From cedd98f9406abcc56610c5f85ce78d51d014e6a0 Mon Sep 17 00:00:00 2001
From: Tan Li Hau <lhtan93@gmail.com>
Date: Tue, 27 Jul 2021 22:23:58 +0800
Subject: [PATCH] fix do not warn about missing props for bindings

---
 src/compiler/compile/render_dom/index.ts           | 14 ++++++++------
 .../Foo.svelte                                     |  8 ++++++++
 .../_config.js                                     |  9 +++++++++
 .../main.svelte                                    |  8 ++++++++
 4 files changed, 33 insertions(+), 6 deletions(-)
 create mode 100644 test/runtime/samples/dev-warning-missing-data-component-bind/Foo.svelte
 create mode 100644 test/runtime/samples/dev-warning-missing-data-component-bind/_config.js
 create mode 100644 test/runtime/samples/dev-warning-missing-data-component-bind/main.svelte

diff --git a/src/compiler/compile/render_dom/index.ts b/src/compiler/compile/render_dom/index.ts
index 535983cfd08e..6a443019516d 100644
--- a/src/compiler/compile/render_dom/index.ts
+++ b/src/compiler/compile/render_dom/index.ts
@@ -180,12 +180,14 @@ export default function dom(
 
 		if (expected.length) {
 			dev_props_check = b`
-				const { ctx: #ctx } = this.$$;
-				const props = ${options.customElement ? x`this.attributes` : x`options.props || {}`};
-				${expected.map(prop => b`
-				if (${renderer.reference(prop.name)} === undefined && !('${prop.export_name}' in props)) {
-					@_console.warn("<${component.tag}> was created without expected prop '${prop.export_name}'");
-				}`)}
+				const { ctx: #ctx, on_mount: #on_mount, bound: #bound, props: #props } = this.$$;
+				#on_mount.push(function () {
+					const props = ${options.customElement ? x`this.attributes` : x`options.props || {}`};
+					${expected.map(prop => b`
+					if (${renderer.reference(prop.name)} === undefined && !('${prop.export_name}' in props || #bound[#props['${prop.export_name}']])) {
+						@_console.warn("<${component.tag}> was created without expected prop '${prop.export_name}'");
+					}`)}
+				});
 			`;
 		}
 
diff --git a/test/runtime/samples/dev-warning-missing-data-component-bind/Foo.svelte b/test/runtime/samples/dev-warning-missing-data-component-bind/Foo.svelte
new file mode 100644
index 000000000000..60278c4845e2
--- /dev/null
+++ b/test/runtime/samples/dev-warning-missing-data-component-bind/Foo.svelte
@@ -0,0 +1,8 @@
+<script>
+	export let w;
+	export let x;
+	export let y;
+	export let z = undefined;
+</script>
+
+<div>{w} {x} {y}</div>
\ No newline at end of file
diff --git a/test/runtime/samples/dev-warning-missing-data-component-bind/_config.js b/test/runtime/samples/dev-warning-missing-data-component-bind/_config.js
new file mode 100644
index 000000000000..ececa00a8c40
--- /dev/null
+++ b/test/runtime/samples/dev-warning-missing-data-component-bind/_config.js
@@ -0,0 +1,9 @@
+export default {
+	compileOptions: {
+		dev: true
+	},
+
+	warnings: [
+		"<Foo> was created without expected prop 'y'"
+	]
+};
diff --git a/test/runtime/samples/dev-warning-missing-data-component-bind/main.svelte b/test/runtime/samples/dev-warning-missing-data-component-bind/main.svelte
new file mode 100644
index 000000000000..eab3c8336fc7
--- /dev/null
+++ b/test/runtime/samples/dev-warning-missing-data-component-bind/main.svelte
@@ -0,0 +1,8 @@
+<script>
+	import Foo from './Foo.svelte';
+
+	let x = undefined;
+	let w = 'w';
+</script>
+
+<Foo bind:w bind:x />
\ No newline at end of file