feat(mf2): Support u:id option (unicode-org/message-format-wg#846)

Author: XM5jDcsHTyGJtQqlCi

mf2/messageformat/src/data-model/format-markup.ts

@@ -23,7 +23,8 @@ export function formatMarkup(
         if (typeof rv === 'object' && typeof rv?.valueOf === 'function') {
           rv = rv.valueOf();
         }
-        part.options[name] = rv;
+        if (name === 'u:id') part.id = String(rv);
+        else part.options[name] = rv;
       }
     }
   }

mf2/messageformat/src/data-model/function-context.ts

@@ -7,6 +7,7 @@ export class MessageFunctionContext {
   #ctx: Context;
   #locales: Intl.Locale[];
   readonly dir: 'ltr' | 'rtl' | 'auto' | undefined;
+  readonly id: string | undefined;
   readonly source: string;
   constructor(ctx: Context, source: string, options?: Options) {
     this.#ctx = ctx;
@@ -42,6 +43,9 @@ export class MessageFunctionContext {
       }
     }
 
+    const idOpt = options?.get('u:id');
+    this.id = idOpt ? String(resolveValue(ctx, idOpt)) : undefined;
+
     this.source = source;
   }
 

mf2/messageformat/src/data-model/resolve-function-ref.ts

@@ -39,6 +39,16 @@ export function resolveFunctionRef(
         `Function :${name} did not return a MessageValue`
       );
     }
+    if (msgCtx.id && typeof res.toParts === 'function') {
+      return {
+        ...res,
+        toParts() {
+          const parts = res.toParts!();
+          for (const part of parts) part.id = msgCtx.id;
+          return parts;
+        }
+      };
+    }
     return res;
   } catch (error) {
     ctx.onError(error);
@@ -51,7 +61,7 @@ function resolveOptions(ctx: Context, options: Options | undefined) {
   const opt: Record<string, unknown> = Object.create(null);
   if (options) {
     for (const [name, value] of options) {
-      if (name !== 'u:dir' && name !== 'u:locale') {
+      if (name !== 'u:dir' && name !== 'u:id' && name !== 'u:locale') {
         opt[name] = resolveValue(ctx, value);
       }
     }

mf2/messageformat/src/formatted-parts.ts

@@ -16,6 +16,7 @@ export interface MessageExpressionPart {
   source: string;
   dir?: 'ltr' | 'rtl';
   locale?: string;
+  id?: string;
   parts?: Array<{ type: string; source?: string; value?: unknown }>;
   value?: unknown;
 }
@@ -32,6 +33,7 @@ export interface MessageMarkupPart {
   kind: 'open' | 'standalone' | 'close';
   source: string;
   name: string;
+  id?: string;
   options?: { [key: string]: unknown };
 }