cli: add revsets.log-graph-prioritize setting

The option will be used to prioritize branches of the `jj log` graph to
be displayed on the left.
This can make them more readable in some situations.
An example would be
```
[revsets]
log-graph-prioritize = "coalesce(description("megamerge\n"), trunk())"
```

CHANGELOG.md

@@ -36,6 +36,10 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   `ellipsis` parameter; passing this prepends or appends the ellipsis to the
   content if it is truncated to fit the maximum width.
 
+* Added `revsets.log-graph-prioritize`, which can be used to configure
+  which branch in the `jj log` graph is displayed on the left instead of `@`
+  (e.g. `coalesce(description("megamerge\n"), trunk())`)
+
 ### Fixed bugs
 
 * `jj status` now shows untracked files under untracked directories.

cli/src/commands/log.rs

@@ -147,6 +147,8 @@ pub(crate) fn cmd_log(
         }
         expression
     };
+    let prio_revset = settings.get_string("revsets.log-graph-prioritize")?;
+    let prio_revset = workspace_command.parse_revset(ui, &RevisionArg::from(prio_revset))?;
 
     let repo = workspace_command.repo();
     let matcher = fileset_expression.to_matcher();
@@ -195,14 +197,16 @@ pub(crate) fn cmd_log(
             let mut graph = get_graphlog(graph_style, raw_output.as_mut());
             let iter: Box<dyn Iterator<Item = _>> = {
                 let mut forward_iter = TopoGroupedGraphIterator::new(revset.iter_graph());
-                // Emit the working-copy branch first, which is usually most
-                // interesting. This also helps stabilize output order.
-                if let Some(id) = workspace_command.get_wc_commit_id() {
-                    let has_commit = revset.containing_fn();
-                    if has_commit(id)? {
-                        forward_iter.prioritize_branch(id.clone());
+
+                let has_commit = revset.containing_fn();
+
+                for prio in prio_revset.evaluate_to_commit_ids()? {
+                    let prio = prio?;
+                    if has_commit(&prio)? {
+                        forward_iter.prioritize_branch(prio);
                     }
                 }
+
                 // The input to TopoGroupedGraphIterator shouldn't be truncated
                 // because the prioritized commit must exist in the input set.
                 let forward_iter = forward_iter.take(args.limit.unwrap_or(usize::MAX));

cli/src/config-schema.json

@@ -479,6 +479,11 @@
                     "type": "string",
                     "description": "Default set of revisions to simplify when no explicit revset is given for jj simplify-parents",
                     "default": "reachable(@, mutable())"
+                },
+                "log-graph-prioritize": {
+                    "type": "string",
+                    "description": "Set of revisions to prioritize when rendering the graph for jj log",
+                    "default": "@"
                 }
             },
             "additionalProperties": {

cli/src/config/revsets.toml

@@ -8,6 +8,7 @@ simplify-parents = "reachable(@, mutable())"
 # evaluate, lengthy warning messages would be printed. Use present(expr) to
 # suppress symbol resolution error.
 log = "present(@) | ancestors(immutable_heads().., 2) | present(trunk())"
+log-graph-prioritize = "@"
 
 [revset-aliases]
 # trunk() can be overridden as '<bookmark>@<remote>'. Use present(trunk()) if