partial fix

packages/svelte/src/compiler/phases/1-parse/read/style.js

@@ -206,13 +206,15 @@ function read_selector(parser, inside_pseudo_class = false) {
 
 		if (combinator) {
 			if (relative_selector.selectors.length === 0) {
-				error(start, 'TODO', 'expected a selector');
+				if (!inside_pseudo_class) {
+					error(start, 'invalid-css-selector');
+				}
+			} else {
+				// flush previous relative selector...
+				relative_selector.end = start;
+				children.push(relative_selector);
 			}
 
-			// flush previous relative selector...
-			relative_selector.end = start;
-			children.push(relative_selector);
-
 			// ...and start a new one
 			relative_selector = {
 				type: 'RelativeSelector',
@@ -358,7 +360,7 @@ function read_selector(parser, inside_pseudo_class = false) {
 			parser.index = index;
 
 			if (relative_selector.selectors.length === 0) {
-				error(index, 'TODO', 'expected a selector');
+				error(index, 'invalid-css-selector');
 			}
 
 			// flush

packages/svelte/tests/validator/samples/css-invalid-combinator-selector-1/errors.json

@@ -2,7 +2,13 @@
 	{
 		"code": "invalid-css-selector",
 		"message": "Invalid selector",
-		"start": { "line": 10, "column": 1 },
-		"end": { "line": 10, "column": 7 }
+		"start": {
+			"line": 10,
+			"column": 1
+		},
+		"end": {
+			"line": 10,
+			"column": 1
+		}
 	}
 ]

packages/svelte/tests/validator/samples/css-invalid-combinator-selector-2/errors.json

@@ -2,7 +2,13 @@
 	{
 		"code": "invalid-css-selector",
 		"message": "Invalid selector",
-		"start": { "line": 8, "column": 1 },
-		"end": { "line": 8, "column": 4 }
+		"start": {
+			"line": 8,
+			"column": 1
+		},
+		"end": {
+			"line": 8,
+			"column": 1
+		}
 	}
 ]

packages/svelte/tests/validator/samples/css-invalid-combinator-selector-3/errors.json

@@ -2,7 +2,13 @@
 	{
 		"code": "invalid-css-selector",
 		"message": "Invalid selector",
-		"start": { "line": 5, "column": 2 },
-		"end": { "line": 5, "column": 8 }
+		"start": {
+			"line": 5,
+			"column": 2
+		},
+		"end": {
+			"line": 5,
+			"column": 2
+		}
 	}
 ]