no scale if no data and no type (#756)

Author: mbostock

src/scales.js

@@ -229,6 +229,9 @@ function inferScaleType(key, channels, {type, domain, range, scheme}) {
   // If the scale, a channel, or user specified a (consistent) type, return it.
   if (type !== undefined) return type;
 
+  // If there’s no data (and no type) associated with this scale, don’t create a scale.
+  if (domain === undefined && !channels.some(({value}) => value !== undefined)) return;
+
   const kind = registry.get(key);
 
   // For color scales, if no range or scheme is specified and all associated

test/plots/empty.js

@@ -5,8 +5,8 @@ export default async function() {
   return Plot.plot({
     grid: true,
     inset: 6,
-    x: {},
-    y: {},
+    x: {type: "linear"},
+    y: {type: "linear"},
     marks: [
       Plot.frame(),
       undefined,

test/scales/scales-test.js

@@ -1112,13 +1112,13 @@ it("plot(…).scale('opacity') respects the percent option, affecting domain and
 });
 
 it("plot({inset, …}).scale('x') does not allow insets or margins to invert the range", () => {
-  assert.deepStrictEqual(Plot.plot({x: {inset: 60}, width: 100}).scale("x").range, [80, 80]);
-  assert.deepStrictEqual(Plot.plot({x: {inset: 30}, margin: 30, width: 100}).scale("x").range, [60, 60]);
+  assert.deepStrictEqual(Plot.plot({x: {type: "linear", inset: 60}, width: 100}).scale("x").range, [80, 80]);
+  assert.deepStrictEqual(Plot.plot({x: {type: "linear", inset: 30}, margin: 30, width: 100}).scale("x").range, [60, 60]);
 });
 
 it("plot({inset, …}).scale('y') does not allow insets or margins to invert the range", () => {
-  assert.deepStrictEqual(Plot.plot({y: {inset: 60}, height: 100}).scale("y").range, [80, 80]);
-  assert.deepStrictEqual(Plot.plot({y: {inset: 30}, margin: 30, height: 100}).scale("y").range, [60, 60]);
+  assert.deepStrictEqual(Plot.plot({y: {type: "linear", inset: 60}, height: 100}).scale("y").range, [80, 80]);
+  assert.deepStrictEqual(Plot.plot({y: {type: "linear", inset: 30}, margin: 30, height: 100}).scale("y").range, [60, 60]);
 });
 
 it("plot({inset, …}).scale('x').range respects the given top-level inset", () => {