Validate time zone in quickDT prior to guessing offset (#1575)

We validate the zone in the constructor anyway, but the tests missed a
branch where we attempt to use an invalid zone to compute an offset,
which will result in an exception. Zone#isValid is calculated at
creation time (and checked in DateTime constructor already) so this will
not degrade performance in the happy case.

src/datetime.js

@@ -373,8 +373,12 @@ function normalizeUnitWithLocalWeeks(unit) {
 // but doesn't do any validation, makes a bunch of assumptions about what units
 // are present, and so on.
 function quickDT(obj, opts) {
-  const zone = normalizeZone(opts.zone, Settings.defaultZone),
-    loc = Locale.fromObject(opts),
+  const zone = normalizeZone(opts.zone, Settings.defaultZone);
+  if (!zone.isValid) {
+    return DateTime.invalid(unsupportedZone(zone));
+  }
+
+  const loc = Locale.fromObject(opts),
     tsNow = Settings.now();
 
   let ts, o;

test/datetime/invalid.test.js

@@ -5,7 +5,11 @@ import { DateTime, Settings } from "../../src/luxon";
 const organic1 = DateTime.utc(2014, 13, 33),
   // not an actual Wednesday
   organic2 = DateTime.fromObject({ weekday: 3, year: 1982, month: 5, day: 25 }, { zone: "UTC" }),
-  organic3 = DateTime.fromObject({ year: 1982, month: 5, day: 25, hour: 27 });
+  organic3 = DateTime.fromObject({ year: 1982, month: 5, day: 25, hour: 27 }),
+  organic4 = DateTime.fromObject(
+    { year: 1982, month: 5, day: 25, hour: 2 },
+    { zone: "America/Lasers" }
+  );
 
 test("Explicitly invalid dates are invalid", () => {
   const dt = DateTime.invalid("just because", "seriously, just because");
@@ -22,14 +26,28 @@ test("Invalid creations are invalid", () => {
 
 test("invalid zones result in invalid dates", () => {
   expect(DateTime.now().setZone("America/Lasers").isValid).toBe(false);
+  expect(DateTime.now().setZone("America/Lasers").invalidReason).toBe("unsupported zone");
+
   expect(DateTime.local({ zone: "America/Lasers" }).isValid).toBe(false);
+  expect(DateTime.local({ zone: "America/Lasers" }).invalidReason).toBe("unsupported zone");
+
+  expect(DateTime.local(1982, { zone: "America/Lasers" }).isValid).toBe(false);
+  expect(DateTime.local(1982, { zone: "America/Lasers" }).invalidReason).toBe("unsupported zone");
+
   expect(DateTime.fromJSDate(new Date(), { zone: "America/Lasers" }).isValid).toBe(false);
+  expect(DateTime.fromJSDate(new Date(), { zone: "America/Lasers" }).invalidReason).toBe(
+    "unsupported zone"
+  );
+
+  expect(DateTime.fromMillis(0, { zone: "America/Lasers" }).isValid).toBe(false);
+  expect(DateTime.fromMillis(0, { zone: "America/Lasers" }).invalidReason).toBe("unsupported zone");
 });
 
 test("Invalid DateTimes tell you why", () => {
   expect(organic1.invalidReason).toBe("unit out of range");
   expect(organic2.invalidReason).toBe("mismatched weekday");
   expect(organic3.invalidReason).toBe("unit out of range");
+  expect(organic4.invalidReason).toBe("unsupported zone");
 });
 
 test("Invalid DateTimes can provide an extended explanation", () => {