[fix]: strip leading newline after `<pre>`

src/compiler/compile/nodes/Text.ts

@@ -49,6 +49,15 @@ export default class Text extends Node {
 		return this.within_pre();
 	}
 
+	/**
+	 * @returns If true, the leading newline character should be stripped.
+	 * @see https://html.spec.whatwg.org/multipage/grouping-content.html#the-pre-element
+	 */
+	should_strip_leading_newline(): boolean {
+		const parent = this.parent;
+		return parent.type === 'Element' && parent.name === 'pre' && parent.children[0] === this;
+	}
+
 	within_pre(): boolean {
 		let node = this.parent;
 		while (node) {

src/compiler/compile/render_dom/wrappers/Element/index.ts

@@ -12,7 +12,7 @@ import { namespaces } from '../../../../utils/namespaces';
 import AttributeWrapper from './Attribute';
 import StyleAttributeWrapper from './StyleAttribute';
 import SpreadAttributeWrapper from './SpreadAttribute';
-import { dimensions } from '../../../../utils/patterns';
+import { dimensions, start_newline } from '../../../../utils/patterns';
 import Binding from './Binding';
 import add_to_set from '../../../utils/add_to_set';
 import { add_event_handler } from '../shared/add_event_handlers';
@@ -1015,6 +1015,15 @@ function to_html(wrappers: Array<ElementWrapper | TextWrapper | MustacheTagWrapp
 			if (!wrapper.void) {
 				state.quasi.value.raw += '>';
 
+				if (wrapper.node.name === 'pre') {
+					// Two or more leading newlines are required to restore the leading newline immediately after `<pre>`.
+					// see https://html.spec.whatwg.org/multipage/grouping-content.html#the-pre-element
+					const first = wrapper.fragment.nodes[0];
+					if (first && first.node.type === 'Text' && start_newline.test(first.node.data)) {
+						state.quasi.value.raw += '\n';
+					}
+				}
+
 				to_html(wrapper.fragment.nodes as Array<ElementWrapper | TextWrapper>, block, literal, state);
 
 				state.quasi.value.raw += `</${wrapper.node.name}>`;

src/compiler/compile/render_dom/wrappers/Fragment.ts

@@ -21,6 +21,7 @@ import Block from '../Block';
 import { trim_start, trim_end } from '../../../utils/trim';
 import { link } from '../../../utils/link';
 import { Identifier } from 'estree';
+import { start_newline } from '../../../utils/patterns';
 
 const wrappers = {
 	AwaitBlock,
@@ -127,8 +128,12 @@ export default class FragmentWrapper {
 		if (strip_whitespace) {
 			const first = this.nodes[0] as Text;
 
-			if (first && first.node.type === 'Text' && !first.node.keep_space()) {
-				first.data = trim_start(first.data);
+			if (first && first.node.type === 'Text') {
+				if (!first.node.keep_space()) {
+					first.data = trim_start(first.data);
+				} else if (first.node.should_strip_leading_newline()) {
+					first.data = first.data.replace(start_newline, '');
+				}
 				if (!first.data) {
 					first.var = null;
 					this.nodes.shift();

src/compiler/utils/patterns.ts

@@ -1,5 +1,6 @@
 export const whitespace = /[ \t\r\n]/;
 export const start_whitespace = /^[ \t\r\n]*/;
 export const end_whitespace = /[ \t\r\n]*$/;
+export const start_newline = /^\r?\n/;
 
 export const dimensions = /^(?:offset|client)(?:Width|Height)$/;

test/runtime/samples/pre-tag/.editorconfig

@@ -0,0 +1,2 @@
+[main.svelte]
+trim_trailing_whitespace = unset

test/runtime/samples/pre-tag/_config.js

@@ -6,23 +6,14 @@ export default {
 		const elementDiv = target.querySelector('#div');
 		// Test for <pre> tag in non <pre> tag
 		const elementDivWithPre = target.querySelector('#div-with-pre');
-
-		// There is a slight difference in innerHTML because there is a difference in HTML optimization (in jsdom)
-		// depending on how the innerHTML is set.
-		// (There is no difference in the display.)
-		// Reassign innerHTML to add the same optimizations to innerHTML.
-
-		// eslint-disable-next-line no-self-assign
-		elementPre.innerHTML = elementPre.innerHTML;
-		// eslint-disable-next-line no-self-assign
-		elementDiv.innerHTML = elementDiv.innerHTML;
-		// eslint-disable-next-line no-self-assign
-		elementDivWithPre.innerHTML = elementDivWithPre.innerHTML;
+		// Test for <pre> tag with leading newline
+		const elementPreWithLeadingNewline = target.querySelector('#pre-with-leading-newline');
+		const elementPreWithoutLeadingNewline = target.querySelector('#pre-without-leading-newline');
+		const elementPreWithMultipleLeadingNewline = target.querySelector('#pre-with-multiple-leading-newlines');
 
 		assert.equal(
 			elementPre.innerHTML,
-			`
-  A
+			`  A
   B
   <span>
     C
@@ -53,5 +44,12 @@ export default {
     F
   </pre>`
 		);
+		assert.equal(elementPreWithLeadingNewline.children[0].innerHTML, 'leading newline');
+		assert.equal(elementPreWithLeadingNewline.children[1].innerHTML, '  leading newline and spaces');
+		assert.equal(elementPreWithLeadingNewline.children[2].innerHTML, '\nleading newlines');
+		assert.equal(elementPreWithoutLeadingNewline.children[0].innerHTML, 'without spaces');
+		assert.equal(elementPreWithoutLeadingNewline.children[1].innerHTML, '  with spaces  ');
+		assert.equal(elementPreWithoutLeadingNewline.children[2].innerHTML, ' \nnewline after leading space');
+		assert.equal(elementPreWithMultipleLeadingNewline.innerHTML, '\n\nmultiple leading newlines');
 	}
 };

test/runtime/samples/pre-tag/main.svelte

@@ -32,3 +32,25 @@
     F
   </pre>
 </div>
+
+<div id="pre-with-leading-newline">
+  <pre>
+leading newline</pre>
+  <pre>
+  leading newline and spaces</pre>
+  <pre>
+
+leading newlines</pre>
+</div>
+
+<div id="pre-without-leading-newline">
+  <pre>without spaces</pre>
+  <pre>  with spaces  </pre>
+  <pre> 
+newline after leading space</pre>
+</div>
+
+<pre id="pre-with-multiple-leading-newlines">
+
+
+multiple leading newlines</pre>

test/runtime/samples/preserve-whitespaces/_config.js

@@ -10,22 +10,9 @@ export default {
 		// Test for <pre> tag in non <pre> tag
 		const elementDivWithPre = target.querySelector('#div-with-pre');
 
-		// There is a slight difference in innerHTML because there is a difference in HTML optimization (in jsdom)
-		// depending on how the innerHTML is set.
-		// (There is no difference in the display.)
-		// Reassign innerHTML to add the same optimizations to innerHTML.
-
-		// eslint-disable-next-line no-self-assign
-		elementPre.innerHTML = elementPre.innerHTML;
-		// eslint-disable-next-line no-self-assign
-		elementDiv.innerHTML = elementDiv.innerHTML;
-		// eslint-disable-next-line no-self-assign
-		elementDivWithPre.innerHTML = elementDivWithPre.innerHTML;
-
 		assert.equal(
 			elementPre.innerHTML,
-			`
-  A
+			`  A
   B
   <span>
     C

test/server-side-rendering/samples/pre-tag/.editorconfig

@@ -0,0 +1,2 @@
+[{main.svelte,_expected.html}]
+trim_trailing_whitespace = unset

test/server-side-rendering/samples/pre-tag/_expected.html

@@ -28,3 +28,16 @@
     E
     F
   </pre></div>
+
+<div id="pre-with-leading-newline"><pre>
+leading newline</pre>
+  <pre>
+  leading newline and spaces</pre>
+  <pre>
+
+leading newlines</pre></div>
+
+<div id="pre-without-leading-newline"><pre>without spaces</pre>
+  <pre>  with spaces  </pre>
+  <pre> 
+newline after leading space</pre></div>

test/server-side-rendering/samples/pre-tag/main.svelte

@@ -32,3 +32,20 @@
     F
   </pre>
 </div>
+
+<div id="pre-with-leading-newline">
+  <pre>
+leading newline</pre>
+  <pre>
+  leading newline and spaces</pre>
+  <pre>
+
+leading newlines</pre>
+</div>
+
+<div id="pre-without-leading-newline">
+  <pre>without spaces</pre>
+  <pre>  with spaces  </pre>
+  <pre> 
+newline after leading space</pre>
+</div>