From 57ae613b6ac44ab77b4a15cf843b60331f437382 Mon Sep 17 00:00:00 2001
From: Fabrice Weinberg <Fabrice@weinberg.me>
Date: Thu, 1 Dec 2016 19:41:18 +0100
Subject: [PATCH] Ensure that only one {{yield}} can be used

---
 compiler/generate/index.js                   |  2 +-
 compiler/generate/visitors/MustacheTag.js    | 11 ++++++++---
 test/compiler/component-yield-one/_config.js |  5 +++++
 test/compiler/component-yield-one/main.html  |  2 ++
 test/test.js                                 |  2 +-
 5 files changed, 17 insertions(+), 5 deletions(-)
 create mode 100644 test/compiler/component-yield-one/_config.js
 create mode 100644 test/compiler/component-yield-one/main.html

diff --git a/compiler/generate/index.js b/compiler/generate/index.js
index ae9d979952..68d7f36b2d 100644
--- a/compiler/generate/index.js
+++ b/compiler/generate/index.js
@@ -490,7 +490,7 @@ export default function generate ( parsed, source, options ) {
 			};
 
 			this.appendChild = function appendChild ( child ) {
-				this.yield.appendChild(child)
+				this.yield.appendChild(child);
 			}
 
 			${initStatements.join( '\n\n' )}
diff --git a/compiler/generate/visitors/MustacheTag.js b/compiler/generate/visitors/MustacheTag.js
index a0b94c908e..e3dcca73d3 100644
--- a/compiler/generate/visitors/MustacheTag.js
+++ b/compiler/generate/visitors/MustacheTag.js
@@ -8,9 +8,14 @@ export default {
 		generator.addSourcemapLocations( node.expression );
 
 		if (node.expression.name === 'yield') {
-			generator.current.initStatements.push( deindent`
-				component.yield = ${generator.current.target};
-			` );
+			if (generator.hasYield === undefined) {
+				generator.hasYield	= true;
+				generator.current.initStatements.push( deindent`
+					component.yield = ${generator.current.target};
+				` );
+			} else {
+				throw new Error( `Only one {{yield}} per component.` );
+			}
 		} else {
 			generator.addElement( name, `document.createTextNode( ${snippet} )`, true );
 
diff --git a/test/compiler/component-yield-one/_config.js b/test/compiler/component-yield-one/_config.js
new file mode 100644
index 0000000000..e4d34ffdb6
--- /dev/null
+++ b/test/compiler/component-yield-one/_config.js
@@ -0,0 +1,5 @@
+export default {
+	compileError: function ( assert, err ) {
+		assert.equal('Error: Only one {{yield}} per component.', err)
+	}
+};
diff --git a/test/compiler/component-yield-one/main.html b/test/compiler/component-yield-one/main.html
new file mode 100644
index 0000000000..012a14c3ef
--- /dev/null
+++ b/test/compiler/component-yield-one/main.html
@@ -0,0 +1,2 @@
+<p>{{yield}}</p>
+<p>{{yield}}</p>
diff --git a/test/test.js b/test/test.js
index 9d132849e3..0097938b16 100644
--- a/test/test.js
+++ b/test/test.js
@@ -228,7 +228,7 @@ describe( 'svelte', () => {
 					compiled = svelte.compile( source );
 				} catch ( err ) {
 					if ( config.compileError ) {
-						config.compileError( err );
+						config.compileError( assert, err );
 						return;
 					} else {
 						throw err;