disallow global references to $$-prefixed vars

src/compiler/compile/Component.ts

@@ -679,10 +679,10 @@ export default class Component {
 					injected: true
 				});
 			} else if (name[0] === '$') {
-				if (name === '$') {
+				if (name === '$' || name[1] === '$') {
 					this.error(node, {
 						code: 'illegal-global',
-						message: 'The $ sign is an illegal variable name'
+						message: `${name} is an illegal variable name`
 					});
 				}
 
@@ -1242,16 +1242,18 @@ export default class Component {
 
 	warn_if_undefined(name: string, node, template_scope: TemplateScope) {
 		if (name[0] === '$') {
-			name = name.slice(1);
+			if (name === '$' || name[1] === '$' && name !== '$$props') {
-			this.has_reactive_assignments = true; // TODO does this belong here?
-
-			if (name[0] === '$') return; // $$props
-			if (name === '') {
 				this.error(node, {
 					code: 'illegal-global',
-					message: 'The $ sign is an illegal variable name'
+					message: `${name} is an illegal variable name`
 				});
 			}
+
+			this.has_reactive_assignments = true; // TODO does this belong here?
+
+			if (name === '$$props') return;
+
+			name = name.slice(1);
 		}
 
 		if (this.var_lookup.has(name) && !this.var_lookup.get(name).global) return;

test/validator/samples/dollar-dollar-global-in-markup/errors.json

@@ -0,0 +1,15 @@
+[{
+	"code": "illegal-global",
+	"message": "$$billsyall is an illegal variable name",
+	"pos": 1,
+	"start": {
+		"line": 1,
+		"column": 1,
+		"character": 1
+	},
+	"end": {
+		"line": 1,
+		"column": 12,
+		"character": 12
+	}
+}]

test/validator/samples/dollar-dollar-global-in-markup/input.svelte

@@ -0,0 +1 @@
+{$$billsyall}

test/validator/samples/dollar-dollar-global-in-script/errors.json

@@ -0,0 +1,15 @@
+[{
+	"code": "illegal-global",
+	"message": "$$billsyall is an illegal variable name",
+	"pos": 10,
+	"start": {
+		"line": 2,
+		"column": 1,
+		"character": 10
+	},
+	"end": {
+		"line": 2,
+		"column": 12,
+		"character": 21
+	}
+}]

test/validator/samples/dollar-dollar-global-in-script/input.svelte

@@ -0,0 +1,3 @@
+<script>
+	$$billsyall;
+</script>

test/validator/samples/dollar-global-in-markup/errors.json

@@ -1,6 +1,6 @@
 [{
 	"code": "illegal-global",
-	"message": "The $ sign is an illegal variable name",
+	"message": "$ is an illegal variable name",
 	"pos": 1,
 	"start": {
 		"line": 1,

test/validator/samples/dollar-global-in-script/errors.json

@@ -1,6 +1,6 @@
 [{
 	"code": "illegal-global",
-	"message": "The $ sign is an illegal variable name",
+	"message": "$ is an illegal variable name",
 	"pos": 10,
 	"start": {
 		"line": 2,