Improve fallback provider for timeseries Name component (#7203)

### What

#7140 improved the handling of timeseries label, but made the
visualisers UI for `Name` not very nice. This PR fixes this.

<img width="476" alt="image"
src="https://github.com/user-attachments/assets/5984b18d-d725-4bba-9fa1-cb9d58a1546e">


### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/7203?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/7203?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!
* [x] If have noted any breaking changes to the log API in
`CHANGELOG.md` and the migration guide

- [PR Build Summary](https://build.rerun.io/pr/7203)
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
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full-check`.

crates/viewer/re_space_view_time_series/src/lib.rs

@@ -74,10 +74,7 @@ pub enum PlotSeriesKind {
 #[derive(Clone, Debug)]
 pub struct PlotSeries {
     /// Label of the series.
-    ///
-    /// If `None`, it means no label was logged or overridden. In this case, it should be derived
-    /// from the entity path.
-    pub label: Option<String>,
+    pub label: String,
 
     pub color: egui::Color32,
 

crates/viewer/re_space_view_time_series/src/line_visualizer_system.rs

@@ -78,7 +78,28 @@ impl TypedComponentFallbackProvider<StrokeWidth> for SeriesLineSystem {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(SeriesLineSystem => [Color, StrokeWidth]);
+impl TypedComponentFallbackProvider<Name> for SeriesLineSystem {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> Name {
+        let state = ctx.view_state.downcast_ref::<TimeSeriesSpaceViewState>();
+
+        state
+            .ok()
+            .and_then(|state| {
+                state
+                    .default_names_for_entities
+                    .get(ctx.target_entity_path)
+                    .map(|name| name.clone().into())
+            })
+            .or_else(|| {
+                ctx.target_entity_path
+                    .last()
+                    .map(|part| part.ui_string().into())
+            })
+            .unwrap_or_default()
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(SeriesLineSystem => [Color, StrokeWidth, Name]);
 
 impl SeriesLineSystem {
     fn load_scalars(&mut self, ctx: &ViewContext<'_>, query: &ViewQuery<'_>) {
@@ -367,7 +388,7 @@ impl SeriesLineSystem {
                 .iter()
                 .find(|chunk| !chunk.is_empty())
                 .and_then(|chunk| chunk.component_mono::<Name>(0)?.ok())
-                .map(|name| name.0.to_string());
+                .unwrap_or_else(|| self.fallback_for(&query_ctx));
 
             // Now convert the `PlotPoints` into `Vec<PlotSeries>`
             let aggregator = results
@@ -424,7 +445,7 @@ impl SeriesLineSystem {
                 points,
                 ctx.recording_store(),
                 view_query,
-                series_name,
+                series_name.into(),
                 aggregator,
                 all_series,
             );

crates/viewer/re_space_view_time_series/src/point_visualizer_system.rs

@@ -78,7 +78,28 @@ impl TypedComponentFallbackProvider<MarkerSize> for SeriesPointSystem {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(SeriesPointSystem => [Color, MarkerSize]);
+impl TypedComponentFallbackProvider<Name> for SeriesPointSystem {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> Name {
+        let state = ctx.view_state.downcast_ref::<TimeSeriesSpaceViewState>();
+
+        state
+            .ok()
+            .and_then(|state| {
+                state
+                    .default_names_for_entities
+                    .get(ctx.target_entity_path)
+                    .map(|name| name.clone().into())
+            })
+            .or_else(|| {
+                ctx.target_entity_path
+                    .last()
+                    .map(|part| part.ui_string().into())
+            })
+            .unwrap_or_default()
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(SeriesPointSystem => [Color, MarkerSize, Name]);
 
 impl SeriesPointSystem {
     fn load_scalars(&mut self, ctx: &ViewContext<'_>, query: &ViewQuery<'_>) {
@@ -446,7 +467,7 @@ impl SeriesPointSystem {
                 .iter()
                 .find(|chunk| !chunk.is_empty())
                 .and_then(|chunk| chunk.component_mono::<Name>(0)?.ok())
-                .map(|name| name.0.to_string());
+                .unwrap_or_else(|| self.fallback_for(&query_ctx));
 
             // Now convert the `PlotPoints` into `Vec<PlotSeries>`
             points_to_series(
@@ -455,7 +476,7 @@ impl SeriesPointSystem {
                 points,
                 ctx.recording_store(),
                 view_query,
-                series_name,
+                series_name.into(),
                 // Aggregation for points is not supported.
                 re_types::components::AggregationPolicy::Off,
                 all_series,

crates/viewer/re_space_view_time_series/src/space_view_class.rs

@@ -49,6 +49,13 @@ pub struct TimeSeriesSpaceViewState {
     /// Other parts of the system, such as query clamping, need to be aware of that offset in order
     /// to work properly.
     pub(crate) time_offset: i64,
+
+    /// Default names for entities, used when no label is provided.
+    ///
+    /// This is here because it must be computed with full knowledge of all entities in the plot
+    /// (e.g. to avoid `hello/x` and `world/x` both being named `x`), and this knowledge must be
+    /// forwarded to the default providers.
+    pub(crate) default_names_for_entities: HashMap<EntityPath, String>,
 }
 
 impl Default for TimeSeriesSpaceViewState {
@@ -59,6 +66,7 @@ impl Default for TimeSeriesSpaceViewState {
             saved_auto_bounds: Default::default(),
             scalar_range: [0.0, 0.0].into(),
             time_offset: 0,
+            default_names_for_entities: Default::default(),
         }
     }
 }
@@ -427,7 +435,8 @@ Display time series data in a plot.
             *state.scalar_range.start_mut() = f64::INFINITY;
             *state.scalar_range.end_mut() = f64::NEG_INFINITY;
 
-            let label_from_entity = EntityPath::short_names_with_disambiguation(
+            // Needed by for the visualizers' fallback provider.
+            state.default_names_for_entities = EntityPath::short_names_with_disambiguation(
                 all_plot_series
                     .iter()
                     .map(|series| series.entity_path.clone()),
@@ -453,24 +462,17 @@ Display time series data in a plot.
                 let id = egui::Id::new(series.entity_path.hash());
                 plot_item_id_to_entity_path.insert(id, series.entity_path.clone());
 
-                let label = series
-                    .label
-                    .as_ref()
-                    .or_else(|| label_from_entity.get(&series.entity_path))
-                    .cloned()
-                    .unwrap_or_else(|| "unknown".to_owned());
-
                 match series.kind {
                     PlotSeriesKind::Continuous => plot_ui.line(
                         Line::new(points)
-                            .name(label)
+                            .name(&series.label)
                             .color(color)
                             .width(2.0 * series.radius_ui)
                             .id(id),
                     ),
                     PlotSeriesKind::Scatter(scatter_attrs) => plot_ui.points(
                         Points::new(points)
-                            .name(label)
+                            .name(&series.label)
                             .color(color)
                             .radius(series.radius_ui)
                             .shape(scatter_attrs.marker.into())

crates/viewer/re_space_view_time_series/src/util.rs

@@ -88,7 +88,7 @@ pub fn points_to_series(
     points: Vec<PlotPoint>,
     store: &re_chunk_store::ChunkStore,
     query: &ViewQuery<'_>,
-    series_label: Option<String>,
+    series_label: String,
     aggregator: AggregationPolicy,
     all_series: &mut Vec<PlotSeries>,
 ) {
@@ -122,7 +122,7 @@ pub fn points_to_series(
         });
     } else {
         add_series_runs(
-            &series_label,
+            series_label,
             points,
             entity_path,
             aggregator,
@@ -199,9 +199,10 @@ pub fn apply_aggregation(
     (actual_aggregation_factor, points)
 }
 
+#[allow(clippy::needless_pass_by_value)]
 #[inline(never)] // Better callstacks on crashes
 fn add_series_runs(
-    series_label: &Option<String>,
+    series_label: String,
     points: Vec<PlotPoint>,
     entity_path: &EntityPath,
     aggregator: AggregationPolicy,