Allow merging two matchit Routers

[jplatte]

axum currently does a bunch of extra bookkeeping of its own in order to be able to merge two of its own Routers. I think some of this could be simplified if there was some functionality in matchit to merge two matchit::Routers. Would you consider a PR for this?

[ibraheemdev]

That seems reasonable, I would accept a PR for this.

[jplatte]

Any implementation hints? ^^
I took a brief look at this, but it doesn't seem straight-forward without understanding the internals of matchit's data structure(s). Is there a document going into that anywhere?

[ibraheemdev]

matchit is a standard prefix trie internally. I think the simplest way to implement this is to create an internal iterator and call insert for every route. A true efficient merge is a little more complex as you have to handle splitting prefixes recursively.

An iterator would involve performing depth/breadth-first search on the tree, collecting the prefix of each node to construct a given route. There's an existing example of reconstructing a specific route here. It may be easier to structure this as a for_each method instead of an iterator due to the recursive search.

[ibraheemdev]

Released in 0.8.5.