Now as default and elided node symbols come from the config, the next logical
step is to use them directly bypassing GraphLog. Note that commands like `jj op
log` and `jj obslog` do not use the elided node symbol at all.
The default immutable_heads() includes tags(), which makes sense, but computing
heads(tags()) can be expensive because the tags() set is usually sparse. For
example, "jj bench revset 'heads(tags())'" took 157ms in my linux stable
mirror. We can of course optimize the heads evaluation by using bit set or
segmented index, but the query includes many historical heads if the repository
has per-release branches, which are uninteresting anyway. So, this patch
replaces heads(immutable_heads()) with trunk().
The reason we include heads(immutable_heads()) is to mitigate the following
problem. Suppose trunk() is the branch to be based off, I think using trunk()
here is pretty good.
```
A B
*---*----* trunk() ⊆ immutable_heads()
\
* C
```
https://github.com/martinvonz/jj/pull/2247#discussion_r1335078879
`graphlog::Edge` is used somewhat inconsistently. I've replaced `Edge::Present`
with two distinct `Edge::Direct` and `Edge::Indirect` which simplifies the
construction of the enum.
This adds a config to render a synthetic node with a "(elided
revisions)" description for elided segments of the graph.
I didn't add any templating support for the elided nodes because I'm
not sure how we would want that to work. In particular, I don't know
what `commit_id` and most other keywords should return for elided
revisions.
