fix: don't collapse whitespace within text nodes (#10691)

fixes #9892

.changeset/happy-beds-scream.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: don't collapse whitespace within text nodes

packages/svelte/src/compiler/phases/3-transform/utils.js

@@ -162,24 +162,36 @@ export function clean_nodes(
 	/** @type {import('#compiler').SvelteNode[]} */
 	const trimmed = [];
 
-	/** @type {import('#compiler').Text | null} */
-	let last_text = null;
+	// Replace any whitespace between a text and non-text node with a single spaceand keep whitespace
+	// as-is within text nodes, or between text nodes and expression tags (because in the end they count
+	// as one text). This way whitespace is mostly preserved when using CSS with `white-space: pre-line`
+	// and default slot content going into a pre tag (which we can't see).
+	for (let i = 0; i < regular.length; i++) {
+		const prev = regular[i - 1];
+		const node = regular[i];
+		const next = regular[i + 1];
 
-	// Replace any inbetween whitespace with a single space
-	for (const node of regular) {
 		if (node.type === 'Text') {
-			node.data = node.data.replace(regex_whitespaces_strict, ' ');
-			node.raw = node.raw.replace(regex_whitespaces_strict, ' ');
-			if (
-				(last_text === null && !can_remove_entirely) ||
-				node.data !== ' ' ||
-				node.data.charCodeAt(0) === 160 // non-breaking space
-			) {
+			if (prev?.type !== 'ExpressionTag') {
+				const prev_is_text_ending_with_whitespace =
+					prev?.type === 'Text' && regex_ends_with_whitespaces.test(prev.data);
+				node.data = node.data.replace(
+					regex_starts_with_whitespaces,
+					prev_is_text_ending_with_whitespace ? '' : ' '
+				);
+				node.raw = node.raw.replace(
+					regex_starts_with_whitespaces,
+					prev_is_text_ending_with_whitespace ? '' : ' '
+				);
+			}
+			if (next?.type !== 'ExpressionTag') {
+				node.data = node.data.replace(regex_ends_with_whitespaces, ' ');
+				node.raw = node.raw.replace(regex_ends_with_whitespaces, ' ');
+			}
+			if (node.data && (node.data !== ' ' || !can_remove_entirely)) {
 				trimmed.push(node);
 			}
-			last_text = node;
 		} else {
-			last_text = null;
 			trimmed.push(node);
 		}
 	}

packages/svelte/src/compiler/phases/patterns.js

@@ -2,9 +2,9 @@ export const regex_whitespace = /\s/;
 export const regex_whitespaces = /\s+/;
 export const regex_starts_with_newline = /^\r?\n/;
 export const regex_starts_with_whitespace = /^\s/;
-export const regex_starts_with_whitespaces = /^[ \t\r\n]*/;
+export const regex_starts_with_whitespaces = /^[ \t\r\n]+/;
 export const regex_ends_with_whitespace = /\s$/;
-export const regex_ends_with_whitespaces = /[ \t\r\n]*$/;
+export const regex_ends_with_whitespaces = /[ \t\r\n]+$/;
 /** Not \S because that also removes explicit whitespace defined through things like ` ` */
 export const regex_not_whitespace = /[^ \t\r\n]/;
 /** Not \s+ because that also includes explicit whitespace defined through things like ` ` */

packages/svelte/tests/runtime-legacy/samples/pre-tag/_config.js

@@ -20,7 +20,10 @@ function get_html(ssr) {
   </span>
   E
   F
-</pre> <div id="div">A B <span>C D</span> E F</div> <div id="div-with-pre"><pre>    A
+</pre> <div id="div">A
+  B <span>C
+    D</span> E
+  F</div> <div id="div-with-pre"><pre>    A
     B
     <span>
       C

packages/svelte/tests/runtime-legacy/shared.ts

@@ -66,7 +66,7 @@ export interface RuntimeTest<Props extends Record<string, any> = Record<string,
 	runtime_error?: string;
 	warnings?: string[];
 	expect_unhandled_rejections?: boolean;
-	withoutNormalizeHtml?: boolean;
+	withoutNormalizeHtml?: boolean | 'only-strip-comments';
 	recover?: boolean;
 }
 
@@ -213,13 +213,15 @@ async function run_test_variant(
 		if (variant === 'ssr') {
 			if (config.ssrHtml) {
 				assert_html_equal_with_options(target.innerHTML, config.ssrHtml, {
-					preserveComments: config.compileOptions?.preserveComments,
-					withoutNormalizeHtml: config.withoutNormalizeHtml
+					preserveComments:
+						config.withoutNormalizeHtml === 'only-strip-comments' ? false : undefined,
+					withoutNormalizeHtml: !!config.withoutNormalizeHtml
 				});
 			} else if (config.html) {
 				assert_html_equal_with_options(target.innerHTML, config.html, {
-					preserveComments: config.compileOptions?.preserveComments,
-					withoutNormalizeHtml: config.withoutNormalizeHtml
+					preserveComments:
+						config.withoutNormalizeHtml === 'only-strip-comments' ? false : undefined,
+					withoutNormalizeHtml: !!config.withoutNormalizeHtml
 				});
 			}
 
@@ -283,7 +285,9 @@ async function run_test_variant(
 			if (config.html) {
 				$.flushSync();
 				assert_html_equal_with_options(target.innerHTML, config.html, {
-					withoutNormalizeHtml: config.withoutNormalizeHtml
+					preserveComments:
+						config.withoutNormalizeHtml === 'only-strip-comments' ? false : undefined,
+					withoutNormalizeHtml: !!config.withoutNormalizeHtml
 				});
 			}
 

packages/svelte/tests/runtime-runes/samples/snippet-whitespace/_config.js

@@ -4,5 +4,11 @@ export default test({
 	compileOptions: {
 		dev: true // Render in dev mode to check that the validation error is not thrown
 	},
-	html: `A\nB\nC\nD`
+	withoutNormalizeHtml: 'only-strip-comments',
+	html: `A B C D <pre>Testing
+123          ;
+    456</pre>`,
+	ssrHtml: `A B C D <pre>Testing
+123          ;
+    456</pre>`
 });

packages/svelte/tests/runtime-runes/samples/snippet-whitespace/main.svelte

@@ -1,5 +1,15 @@
+<script>
+	import Pre from "./pre.svelte";
+
+</script>
 A
 {#snippet snip()}C{/snippet}
 B
 {@render snip()}
 D
+
+<Pre>
+    Testing
+123          ;
+    456
+</Pre>

packages/svelte/tests/runtime-runes/samples/snippet-whitespace/pre.svelte

@@ -0,0 +1,5 @@
+<script>
+    let { children } = $props();
+</script>
+
+<pre>{@render children()}</pre>