feat(mf2): Support leading whitespace for complex messages (unicode-org/message-format-wg#854)

Author: XM5jDcsHTyGJtQqlCi

packages/mf2-messageformat/src/cst/declarations.ts

@@ -5,12 +5,15 @@ import type * as CST from './types.js';
 import { whitespaces } from './util.js';
 import { parseVariable } from './values.js';
 
-export function parseDeclarations(ctx: ParseContext): {
+export function parseDeclarations(
+  ctx: ParseContext,
+  start: number
+): {
   declarations: CST.Declaration[];
   end: number;
 } {
   const { source } = ctx;
-  let pos = whitespaces(source, 0);
+  let pos = start;
   const declarations: CST.Declaration[] = [];
   loop: while (source[pos] === '.') {
     const keyword = parseNameValue(source, pos + 1);

packages/mf2-messageformat/src/cst/parse-cst.ts

@@ -52,13 +52,16 @@ export function parseCST(
 ): CST.Message {
   const ctx = new ParseContext(source, opt);
 
-  if (source.startsWith('.')) {
-    const { declarations, end: pos } = parseDeclarations(ctx);
-    return source.startsWith('.match', pos)
-      ? parseSelectMessage(ctx, pos, declarations)
-      : parsePatternMessage(ctx, pos, declarations, true);
+  const pos = whitespaces(source, 0);
+  if (source.startsWith('.', pos)) {
+    const { declarations, end } = parseDeclarations(ctx, pos);
+    return source.startsWith('.match', end)
+      ? parseSelectMessage(ctx, end, declarations)
+      : parsePatternMessage(ctx, end, declarations, true);
   } else {
-    return parsePatternMessage(ctx, 0, [], source.startsWith('{{'));
+    return source.startsWith('{{', pos)
+      ? parsePatternMessage(ctx, pos, [], true)
+      : parsePatternMessage(ctx, 0, [], false);
   }
 }
 

packages/mf2-messageformat/src/data-model/parse.ts

@@ -72,6 +72,7 @@ export function parseMessage(
   if (source.startsWith('.match', pos)) return selectMessage(decl);
 
   const quoted = decl.length > 0 || source.startsWith('{{', pos);
+  if (!quoted && pos > 0) pos = 0;
   const pattern_ = pattern(quoted);
   if (quoted) {
     ws();
@@ -149,6 +150,7 @@ function pattern(quoted: boolean): Model.Pattern {
 
 function declarations(): Model.Declaration[] {
   const declarations: Model.Declaration[] = [];
+  ws();
   loop: while (source[pos] === '.') {
     const keyword = parseNameValue(source, pos + 1);
     switch (keyword) {

packages/mf2-messageformat/src/data-model/stringify.ts

@@ -105,7 +105,7 @@ function stringifyAttribute({ name, value }: Attribute) {
 
 function stringifyPattern(pattern: Pattern, quoted: boolean) {
   let res = '';
-  if (!quoted && typeof pattern[0] === 'string' && pattern[0][0] === '.') {
+  if (!quoted && typeof pattern[0] === 'string' && /^\s*\./.test(pattern[0])) {
     quoted = true;
   }
   for (const el of pattern) {