Improved Ember dev server startup

[jonatansberg]

Summary

• Skip Ember test and hinting trees during normal development builds.
• Exclude Mirage files from normal development builds unless explicitly opted in.
• Keep /tests support available with EMBER_INCLUDE_TESTS=true.

Why

ember serve was building test and Mirage assets by default in development, pulling large dev-only dependencies such as Faker into the default startup path. This keeps the normal dev server focused on the app graph while preserving explicit test-server support.

Validation

• Ran isolated ember serve --port 4210 --live-reload false profiling before and after the change.
• Before: ~31.4s Ember build, 777 Broccoli steps, ~2.85 GB max RSS, 16.6 MiB Faker/Mirage webpack chunk.
• After: server reached Build successful, ~19.8s profiled Ember build, 716 Broccoli steps, ~1.68 GB max RSS.
• Commit hooks ran eslint and secret scanning successfully.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: fc220bd0-91db-4d87-81fe-6499f54a1fd4

📥 Commits

Reviewing files that changed from the base of the PR and between 333ba93 and 8ad8e7b.

📒 Files selected for processing (1)

• ghost/admin/ember-cli-build.js

🚧 Files skipped from review as they are similar to previous changes (1)

• ghost/admin/ember-cli-build.js

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Walkthrough

The pull request introduces centralized control for test asset inclusion in the build process. Two files are modified: config/environment.js now adds an excludeFilesFromBuild property to ember-cli-mirage configuration based on the EMBER_INCLUDE_TESTS environment variable. ember-cli-build.js introduces an includeTestAssets constant that conditionally enables test asset loading based on environment and EMBER_INCLUDE_TESTS. This flag controls inclusion of test-related assets (including Codemirror vendor assets) and dynamic test imports, applying conditions to the EmberApp configuration for tests, hinting, and trees settings.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Improved Ember dev server startup' accurately reflects the main objective of the changeset—optimizing the Ember development server's startup performance.
Description check	✅ Passed	The description clearly explains the changes (skipping test/hinting trees, excluding Mirage files) and provides validation metrics demonstrating the performance improvements achieved.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch speed-up-ember-dev-server

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