fix: remove incorrect stack transform from charts with one linear Q-axis one non-linear Q-axis.

examples/compiled/bar_q_qpow.vg.json

@@ -0,0 +1,125 @@
+{
+  "$schema": "https://vega.github.io/schema/vega/v5.json",
+  "background": "white",
+  "padding": 5,
+  "width": 200,
+  "height": 200,
+  "style": "cell",
+  "data": [
+    {
+      "name": "source_0",
+      "values": [
+        {"a": 3000, "b": 55},
+        {"a": 3500, "b": 28},
+        {"a": 4000, "b": 55}
+      ]
+    },
+    {
+      "name": "data_0",
+      "source": "source_0",
+      "transform": [
+        {
+          "type": "stack",
+          "groupby": ["b"],
+          "field": "a",
+          "sort": {"field": [], "order": []},
+          "as": ["a_start", "a_end"],
+          "offset": "zero"
+        },
+        {
+          "type": "filter",
+          "expr": "isValid(datum[\"a\"]) && isFinite(+datum[\"a\"]) && isValid(datum[\"b\"]) && isFinite(+datum[\"b\"])"
+        }
+      ]
+    }
+  ],
+  "marks": [
+    {
+      "name": "marks",
+      "type": "rect",
+      "style": ["bar"],
+      "from": {"data": "data_0"},
+      "encode": {
+        "update": {
+          "fill": {"value": "#4c78a8"},
+          "ariaRoleDescription": {"value": "bar"},
+          "description": {
+            "signal": "\"a: \" + (format(datum[\"a\"], \"\")) + \"; b: \" + (format(datum[\"b\"], \"\"))"
+          },
+          "xc": {"scale": "x", "field": "a"},
+          "width": {"value": 5},
+          "y": {"scale": "y", "field": "b"},
+          "y2": {"scale": "y", "value": 0}
+        }
+      }
+    }
+  ],
+  "scales": [
+    {
+      "name": "x",
+      "type": "linear",
+      "domain": {"data": "data_0", "fields": ["a_start", "a_end"]},
+      "range": [0, {"signal": "width"}],
+      "nice": true,
+      "zero": false,
+      "padding": 5
+    },
+    {
+      "name": "y",
+      "type": "pow",
+      "domain": {"data": "data_0", "field": "b"},
+      "range": [{"signal": "height"}, 0],
+      "nice": true,
+      "zero": true
+    }
+  ],
+  "axes": [
+    {
+      "scale": "x",
+      "orient": "bottom",
+      "gridScale": "y",
+      "grid": true,
+      "tickCount": {"signal": "ceil(width/40)"},
+      "domain": false,
+      "labels": false,
+      "aria": false,
+      "maxExtent": 0,
+      "minExtent": 0,
+      "ticks": false,
+      "zindex": 0
+    },
+    {
+      "scale": "y",
+      "orient": "left",
+      "gridScale": "x",
+      "grid": true,
+      "tickCount": {"signal": "ceil(height/40)"},
+      "domain": false,
+      "labels": false,
+      "aria": false,
+      "maxExtent": 0,
+      "minExtent": 0,
+      "ticks": false,
+      "zindex": 0
+    },
+    {
+      "scale": "x",
+      "orient": "bottom",
+      "grid": false,
+      "title": "a",
+      "labelFlush": true,
+      "labelOverlap": true,
+      "tickCount": {"signal": "ceil(width/40)"},
+      "zindex": 0
+    },
+    {
+      "scale": "y",
+      "orient": "left",
+      "grid": false,
+      "title": "b",
+      "labelOverlap": true,
+      "tickCount": {"signal": "ceil(height/40)"},
+      "zindex": 0
+    }
+  ]
+}

examples/specs/bar_q_qpow.vl.json

@@ -0,0 +1,15 @@
+{
+  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
+  "data": {
+    "values": [
+      {"a": 3000, "b": 55},
+      {"a": 3500, "b": 28},
+      {"a": 4000, "b": 55}
+    ]
+  },
+  "mark": "bar",
+  "encoding": {
+    "x": {"field": "a", "type": "quantitative"},
+    "y": {"field": "b", "type": "quantitative", "scale": {"type": "pow"}}
+  }
+}

src/stack.ts

@@ -104,15 +104,6 @@ function potentialStackedChannel(
       // if there is no explicit stacking, only apply stack if there is only one aggregate for x or y
       if (xAggregate !== yAggregate) {
         return xAggregate ? x : y;
-      } else {
-        const xScale = xDef.scale?.type;
-        const yScale = yDef.scale?.type;
-
-        if (xScale && xScale !== 'linear') {
-          return y;
-        } else if (yScale && yScale !== 'linear') {
-          return x;
-        }
       }
 
       if (isCartesian && mark === 'bar') {