only create anchors for if blocks when necessary

src/generators/dom/preprocess.js

@@ -223,7 +223,7 @@ const preprocessors = {
 	}
 };
 
-function preprocessChildren ( generator, block, state, node ) {
+function preprocessChildren ( generator, block, state, node, isTopLevel ) {
 	// glue text nodes together
 	const cleaned = [];
 	let lastChild;
@@ -238,16 +238,43 @@ function preprocessChildren ( generator, block, state, node ) {
 			cleaned.push( child );
 		}
 
-		if ( lastChild ) lastChild.next = child;
 		lastChild = child;
 	});
 
-	node.children = cleaned;
+	if ( isTopLevel ) {
+		// trim leading and trailing whitespace from the top level
+		const firstChild = cleaned[0];
+		if ( firstChild && firstChild.type === 'Text' ) {
+			firstChild.data = trimStart( firstChild.data );
+			if ( !firstChild.data ) cleaned.shift();
+		}
+
+		const lastChild = cleaned[ cleaned.length - 1 ];
+		if ( lastChild && lastChild.type === 'Text' ) {
+			lastChild.data = trimEnd( lastChild.data );
+			if ( !lastChild.data ) cleaned.pop();
+		}
+	}
+
+	lastChild = null;
 
 	cleaned.forEach( child => {
 		const preprocess = preprocessors[ child.type ];
 		if ( preprocess ) preprocess( generator, block, state, child );
+
+		if ( lastChild ) {
+			lastChild.next = child;
+			lastChild.needsAnchor = !child._state.name;
+		}
+
+		lastChild = child;
 	});
+
+	if ( lastChild ) {
+		lastChild.needsAnchor = !state.parentNode;
+	}
+
+	node.children = cleaned;
 }
 
 export default function preprocess ( generator, state, node ) {
@@ -268,21 +295,8 @@ export default function preprocess ( generator, state, node ) {
 	});
 
 	generator.blocks.push( block );
-	preprocessChildren( generator, block, state, node );
+	preprocessChildren( generator, block, state, node, true );
 	block.hasUpdateMethod = block.dependencies.size > 0;
 
-	// trim leading and trailing whitespace from the top level
-	const firstChild = node.children[0];
-	if ( firstChild && firstChild.type === 'Text' ) {
-		firstChild.data = trimStart( firstChild.data );
-		if ( !firstChild.data ) node.children.shift();
-	}
-
-	const lastChild = node.children[ node.children.length - 1 ];
-	if ( lastChild && lastChild.type === 'Text' ) {
-		lastChild.data = trimEnd( lastChild.data );
-		if ( !lastChild.data ) node.children.pop();
-	}
-
 	return block;
 }

src/generators/dom/visitors/IfBlock.js

@@ -41,12 +41,16 @@ function visitChildren ( generator, block, state, node ) {
 
 export default function visitIfBlock ( generator, block, state, node ) {
 	const name = generator.getUniqueName( `if_block` );
-	const anchor = generator.getUniqueName( `${name}_anchor` );
+	const anchor = node.needsAnchor ? block.getUniqueName( `${name}_anchor` ) : ( node.next && node.next._state.name ) || 'null';
 	const params = block.params.join( ', ' );
 
 	const vars = { name, anchor, params };
 
+	if ( node.needsAnchor ) {
 		block.createAnchor( anchor, state.parentNode );
+	} else if ( node.next ) {
+		node.next.usedAsAnchor = true;
+	}
 
 	const branches = getBranches( generator, block, state, node, generator.getUniqueName( `create_if_block` ) );
 	const dynamic = branches.some( branch => branch.dynamic );
@@ -70,11 +74,13 @@ function simple ( generator, block, state, node, branch, dynamic, { name, anchor
 	const isToplevel = !state.parentNode;
 
 	if ( isToplevel ) {
-		block.builders.mount.addLine( `if ( ${name} ) ${name}.mount( ${block.target}, ${anchor} );` );
+		block.builders.mount.addLine( `if ( ${name} ) ${name}.mount( ${block.target}, null );` );
 	} else {
 		block.builders.create.addLine( `if ( ${name} ) ${name}.mount( ${state.parentNode}, null );` );
 	}
 
+	const parentNode = state.parentNode || `${anchor}.parentNode`;
+
 	if ( dynamic ) {
 		block.builders.update.addBlock( deindent`
 			if ( ${branch.condition} ) {
@@ -82,7 +88,7 @@ function simple ( generator, block, state, node, branch, dynamic, { name, anchor
 					${name}.update( changed, ${params} );
 				} else {
 					${name} = ${branch.block}( ${params}, ${block.component} );
-					${name}.mount( ${anchor}.parentNode, ${anchor} );
+					${name}.mount( ${parentNode}, ${anchor} );
 				}
 			} else if ( ${name} ) {
 				${name}.destroy( true );
@@ -94,7 +100,7 @@ function simple ( generator, block, state, node, branch, dynamic, { name, anchor
 			if ( ${branch.condition} ) {
 				if ( !${name} ) {
 					${name} = ${branch.block}( ${params}, ${block.component} );
-					${name}.mount( ${anchor}.parentNode, ${anchor} );
+					${name}.mount( ${parentNode}, ${anchor} );
 				}
 			} else if ( ${name} ) {
 				${name}.destroy( true );
@@ -122,11 +128,13 @@ function compound ( generator, block, state, node, branches, dynamic, { name, an
 	const isToplevel = !state.parentNode;
 
 	if ( isToplevel ) {
-		block.builders.mount.addLine( `if ( ${name} ) ${name}.mount( ${block.target}, ${anchor} );` );
+		block.builders.mount.addLine( `if ( ${name} ) ${name}.mount( ${block.target}, null );` );
 	} else {
 		block.builders.create.addLine( `if ( ${name} ) ${name}.mount( ${state.parentNode}, null );` );
 	}
 
+	const parentNode = state.parentNode || `${anchor}.parentNode`;
+
 	if ( dynamic ) {
 		block.builders.update.addBlock( deindent`
 			if ( ${current_block} === ( ${current_block} = ${getBlock}( ${params} ) ) && ${name} ) {
@@ -134,7 +142,7 @@ function compound ( generator, block, state, node, branches, dynamic, { name, an
 			} else {
 				if ( ${name} ) ${name}.destroy( true );
 				${name} = ${current_block} && ${current_block}( ${params}, ${block.component} );
-				if ( ${name} ) ${name}.mount( ${anchor}.parentNode, ${anchor} );
+				if ( ${name} ) ${name}.mount( ${parentNode}, ${anchor} );
 			}
 		` );
 	} else {
@@ -142,7 +150,7 @@ function compound ( generator, block, state, node, branches, dynamic, { name, an
 			if ( ${current_block} !== ( ${current_block} = ${getBlock}( ${params} ) ) ) {
 				if ( ${name} ) ${name}.destroy( true );
 				${name} = ${current_block} && ${current_block}( ${params}, ${block.component} );
-				if ( ${name} ) ${name}.mount( ${anchor}.parentNode, ${anchor} );
+				if ( ${name} ) ${name}.mount( ${parentNode}, ${anchor} );
 			}
 		` );
 	}

src/generators/dom/visitors/Text.js

@@ -2,5 +2,5 @@
 
 export default function visitText ( generator, block, state, node ) {
 	if ( !node._state.shouldCreate ) return;
-	block.addElement( node._state.name, `${generator.helper( 'createText' )}( ${JSON.stringify( node.data )} )`, state.parentNode, false );
+	block.addElement( node._state.name, `${generator.helper( 'createText' )}( ${JSON.stringify( node.data )} )`, state.parentNode, node.usedAsAnchor );
 }

test/js/samples/if-block-no-update/expected.js

@@ -14,7 +14,7 @@ function create_main_fragment ( state, component ) {
 	return {
 		mount: function ( target, anchor ) {
 			insertNode( if_block_anchor, target, anchor );
-			if ( if_block ) if_block.mount( target, if_block_anchor );
+			if ( if_block ) if_block.mount( target, null );
 		},
 
 		update: function ( changed, state ) {

test/js/samples/if-block-simple/expected.js

@@ -8,7 +8,7 @@ function create_main_fragment ( state, component ) {
 	return {
 		mount: function ( target, anchor ) {
 			insertNode( if_block_anchor, target, anchor );
-			if ( if_block ) if_block.mount( target, if_block_anchor );
+			if ( if_block ) if_block.mount( target, null );
 		},
 
 		update: function ( changed, state ) {

test/js/samples/use-elements-as-anchors/expected.js

@@ -2,13 +2,12 @@ import { appendNode, assign, createComment, createElement, createText, detachNod
 
 function create_main_fragment ( state, component ) {
 	var div = createElement( 'div' );
-	var if_block_anchor = createComment();
-	appendNode( if_block_anchor, div );
 
 	var if_block = state.a && create_if_block( state, component );
 
 	if ( if_block ) if_block.mount( div, null );
-	appendNode( createText( "\n\n\t" ), div );
+	var text = createText( "\n\n\t" );
+	appendNode( text, div );
 	var p = createElement( 'p' );
 	appendNode( p, div );
 	appendNode( createText( "this can be used as an anchor" ), p );
@@ -17,15 +16,14 @@ function create_main_fragment ( state, component ) {
 	var if_block_1 = state.b && create_if_block_1( state, component );
 
 	if ( if_block_1 ) if_block_1.mount( div, null );
-	var if_block_1_anchor = createComment();
+	var text_3 = createText( "\n\n\t" );
-	appendNode( if_block_1_anchor, div );
+	appendNode( text_3, div );
-
-	appendNode( createText( "\n\n\t" ), div );
 
 	var if_block_2 = state.c && create_if_block_2( state, component );
 
 	if ( if_block_2 ) if_block_2.mount( div, null );
-	appendNode( createText( "\n\n\t" ), div );
+	var text_4 = createText( "\n\n\t" );
+	appendNode( text_4, div );
 	var p_1 = createElement( 'p' );
 	appendNode( p_1, div );
 	appendNode( createText( "so can this" ), p_1 );
@@ -34,7 +32,8 @@ function create_main_fragment ( state, component ) {
 	var if_block_3 = state.d && create_if_block_3( state, component );
 
 	if ( if_block_3 ) if_block_3.mount( div, null );
-	appendNode( createText( "\n\n\t" ), div );
+	var text_7 = createText( "\n\n\t" );
+	appendNode( text_7, div );
 	var text_8 = createText( "\n\n" );
 	var if_block_4_anchor = createComment();
 
@@ -45,14 +44,14 @@ function create_main_fragment ( state, component ) {
 			insertNode( div, target, anchor );
 			insertNode( text_8, target, anchor );
 			insertNode( if_block_4_anchor, target, anchor );
-			if ( if_block_4 ) if_block_4.mount( target, if_block_4_anchor );
+			if ( if_block_4 ) if_block_4.mount( target, null );
 		},
 
 		update: function ( changed, state ) {
 			if ( state.a ) {
 				if ( !if_block ) {
 					if_block = create_if_block( state, component );
-					if_block.mount( if_block_anchor.parentNode, p );
+					if_block.mount( div, text );
 				}
 			} else if ( if_block ) {
 				if_block.destroy( true );
@@ -62,7 +61,7 @@ function create_main_fragment ( state, component ) {
 			if ( state.b ) {
 				if ( !if_block_1 ) {
 					if_block_1 = create_if_block_1( state, component );
-					if_block_1.mount( if_block_1_anchor.parentNode, if_block_1_anchor );
+					if_block_1.mount( div, text_3 );
 				}
 			} else if ( if_block_1 ) {
 				if_block_1.destroy( true );
@@ -72,7 +71,7 @@ function create_main_fragment ( state, component ) {
 			if ( state.c ) {
 				if ( !if_block_2 ) {
 					if_block_2 = create_if_block_2( state, component );
-					if_block_2.mount( if_block_2_anchor.parentNode, p_2 );
+					if_block_2.mount( div, text_4 );
 				}
 			} else if ( if_block_2 ) {
 				if_block_2.destroy( true );
@@ -82,7 +81,7 @@ function create_main_fragment ( state, component ) {
 			if ( state.d ) {
 				if ( !if_block_3 ) {
 					if_block_3 = create_if_block_3( state, component );
-					if_block_3.mount( if_block_3_anchor.parentNode, null );
+					if_block_3.mount( div, text_7 );
 				}
 			} else if ( if_block_3 ) {
 				if_block_3.destroy( true );

test/runtime/samples/if-block-widget/_config.js

@@ -2,11 +2,26 @@ export default {
 	data: {
 		visible: true
 	},
-	html: 'before\n<p>Widget</p><!---->\nafter',
+
+	html: `
+		before
+		<p>Widget</p>
+		after
+	`,
+
 	test ( assert, component, target ) {
 		component.set({ visible: false });
-		assert.equal( target.innerHTML, 'before\n<!---->\nafter' );
+		assert.htmlEqual( target.innerHTML, `
+			before
+
+			after
+		` );
+
 		component.set({ visible: true });
-		assert.equal( target.innerHTML, 'before\n<p>Widget</p><!---->\nafter' );
+		assert.htmlEqual( target.innerHTML, `
+			before
+			<p>Widget</p>
+			after
+		` );
 	}
 };