fix autoHeight and outerRange for empty scale domains

closes #1856

src/dimensions.js

@@ -92,7 +92,7 @@ function autoHeight(
   {projection, aspectRatio},
   {width, marginTopDefault, marginRightDefault, marginBottomDefault, marginLeftDefault}
 ) {
-  const nfy = fy ? fy.scale.domain().length : 1;
+  const nfy = fy ? fy.scale.domain().length || 1 : 1;
 
   // If a projection is specified, use its natural aspect ratio (if known).
   const ar = projectionAspectRatio(projection);
@@ -102,8 +102,7 @@ function autoHeight(
     const lar = Math.max(0.1, Math.min(10, far)); // clamp the aspect ratio to a “reasonable” value
     return Math.round((width - marginLeftDefault - marginRightDefault) * lar + marginTopDefault + marginBottomDefault);
   }
-
-  const ny = y ? (isOrdinalScale(y) ? y.scale.domain().length : Math.max(7, 17 / nfy)) : 1;
+  const ny = y ? (isOrdinalScale(y) ? y.scale.domain().length || 1 : Math.max(7, 17 / nfy)) : 1;
 
   // If a desired aspect ratio is given, compute a default height to match.
   if (aspectRatio != null) {

src/plot.js

@@ -737,6 +737,7 @@ function actualDimensions({fx, fy}, dimensions) {
 
 function outerRange(scale) {
   const domain = scale.domain();
+  if (domain.length === 0) return [0, scale.bandwidth()];
   let x1 = scale(domain[0]);
   let x2 = scale(domain[domain.length - 1]);
   if (x2 < x1) [x1, x2] = [x2, x1];

test/plots/autoheight.ts

@@ -0,0 +1,5 @@
+import * as Plot from "@observablehq/plot";
+
+export async function autoHeightEmpty() {
+  return Plot.rectY([], {x: "date", y: "visitors", fy: "path"}).plot();
+}

test/plots/index.ts

@@ -27,6 +27,7 @@ export * from "./athletes-sport-sex.js";
 export * from "./athletes-sport-weight.js";
 export * from "./athletes-weight-cumulative.js";
 export * from "./athletes-weight.js";
+export * from "./autoheight.js";
 export * from "./autoplot.js";
 export * from "./availability.js";
 export * from "./axis-filter.js";