This patch tries to discourage that by narrowing the allowed
characters to alphanumeric. In particular, it doesn't allow "."
(method, function names, and file extensions) and "/" (filenames). It
also gives a short reminder of what a keyword ought to be.

contrib/check-commit

@@ -1,57 +1,59 b''
 #!/usr/bin/env python
 #
 # Copyright 2014 Matt Mackall <[e-mail]>
 #
 # A tool/hook to run basic sanity checks on commits/patches for
 # submission to Mercurial. Install by adding the following to your
 # .hg/hgrc:
 #
 # [hooks]
 # pretxncommit = contrib/check-commit
 #
 # The hook can be temporarily bypassed with:
 #
 # $ BYPASS= hg commit
 #
 # See also: https://mercurial-scm.org/wiki/ContributingChanges
 
 import re, sys, os
 
 errors = [
     (r"[(]bc[)]", "(BC) needs to be uppercase"),
     (r"[(]issue \d\d\d", "no space allowed between issue and number"),
     (r"[(]bug(\d|\s)", "use (issueDDDD) instead of bug"),
     (r"^# User [^@\n]+$", "username is not an email address"),
     (r"^# .*\n(?!merge with )[^#]\S+[^:] ",
      "summary line doesn't start with 'topic: '"),
     (r"^# .*\n[A-Z][a-z]\S+", "don't capitalize summary lines"),
     (r"^# .*\n[^\n]*: *[A-Z][a-z]\S+", "don't capitalize summary lines"),
+    (r"^# [^\n]*\n\S*[^A-Za-z0-9-]\S*: ",
+     "summary keyword should be most user-relevant one-word command or topic"),
     (r"^# .*\n.*\.\s+$", "don't add trailing period on summary line"),
     (r"^# .*\n[^#].{77,}", "summary line too long (limit is 78)"),
     (r"^\+\n \n", "adds double empty line"),
     (r"^ \n\+\n", "adds double empty line"),
     (r"^\+[ \t]+def [a-z]+_[a-z]", "adds a function with foo_bar naming"),
 ]
 
 node = os.environ.get("HG_NODE")
 
 if node:
     commit = os.popen("hg export %s" % node).read()
 else:
     commit = sys.stdin.read()
 
 exitcode = 0
 for exp, msg in errors:
     m = re.search(exp, commit, re.MULTILINE)
     if m:
         pos = 0
         for n, l in enumerate(commit.splitlines(True)):
             pos += len(l)
             if pos >= m.end():
                 print "%d: %s" % (n, msg)
                 print " %s" % l[:-1]
                 if "BYPASS" not in os.environ:
                     exitcode = 1
                 break
 
 sys.exit(exitcode)