optimize generated code for if statements

Instead of walking elseif statements recursively, collect all the
conditions and blocks into a single if block

compiler/generate/visitors/ElseBlock.js

@@ -1,23 +0,0 @@
-import counter from '../utils/counter.js';
-
-export default {
-	enter ( generator ) {
-		const name = generator.current.name.replace( 'If', 'Else' );
-
-		generator.push({
-			name,
-			localElementDepth: 0,
-
-			initStatements: [],
-			updateStatements: [],
-			teardownStatements: [],
-
-			counter: counter()
-		});
-	},
-
-	leave ( generator ) {
-		generator.addRenderer( generator.current );
-		generator.pop();
-	}
-};

compiler/generate/visitors/IfBlock.js

@@ -1,125 +1,99 @@
 import deindent from '../utils/deindent.js';
 import counter from '../utils/counter.js';
 
+// collect all the conditions and blocks in the if/elseif/else chain
+function generateBlock ( generator, node, name ) {
+	// walk the children here
+	generator.push({
+		useAnchor: true,
+		name,
+		target: 'target',
+		localElementDepth: 0,
+
+		initStatements: [],
+		updateStatements: [],
+		teardownStatements: [],
+
+		counter: counter()
+	});
+	node.children.forEach( generator.visit );
+	//generator.visit( node.children );
+	generator.addRenderer( generator.current );
+	generator.pop();
+	// unset the children, to avoid them being visited again
+	node.children = [];
+}
+function getConditionsAndBlocks ( generator, node, _name, i = 0 ) {
+	generator.addSourcemapLocations( node.expression );
+	const name = `${_name}_${i}`;
+
+	const conditionsAndBlocks = [{
+		condition: generator.contextualise( node.expression ).snippet,
+		block: name
+	}];
+	generateBlock( generator, node, name );
+
+	if ( node.else && node.else.children.length === 1 &&
+		node.else.children[0].type === 'IfBlock' ) {
+		conditionsAndBlocks.push(
+			...getConditionsAndBlocks( generator, node.else.children[0], _name, i + 1 ) );
+	} else {
+		const name = `${_name}_${i + 1}`;
+		conditionsAndBlocks.push({
+			condition: null,
+			block: node.else ? name : null,
+		});
+		if (node.else) {
+			generateBlock( generator, node.else, name );
+		}
+	}
+	return conditionsAndBlocks;
+}
+
 export default {
 	enter ( generator, node ) {
 		const i = generator.counters.if++;
-		const name = `ifBlock_${i}`;
-		const renderer = `renderIfBlock_${i}`;
 
-		const elseName = `elseBlock_${i}`;
-		const elseRenderer = `renderElseBlock_${i}`;
+		const { params, target } = generator.current;
+		const name = `ifBlock_${i}`;
+		const getBlock = `getBlock_${i}`;
+		const currentBlock = `currentBlock_${i}`;
 
-		generator.addSourcemapLocations( node.expression );
-		const { snippet } = generator.contextualise( node.expression );
+		const conditionsAndBlocks = getConditionsAndBlocks( generator, node, `renderIfBlock_${i}` );
 
 		generator.current.initStatements.push( deindent`
 			var ${name}_anchor = document.createComment( ${JSON.stringify( `#if ${generator.source.slice( node.expression.start, node.expression.end )}` )} );
 			${generator.appendToTarget( `${name}_anchor` )};
-		` );
 
-		if ( node.else ) {
-			generator.current.initStatements.push( deindent`
-				var ${name} = null;
-				var ${elseName} = null;
-
-				if ( ${snippet} ) {
-					${name} = ${renderer}( ${generator.current.params}, component, ${generator.current.target}, ${name}_anchor );
-				} else {
-					${elseName} = ${elseRenderer}( ${generator.current.params}, component, ${generator.current.target}, ${name}_anchor );
-				}
-			` );
-		} else {
-			generator.current.initStatements.push( deindent`
-				var ${name} = ${snippet} ? ${renderer}( ${generator.current.params}, component, ${generator.current.target}, ${name}_anchor ) : null;
-			` );
-		}
-
-		const ifTrue = [ deindent`
-			if ( !${name } ) {
-				${name} = ${renderer}( ${generator.current.params}, component, ${generator.current.target}, ${name}_anchor );
-			} else {
-				${name}.update( changed, ${generator.current.params} );
-			}
-		` ];
-
-		if ( node.else ) {
-			ifTrue.push( deindent`
-				if ( ${elseName } ) {
-					${elseName}.teardown( true );
-					${elseName} = null;
-				}
-			` );
-		}
-
-		const ifFalse = [ deindent`
-			if ( ${name} ) {
-				${name}.teardown( true );
-				${name} = null;
+			function ${getBlock} ( ${params} ) {
+				${conditionsAndBlocks.map( ({ condition, block }) => {
+					return `${condition ? `if ( ${condition} ) ` : ''}return ${block};`;
+				} ).join( '\n' )}
 			}
-		` ];
-
-		if ( node.else ) {
-			ifFalse.push( deindent`
-				if ( !${elseName } ) {
-					${elseName} = ${elseRenderer}( ${generator.current.params}, component, ${generator.current.target}, ${name}_anchor );
-				} else {
-					${elseName}.update( changed, ${generator.current.params} );
-				}
-			` );
-		}
 
-		let update = deindent`
-			if ( ${snippet} ) {
-				${ifTrue.join( '\n\n' )}
-			}
+			var ${currentBlock} = ${getBlock}( ${params} );
+			var ${name} = ${currentBlock} && ${currentBlock}( ${params}, component, ${target}, ${name}_anchor );
+		` );
 
-			else {
-				${ifFalse.join( '\n\n' )}
+		generator.current.updateStatements.push( deindent`
+			var _${currentBlock} = ${currentBlock};
+			${currentBlock} = ${getBlock}( ${params} );
+			if ( _${currentBlock} === ${currentBlock} && ${name}) {
+				${name}.update( changed, ${params} );
+			} else {
+				if ( ${name} ) ${name}.teardown( true );
+				${name} = ${currentBlock} && ${currentBlock}( ${params}, component, ${target}, ${name}_anchor );
 			}
-		`;
-
-		if ( node.else ) {
-			update += `\nif ( ${elseName} ) ${elseName}.update( changed, ${generator.current.params} );`;
-		}
-
-		generator.current.updateStatements.push( update );
+		` );
 
 		const teardownStatements = [
 			`if ( ${name} ) ${name}.teardown( detach );`
 		];
 
-		if ( node.else ) {
-			teardownStatements.push( `if ( ${elseName} ) ${elseName}.teardown( detach );` );
-		}
-
 		if ( generator.current.localElementDepth === 0 ) {
 			teardownStatements.push( `if ( detach ) ${name}_anchor.parentNode.removeChild( ${name}_anchor );` );
 		}
 
 		generator.current.teardownStatements.push( teardownStatements.join( '\n' ) );
-
-		generator.push({
-			useAnchor: true,
-			name: renderer,
-			target: 'target',
-			localElementDepth: 0,
-
-			initStatements: [],
-			updateStatements: [],
-			teardownStatements: [],
-
-			counter: counter()
-		});
-	},
-
-	leave ( generator, node ) {
-		generator.addRenderer( generator.current );
-
-		if ( node.else ) {
-			generator.visit( node.else );
-		}
-
-		generator.pop();
 	}
 };

compiler/generate/visitors/index.js

@@ -1,7 +1,6 @@
 import Comment from './Comment.js';
 import EachBlock from './EachBlock.js';
 import Element from './Element.js';
-import ElseBlock from './ElseBlock.js';
 import IfBlock from './IfBlock.js';
 import MustacheTag from './MustacheTag.js';
 import Text from './Text.js';
@@ -10,7 +9,6 @@ export default {
 	Comment,
 	EachBlock,
 	Element,
-	ElseBlock,
 	IfBlock,
 	MustacheTag,
 	Text