case independent scale type matching (observablehq#1904)

* case independent scale type matching

closes observablehq#1894

* normalize type in inferScaleType

---------

Co-authored-by: Mike Bostock <mbostock@gmail.com>

src/scales.js

@@ -376,10 +376,16 @@ function formatScaleType(type) {
   return typeof type === "symbol" ? type.description : type;
 }
 
+function maybeScaleType(type) {
+  return typeof type === "string" ? `${type}`.toLowerCase() : type;
+}
+
 // A special type symbol when the x and y scales are replaced with a projection.
 const typeProjection = {toString: () => "projection"};
 
 function inferScaleType(key, channels, {type, domain, range, scheme, pivot, projection}) {
+  type = maybeScaleType(type);
+
   // The facet scales are always band scales; this cannot be changed.
   if (key === "fx" || key === "fy") return "band";
 
@@ -391,7 +397,8 @@ function inferScaleType(key, channels, {type, domain, range, scheme, pivot, proj
   // 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,
   // barY requires x to be a band scale and disallows any other scale type.
-  for (const {type: t} of channels) {
+  for (const channel of channels) {
+    const t = maybeScaleType(channel.type);
     if (t === undefined) continue;
     else if (type === undefined) type = t;
     else if (type !== t) throw new Error(`scale incompatible with channel: ${type} !== ${t}`);

test/scales/scales-test.js

@@ -37,6 +37,12 @@ it("Plot does not throw an error if a quantile scale has a non-monotonic domain"
   });
 });
 
+it("Scale types are lowercased", () => {
+  assert.strictEqual(Plot.scale({x: {type: "UTC"}}).type, "utc");
+  assert.strictEqual(Plot.scale({color: {type: "OrDiNaL"}}).type, "ordinal");
+  assert.strictEqual(Plot.scale({fx: {type: "BAND"}}).type, "band");
+});
+
 it("Plot.scale(description) returns a standalone scale", () => {
   const color = Plot.scale({color: {type: "linear"}});
   scaleEqual(color, {