news_merge should be configurable, in-tree

[Robert Collins]

Many projects have a NEWS-like file, but slightly different heuristics
will be needed. E.g. they use ~~~~ not #####, or ----- not *****.

It would be great if we could set the appropriate info
in .bzrmeta/news_merge [perhaps .conf], so that a tree with slightly
different needs can be customised. I'd also like to be able to set the
filename for news_merge there.

 affects bzr
 status confirmed
 done

I don't know what the importance is. Arguably this is 'make merge great'
so part of the current focus, otoh maybe its not.

-Rob

[Andrew Bennetts (spiv)]

I'm tempted to think this does fit with "make merge great". Not so much because a custom merger for NEWS is great (although it is nice), but because building the infrastructure to make it easy for people to build good (configurable, powerful, reasonably efficient, etc) custom mergers would be great.

[Martin Pool (mbp)]

When you file bugs please at least take a stab at importance as immediate/soon/later (critical/high/other). We can always change it or do them out-of-order.

As a straw man I'd like to see this go through the rules configuration layer so you can have

cat >>.bzrrules
[NEWS*]
  merge_helper = news

There may be a better name corresponding to the internal interface name.

Then we can later also allow for them to be looked up by file-id properties, global configuration, or in other means.