allow setting files binding

Author: teemingc

documentation/docs/02-template-syntax/05-element-directives.md

@@ -121,7 +121,7 @@ Numeric input values are coerced; even though `input.value` is a string as far a
 <input type="range" bind:value={num} />
 ```
 
-On `<input>` elements with `type="file"`, you can use `bind:files` to get the [`FileList` of selected files](https://developer.mozilla.org/en-US/docs/Web/API/FileList). It is readonly.
+On `<input>` elements with `type="file"`, you can use `bind:files` to get the [`FileList` of selected files](https://developer.mozilla.org/en-US/docs/Web/API/FileList).
 
 ```svelte
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packages/svelte/src/compiler/compile/nodes/Binding.js

@@ -94,13 +94,12 @@ export default class Binding extends Node {
 				return;
 			}
 		}
-		const type = parent.get_static_attribute_value('type');
 		this.is_readonly =
 			regex_dimensions.test(this.name) ||
 			regex_box_size.test(this.name) ||
 			(isElement(parent) &&
-				((parent.is_media_node() && read_only_media_attributes.has(this.name)) ||
-					(parent.name === 'input' && type === 'file'))) /* TODO others? */;
+				parent.is_media_node() &&
+				read_only_media_attributes.has(this.name)) /* TODO others? */;
 	}
 	is_readonly_media_attribute() {
 		return read_only_media_attributes.has(this.name);

packages/svelte/src/compiler/compile/render_ssr/handlers/Element.js

@@ -176,6 +176,15 @@ export default function (node, renderer, options) {
 			node_contents = x`@escape(${snippet} || "")`;
 		} else if (binding.name === 'value' && node.name === 'select') {
 			// NOTE: do not add "value" attribute on <select />
+		} else if (
+			binding.name === 'value' &&
+			node.name === 'input' &&
+			node.get_static_attribute_value('type') === 'file'
+		) {
+			const value = node.get_static_attribute_value('value');
+			if (value !== '') {
+				// NOTE: do not add "value" attribute on <input type="file" />
+			}
 		} else {
 			const snippet = expression.node;
 			renderer.add_expression(

packages/svelte/test/js/samples/bindings-readonly-order/expected.js

@@ -30,8 +30,10 @@ function create_fragment(ctx) {
 		},
 		m(target, anchor) {
 			insert(target, input0, anchor);
+			input0.files = /*files*/ ctx[0];
 			insert(target, t, anchor);
 			insert(target, input1, anchor);
+			input1.files = /*files*/ ctx[0];
 
 			if (!mounted) {
 				dispose = [
@@ -42,7 +44,15 @@ function create_fragment(ctx) {
 				mounted = true;
 			}
 		},
-		p: noop,
+		p(ctx, [dirty]) {
+			if (dirty & /*files*/ 1) {
+				input0.files = /*files*/ ctx[0];
+			}
+
+			if (dirty & /*files*/ 1) {
+				input1.files = /*files*/ ctx[0];
+			}
+		},
 		i: noop,
 		o: noop,
 		d(detaching) {

packages/svelte/test/js/samples/input-files/expected.js

@@ -24,13 +24,18 @@ function create_fragment(ctx) {
 		},
 		m(target, anchor) {
 			insert(target, input, anchor);
+			input.files = /*files*/ ctx[0];
 
 			if (!mounted) {
 				dispose = listen(input, "change", /*input_change_handler*/ ctx[1]);
 				mounted = true;
 			}
 		},
-		p: noop,
+		p(ctx, [dirty]) {
+			if (dirty & /*files*/ 1) {
+				input.files = /*files*/ ctx[0];
+			}
+		},
 		i: noop,
 		o: noop,
 		d(detaching) {