Repository: sveltejs/svelte (JavaScript)
Date: 2018-05-02 01:43:05+00:00
Task type: Bug Fix

Issue:
Literals in props should not be updated
In a case like [this](https://svelte.technology/repl?version=2.4.0&gist=37fdb194fd90bf5e3b19996cc10d5bd2)...

```html
<List items='{[1, 2, 3]}'/>
```

...`items` should never be updated, even if `<List>` had other properties that *were* being updated.


Issue discussion:
To clarify:

```diff
function create_main_fragment(component, ctx) {

	var list_initial_data = { items: [1, 2, 3] };
	var list = new List({
		root: component.root,
		data: list_initial_data
	});

	return {
		c: function create() {
			list._fragment.c();
		},

		m: function mount(target, anchor) {
			list._mount(target, anchor);
		},

+		p: noop,
-		p: function update(changed, ctx) {
-			var list_changes = {};
-			list_changes.items = [1, 2, 3];
-			list._set(list_changes);
-		},

		u: function unmount() {
			list._unmount();
		},

		d: function destroy() {
			list.destroy(false);
		}
	};
}
```

Solution patch:
diff --git a/src/compile/nodes/Attribute.ts b/src/compile/nodes/Attribute.ts
--- a/src/compile/nodes/Attribute.ts
+++ b/src/compile/nodes/Attribute.ts
@@ -66,11 +66,7 @@ export default class Attribute extends Node {
 					return expression;
 				});
 
-			// TODO this would be better, but it breaks some stuff
-			// this.isDynamic = this.dependencies.size > 0;
-			this.isDynamic = this.chunks.length === 1
-				? this.chunks[0].type !== 'Text'
-				: this.chunks.length > 1;
+			this.isDynamic = this.dependencies.size > 0;
 
 			this.shouldCache = this.isDynamic
 				? this.chunks.length === 1
@@ -82,7 +78,7 @@ export default class Attribute extends Node {
 
 	getValue() {
 		if (this.isTrue) return true;
-		if (this.chunks.length === 0) return `''`;
+		if (this.chunks.length === 0) return `""`;
 
 		if (this.chunks.length === 1) {
 			return this.chunks[0].type === 'Text'
@@ -252,9 +248,7 @@ export default class Attribute extends Node {
 				);
 			}
 		} else {
-			const value = this.isTrue
-				? 'true'
-				: this.chunks.length === 0 ? `""` : stringify(this.chunks[0].data);
+			const value = this.getValue();
 
 			const statement = (
 				isLegacyInputType
diff --git a/src/compile/nodes/Component.ts b/src/compile/nodes/Component.ts
--- a/src/compile/nodes/Component.ts
+++ b/src/compile/nodes/Component.ts
@@ -209,12 +209,6 @@ export default class Component extends Node {
 									.join(' || ')}) ${name_changes}.${attribute.name} = ${attribute.getValue()};
 							`);
 						}
-
-						else {
-							// TODO this is an odd situation to encounter – I *think* it should only happen with
-							// each block indices, in which case it may be possible to optimise this
-							updates.push(`${name_changes}.${attribute.name} = ${attribute.getValue()};`);
-						}
 					});
 				}
 		}


Test patch:
diff --git a/test/js/samples/component-static-array/expected-bundle.js b/test/js/samples/component-static-array/expected-bundle.js
new file mode 100644
--- /dev/null
+++ b/test/js/samples/component-static-array/expected-bundle.js
@@ -0,0 +1,183 @@
+function noop() {}
+
+function assign(tar, src) {
+	for (var k in src) tar[k] = src[k];
+	return tar;
+}
+
+function blankObject() {
+	return Object.create(null);
+}
+
+function destroy(detach) {
+	this.destroy = noop;
+	this.fire('destroy');
+	this.set = noop;
+
+	if (detach !== false) this._fragment.u();
+	this._fragment.d();
+	this._fragment = null;
+	this._state = {};
+}
+
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+}
+
+function fire(eventName, data) {
+	var handlers =
+		eventName in this._handlers && this._handlers[eventName].slice();
+	if (!handlers) return;
+
+	for (var i = 0; i < handlers.length; i += 1) {
+		var handler = handlers[i];
+
+		if (!handler.__calling) {
+			handler.__calling = true;
+			handler.call(this, data);
+			handler.__calling = false;
+		}
+	}
+}
+
+function get() {
+	return this._state;
+}
+
+function init(component, options) {
+	component._handlers = blankObject();
+	component._bind = options._bind;
+
+	component.options = options;
+	component.root = options.root || component;
+	component.store = component.root.store || options.store;
+}
+
+function on(eventName, handler) {
+	var handlers = this._handlers[eventName] || (this._handlers[eventName] = []);
+	handlers.push(handler);
+
+	return {
+		cancel: function() {
+			var index = handlers.indexOf(handler);
+			if (~index) handlers.splice(index, 1);
+		}
+	};
+}
+
+function set(newState) {
+	this._set(assign({}, newState));
+	if (this.root._lock) return;
+	this.root._lock = true;
+	callAll(this.root._beforecreate);
+	callAll(this.root._oncreate);
+	callAll(this.root._aftercreate);
+	this.root._lock = false;
+}
+
+function _set(newState) {
+	var oldState = this._state,
+		changed = {},
+		dirty = false;
+
+	for (var key in newState) {
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
+	}
+	if (!dirty) return;
+
+	this._state = assign(assign({}, oldState), newState);
+	this._recompute(changed, this._state);
+	if (this._bind) this._bind(changed, this._state);
+
+	if (this._fragment) {
+		this.fire("state", { changed: changed, current: this._state, previous: oldState });
+		this._fragment.p(changed, this._state);
+		this.fire("update", { changed: changed, current: this._state, previous: oldState });
+	}
+}
+
+function callAll(fns) {
+	while (fns && fns.length) fns.shift()();
+}
+
+function _mount(target, anchor) {
+	this._fragment[this._fragment.i ? 'i' : 'm'](target, anchor || null);
+}
+
+function _unmount() {
+	if (this._fragment) this._fragment.u();
+}
+
+var proto = {
+	destroy,
+	get,
+	fire,
+	on,
+	set,
+	_recompute: noop,
+	_set,
+	_mount,
+	_unmount,
+	_differs
+};
+
+/* generated by Svelte vX.Y.Z */
+
+var Nested = window.Nested;
+
+function create_main_fragment(component, ctx) {
+
+	var nested_initial_data = { foo: [1, 2, 3] };
+	var nested = new Nested({
+		root: component.root,
+		data: nested_initial_data
+	});
+
+	return {
+		c() {
+			nested._fragment.c();
+		},
+
+		m(target, anchor) {
+			nested._mount(target, anchor);
+		},
+
+		p: noop,
+
+		u() {
+			nested._unmount();
+		},
+
+		d() {
+			nested.destroy(false);
+		}
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	this._state = assign({}, options.data);
+
+	if (!options.root) {
+		this._oncreate = [];
+		this._beforecreate = [];
+		this._aftercreate = [];
+	}
+
+	this._fragment = create_main_fragment(this, this._state);
+
+	if (options.target) {
+		this._fragment.c();
+		this._mount(options.target, options.anchor);
+
+		this._lock = true;
+		callAll(this._beforecreate);
+		callAll(this._oncreate);
+		callAll(this._aftercreate);
+		this._lock = false;
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+
+export default SvelteComponent;
diff --git a/test/js/samples/component-static-array/expected.js b/test/js/samples/component-static-array/expected.js
new file mode 100644
--- /dev/null
+++ b/test/js/samples/component-static-array/expected.js
@@ -0,0 +1,60 @@
+/* generated by Svelte vX.Y.Z */
+import { assign, callAll, init, noop, proto } from "svelte/shared.js";
+
+var Nested = window.Nested;
+
+function create_main_fragment(component, ctx) {
+
+	var nested_initial_data = { foo: [1, 2, 3] };
+	var nested = new Nested({
+		root: component.root,
+		data: nested_initial_data
+	});
+
+	return {
+		c() {
+			nested._fragment.c();
+		},
+
+		m(target, anchor) {
+			nested._mount(target, anchor);
+		},
+
+		p: noop,
+
+		u() {
+			nested._unmount();
+		},
+
+		d() {
+			nested.destroy(false);
+		}
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	this._state = assign({}, options.data);
+
+	if (!options.root) {
+		this._oncreate = [];
+		this._beforecreate = [];
+		this._aftercreate = [];
+	}
+
+	this._fragment = create_main_fragment(this, this._state);
+
+	if (options.target) {
+		this._fragment.c();
+		this._mount(options.target, options.anchor);
+
+		this._lock = true;
+		callAll(this._beforecreate);
+		callAll(this._oncreate);
+		callAll(this._aftercreate);
+		this._lock = false;
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+export default SvelteComponent;
\ No newline at end of file
diff --git a/test/js/samples/component-static-array/input.html b/test/js/samples/component-static-array/input.html
new file mode 100644
--- /dev/null
+++ b/test/js/samples/component-static-array/input.html
@@ -0,0 +1,9 @@
+<Nested foo={[1, 2, 3]}/>
+
+<script>
+	export default {
+		components: {
+			Nested: window.Nested
+		}
+	};
+</script>
\ No newline at end of file