detect ordinal year intervals (#1512)

* detect ordinal year intervals

* comment re. equality

Author: mbostock

src/marks/axis.js

@@ -1,4 +1,4 @@
-import {extent, format, utcFormat} from "d3";
+import {extent, format, timeFormat, utcFormat} from "d3";
 import {formatDefault} from "../format.js";
 import {marks} from "../mark.js";
 import {radians} from "../math.js";
@@ -7,6 +7,7 @@ import {isIterable, isNoneish, isTemporal, orderof} from "../options.js";
 import {maybeColorChannel, maybeNumberChannel, maybeRangeInterval} from "../options.js";
 import {isTemporalScale} from "../scales.js";
 import {offset} from "../style.js";
+import {isTimeYear, isUtcYear} from "../time.js";
 import {initializer} from "../transforms/basic.js";
 import {ruleX, ruleY} from "./rule.js";
 import {text, textX, textY} from "./text.js";
@@ -579,7 +580,11 @@ function inferTickFormat(scale, ticks, tickFormat) {
   return scale.tickFormat
     ? scale.tickFormat(isIterable(ticks) ? null : ticks, tickFormat)
     : tickFormat === undefined
-    ? formatDefault
+    ? isUtcYear(scale.interval)
+      ? utcFormat("%Y")
+      : isTimeYear(scale.interval)
+      ? timeFormat("%Y")
+      : formatDefault
     : typeof tickFormat === "string"
     ? (isTemporal(scale.domain()) ? utcFormat : format)(tickFormat)
     : constant(tickFormat);

src/time.js

@@ -70,3 +70,15 @@ export function maybeTimeInterval(interval) {
 export function maybeUtcInterval(interval) {
   return parseInterval(interval, utcIntervals);
 }
+
+export function isUtcYear(i) {
+  if (!i) return false;
+  const date = i.floor(new Date(Date.UTC(2000, 11, 31)));
+  return utcYear(date) >= date; // coercing equality
+}
+
+export function isTimeYear(i) {
+  if (!i) return false;
+  const date = i.floor(new Date(2000, 11, 31));
+  return timeYear(date) >= date; // coercing equality
+}

test/output/internFacetDate.svg

@@ -7,16 +7,8 @@ export async function yearlyRequestsDot() {
     [new Date("2005-01-01"), 5]
   ];
   return Plot.plot({
-    label: null,
-    x: {
-      type: "utc",
-      interval: "year",
-      inset: 40,
-      grid: true
-    },
-    y: {
-      zero: true
-    },
+    x: {type: "point", interval: "year", grid: true},
+    y: {zero: true},
     marks: [Plot.ruleY([0]), Plot.dot(requests)]
   });
 }