test: try strict comparison for field def comparisons

Author: hydrosquall

src/channeldef.ts

@@ -867,6 +867,29 @@ export function vgField(
   }
 }
 
+/**
+ * Return true if fieldDefs are equal in field name and all "fn" opt.nofn related properties
+ * Different from checking for full field def equivalence, since some (like axis) don't matter for positioning purposes.
+ */
+export function areFieldDefsWithInlineTransformsEquivalent(
+  fieldDef1: FieldDef<string> | WindowFieldDef | AggregatedFieldDef,
+  fieldDef2: FieldDef<string> | WindowFieldDef | AggregatedFieldDef
+) {
+  if (isOpFieldDef(fieldDef1) || isOpFieldDef(fieldDef2)) {
+    return isOpFieldDef(fieldDef1) && isOpFieldDef(fieldDef2) && fieldDef1.op === fieldDef2.op;
+  }
+
+  const {field: field1, aggregate: aggregate1, bin: bin1, timeUnit: timeUnit1} = fieldDef1;
+  const {field: field2, aggregate: aggregate2, bin: bin2, timeUnit: timeUnit2} = fieldDef2;
+
+  return (
+    field1 === field2 &&
+    JSON.stringify(aggregate1) === JSON.stringify(aggregate2) &&
+    JSON.stringify(bin1) === JSON.stringify(bin2) &&
+    timeUnit1 === timeUnit2
+  );
+}
+
 export function isDiscrete(def: TypedFieldDef<Field> | DatumDef<any, any>) {
   switch (def.type) {
     case 'nominal':

src/stack.ts

@@ -17,6 +17,7 @@ import {
   PositionFieldDef,
   TypedFieldDef,
   vgField,
+  areFieldDefsWithInlineTransformsEquivalent,
 } from './channeldef.js';
 import {CompositeAggregate} from './compositemark/index.js';
 import {channelHasField, Encoding, isAggregate} from './encoding.js';
@@ -181,13 +182,15 @@ export function stack(m: Mark | MarkDef, encoding: Encoding<string>): StackPrope
   if (encoding[dimensionChannel]) {
     const dimensionDef = encoding[dimensionChannel];
     const dimensionField = isFieldDef(dimensionDef) ? vgField(dimensionDef, {}) : undefined;
-    const hasSameDimensionAndStackedField = dimensionField && dimensionField === stackedField;
+    // const hasSameDimensionAndStackedField = dimensionField && dimensionField === stackedField;
+    const areDefsEquivalent =
+      isFieldDef(dimensionDef) && areFieldDefsWithInlineTransformsEquivalent(dimensionDef, stackedFieldDef);
 
     // For polar coordinates, do not set a groupBy when working with quantitative fields.
     // const isPolar = isPolarPositionChannel(fieldChannel) || isPolarPositionChannel(dimensionChannel);
     // const shouldAddPolarGroupBy = !isUnbinnedQuantitative(dimensionDef);
 
-    if (!hasSameDimensionAndStackedField) {
+    if (!areDefsEquivalent) {
       // if (isPolar ? shouldAddPolarGroupBy : !hasSameDimensionAndStackedField) {
       // avoid grouping by the stacked field
       groupbyChannels.push(dimensionChannel);