From 65cdead99145232591d079a4305dee127d8eec44 Mon Sep 17 00:00:00 2001
From: Nico Rehwaldt <git_nikku@nixis.de>
Date: Sun, 4 Dec 2016 21:18:13 +0100
Subject: [PATCH] Verify computed property dependencies

Improves the validator to fail if someone forgets to declare
dependent properties for computed state:

```
export default {
  computed: {
    bar: () => { return new Date().getTime(); }
  }
};
```
---
 compiler/validate/js/propValidators/computed.js | 9 ++++++++-
 test/validator/computed-values/errors.json      | 8 ++++++++
 test/validator/computed-values/input.html       | 7 +++++++
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 test/validator/computed-values/errors.json
 create mode 100644 test/validator/computed-values/input.html

diff --git a/compiler/validate/js/propValidators/computed.js b/compiler/validate/js/propValidators/computed.js
index 102ce73333..00b10af00d 100644
--- a/compiler/validate/js/propValidators/computed.js
+++ b/compiler/validate/js/propValidators/computed.js
@@ -21,7 +21,14 @@ export default function computed ( validator, prop ) {
 			return;
 		}
 
-		computation.value.params.forEach( param => {
+		const params = computation.value.params;
+
+		if ( params.length === 0 ) {
+			validator.error( `A computed value must depend on at least one property`, computation.value.start );
+			return;
+		}
+
+		params.forEach( param => {
 			const valid = param.type === 'Identifier' || param.type === 'AssignmentPattern' && param.left.type === 'Identifier';
 
 			if ( !valid ) {
diff --git a/test/validator/computed-values/errors.json b/test/validator/computed-values/errors.json
new file mode 100644
index 0000000000..3f4994e790
--- /dev/null
+++ b/test/validator/computed-values/errors.json
@@ -0,0 +1,8 @@
+[{
+	"message": "A computed value must depend on at least one property",
+	"pos": 49,
+	"loc": {
+		"line": 4,
+		"column": 8
+	}
+}]
\ No newline at end of file
diff --git a/test/validator/computed-values/input.html b/test/validator/computed-values/input.html
new file mode 100644
index 0000000000..92cb29d732
--- /dev/null
+++ b/test/validator/computed-values/input.html
@@ -0,0 +1,7 @@
+<script>
+	export default {
+		computed: {
+			foo: () => {}
+		}
+	};
+</script>