Re: argument parsing refactoring round3

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+From: David Bremner <david@tethera.net>\r
+To: guyzmo <guyzmo+notmuch@m0g.net>\r
+Subject: Re: argument parsing refactoring round3\r
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+Date: Thu, 09 Apr 2015 08:53:56 +0900\r
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+guyzmo <guyzmo+notmuch@m0g.net> writes:\r
+\r
+> Hi David,\r
+\r
+[...]\r
+\r
+> I see you patching and repatching notmuch's CLI to improve it, and I was\r
+> wondering whether you had considered actually using `docopt` to generate\r
+> the CLI parser from the output.\r
+>\r
+> It's possible to chain docopts to create a CLI UI very much alike the\r
+> git command, and it's more easily maintainable, as you're actually\r
+> generating the code from the `--help` page instead of the other way\r
+> around, making you focus on how you want the user to use the CLI only.\r
+\r
+[...]\r
+\r
+> what do you believe?\r
+\r
+It's an interesting idea, and if I was faced with writing CLI parser\r
+from scratch (i.e. 4 years ago) I would investigate it more seriously.\r
+As it stands, I'm not particularly annoyed with the notmuch argument\r
+parsing code, so I mainly see negative issues about your proposal.\r
+\r
+- I'm not sure how much this change would ripple through the rest of the\r
+  notmuch code. At least all of the variables set by the current\r
+  argument parsing code would have to be set foo=args.foo, or replaced\r
+  everywhere with args.foo.\r
+   \r
+- It would require modifying the notmuch CLI to conform to the\r
+  conventions of docopt. Of course, you might consider this a feature,\r
+  but I think as many people would be annoyed as would be happy.\r
+\r
+- The most dramatic example of an appartently missing feature from\r
+  docopt is keyword arguments of the form\r
+  \r
+    --output=(messages|threads|summary).\r
+\r
+  These are the reason we rolled our own parser in the first place,\r
+  rather than using e.g. gnu getopt.  docopt says it doesn't do data\r
+  validation, which is fine philosophically, but by the time we add back\r
+  in validation code, I'm not sure we win very much in the\r
+  maintainability department.\r
+  \r
+- I don't really know about the health of the docopt.c project, compared\r
+  to the python version. It seems somewhat unfinished [1]; in particular\r
+  a lack of positional arguments seems like a showstopper for us.\r
+  arguments. There has never been a release (which is the norm for\r
+  github, but not for dependencies of notmuch), and the last commit was\r
+  in December of 2014.\r
+\r
+- Since docopt_c_py is not widely in distros (it isn't in Debian, for\r
+  example), we'd have to emded it the notmuch source.  It's only 217\r
+  lines of fairly simple python, but embedding 3rd party code is\r
+  something we try pretty hard to avoid.\r
+\r
+As always, my lack of enthusiasm doesn't prevent someone else from\r
+investigating further, but hopefully the points I listed above give\r
+anyone doing such investigation some hints as to what I (and I suspect\r
+not just I) would object to about any hypothetical patches.\r
+\r
+David\r
+\r
+[1]: From the README.md "Note, at this point the code generator handles\r
+only options (positional arguments, commands and pattern matching will\r
+follow)."\r