feat(mf2)!: Drop :currency currencyDisplay=formalSymbol option value (unicode-org/message-format-wg#985)

Author: XM5jDcsHTyGJtQqlCi

mf2/messageformat/src/functions/currency.test.ts

@@ -27,9 +27,8 @@ describe('currencyDisplay', () => {
     'symbol',
     'name',
     'code',
-    'formalSymbol',
     'never'
-  ]) {
+  ] as const) {
     test(`currencyDisplay=${cd}`, () => {
       const mf = new MessageFormat(
         'en',
@@ -38,15 +37,14 @@ describe('currencyDisplay', () => {
       const nf = new Intl.NumberFormat('en', {
         style: 'currency',
         currency: 'EUR',
-        currencyDisplay:
-          cd === 'formalSymbol' || cd === 'never' ? undefined : cd
+        currencyDisplay: cd === 'never' ? undefined : cd
       });
       const onError = jest.fn();
       expect(mf.format(undefined, onError)).toEqual(nf.format(42));
       expect(mf.formatToParts(undefined, onError)).toMatchObject([
         { parts: nf.formatToParts(42) }
       ]);
-      if (cd === 'formalSymbol' || cd === 'never') {
+      if (cd === 'never') {
         expect(onError.mock.calls).toMatchObject([
           [{ type: 'unsupported-operation' }],
           [{ type: 'unsupported-operation' }]

mf2/messageformat/src/functions/currency.ts

@@ -48,15 +48,18 @@ export function currency(
           break;
         case 'currencyDisplay': {
           const strval = asString(optval);
-          if (strval === 'formalSymbol' || strval === 'never') {
-            throw new MessageResolutionError(
-              'unsupported-operation',
-              `Currency display "${strval}" is not supported on :currency`,
-              source
+          if (strval === 'never') {
+            ctx.onError(
+              new MessageResolutionError(
+                'unsupported-operation',
+                'Currency display "never" is not yet supported',
+                source
+              )
             );
+          } else {
+            // @ts-expect-error Let Intl.NumberFormat construction fail
+            options[name] = strval;
           }
-          // @ts-expect-error Let Intl.NumberFormat construction fail
-          options[name] = strval;
           break;
         }
         case 'fractionDigits': {