Fix #2281: geom_blank no longer drops legend for other geoms

Two changes were needed:
1. geom2trace.GeomBlank now returns showlegend = FALSE to prevent
   blank traces from claiming the legendgroup
2. The legendgroup deduplication logic now skips invisible traces
   so they don't prevent visible traces from showing in the legend

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: cpsievert

R/ggplotly.R

@@ -574,12 +574,17 @@ gg2list <- function(p, width = NULL, height = NULL,
     tr
   })
   # show only one legend entry per legendgroup
+  # For deduplication, skip invisible traces (like GeomBlank) so they don't
+  # "claim" the legendgroup and prevent visible traces from showing in legend
   grps <- sapply(traces, "[[", "legendgroup")
+  is_visible <- sapply(traces, function(tr) !isFALSE(tr$visible))
+  # Only consider visible traces for deduplication - invisible traces shouldn't claim legendgroup
+  grps_for_dedup <- ifelse(is_visible, grps, paste0(grps, "_invisible_", seq_along(grps)))
   traces <- Map(function(x, y) {
     if (!is.null(x[["frame"]])) return(x)
     x$showlegend <- isTRUE(x$showlegend) && y
     x
-  }, traces, !duplicated(grps))
+  }, traces, !duplicated(grps_for_dedup))
 
   # ------------------------------------------------------------------------
   # axis/facet/margin conversion

R/layers2traces.R

@@ -712,7 +712,9 @@ geom2trace <- function(data, params, p) {
 
 #' @export
 geom2trace.GeomBlank <- function(data, params, p) {
-  list(visible = FALSE)
+  # GeomBlank should never show in legend - it would claim the legendgroup
+  # and cause visible traces with the same group to not show their legend entry
+  list(visible = FALSE, showlegend = FALSE)
 }
 
 #' @export

tests/testthat/test-ggplot-blank.R

@@ -3,13 +3,31 @@ test_that("geom_blank", {
   skip_if_not_installed("ggplot2", "3.4.0")
   qp <- expect_warning(qplot(), "deprecated")
   l <- ggplotly(qp)$x
-  
+
   expect_length(l$data, 1)
   expect_false(l$data[[1]]$visible)
-  
+
   l <- ggplotly(ggplot())$x
-  
+
   expect_length(l$data, 1)
   expect_false(l$data[[1]]$visible)
-  
+
+})
+
+test_that("geom_blank does not drop legend (#2281)", {
+  # When geom_blank() is combined with other geoms, legend should still appear
+  p <- ggplot(iris, aes(Sepal.Length, Sepal.Width, col = Species)) +
+    geom_blank() +
+    geom_point()
+
+  L <- plotly_build(ggplotly(p))$x
+
+  # geom_point should create 3 visible traces with legend
+  visible_traces <- Filter(function(d) !isFALSE(d$visible) && d$type == "scatter", L$data)
+  expect_equal(length(visible_traces), 3)
+  expect_true(any(sapply(visible_traces, function(d) isTRUE(d$showlegend))))
+
+  # Trace names should be species names
+  trace_names <- sapply(visible_traces, function(d) d$name)
+  expect_true(all(c("setosa", "versicolor", "virginica") %in% trace_names))
 })