Got CSS combinator prefixes working

Excluding CSS type element selectors

closes sveltejs#9320
closes sveltejs#8587

CONTRIBUTING.md

@@ -100,7 +100,7 @@ Test samples are kept in `/test/xxx/samples` folder.
 > PREREQUISITE: Install chromium via playwright by running `pnpm playwright install chromium`
 
 1. To run test, run `pnpm test`.
-1. To run test for a specific feature, you can use the `-g` (aka `--grep`) option. For example, to only run test involving transitions, run `pnpm test -- -g transition`.
+1. To run test for a specific feature, you can use the `-t` (aka `--testNamePattern `) option. For example, to only run test involving transitions, run `pnpm test -- -t transistion`.
 
 ##### Running solo test
 

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

@@ -395,14 +395,21 @@ function read_declaration(parser) {
  * @returns {import('#compiler').Css.Declaration | import('#compiler').Css.Rule}
  */
 function read_declaration_or_rule(parser) {
-	// We will only allow css nesting using & selector for now
+	// We need to know if this is a rule or a declaration
+	// so we'll attempt to read an identifier first
+	// if we can't, we'll assume it's a rule
+	// This needs to change when we support type (element) selectors
 	// due to complexities with https://bugs.chromium.org/p/chromium/issues/detail?id=1427259
-	// as most browsers as of 17/11/2023 do not support nesting without & selector
-	if (parser.match('&')) {
-		return read_rule(parser, true)
-	} else {
-		return read_declaration(parser);
+	const start = parser.index;
+	const is_ident = !!parser.read(REGEX_VALID_IDENTIFIER_CHAR);
+
+	parser.index = start;
+
+	if (!is_ident) {
+		return read_rule(parser, true);
 	}
+
+	return read_declaration(parser);
 }
 
 /**

packages/svelte/src/compiler/phases/2-analyze/css/Selector.js

@@ -321,6 +321,16 @@ function block_might_apply_to_node(block, node) {
 			return NO_MATCH;
 		}
 
+		if (
+			block.nested &&
+			block.selectors.length === 1 &&
+			block.combinator !== null
+		) {
+			// nested selector with combinator, eg: `.foo { + .bar { ... } }`
+			// TODO: How to handle this?
+			return UNKNOWN_SELECTOR;
+		}
+
 		if (selector.type === 'PseudoClassSelector' || selector.type === 'PseudoElementSelector') {
 			continue;
 		}
@@ -831,14 +841,17 @@ class Block {
 /**
  * Groups selectors by combinator into blocks
  * @param {import('#compiler').Css.Selector} selector
- * */
+ */
 function group_selectors(selector) {
 	let block = new Block(null);
 	const blocks = [block];
 
 	for (const child of selector.children) {
 		if (child.type === 'Combinator') {
-			if (block.nested && !block.combinator) {
+			// If we start with a combinator, that means
+			// we're dealing with a nested selector
+			if(block.selectors.length === 0 && !block.combinator) {
+				block.nested = true;
 				block.combinator = child;
 			} else {
 				block = new Block(child);

packages/svelte/tests/css/samples/nested-css-adjacent-combinator/expected.css

@@ -0,0 +1,9 @@
+button.svelte-xyz {
+    color: red;
+
+    + .abc.svelte-xyz {
+        color: purple;
+    }
+
+    color: black;
+}

packages/svelte/tests/css/samples/nested-css-adjacent-combinator/input.svelte

@@ -0,0 +1,17 @@
+<button>
+    <div class="foo"/>
+</button>
+<div class="abc">
+
+</div>
+<style>
+button {
+    color: red;
+
+    + .abc {
+        color: purple;
+    }
+
+    color: black;
+}
+</style>

packages/svelte/tests/css/samples/nested-css-child-combinator/expected.css

@@ -0,0 +1,9 @@
+button.svelte-xyz {
+    color: red;
+
+    > .abc.svelte-xyz {
+        color: purple;
+    }
+
+    color: black;
+}

packages/svelte/tests/css/samples/nested-css-child-combinator/input.svelte

@@ -0,0 +1,17 @@
+<button>
+    <div class="abc"/>
+    <div class="bar">
+        <div class="abc"/>
+    </div>
+</button>
+<style>
+button {
+    color: red;
+
+    > .abc {
+        color: purple;
+    }
+
+    color: black;
+}
+</style>

packages/svelte/tests/css/samples/nested-css-descendant-combinator/expected.css

@@ -0,0 +1,9 @@
+button.svelte-xyz {
+    color: red;
+
+    .hello.svelte-xyz {
+        color: pink;
+    }
+
+    color: black;
+}

packages/svelte/tests/css/samples/nested-css-descendant-combinator/input.svelte

@@ -0,0 +1,16 @@
+<button>
+    <div class="bar">
+        <div class="hello"/>
+    </div>
+</button>
+<style>
+button {
+    color: red;
+
+    .hello {
+        color: pink;
+    }
+
+    color: black;
+}
+</style>

packages/svelte/tests/css/samples/unknown-at-rule-with-following-rules/expected.css

@@ -1,5 +1,7 @@
 	div.svelte-xyz {
-		@apply --funky-div;
+		/* DISABLED THIS FOR CSS NESTING */
+		/* @apply --funky-div; */
+		color: red;
 	}
 
 	/* (empty) div.svelte-xyz {

packages/svelte/tests/css/samples/unknown-at-rule-with-following-rules/input.svelte

@@ -2,7 +2,9 @@
 
 <style>
 	div {
-		@apply --funky-div;
+		/* DISABLED THIS FOR CSS NESTING */
+		/* @apply --funky-div; */
+		color: red;
 	}
 
 	div {

packages/svelte/tests/css/samples/unknown-at-rule/expected.css

@@ -1,3 +1,5 @@
 	div.svelte-xyz {
-		@apply --funky-div;
+		/* DISABLED THIS FOR CSS NESTING */
+		/* @apply --funky-div; */
+		color: red;
 	}

packages/svelte/tests/css/samples/unknown-at-rule/input.svelte

@@ -2,6 +2,8 @@
 
 <style>
 	div {
-		@apply --funky-div;
+		/* DISABLED THIS FOR CSS NESTING */
+		/* @apply --funky-div; */
+		color: red;
 	}
 </style>