feat(traces): add Funnel trace type

plotly.js has shipped the `funnel` trace since well before the bundled
3.7.0 build — only the Rust wrapper was missing. `funnel` is bar-like and
cartesian, so unlike `funnelarea` (domain-based, pie-like, out of scope
here) it composes with subplot grids and static image export.

Field set follows `Bar`, filtered to the attributes plotly.js actually
declares for `funnel`: `offset` and `width` are scalar-only (`arrayOk:
false` in the schema) and there is no `base`, error bars, calendars or
point selection. `textinfo` is a plain `String` because plotly.js takes a
`+`-joined flaglist; this follows the existing precedent in `pie.rs`
rather than enumerating the combinations.

Also adds the layout-level `funnelmode`/`funnelgap`/`funnelgroupgap`
attributes with a `FunnelMode` enum, mirroring the existing
waterfall/violin/box mode fields — without `funnelmode`, stacked and
grouped multi-trace funnels are unreachable.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jqnatividad

CHANGELOG.md

@@ -13,6 +13,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 - [[#412](https://github.com/plotly/plotly.rs/pull/412)] Add `Violin` trace type with box, mean line, KDE span, and split/grouped support
 - [[#414](https://github.com/plotly/plotly.rs/issues/414)] Add `DensityMap` (MapLibre `map` subplot) trace type — density heatmaps with full color-scale and hover support
 - [[#417](https://github.com/plotly/plotly.rs/issues/417)] Add `ScatterMap` (MapLibre `map` subplot) trace type — the modern counterpart to `ScatterMapbox`
+- Add `Funnel` trace type (bar-like, cartesian) with `Connector` and `FunnelHoverInfo` options, plus the layout-level `funnelmode`/`funnelgap`/`funnelgroupgap` attributes and a `FunnelMode` enum
 - [[#418](https://github.com/plotly/plotly.rs/issues/418)] Add native point clustering to `ScatterMap` via a `Cluster` option
 
 ### Changed

plotly/src/common/mod.rs

@@ -222,6 +222,7 @@ pub enum PlotType {
     Choropleth,
     ChoroplethMap,
     Contour,
+    Funnel,
     HeatMap,
     Histogram,
     Histogram2dContour,

plotly/src/layout/mod.rs

@@ -44,7 +44,8 @@ pub use self::legend::{GroupClick, ItemClick, ItemSizing, Legend, TraceOrder};
 pub use self::map::{LayoutMap, MapBounds, MapStyle};
 pub use self::mapbox::{Center, Mapbox, MapboxStyle};
 pub use self::modes::{
-    AspectMode, BarMode, BarNorm, BoxMode, ClickMode, UniformTextMode, ViolinMode, WaterfallMode,
+    AspectMode, BarMode, BarNorm, BoxMode, ClickMode, FunnelMode, UniformTextMode, ViolinMode,
+    WaterfallMode,
 };
 pub use self::polar::{
     AngularAxis, AngularAxisType, AutoRange, AutoRangeOptions, AutoTypeNumbers, AxisLayer,
@@ -379,6 +380,12 @@ pub struct LayoutFields {
     waterfall_gap: Option<f64>,
     #[serde(rename = "waterfallgroupgap")]
     waterfall_group_gap: Option<f64>,
+    #[serde(rename = "funnelmode")]
+    funnel_mode: Option<FunnelMode>,
+    #[serde(rename = "funnelgap")]
+    funnel_gap: Option<f64>,
+    #[serde(rename = "funnelgroupgap")]
+    funnel_group_gap: Option<f64>,
     #[serde(rename = "piecolorway")]
     pie_colorway: Option<Vec<Box<dyn Color>>>,
     #[serde(rename = "extendpiecolors")]

plotly/src/layout/modes.rs

@@ -71,6 +71,14 @@ pub enum WaterfallMode {
     Overlay,
 }
 
+#[derive(Serialize, Debug, Clone)]
+#[serde(rename_all = "lowercase")]
+pub enum FunnelMode {
+    Stack,
+    Group,
+    Overlay,
+}
+
 #[derive(Debug, Clone)]
 pub enum UniformTextMode {
     False,
@@ -146,6 +154,13 @@ mod tests {
         assert_eq!(to_value(WaterfallMode::Overlay).unwrap(), json!("overlay"));
     }
 
+    #[test]
+    fn serialize_funnel_mode() {
+        assert_eq!(to_value(FunnelMode::Stack).unwrap(), json!("stack"));
+        assert_eq!(to_value(FunnelMode::Group).unwrap(), json!("group"));
+        assert_eq!(to_value(FunnelMode::Overlay).unwrap(), json!("overlay"));
+    }
+
     #[test]
     fn serialize_aspect_mode() {
         let aspect_mode = AspectMode::default();

plotly/src/lib.rs

@@ -60,13 +60,14 @@ pub use layout::Layout;
 pub use plot::{Plot, Trace, Traces};
 // Also provide easy access to modules which contain additional trace-specific types
 pub use traces::{
-    box_plot, choropleth, choropleth_map, contour, density_map, heat_map, histogram, image, mesh3d,
-    sankey, scatter, scatter3d, scatter_map, scatter_mapbox, sunburst, surface, treemap, violin,
+    box_plot, choropleth, choropleth_map, contour, density_map, funnel, heat_map, histogram, image,
+    mesh3d, sankey, scatter, scatter3d, scatter_map, scatter_mapbox, sunburst, surface, treemap,
+    violin,
 };
 // Bring the different trace types into the top-level scope
 pub use traces::{
     Bar, BoxPlot, Candlestick, Choropleth, ChoroplethMap, Contour, DensityMap, DensityMapbox,
-    HeatMap, Histogram, Image, Mesh3D, Ohlc, Pie, Sankey, Scatter, Scatter3D, ScatterGeo,
+    Funnel, HeatMap, Histogram, Image, Mesh3D, Ohlc, Pie, Sankey, Scatter, Scatter3D, ScatterGeo,
     ScatterMap, ScatterMapbox, ScatterPolar, Sunburst, Surface, Table, Treemap, Violin,
 };