Make clang-format better about finding itself on Debian Jessie

[• eklitzke]

Summary

This tries to fall back to clang-format-3.5 or clang-format-3.4. This is hacky, but Jessie is the only major distro with this issue so I don't ancipiate this code getting more complicated.

I couldn't figure out how to get arcanist set up so instead you get this kind of ghetto diff.

[djasper]

I don't think it is a good idea to make support for clang-format-3.4 and clang-format-3.5 better at this point. clang-format-3.4 is from 2013 and we have developed many very significant improvements since then. If a Linux distribution comes with only those, we should strongly recommend to install an up-to-date version through some other means.

For now, can we do the same here as we do in the vim integration (clang-format.py)? Specifically:

• Add a configuration option that users can set
• Extend the comment to explain that "clang-format" has to be on the path if it isn't explicitly set through that option

[• eklitzke]

There already is a configuration option here, so I guess the question is just whether the docs need to be more thorough.

[djasper]

Docs can always be better. Feel free to send a patch to improve them!

[• eklitzke]

It looks like someone beat me to it -- modern verions of clang-format.el will warn when clang-format cannot be found.

clang-format.el

   "Format code using clang-format."
   :group 'tools)
 
+;; Some distros don't provide a real clang-format. A noteable example is on
+;; Debian Jessie where clang-format-3.4 and clang-format-3.5 are both available
+;; packages, but the work hasn't been done to set up /etc/alternatives to allow
+;; aliasing one to be clang-format
+;;
+;; This is kind of a hack because there could be a potentially large list of
+;; clang versions we need to support, but AFAK Debian Jessie is the only major
+;; Linux distro that has this idiosyncacy (and I'd imagine it will be fixed by
+;; the next the next Debian stable release is out).
 (defcustom clang-format-executable
-  (or (executable-find "clang-format")
-      "clang-format")
+  (cond
+   ((executable-find "clang-format") "clang-format")
+   ((executable-find "clang-format-3.5") "clang-format-3.5")
+   ((executable-find "clang-format-3.4") "clang-format-3.4"))
+
   "Location of the clang-format executable.
 
 A string containing the name or the full path of the executable."