error if projection and band-requiring channels

Author: mbostock

src/scales.js

@@ -307,9 +307,9 @@ function inferScaleType(key, channels, {type, domain, range, scheme, pivot, proj
   if (key === "fx" || key === "fy") return "band";
 
   // If a projection is specified, the x- and y-scales are disabled; these
-  // channels will be projected rather than scaled. TODO Throw an error if these
-  // scales are specified in conjunction with a projection.
-  if ((key === "x" || key === "y") && projection != null) return;
+  // channels will be projected rather than scaled. (But still check that none
+  // of the associated channels are incompatible with a projection.)
+  if ((key === "x" || key === "y") && projection != null) type = "projection";
 
   // If a channel dictates a scale type, make sure that it is consistent with
   // the user-specified scale type (if any) and all other channels. For example,
@@ -321,6 +321,7 @@ function inferScaleType(key, channels, {type, domain, range, scheme, pivot, proj
   }
 
   // If the scale, a channel, or user specified a (consistent) type, return it.
+  if (type === "projection") return;
   if (type !== undefined) return type;
 
   // If there’s no data (and no type) associated with this scale, don’t create a scale.

test/marks/cell-test.js

@@ -125,3 +125,7 @@ it("cellY() defaults y to identity and x to null", () => {
   );
   assert.strictEqual(cell.channels.y.type, "band");
 });
+
+it("cell() is incompatible with a projection", () => {
+  assert.throws(() => Plot.cell([]).plot({projection: "equal-earth"}), /scale incompatible with channel: projection !== band/);
+});