From 98aba128e9f2a0fd72c0662c3d5623e12845ec52 Mon Sep 17 00:00:00 2001
From: Conduitry <git@chor.date>
Date: Sun, 9 Feb 2020 09:24:59 -0500
Subject: [PATCH] fix invalidation in ++foo.bar (#4395)

---
 CHANGELOG.md                                  |  1 +
 src/compiler/compile/render_dom/invalidate.ts |  2 +-
 .../_config.js                                | 31 +++++++++++++++++++
 .../main.svelte                               | 14 +++++++++
 4 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 test/runtime/samples/instrumentation-update-expression/_config.js
 create mode 100644 test/runtime/samples/instrumentation-update-expression/main.svelte

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 16e6484ab31f..ee84f7b79927 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@
 * Permit reserved keywords as destructuring keys in `{#each}` ([#4372](https://github.com/sveltejs/svelte/issues/4372))
 * Disallow reserved keywords in `{expressions}` ([#4372](https://github.com/sveltejs/svelte/issues/4372))
 * Fix code generation error with precedence of arrow functions ([#4384](https://github.com/sveltejs/svelte/issues/4384))
+* Fix invalidation in expressions like `++foo.bar` ([#4393](https://github.com/sveltejs/svelte/issues/4393))
 
 ## 3.18.1
 
diff --git a/src/compiler/compile/render_dom/invalidate.ts b/src/compiler/compile/render_dom/invalidate.ts
index dc2850186339..20aff05d1e19 100644
--- a/src/compiler/compile/render_dom/invalidate.ts
+++ b/src/compiler/compile/render_dom/invalidate.ts
@@ -49,7 +49,7 @@ export function invalidate(renderer: Renderer, scope: Scope, node: Node, names:
 			const pass_value = (
 				extra_args.length > 0 ||
 				(node.type === 'AssignmentExpression' && node.left.type !== 'Identifier') ||
-				(node.type === 'UpdateExpression' && !node.prefix)
+				(node.type === 'UpdateExpression' && (!node.prefix || node.argument.type !== 'Identifier'))
 			);
 
 			if (pass_value) {
diff --git a/test/runtime/samples/instrumentation-update-expression/_config.js b/test/runtime/samples/instrumentation-update-expression/_config.js
new file mode 100644
index 000000000000..cc33422f6fb4
--- /dev/null
+++ b/test/runtime/samples/instrumentation-update-expression/_config.js
@@ -0,0 +1,31 @@
+export default {
+	html: `
+		<p>0</p>
+		<button>foo++</button>
+		<button>++foo</button>
+		<p>0</p>
+		<button>bar.bar++</button>
+		<button>++bar.bar</button>
+	`,
+	async test({ assert, target, window }) {
+		const [foo, bar] = target.querySelectorAll('p');
+		const [button1, button2, button3, button4] = target.querySelectorAll('button');
+		const event = new window.MouseEvent('click');
+
+		await button1.dispatchEvent(event);
+		assert.equal(foo.innerHTML, '1');
+		assert.equal(bar.innerHTML, '0');
+
+		await button2.dispatchEvent(event);
+		assert.equal(foo.innerHTML, '2');
+		assert.equal(bar.innerHTML, '0');
+
+		await button3.dispatchEvent(event);
+		assert.equal(foo.innerHTML, '2');
+		assert.equal(bar.innerHTML, '1');
+
+		await button4.dispatchEvent(event);
+		assert.equal(foo.innerHTML, '2');
+		assert.equal(bar.innerHTML, '2');
+	}
+};
diff --git a/test/runtime/samples/instrumentation-update-expression/main.svelte b/test/runtime/samples/instrumentation-update-expression/main.svelte
new file mode 100644
index 000000000000..0672f6330d83
--- /dev/null
+++ b/test/runtime/samples/instrumentation-update-expression/main.svelte
@@ -0,0 +1,14 @@
+<script>
+	let foo = 0;
+	let bar = { bar: 0 };
+</script>
+
+<p>{foo}</p>
+
+<button on:click={() => foo++}>foo++</button>
+<button on:click={() => ++foo}>++foo</button>
+
+<p>{bar.bar}</p>
+
+<button on:click={() => bar.bar++}>bar.bar++</button>
+<button on:click={() => ++bar.bar}>++bar.bar</button>