--amend

src/datetime.js

@@ -207,7 +207,14 @@ function toISODate(o, extended) {
   return c;
 }
 
-function toISOTime(o, extended, suppressSeconds, suppressMilliseconds, includeOffset) {
+function toISOTime(
+  o,
+  extended,
+  suppressSeconds,
+  suppressMilliseconds,
+  includeOffset,
+  extendedZone
+) {
   let c = padStart(o.c.hour);
   if (extended) {
     c += ":";
@@ -229,7 +236,7 @@ function toISOTime(o, extended, suppressSeconds, suppressMilliseconds, includeOf
   }
 
   if (includeOffset) {
-    if (o.isOffsetFixed && o.offset === 0) {
+    if (o.isOffsetFixed && o.offset === 0 && !extendedZone) {
       c += "Z";
     } else if (o.o < 0) {
       c += "-";
@@ -243,6 +250,10 @@ function toISOTime(o, extended, suppressSeconds, suppressMilliseconds, includeOf
       c += padStart(Math.trunc(o.o % 60));
     }
   }
+
+  if (extendedZone) {
+    c += "[" + o.zone.ianaName + "]";
+  }
   return c;
 }
 
@@ -1554,6 +1565,7 @@ export default class DateTime {
    * @param {boolean} [opts.suppressMilliseconds=false] - exclude milliseconds from the format if they're 0
    * @param {boolean} [opts.suppressSeconds=false] - exclude seconds from the format if they're 0
    * @param {boolean} [opts.includeOffset=true] - include the offset, such as 'Z' or '-04:00'
+   * @param {boolean} [opts.extendedZone=true] - add the time zone format extension
    * @param {string} [opts.format='extended'] - choose between the basic and extended format
    * @example DateTime.utc(1983, 5, 25).toISO() //=> '1982-05-25T00:00:00.000Z'
    * @example DateTime.now().toISO() //=> '2017-04-22T20:47:05.335-04:00'
@@ -1566,6 +1578,7 @@ export default class DateTime {
     suppressSeconds = false,
     suppressMilliseconds = false,
     includeOffset = true,
+    extendedZone = false,
   } = {}) {
     if (!this.isValid) {
       return null;
@@ -1575,7 +1588,7 @@ export default class DateTime {
 
     let c = toISODate(this, ext);
     c += "T";
-    c += toISOTime(this, ext, suppressSeconds, suppressMilliseconds, includeOffset);
+    c += toISOTime(this, ext, suppressSeconds, suppressMilliseconds, includeOffset, extendedZone);
     return c;
   }
 
@@ -1610,6 +1623,7 @@ export default class DateTime {
    * @param {boolean} [opts.suppressMilliseconds=false] - exclude milliseconds from the format if they're 0
    * @param {boolean} [opts.suppressSeconds=false] - exclude seconds from the format if they're 0
    * @param {boolean} [opts.includeOffset=true] - include the offset, such as 'Z' or '-04:00'
+   * @param {boolean} [opts.extendedZone=true] - add the time zone format extension
    * @param {boolean} [opts.includePrefix=false] - include the `T` prefix
    * @param {string} [opts.format='extended'] - choose between the basic and extended format
    * @example DateTime.utc().set({ hour: 7, minute: 34 }).toISOTime() //=> '07:34:19.361Z'
@@ -1623,6 +1637,7 @@ export default class DateTime {
     suppressSeconds = false,
     includeOffset = true,
     includePrefix = false,
+    extendedZone = false,
     format = "extended",
   } = {}) {
     if (!this.isValid) {
@@ -1632,7 +1647,14 @@ export default class DateTime {
     let c = includePrefix ? "T" : "";
     return (
       c +
-      toISOTime(this, format === "extended", suppressSeconds, suppressMilliseconds, includeOffset)
+      toISOTime(
+        this,
+        format === "extended",
+        suppressSeconds,
+        suppressMilliseconds,
+        includeOffset,
+        extendedZone
+      )
     );
   }
 

src/impl/regexParser.js

@@ -32,7 +32,7 @@ function combineExtractors(...extractors) {
       .reduce(
         ([mergedVals, mergedZone, cursor], ex) => {
           const [val, zone, next] = ex(m, cursor);
-          return [{ ...mergedVals, ...val }, mergedZone || zone, next];
+          return [{ ...mergedVals, ...val }, zone || mergedZone, next];
         },
         [{}, null, 1]
       )
@@ -67,7 +67,7 @@ function simpleParse(...keys) {
 
 // ISO and SQL parsing
 const offsetRegex = /(?:(Z)|([+-]\d\d)(?::?(\d\d))?)/;
-const isoExtendedZone = `(?:${offsetRegex.source}|\\[(${ianaRegex.source})\\])?`;
+const isoExtendedZone = `(?:${offsetRegex.source}?(?:\\[(${ianaRegex.source})\\])?)?`;
 const isoTimeBaseRegex = /(\d\d)(?::?(\d\d)(?::?(\d\d)(?:[.,](\d{1,30}))?)?)?/;
 const isoTimeRegex = RegExp(`${isoTimeBaseRegex.source}${isoExtendedZone}`);
 const isoTimeExtensionRegex = RegExp(`(?:T${isoTimeRegex.source})?`);

src/zone.js

@@ -22,6 +22,10 @@ export default class Zone {
     throw new ZoneIsAbstractError();
   }
 
+  get ianaName() {
+    return this.name;
+  }
+
   /**
    * Returns whether the offset is known to be fixed for the whole year.
    * @abstract

src/zones/fixedOffsetZone.js

@@ -62,6 +62,14 @@ export default class FixedOffsetZone extends Zone {
     return this.fixed === 0 ? "UTC" : `UTC${formatOffset(this.fixed, "narrow")}`;
   }
 
+  get ianaName() {
+    if (this.fixed === 0) {
+      return "Etc/UTC";
+    } else {
+      return `Etc/GMT${formatOffset(-this.fixed, "narrow")}`;
+    }
+  }
+
   /** @override **/
   offsetName() {
     return this.name;

test/datetime/format.test.js

@@ -85,6 +85,29 @@ test("DateTime#toISO() renders 00:00 for non-offset but non utc datetimes", () =
   expect(negativeYear.toISO()).toBe("1982-05-25T09:23:54.123+00:00");
 });
 
+test("DateTime#toISO() supports the extendedZone option", () => {
+  let zoned = dt.setZone("America/Chicago");
+  expect(zoned.toISO({ extendedZone: true })).toBe(
+    "1982-05-25T04:23:54.123-05:00[America/Chicago]"
+  );
+  expect(zoned.toISO({ includeOffset: false, extendedZone: true })).toBe(
+    "1982-05-25T04:23:54.123[America/Chicago]"
+  );
+
+  zoned = dt.setZone("UTC+6");
+  expect(zoned.toISO({ extendedZone: true })).toBe("1982-05-25T15:23:54.123+06:00[Etc/GMT-6]");
+  expect(zoned.toISO({ includeOffset: false, extendedZone: true })).toBe(
+    "1982-05-25T15:23:54.123[Etc/GMT-6]"
+  );
+
+  zoned = dt.setZone("UTC");
+  // note no Z
+  expect(zoned.toISO({ extendedZone: true })).toBe("1982-05-25T09:23:54.123+00:00[Etc/UTC]");
+  expect(zoned.toISO({ includeOffset: false, extendedZone: true })).toBe(
+    "1982-05-25T09:23:54.123[Etc/UTC]"
+  );
+});
+
 //------
 // #toISODate()
 //------

test/datetime/regexParse.test.js

@@ -575,6 +575,37 @@ test("DateTime.fromISO() accepts extended zones", () => {
   });
 });
 
+test("DateTime.fromISO() accepts extended zones and offsets", () => {
+  let dt = DateTime.fromISO("2016-05-14T10:23:54+01:00[Europe/Paris]", {
+    setZone: true,
+  });
+  expect(dt.isValid).toBe(true);
+  expect(dt.zoneName).toBe("Europe/Paris");
+  expect(dt.toObject()).toEqual({
+    year: 2016,
+    month: 5,
+    day: 14,
+    hour: 10,
+    minute: 23,
+    second: 54,
+    millisecond: 0,
+  });
+
+  dt = DateTime.fromISO("2016-05-14T10:23:54+00:00[Etc/UTC]", { setZone: true });
+  expect(dt.isValid).toBe(true);
+  expect(dt.zoneName).toBe("Etc/UTC");
+  expect(dt.offset).toBe(0);
+  expect(dt.toObject()).toEqual({
+    year: 2016,
+    month: 5,
+    day: 14,
+    hour: 10,
+    minute: 23,
+    second: 54,
+    millisecond: 0,
+  });
+});
+
 test("DateTime.fromISO() accepts extended zones on bare times", () => {
   const { year, month, day } = DateTime.now().setZone("Europe/Paris");
   let dt = DateTime.fromISO("10:23:54[Europe/Paris]", {