await...then shorthand - fixes #957

Author: Rich-Harris

src/parse/state/mustache.ts

@@ -283,14 +283,22 @@ export default function mustache(parser: Parser) {
 			}
 		}
 
+		let awaitBlockShorthand = type === 'AwaitBlock' && parser.eat('then');
+		if (awaitBlockShorthand) {
+			parser.requireWhitespace();
+			block.value = parser.readIdentifier();
+			parser.allowWhitespace();
+		}
+
 		parser.eat('}}', true);
 
 		parser.current().children.push(block);
 		parser.stack.push(block);
 
 		if (type === 'AwaitBlock') {
-			block.pending.start = parser.index;
-			parser.stack.push(block.pending);
+			const childBlock = awaitBlockShorthand ? block.then : block.pending;
+			childBlock.start = parser.index;
+			parser.stack.push(childBlock);
 		}
 	} else if (parser.eat('yield')) {
 		// {{yield}}

test/runtime/samples/await-then-shorthand/_config.js

@@ -0,0 +1,45 @@
+let fulfil;
+
+let thePromise = new Promise(f => {
+	fulfil = f;
+});
+
+export default {
+	data: {
+		thePromise
+	},
+
+	html: ``,
+
+	test(assert, component, target) {
+		fulfil(42);
+
+		return thePromise
+			.then(() => {
+				assert.htmlEqual(target.innerHTML, `
+					<p>the value is 42</p>
+				`);
+
+				let reject;
+
+				thePromise = new Promise((f, r) => {
+					reject = r;
+				});
+
+				component.set({
+					thePromise
+				});
+
+				assert.htmlEqual(target.innerHTML, ``);
+
+				reject(new Error('something broke'));
+
+				return thePromise.catch(() => {});
+			})
+			.then(() => {
+				assert.htmlEqual(target.innerHTML, `
+					<p>oh no! something broke</p>
+				`);
+			});
+	}
+};

test/runtime/samples/await-then-shorthand/main.html

@@ -0,0 +1,5 @@
+{{#await thePromise then theValue}}
+	<p>the value is {{theValue}}</p>
+{{catch theError}}
+	<p>oh no! {{theError.message}}</p>
+{{/await}}