From a2c68328a02790ddb024b4846f638b030a378795 Mon Sep 17 00:00:00 2001
From: Rich Harris <richard.a.harris@gmail.com>
Date: Tue, 4 Dec 2018 18:20:56 -0500
Subject: [PATCH] hoist declarations where possible

---
 src/compile/Component.ts        | 116 +++++++++++++++++++++++++++++++-
 src/utils/annotateWithScopes.ts |   2 +-
 src/utils/remove_indentation.ts |  33 +++++++++
 3 files changed, 149 insertions(+), 2 deletions(-)
 create mode 100644 src/utils/remove_indentation.ts

diff --git a/src/compile/Component.ts b/src/compile/Component.ts
index c0c0d321b1..de43f13646 100644
--- a/src/compile/Component.ts
+++ b/src/compile/Component.ts
@@ -19,6 +19,7 @@ import addToSet from '../utils/addToSet';
 import isReference from 'is-reference';
 import TemplateScope from './nodes/shared/TemplateScope';
 import fuzzymatch from '../utils/fuzzymatch';
+import { remove_indentation } from '../utils/remove_indentation';
 
 type Meta = {
 	namespace?: string;
@@ -74,6 +75,8 @@ export default class Component {
 	props: Array<{ name: string, as: string }> = [];
 	writable_declarations: Set<string> = new Set();
 	initialised_declarations: Set<string> = new Set();
+	hoistable_names: Set<string> = new Set();
+	hoistable_nodes: Set<Node> = new Set();
 	node_for_declaration: Map<string, Node> = new Map();
 	module_exports: Array<{ name: string, as: string }> = [];
 	partly_hoisted: string[] = [];
@@ -479,13 +482,26 @@ export default class Component {
 	}
 
 	extract_javascript(script) {
+		if (script.content.body.length === this.hoistable_nodes.size) return null;
+
 		let a = script.content.start;
 		while (/\s/.test(this.source[a])) a += 1;
 
+		let result = '';
+
+		script.content.body.forEach(node => {
+			if (this.hoistable_nodes.has(node)) {
+				result += `[✂${a}-${node.start}✂]/* HOISTED */`;
+				a = node.end;
+			}
+		});
+
 		let b = script.content.end;
 		while (/\s/.test(this.source[b - 1])) b -= 1;
 
-		return a !== b ? `[✂${a}-${b}✂]` : null;
+		if (a !== b) result += `[✂${a}-${b}✂]`;
+
+		return result || null;
 	}
 
 	walk_module_js() {
@@ -529,6 +545,7 @@ export default class Component {
 
 		this.extract_imports_and_exports(script.content, this.imports, this.props);
 		this.rewrite_props();
+		this.hoist_instance_declarations();
 		this.javascript = this.extract_javascript(script);
 	}
 
@@ -637,6 +654,103 @@ export default class Component {
 		});
 	}
 
+	hoist_instance_declarations() {
+		// we can safely hoist `const` declarations that are
+		// initialised to literals, and functions that don't
+		// reference instance variables other than other
+		// hoistable functions. TODO others?
+
+		const { hoistable_names, hoistable_nodes } = this;
+
+		const top_level_function_declarations = new Map();
+
+		this.instance_script.content.body.forEach(node => {
+			if (node.kind === 'const') { // TODO or let or var, if never reassigned in <script> or template
+				if (node.declarations.every(d => d.init.type === 'Literal')) {
+					node.declarations.forEach(d => {
+						hoistable_names.add(d.id.name);
+					});
+
+					hoistable_nodes.add(node);
+				}
+			}
+
+			if (node.type === 'FunctionDeclaration') {
+				top_level_function_declarations.set(node.id.name, node);
+			}
+		});
+
+		const checked = new Set();
+		let walking = new Set();
+
+		const is_hoistable = fn_declaration => {
+			const instance_scope = this.instance_scope;
+			let scope = this.instance_scope;
+			let map = this.instance_scope_map;
+
+			let hoistable = true;
+
+			// handle cycles
+			walking.add(fn_declaration);
+
+			walk(fn_declaration, {
+				enter(node, parent) {
+					if (map.has(node)) {
+						scope = map.get(node);
+					}
+
+					if (isReference(node, parent)) {
+						const { name } = flattenReference(node);
+						const owner = scope.findOwner(name);
+
+						if (owner === instance_scope) {
+							if (name === fn_declaration.id.name) return;
+							if (hoistable_names.has(name)) return;
+
+							if (top_level_function_declarations.has(name)) {
+								const other_declaration = top_level_function_declarations.get(name);
+
+								if (walking.has(other_declaration)) {
+									hoistable = false;
+								} else if (!is_hoistable(other_declaration)) {
+									hoistable = false;
+								}
+							}
+
+							else {
+								hoistable = false;
+							}
+						}
+
+						this.skip();
+					}
+				},
+
+				leave(node) {
+					if (map.has(node)) {
+						scope = scope.parent;
+					}
+				}
+			});
+
+			checked.add(fn_declaration);
+			walking.delete(fn_declaration);
+
+			return hoistable;
+		};
+
+		for (const [name, node] of top_level_function_declarations) {
+			if (!checked.has(node) && is_hoistable(node)) {
+				hoistable_names.add(name);
+				hoistable_nodes.add(node);
+
+				remove_indentation(this.code, node);
+
+				this.fully_hoisted.push(`[✂${node.start}-${node.end}✂]`);
+			}
+		}
+	}
+
 	warn_if_undefined(node, template_scope: TemplateScope) {
 		const { name } = node;
 		if (this.module_scope && this.module_scope.declarations.has(name)) return;
diff --git a/src/utils/annotateWithScopes.ts b/src/utils/annotateWithScopes.ts
index 602e9c3cad..0ea4f60068 100644
--- a/src/utils/annotateWithScopes.ts
+++ b/src/utils/annotateWithScopes.ts
@@ -69,7 +69,7 @@ export class Scope {
 	}
 
 	addDeclaration(node: Node) {
-		if (node.kind === 'var' && !this.block && this.parent) {
+		if (node.kind === 'var' && this.block && this.parent) {
 			this.parent.addDeclaration(node);
 		} else if (node.type === 'VariableDeclaration') {
 			const writable = node.kind !== 'const';
diff --git a/src/utils/remove_indentation.ts b/src/utils/remove_indentation.ts
new file mode 100644
index 0000000000..7afa2d5260
--- /dev/null
+++ b/src/utils/remove_indentation.ts
@@ -0,0 +1,33 @@
+import MagicString from 'magic-string';
+import { Node } from '../interfaces';
+import { walk } from 'estree-walker';
+
+export function remove_indentation(code: MagicString, node: Node) {
+	const indent = code.getIndentString();
+	const pattern = new RegExp(`^${indent}`, 'gm');
+
+	const excluded = [];
+
+	walk(node, {
+		enter(node) {
+			if (node.type === 'TemplateElement') {
+				excluded.push(node);
+			}
+		}
+	});
+
+	let dirty = false;
+
+	const str = code.original
+		.slice(node.start, node.end)
+		.replace(pattern, (match, i) => {
+			const index = node.start + i;
+			while (excluded[0] && excluded[0].end < index) excluded.shift();
+			if (excluded[0] && excluded[0].start < index) return match;
+
+			dirty = true;
+			return '';
+		});
+
+	if (dirty) code.overwrite(node.start, node.end, str);
+}
\ No newline at end of file