chore: more specific typings, and add README note about Yarn (#4483)

README.md

@@ -32,6 +32,8 @@ cd svelte
 npm install
 ```
 
+> Do not use Yarn to install the dependencies, as the specific package versions in `package-lock.json` are used to build and test Svelte.
+
 > Many tests depend on newlines being preserved as `<LF>`. On Windows, you can ensure this by cloning with:
 > ```bash
 > git -c core.autocrlf=false clone https://github.com/sveltejs/svelte.git

src/compiler/compile/Component.ts

@@ -239,7 +239,7 @@ export default class Component {
 			const program: any = { type: 'Program', body: result.js };
 
 			walk(program, {
-				enter: (node, parent, key) => {
+				enter: (node: Node, parent: Node, key) => {
 					if (node.type === 'Identifier') {
 						if (node.name[0] === '@') {
 							if (node.name[1] === '_') {
@@ -526,7 +526,7 @@ export default class Component {
 		if (!script) return;
 
 		walk(script.content, {
-			enter(node) {
+			enter(node: Node) {
 				if (node.type === 'LabeledStatement' && node.label.name === '$') {
 					component.warn(node as any, {
 						code: 'module-script-reactive-declaration',
@@ -715,7 +715,7 @@ export default class Component {
 		let scope_updated = false;
 
 		walk(content, {
-			enter(node, parent, prop, index) {
+			enter(node: Node, parent, prop, index) {
 				if (map.has(node)) {
 					scope = map.get(node);
 				}
@@ -741,7 +741,7 @@ export default class Component {
 				component.warn_on_undefined_store_value_references(node, parent, scope);
 			},
 
-			leave(node) {
+			leave(node: Node) {
 				// do it on leave, to prevent infinite loop
 				if (component.compile_options.dev && component.compile_options.loopGuardTimeout > 0) {
 					const to_replace_for_loop_protect = component.loop_protect(node, scope, component.compile_options.loopGuardTimeout);
@@ -785,7 +785,7 @@ export default class Component {
 		let scope = instance_scope;
 
 		walk(content, {
-			enter(node, parent) {
+			enter(node: Node, parent: Node) {
 				if (map.has(node)) {
 					scope = map.get(node);
 				}
@@ -818,7 +818,7 @@ export default class Component {
 				}
 			},
 
-			leave(node) {
+			leave(node: Node) {
 				if (map.has(node)) {
 					scope = scope.parent;
 				}
@@ -886,7 +886,7 @@ export default class Component {
 		let scope = instance_scope;
 
 		walk(this.ast.instance.content, {
-			enter(node, parent, key, index) {
+			enter(node: Node, parent, key, index) {
 				if (/Function/.test(node.type)) {
 					return this.skip();
 				}
@@ -963,7 +963,7 @@ export default class Component {
 				}
 			},
 
-			leave(node, parent, _key, index) {
+			leave(node: Node, parent, _key, index) {
 				if (map.has(node)) {
 					scope = scope.parent;
 				}
@@ -1064,7 +1064,7 @@ export default class Component {
 			walking.add(fn_declaration);
 
 			walk(fn_declaration, {
-				enter(node, parent) {
+				enter(node: Node, parent) {
 					if (!hoistable) return this.skip();
 
 					if (map.has(node)) {
@@ -1112,7 +1112,7 @@ export default class Component {
 					}
 				},
 
-				leave(node) {
+				leave(node: Node) {
 					if (map.has(node)) {
 						scope = scope.parent;
 					}
@@ -1155,7 +1155,7 @@ export default class Component {
 				const map = this.instance_scope_map;
 
 				walk(node.body, {
-					enter(node, parent) {
+					enter(node: Node, parent) {
 						if (map.has(node)) {
 							scope = map.get(node);
 						}
@@ -1195,7 +1195,7 @@ export default class Component {
 						}
 					},
 
-					leave(node) {
+					leave(node: Node) {
 						if (map.has(node)) {
 							scope = scope.parent;
 						}

src/compiler/compile/nodes/Let.ts

@@ -1,7 +1,7 @@
 import Node from './shared/Node';
 import Component from '../Component';
 import { walk } from 'estree-walker';
-import { Identifier } from 'estree';
+import { BasePattern, Identifier } from 'estree';
 
 const applicable = new Set(['Identifier', 'ObjectExpression', 'ArrayExpression', 'Property']);
 
@@ -22,7 +22,7 @@ export default class Let extends Node {
 			this.value = info.expression;
 
 			walk(info.expression, {
-				enter(node) {
+				enter(node: Identifier|BasePattern) {
 					if (!applicable.has(node.type)) {
 						component.error(node as any, {
 							code: 'invalid-let',
@@ -31,16 +31,16 @@ export default class Let extends Node {
 					}
 
 					if (node.type === 'Identifier') {
-						names.push(node.name);
+						names.push((node as Identifier).name);
 					}
 
 					// slightly unfortunate hack
 					if (node.type === 'ArrayExpression') {
-						(node as any).type = 'ArrayPattern';
+						node.type = 'ArrayPattern';
 					}
 
 					if (node.type === 'ObjectExpression') {
-						(node as any).type = 'ObjectPattern';
+						node.type = 'ObjectPattern';
 					}
 				}
 			});

src/compiler/compile/nodes/shared/Expression.ts

@@ -143,7 +143,7 @@ export default class Expression {
 				}
 			},
 
-			leave(node) {
+			leave(node: Node) {
 				if (map.has(node)) {
 					scope = scope.parent;
 				}
@@ -338,7 +338,7 @@ export default class Expression {
 			});
 		}
 
-		return (this.manipulated = node);
+		return (this.manipulated = node as Node);
 	}
 }
 

src/compiler/compile/render_dom/index.ts

@@ -200,7 +200,7 @@ export default function dom(
 		let execution_context: Node | null = null;
 
 		walk(component.ast.instance.content, {
-			enter(node) {
+			enter(node: Node) {
 				if (map.has(node)) {
 					scope = map.get(node) as Scope;
 
@@ -212,7 +212,7 @@ export default function dom(
 				}
 			},
 
-			leave(node) {
+			leave(node: Node) {
 				if (map.has(node)) {
 					scope = scope.parent;
 				}