fix: keep transform under coord-flip reverse

CHANGELOG.md

@@ -12,6 +12,7 @@
 - feat: `labs()` fields default to `auto`; pass `none` to suppress an axis or legend title and reclaim the space it reserved. (#12)
 - feat: `element-blank()` on a text surface (axis, plot, or legend title) collapses the space the text would reserve. (#12)
 - feat: `width`/`height` accept `auto` to fill the available space of a bounded container. (#10)
+- fix: `coord-flip(reverse: true)` preserves a `log10`/`sqrt` axis transform instead of overwriting it. (#42)
 - fix: `geom-col()` on a continuous x with a single distinct value no longer panics when inferring the bar width. (#41)
 - fix: `log10`/`sqrt` scales validate user `limits` and report a clear error for non-positive bounds. (#40)
 - fix: `geom-smooth()` honours the `level` argument when sizing the confidence band instead of always using 95%. (#39)

src/render.typ

@@ -1969,7 +1969,7 @@
   if x.type == "discrete" {
     new-y.insert("reverse", true)
   } else if x.type == "continuous" {
-    new-y.insert("transform", "reverse")
+    new-y.insert("reverse", not new-y.at("reverse", default: false))
   }
   trained.insert("y", new-y)
   trained

src/scale/train.typ

@@ -521,7 +521,10 @@
     (_to-stat(trained, d-lo), _to-stat(trained, d-hi))
   }
   let (r-lo, r-hi) = range
-  let target = if transform == "reverse" {
+  // `reverse` rides alongside the numeric transform rather than replacing it,
+  // so a log10/sqrt axis can also be reversed (e.g. under coord-flip).
+  let reverse = transform == "reverse" or trained.at("reverse", default: false)
+  let target = if reverse {
     (r-hi, r-lo)
   } else { (r-lo, r-hi) }
   map-continuous(_to-stat(trained, value), (t-lo, t-hi), target)

tests/unit/test-coord-flip.typ

@@ -49,10 +49,21 @@
 #let cc-flipped = _apply-flip(cc, c1)
 #assert.eq(cc-flipped.y.at("transform", default: "identity"), "identity")
 
-// Explicit `reverse: true` reverses a continuous post-flip y via the
-// existing transform path.
+// Explicit `reverse: true` reverses a continuous post-flip y via a `reverse`
+// flag, leaving any numeric transform intact.
 #let cc-rev = _apply-flip(cc, coord-flip(reverse: true))
-#assert.eq(cc-rev.y.transform, "reverse")
+#assert.eq(cc-rev.y.reverse, true)
+#assert.eq(cc-rev.y.at("transform", default: "identity"), "identity")
+
+// A log10 x keeps its transform under flip + reverse (regression: the
+// reverse used to overwrite the numeric transform with "reverse").
+#let cc-log = (
+  x: (type: "continuous", domain: (0, 3), transform: "log10"),
+  y: (type: "continuous", domain: (0, 1)),
+)
+#let cc-log-rev = _apply-flip(cc-log, coord-flip(reverse: true))
+#assert.eq(cc-log-rev.y.transform, "log10")
+#assert.eq(cc-log-rev.y.reverse, true)
 
 #let untouched = _apply-flip(trained, (kind: "coord", coord: "cartesian"))
 #assert.eq(untouched.x.type, "discrete")