fix: css pruning producing invalid css (#14448)

* fix: css pruning producing invalid css

* Update .changeset/big-hats-wonder.md

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

.changeset/big-hats-wonder.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: correctly remove unused selectors in middle of selector lists

packages/svelte/src/compiler/phases/3-transform/css/index.js

@@ -200,6 +200,7 @@ const visitors = {
 			let pruning = false;
 			let prune_start = children[0].start;
 			let last = prune_start;
+			let has_previous_used = false;
 
 			for (let i = 0; i < children.length; i += 1) {
 				const selector = children[i];
@@ -210,9 +211,9 @@ const visitors = {
 						while (state.code.original[i] !== ',') i--;
 
 						if (state.minify) {
-							state.code.remove(prune_start, i + 1);
+							state.code.remove(prune_start, has_previous_used ? i : i + 1);
 						} else {
-							state.code.overwrite(i, i + 1, '*/');
+							state.code.appendRight(has_previous_used ? i : i + 1, '*/');
 						}
 					} else {
 						if (i === 0) {
@@ -222,24 +223,21 @@ const visitors = {
 								state.code.prependRight(selector.start, '/* (unused) ');
 							}
 						} else {
-							// If this is not the last selector add a separator
-							const separator = i !== children.length - 1 ? ',' : '';
-
 							if (state.minify) {
 								prune_start = last;
-								if (separator) {
-									while (state.code.original[prune_start - 1] !== ',') prune_start++;
-									state.code.update(last, prune_start, separator);
-								}
 							} else {
-								state.code.overwrite(last, selector.start, `${separator} /* (unused) `);
+								state.code.overwrite(last, selector.start, ` /* (unused) `);
 							}
 						}
 					}
 
 					pruning = !pruning;
 				}
 
+				if (!pruning && selector.metadata.used) {
+					has_previous_used = true;
+				}
+
 				last = selector.end;
 			}
 

packages/svelte/tests/css/samples/has/expected.css

@@ -75,7 +75,7 @@
 	/* (unused) .unused x:has(y) {
 		color: red;
 	}*/
-	/* (unused) .unused:has(.unused)*/ x.svelte-xyz:has(y:where(.svelte-xyz)) {
+	/* (unused) .unused:has(.unused),*/ x.svelte-xyz:has(y:where(.svelte-xyz)) {
 		color: green;
 	}
 

packages/svelte/tests/css/samples/unused-selector-in-between/expected.css

@@ -1,7 +1,7 @@
 
 	h1.svelte-xyz,
 	h2.svelte-xyz,
-	h3.svelte-xyz, /* (unused) h4*/
+	h3.svelte-xyz /* (unused) h4*/,
 	p.svelte-xyz {
 		color: red;
 	}

packages/svelte/tests/css/samples/unused-selector-leading/expected.css

@@ -1,3 +1,3 @@
-	/* (unused) .foo*/ .bar.svelte-xyz /* (unused) .baz*/ {
+	/* (unused) .foo,*/ .bar.svelte-xyz /* (unused) .baz*/ {
 		color: red;
 	}

packages/svelte/tests/css/samples/unused-selector-multiple/_config.js

@@ -0,0 +1,160 @@
+import { test } from '../../test';
+
+export default test({
+	warnings: [
+		{
+			code: 'a11y_missing_content',
+			message: '`<h1>` element should contain text',
+			start: {
+				line: 1,
+				column: 0,
+				character: 0
+			},
+			end: {
+				line: 1,
+				column: 9,
+				character: 9
+			}
+		},
+		{
+			code: 'a11y_missing_content',
+			message: '`<h4>` element should contain text',
+			start: {
+				line: 2,
+				column: 0,
+				character: 10
+			},
+			end: {
+				line: 2,
+				column: 9,
+				character: 19
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "h2"',
+			start: {
+				line: 6,
+				column: 5,
+				character: 35
+			},
+			end: {
+				line: 6,
+				column: 7,
+				character: 37
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "h3"',
+			start: {
+				line: 6,
+				column: 9,
+				character: 39
+			},
+			end: {
+				line: 6,
+				column: 11,
+				character: 41
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "h2"',
+			start: {
+				line: 9,
+				column: 5,
+				character: 66
+			},
+			end: {
+				line: 9,
+				column: 7,
+				character: 68
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "h2"',
+			start: {
+				line: 13,
+				column: 5,
+				character: 110
+			},
+			end: {
+				line: 13,
+				column: 7,
+				character: 112
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "h3"',
+			start: {
+				line: 13,
+				column: 9,
+				character: 114
+			},
+			end: {
+				line: 13,
+				column: 11,
+				character: 116
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "h2"',
+			start: {
+				line: 17,
+				column: 5,
+				character: 161
+			},
+			end: {
+				line: 17,
+				column: 7,
+				character: 163
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "h3"',
+			start: {
+				line: 17,
+				column: 9,
+				character: 165
+			},
+			end: {
+				line: 17,
+				column: 11,
+				character: 167
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "h5"',
+			start: {
+				line: 17,
+				column: 17,
+				character: 173
+			},
+			end: {
+				line: 17,
+				column: 19,
+				character: 175
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "h6"',
+			start: {
+				line: 17,
+				column: 21,
+				character: 177
+			},
+			end: {
+				line: 17,
+				column: 23,
+				character: 179
+			}
+		}
+	]
+});

packages/svelte/tests/css/samples/unused-selector-multiple/expected.css

@@ -0,0 +1,15 @@
+
+	h1.svelte-xyz /* (unused) h2, h3*/ {
+		color: red;
+	}
+	h1.svelte-xyz /* (unused) h2*/ {
+		text-decoration: underline;
+	}
+
+	h1.svelte-xyz /* (unused) h2, h3*/, h4.svelte-xyz {
+		text-transform: uppercase;
+	}
+
+	h1.svelte-xyz /* (unused) h2, h3*/, h4.svelte-xyz /* (unused) h5, h6*/ {
+		background-color: green;
+	}

packages/svelte/tests/css/samples/unused-selector-multiple/input.svelte

@@ -0,0 +1,20 @@
+<h1></h1>
+<h4></h4>
+
+
+<style>
+	h1, h2, h3 {
+		color: red;
+	}
+	h1, h2 {
+		text-decoration: underline;
+	}
+
+	h1, h2, h3, h4 {
+		text-transform: uppercase;
+	}
+
+	h1, h2, h3, h4, h5, h6 {
+		background-color: green;
+	}
+</style>