Fix for position_stack(vjust) (#6694)

* update skipping conditions

* cover test case

* add news bullet

Author: teunbrand

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* Fixed regression where `position_stack(vjust)` was ignored when there are
+  only single groups (#6692)
 * Fixed bug where `NA` handling in `geom_path()` was ignoring panels (@teunbrand, #6533)
 * Logical values for the linetype aesthetic will be interpreted numerically,
   so that `linetype = FALSE` becomes 0/'blank' and `linetype = TRUE` becomes 

R/position-stack.R

@@ -154,7 +154,9 @@ PositionStack <- ggproto("PositionStack", Position,
     flipped_aes <- has_flipped_aes(data)
     data <- flip_data(data, flipped_aes)
     var <- self$var %||% stack_var(data)
-    if (!vec_duplicate_any(data$x)  && !isTRUE(self$fill)) {
+    if (!vec_duplicate_any(data$x)  &&
+        !isTRUE(self$fill) &&
+        all(self$vjust == 1)) {
       # We skip stacking when all data have different x positions so that
       # there is nothing to stack
       var <- NULL

tests/testthat/test-position-stack.R

@@ -50,12 +50,14 @@ test_that("data with no extent is stacked correctly", {
     y = c(-40, -75),
     group = letters[1:2]
   )
-  base <- ggplot(df, aes(x, y, group = group))
-  p0 <- base + geom_text(aes(label = y), position = position_stack(vjust = 0))
-  p1 <- base + geom_text(aes(label = y), position = position_stack(vjust = 1))
+  base <- ggplot(df, aes(x, y, group = group, label = y))
+  p0 <- base + geom_text(position = position_stack(vjust = 0))
+  p1 <- base + geom_text(position = position_stack(vjust = 1))
+  p2 <- base + geom_text(aes(group = 1L), position = position_stack(vjust = 0.5))
 
   expect_equal(get_layer_data(p0)$y, c(-115, -75))
   expect_equal(get_layer_data(p1)$y, c(-75, 0))
+  expect_equal(get_layer_data(p2)$y, c(df$y[1] / 2, df$y[1] + df$y[2] / 2))
 })
 
 test_that("position_stack() can stack correctly when ymax is NA", {