Angular NG0912 Component ID Collision After Upgrade

Problem Statement

After upgrading to Angular 17, developers often encounter console warnings about component ID generation collisions (NG0912). These warnings typically appear:

NG0912: Component ID generation collision detected. Components 'DevDashboardComponent' and 'DevDashboardComponent' with selector 'lib-dev-dashboard-page' generated the same component ID.

This occurs when Angular's rendering engine detects duplicate component identifiers during development. While your production build (ng build) might not show these warnings, they indicate deeper architectural issues including:

• Duplicated component definitions from npm packages
• Incorrect module declarations
• Version conflicts after upgrades

Recommended Solutions

1. Eliminate Duplicate Package Imports

Angular 17 enforces stricter component identity rules. Duplicated packages cause the same component to be loaded multiple times.

Steps to Fix:

1. Identify packages mentioned in warnings (e.g., @ng-bootstrap/ng-bootstrap)
2. Audit nested package.json files in your workspace:

3. Remove duplicates from nested modules:

cd projects/libs/ui
npm uninstall @ng-bootstrap/ng-bootstrap

4. Keep only the root-level installation

Why This Works: Ensures components load from a single source, eliminating identity conflicts.

2. Fix Component Declaration Conflicts

When custom components trigger warnings:

// Before (problematic)
@NgModule({
  declarations: [SharedComponent], // ❌ Duplicate declaration
  imports: [SharedModule]          // ❌ Already declares SharedComponent
})
export class FeatureModule {}

Solution:

// After (fixed)
@NgModule({
  imports: [SharedModule] // ✅ Only import - no re-declaration
})
export class FeatureModule {}

Best Practices:

• Declare components in exactly oneNgModule
• Never re-declare exported components from imported modules
• Use exports: when sharing components between modules

3. Force Unique IDs with Host Attributes

For third-party components where source fixes are impossible:

@Component({
  selector: 'lib-dev-dashboard-page',
  template: `...`,
  host: { 'ng-id': crypto.randomUUID() } // 🆔 Unique ID per instance
})
export class MyComponent {}

TIP

Use Angular's DOCUMENT token + uuid polyfill if you need SSR compatibility. The browser's crypto.randomUUID() works for client-side only.

When to Use:

• Temporary mitigation for upstream dependency issues
• Components lacking unique selectors
• Projects requiring immediate warning suppression

Key Insights

1. Why Angular 17?
   Component IDs now incorporate selector uniqueness checks at runtime. Duplicate packages previously undetected now trigger warnings.

2. Development-Only Warning
   Production builds use different optimizations that often deduplicate modules, explaining why ng build suppresses these.

3. Architectural Impact: