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[Blazor] Fix metadata comments incorrectly being processed as logical elements #64529

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Nov 26, 2025
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[Blazor] Fix metadata comments incorrectly being processed as logical elements #64529

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8 changes: 7 additions & 1 deletion src/Components/Web.JS/src/Rendering/LogicalElements.ts
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

import { ComponentDescriptor } from '../Services/ComponentDescriptorDiscovery';
import { ComponentDescriptor, isMetadataComment } from '../Services/ComponentDescriptorDiscovery';

/*
A LogicalElement plays the same role as an Element instance from the point of view of the
Expand Down Expand Up @@ -109,6 +109,12 @@ export function toLogicalElement(element: Node, allowExistingContents?: boolean)
}

element.childNodes.forEach(child => {
// Skip metadata comments that will be consumed during discovery
// These are not components and should not be part of the logical tree
if (isMetadataComment(child)) {
return;
}
Comment on lines 111 to +116
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Copilot AI Nov 25, 2025

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The metadata comment filtering logic in toLogicalElement lacks automated test coverage. This is a critical fix for navigation errors, so consider adding tests to verify:

  1. Metadata comments are excluded from the logical tree during initial construction
  2. Non-metadata comments and other nodes are still included
  3. The logical tree structure remains correct after filtering

Example test:

test('should exclude metadata comments from logical tree', () => {
  const parent = document.createElement('div');
  parent.appendChild(document.createComment('Blazor-WebAssembly:{"options":"test"}'));
  parent.appendChild(document.createElement('span'));
  parent.appendChild(document.createComment('Regular comment'));
  
  const logicalElement = toLogicalElement(parent, true);
  const children = getLogicalChildrenArray(logicalElement);
  
  expect(children.length).toBe(2); // span and regular comment, but not metadata comment
});

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const childLogicalElement = toLogicalElement(child, /* allowExistingContents */ true);
childLogicalElement[logicalParentPropname] = element;
childrenArray.push(childLogicalElement);
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13 changes: 13 additions & 0 deletions src/Components/Web.JS/src/Services/ComponentDescriptorDiscovery.ts
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Original file line number Diff line number Diff line change
@@ -1,6 +1,19 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

// Metadata comments are consumed during discovery and should not be part of the logical tree.
// They include: WebAssembly options, component state, and web initializers.
export function isMetadataComment(node: Node): boolean {
if (node.nodeType !== Node.COMMENT_NODE) {
return false;
}
const content = node.textContent || '';
return content.trim().startsWith('Blazor-Server-Component-State:') ||
content.trim().startsWith('Blazor-WebAssembly-Component-State:') ||
content.trim().startsWith('Blazor-Web-Initializers:') ||
content.trim().startsWith('Blazor-WebAssembly:');
Comment on lines +11 to +14
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Copilot AI Nov 25, 2025

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The content.trim() call is repeated up to 4 times in the boolean expression. Store the trimmed content in a variable to avoid redundant string operations:

const content = node.textContent || '';
const trimmedContent = content.trim();
return trimmedContent.startsWith('Blazor-Server-Component-State:') ||
       trimmedContent.startsWith('Blazor-WebAssembly-Component-State:') ||
       trimmedContent.startsWith('Blazor-Web-Initializers:') ||
       trimmedContent.startsWith('Blazor-WebAssembly:');
Suggested change
return content.trim().startsWith('Blazor-Server-Component-State:') ||
content.trim().startsWith('Blazor-WebAssembly-Component-State:') ||
content.trim().startsWith('Blazor-Web-Initializers:') ||
content.trim().startsWith('Blazor-WebAssembly:');
const trimmedContent = content.trim();
return trimmedContent.startsWith('Blazor-Server-Component-State:') ||
trimmedContent.startsWith('Blazor-WebAssembly-Component-State:') ||
trimmedContent.startsWith('Blazor-Web-Initializers:') ||
trimmedContent.startsWith('Blazor-WebAssembly:');

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}
Comment on lines +6 to +15
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Copilot AI Nov 25, 2025

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The isMetadataComment function lacks automated test coverage. Given that this function is critical for preventing metadata comments from entering the logical tree (which causes navigation errors), consider adding unit tests to verify:

  1. Correct identification of all metadata comment types (Blazor-Server-Component-State, Blazor-WebAssembly-Component-State, Blazor-Web-Initializers, Blazor-WebAssembly)
  2. Rejection of non-comment nodes
  3. Rejection of non-metadata comments (e.g., regular Blazor: component markers)
  4. Handling of whitespace variations in comment content

Example test structure:

describe('isMetadataComment', () => {
  test('should identify server component state comments', () => {
    const comment = document.createComment('Blazor-Server-Component-State:abc123');
    expect(isMetadataComment(comment)).toBe(true);
  });
  
  test('should not identify component marker comments', () => {
    const comment = document.createComment('Blazor:{"type":"server"}');
    expect(isMetadataComment(comment)).toBe(false);
  });
  // ... more tests
});

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export function discoverComponents(root: Node, type: 'webassembly' | 'server' | 'auto'): ComponentDescriptor[] {
switch (type) {
case 'webassembly':
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