From 539c8b9492392eac17af06e49c6cad9ae08d43cc Mon Sep 17 00:00:00 2001
From: "Zakariya Jabbar (Viper Droid)" <gaszaka20@gmail.com>
Date: Fri, 17 Apr 2026 22:42:59 +0300
Subject: [PATCH] feat(react-dom): dynamic In HTML/In SVG labels for DOM
 nesting warnings

Use HostContextNamespace when emitting validateDOMNesting and validateTextNesting
dev errors so SVG subtree warnings say In SVG; foreignObject keeps In HTML as an
HTML integration point.
---
 .../src/client/ReactDOMComponent.js           | 19 +++++++--
 .../src/client/ReactFiberConfigDOM.js         |  8 ++--
 .../src/client/validateDOMNesting.js          | 41 +++++++++++++++++--
 .../src/__tests__/validateDOMNesting-test.js  |  2 +-
 4 files changed, 59 insertions(+), 11 deletions(-)

diff --git a/packages/react-dom-bindings/src/client/ReactDOMComponent.js b/packages/react-dom-bindings/src/client/ReactDOMComponent.js
index 1b25e3727023..86f0cf21dfb9 100644
--- a/packages/react-dom-bindings/src/client/ReactDOMComponent.js
+++ b/packages/react-dom-bindings/src/client/ReactDOMComponent.js
@@ -48,7 +48,10 @@ import {
   restoreControlledTextareaState,
 } from './ReactDOMTextarea';
 import {setSrcObject} from './ReactDOMSrcObject';
-import {validateTextNesting} from './validateDOMNesting';
+import {
+  validateTextNesting,
+  getHostContextNamespaceForDomNamespace,
+} from './validateDOMNesting';
 import setTextContent from './setTextContent';
 import {
   createDangerousStringForStyles,
@@ -393,7 +396,12 @@ function setProp(
     case 'children': {
       if (typeof value === 'string') {
         if (__DEV__) {
-          validateTextNesting(value, tag, false);
+          validateTextNesting(
+            value,
+            tag,
+            false,
+            getHostContextNamespaceForDomNamespace(domElement.namespaceURI),
+          );
         }
         // Avoid setting initial textContent when the text is empty. In IE11 setting
         // textContent on a <textarea> will cause the placeholder to not
@@ -407,7 +415,12 @@ function setProp(
       } else if (typeof value === 'number' || typeof value === 'bigint') {
         if (__DEV__) {
           // $FlowFixMe[unsafe-addition] Flow doesn't want us to use `+` operator with string and bigint
-          validateTextNesting('' + value, tag, false);
+          validateTextNesting(
+            '' + value,
+            tag,
+            false,
+            getHostContextNamespaceForDomNamespace(domElement.namespaceURI),
+          );
         }
         const canSetTextContent = tag !== 'body';
         if (canSetTextContent) {
diff --git a/packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js b/packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js
index 538dd4b70965..b739ac396adc 100644
--- a/packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js
+++ b/packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js
@@ -532,7 +532,7 @@ export function createInstance(
   if (__DEV__) {
     // TODO: take namespace into account when validating.
     const hostContextDev: HostContextDev = (hostContext: any);
-    validateDOMNesting(type, hostContextDev.ancestorInfo);
+    validateDOMNesting(type, hostContextDev.ancestorInfo, hostContextDev.context);
     hostContextProd = hostContextDev.context;
   } else {
     hostContextProd = (hostContext: any);
@@ -758,6 +758,7 @@ export function createTextInstance(
         text,
         ancestor.tag,
         hostContextDev.ancestorInfo.implicitRootScope,
+        hostContextDev.context,
       );
     }
   }
@@ -4249,7 +4250,7 @@ export function validateHydratableInstance(
   if (__DEV__) {
     // TODO: take namespace into account when validating.
     const hostContextDev: HostContextDev = (hostContext: any);
-    return validateDOMNesting(type, hostContextDev.ancestorInfo);
+    return validateDOMNesting(type, hostContextDev.ancestorInfo, hostContextDev.context);
   }
   return true;
 }
@@ -4291,6 +4292,7 @@ export function validateHydratableTextInstance(
         text,
         ancestor.tag,
         hostContextDev.ancestorInfo.implicitRootScope,
+        hostContextDev.context,
       );
     }
   }
@@ -4635,7 +4637,7 @@ export function resolveSingletonInstance(
   if (__DEV__) {
     const hostContextDev = ((hostContext: any): HostContextDev);
     if (validateDOMNestingDev) {
-      validateDOMNesting(type, hostContextDev.ancestorInfo);
+      validateDOMNesting(type, hostContextDev.ancestorInfo, hostContextDev.context);
     }
   }
   const ownerDocument = getOwnerDocumentFromRootContainer(
diff --git a/packages/react-dom-bindings/src/client/validateDOMNesting.js b/packages/react-dom-bindings/src/client/validateDOMNesting.js
index 47aef9353ba8..c50c977b0714 100644
--- a/packages/react-dom-bindings/src/client/validateDOMNesting.js
+++ b/packages/react-dom-bindings/src/client/validateDOMNesting.js
@@ -23,6 +23,31 @@ import {
 
 import {describeDiff} from 'react-reconciler/src/ReactFiberHydrationDiffs';
 
+import {MATH_NAMESPACE, SVG_NAMESPACE} from './DOMNamespaces';
+
+/**
+ * Mirrors HostContextNamespace in ReactFiberConfigDOM.js (None / Svg / Math).
+ * Used only for dev-only nesting warning prefixes.
+ */
+export type HostContextNamespace = 0 | 1 | 2;
+
+export function getHostContextNamespaceForDomNamespace(
+  namespaceURI: string | null,
+): HostContextNamespace {
+  if (namespaceURI === SVG_NAMESPACE) {
+    return 1;
+  }
+  if (namespaceURI === MATH_NAMESPACE) {
+    return 2;
+  }
+  return 0;
+}
+
+function getContextLabel(hostContextNamespace: HostContextNamespace): string {
+  // "In SVG" only in the SVG namespace; foreignObject switches to HTML (integration point).
+  return hostContextNamespace === 1 ? 'In SVG' : 'In HTML';
+}
+
 function describeAncestors(
   ancestor: Fiber,
   child: Fiber,
@@ -549,6 +574,7 @@ function findAncestor(parent: null | Fiber, tagName: string): null | Fiber {
 function validateDOMNesting(
   childTag: string,
   ancestorInfo: AncestorInfoDev,
+  hostContextNamespace: HostContextNamespace,
 ): boolean {
   if (__DEV__) {
     ancestorInfo = ancestorInfo || emptyAncestorInfoDev;
@@ -589,6 +615,7 @@ function validateDOMNesting(
         : '';
 
     const tagDisplayName = '<' + childTag + '>';
+    const contextLabel = getContextLabel(hostContextNamespace);
     if (invalidParent) {
       let info = '';
       if (ancestorTag === 'table' && childTag === 'tr') {
@@ -597,8 +624,9 @@ function validateDOMNesting(
           'the browser.';
       }
       console.error(
-        'In HTML, %s cannot be a child of <%s>.%s\n' +
+        '%s, %s cannot be a child of <%s>.%s\n' +
           'This will cause a hydration error.%s',
+        contextLabel,
         tagDisplayName,
         ancestorTag,
         info,
@@ -606,8 +634,9 @@ function validateDOMNesting(
       );
     } else {
       console.error(
-        'In HTML, %s cannot be a descendant of <%s>.\n' +
+        '%s, %s cannot be a descendant of <%s>.\n' +
           'This will cause a hydration error.%s',
+        contextLabel,
         tagDisplayName,
         ancestorTag,
         ancestorDescription,
@@ -644,6 +673,7 @@ function validateTextNesting(
   childText: string,
   parentTag: string,
   implicitRootScope: boolean,
+  hostContextNamespace: HostContextNamespace,
 ): boolean {
   if (__DEV__) {
     if (implicitRootScope || isTagValidWithParent('#text', parentTag, false)) {
@@ -668,19 +698,22 @@ function validateTextNesting(
           )
         : '';
 
+    const contextLabel = getContextLabel(hostContextNamespace);
     if (/\S/.test(childText)) {
       console.error(
-        'In HTML, text nodes cannot be a child of <%s>.\n' +
+        '%s, text nodes cannot be a child of <%s>.\n' +
           'This will cause a hydration error.%s',
+        contextLabel,
         parentTag,
         ancestorDescription,
       );
     } else {
       console.error(
-        'In HTML, whitespace text nodes cannot be a child of <%s>. ' +
+        '%s, whitespace text nodes cannot be a child of <%s>. ' +
           "Make sure you don't have any extra whitespace between tags on " +
           'each line of your source code.\n' +
           'This will cause a hydration error.%s',
+        contextLabel,
         parentTag,
         ancestorDescription,
       );
diff --git a/packages/react-dom/src/__tests__/validateDOMNesting-test.js b/packages/react-dom/src/__tests__/validateDOMNesting-test.js
index 1940fe913d75..b60f5e919643 100644
--- a/packages/react-dom/src/__tests__/validateDOMNesting-test.js
+++ b/packages/react-dom/src/__tests__/validateDOMNesting-test.js
@@ -192,7 +192,7 @@ describe('validateDOMNesting', () => {
     expectWarnings(
       ['svg', 'foreignObject', 'body', 'p'],
       [
-        // TODO, this should say "In SVG",
+        // foreignObject is an HTML integration point: nested HTML uses the HTML namespace.
         'In HTML, <body> cannot be a child of <foreignObject>.\n' +
           'This will cause a hydration error.\n' +
           '\n' +