From cbd531c295b1b782113497dcfc2532adbd695b2b Mon Sep 17 00:00:00 2001
From: jdecroock <decroockjovi@gmail.com>
Date: Tue, 18 Jun 2024 16:54:15 +0200
Subject: [PATCH] graciously handle array shuffling

---
 src/diff/children.js        | 24 +++++++++++++++++++-----
 test/browser/render.test.js | 33 ++++++++++++++++++++++++++++++---
 2 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/src/diff/children.js b/src/diff/children.js
index 912cc72d7c..757eb33e8a 100644
--- a/src/diff/children.js
+++ b/src/diff/children.js
@@ -302,20 +302,34 @@ function constructNewChildrenArray(newParentVNode, renderResult, oldChildren) {
 				childVNode._flags |= INSERT_VNODE;
 			}
 		} else if (matchingIndex !== skewedIndex) {
-			if (matchingIndex === skewedIndex + 1) {
+			if (matchingIndex == skewedIndex - 1) {
+				skew = matchingIndex - skewedIndex;
+			} else if (matchingIndex == skewedIndex + 1) {
 				skew++;
 			} else if (matchingIndex > skewedIndex) {
+				// Our matched DOM-node is further in the list of children than
+				// where it's at now.
+
+				// When the remaining old children is bigger than the new-children
+				// minus our skewed index we know we are dealing with a shrinking list
+				// we have to increase our skew with the matchedIndex - the skewed index
 				if (remainingOldChildren > newChildrenLength - skewedIndex) {
 					skew += matchingIndex - skewedIndex;
 				} else {
+					// If we have matched all the children just decrease the skew
 					skew--;
 				}
 			} else if (matchingIndex < skewedIndex) {
-				if (matchingIndex == skewedIndex - 1) {
-					skew = matchingIndex - skewedIndex;
+				// Our matched DOM-node is further in the negative way in the list of children
+				// than where it's at now.
+
+				// When the remaining old chiildren is less than the new children
+				// plus our skewed index we know we are dealing with a growing list
+				if (remainingOldChildren < newChildrenLength + skewedIndex) {
+					skew += matchingIndex + skewedIndex;
+				} else {
+					skew++;
 				}
-			} else {
-				skew = 0;
 			}
 
 			// Move this VNode's DOM if the original index (matchingIndex) doesn't
diff --git a/test/browser/render.test.js b/test/browser/render.test.js
index f440962f70..5241cfaf29 100644
--- a/test/browser/render.test.js
+++ b/test/browser/render.test.js
@@ -474,17 +474,17 @@ describe('render()', () => {
 
 	it('should support popover auto', () => {
 		render(<div popover="auto" />, scratch);
-		expect(scratch.innerHTML).to.equal("<div popover=\"auto\"></div>");
+		expect(scratch.innerHTML).to.equal('<div popover="auto"></div>');
 	});
 
 	it('should support popover true boolean', () => {
 		render(<div popover />, scratch);
-		expect(scratch.innerHTML).to.equal("<div popover=\"\"></div>");
+		expect(scratch.innerHTML).to.equal('<div popover=""></div>');
 	});
 
 	it('should support popover false boolean', () => {
 		render(<div popover={false} />, scratch);
-		expect(scratch.innerHTML).to.equal("<div></div>");
+		expect(scratch.innerHTML).to.equal('<div></div>');
 	});
 
 	// Test for preactjs/preact#4340
@@ -1625,4 +1625,31 @@ describe('render()', () => {
 			'<div><div>One</div><div>Six</div><div>Seven</div></div>'
 		);
 	});
+
+	it('shuffle', function () {
+		const App = ({ items }) => (
+			<div>
+				{items.map(key => (
+					<div key={key}>{key}</div>
+				))}
+			</div>
+		);
+		const a = ['0', '1', '2', '3', '4', '5', '6'];
+		const b = ['1', '3', '5', '2', '6', '4', '0'];
+		render(<App items={a} />, scratch);
+		expect(scratch.innerHTML).to.equal(
+			`<div>${a.map(n => `<div>${n}</div>`).join('')}</div>`
+		);
+
+		render(<App items={b} />, scratch);
+
+		expect(scratch.innerHTML).to.equal(
+			`<div>${b.map(n => `<div>${n}</div>`).join('')}</div>`
+		);
+
+		render(<App items={a} />, scratch);
+		expect(scratch.innerHTML).to.equal(
+			`<div>${a.map(n => `<div>${n}</div>`).join('')}</div>`
+		);
+	});
 });