cli: let graphlog provide a default node symbol

I'm about to make the default (non-working-copy) node symbol be a
unicode symbol, but we only want that when using a unicode graph, so
users with a terminal that doesn't support unicode can get plain ASCII
output by setting e.g. `ui.graph.style = "ascii"`.

src/commands/mod.rs

@@ -1484,6 +1484,7 @@ fn cmd_log(ui: &mut Ui, command: &CommandHelper, args: &LogArgs) -> Result<(), C
 
         if !args.no_graph {
             let mut graph = get_graphlog(command.settings(), formatter.raw());
+            let default_node_symbol = graph.default_node_symbol().to_owned();
             let iter: Box<dyn Iterator<Item = (IndexEntry, Vec<RevsetGraphEdge>)>> =
                 if args.reversed {
                     Box::new(RevsetGraphIterator::new(revset.as_ref()).reversed())
@@ -1538,7 +1539,7 @@ fn cmd_log(ui: &mut Ui, command: &CommandHelper, args: &LogArgs) -> Result<(), C
                 let node_symbol = if Some(&commit_id) == wc_commit_id {
                     "@"
                 } else {
-                    "o"
+                    &default_node_symbol
                 };
 
                 graph.add_node(
@@ -1624,6 +1625,7 @@ fn cmd_obslog(ui: &mut Ui, command: &CommandHelper, args: &ObslogArgs) -> Result
     );
     if !args.no_graph {
         let mut graph = get_graphlog(command.settings(), formatter.raw());
+        let default_node_symbol = graph.default_node_symbol().to_owned();
         for commit in commits {
             let mut edges = vec![];
             for predecessor in &commit.predecessors() {
@@ -1650,7 +1652,7 @@ fn cmd_obslog(ui: &mut Ui, command: &CommandHelper, args: &ObslogArgs) -> Result
             let node_symbol = if Some(commit.id()) == wc_commit_id {
                 "@"
             } else {
-                "o"
+                &default_node_symbol
             };
             graph.add_node(
                 commit.id(),

src/commands/operation.rs

@@ -69,6 +69,7 @@ fn cmd_op_log(
     let mut formatter = ui.stdout_formatter();
     let formatter = formatter.as_mut();
     let mut graph = get_graphlog(command.settings(), formatter.raw());
+    let default_node_symbol = graph.default_node_symbol().to_owned();
     for op in topo_order_reverse(
         vec![head_op],
         Box::new(|op: &Operation| op.id().clone()),
@@ -88,7 +89,11 @@ fn cmd_op_log(
         if !buffer.ends_with(b"\n") {
             buffer.push(b'\n');
         }
-        let node_symbol = if is_head_op { "@" } else { "o" };
+        let node_symbol = if is_head_op {
+            "@"
+        } else {
+            &default_node_symbol
+        };
         graph.add_node(
             op.id(),
             &edges,

src/graphlog.rs

@@ -56,12 +56,15 @@ pub trait GraphLog<K: Clone + Eq + Hash> {
         text: &str,
     ) -> io::Result<()>;
 
+    fn default_node_symbol(&self) -> &str;
+
     fn width(&self, id: &K, edges: &[Edge<K>]) -> usize;
 }
 
 pub struct SaplingGraphLog<'writer, R> {
     renderer: R,
     writer: &'writer mut dyn Write,
+    default_node_symbol: String,
 }
 
 impl<K: Clone> From<&Edge<K>> for Ancestor<K> {
@@ -99,6 +102,10 @@ where
         write!(self.writer, "{row}")
     }
 
+    fn default_node_symbol(&self) -> &str {
+        &self.default_node_symbol
+    }
+
     fn width(&self, id: &K, edges: &[Edge<K>]) -> usize {
         let parents = edges.iter().map_into().collect();
         let w: u64 = self.renderer.width(Some(id), Some(&parents));
@@ -110,6 +117,7 @@ impl<'writer, R> SaplingGraphLog<'writer, R> {
     pub fn create<K>(
         renderer: R,
         formatter: &'writer mut dyn Write,
+        default_node_symbol: &str,
     ) -> Box<dyn GraphLog<K> + 'writer>
     where
         K: Clone + Eq + Hash + 'writer,
@@ -118,6 +126,7 @@ impl<'writer, R> SaplingGraphLog<'writer, R> {
         Box::new(SaplingGraphLog {
             renderer,
             writer: formatter,
+            default_node_symbol: default_node_symbol.to_owned(),
         })
     }
 }
@@ -129,12 +138,14 @@ pub fn get_graphlog<'a, K: Clone + Eq + Hash + 'a>(
     let builder = GraphRowRenderer::new().output().with_min_row_height(0);
 
     match settings.graph_style().as_str() {
-        "curved" => SaplingGraphLog::create(builder.build_box_drawing(), formatter),
-        "square" => {
-            SaplingGraphLog::create(builder.build_box_drawing().with_square_glyphs(), formatter)
-        }
-        "ascii" => SaplingGraphLog::create(builder.build_ascii(), formatter),
-        "ascii-large" => SaplingGraphLog::create(builder.build_ascii_large(), formatter),
+        "curved" => SaplingGraphLog::create(builder.build_box_drawing(), formatter, "o"),
+        "square" => SaplingGraphLog::create(
+            builder.build_box_drawing().with_square_glyphs(),
+            formatter,
+            "o",
+        ),
+        "ascii" => SaplingGraphLog::create(builder.build_ascii(), formatter, "o"),
+        "ascii-large" => SaplingGraphLog::create(builder.build_ascii_large(), formatter, "o"),
         _ => Box::new(AsciiGraphDrawer::new(formatter)),
     }
 }
@@ -290,6 +301,10 @@ impl<'writer, K: Clone + Eq + Hash> GraphLog<K> for AsciiGraphDrawer<'writer, K>
         Ok(())
     }
 
+    fn default_node_symbol(&self) -> &str {
+        "o"
+    }
+
     fn width(&self, id: &K, edges: &[Edge<K>]) -> usize {
         let orig = self.edges.len() - usize::from(self.index_by_target(id).is_some());
         let added = cmp::max(edges.len(), 1);