DisplayListExplorer

DisplayList Explorer converts a SwiftUI DisplayList.description S-expression into its compact minimalDescription form, links source elements to their encodings, and explains every token.

The parser and converter are written in Swift. JavaScriptKit compiles the browser executable to WebAssembly, CodeMirror provides the source editor and range decorations, Vite packages the static assets, and GitHub Actions deploys the result to GitHub Pages.

Features

• Converts content, effects, nested flattened lists, effect children, and state variants.
• Reconstructs a readable DisplayList.description from minimalDescription.
• Reproduces the single-line formatting emitted by SExpPrinter.
• Links source and minimalDescription ranges with bidirectional hover highlighting.
• Provides dedicated minimalDesc, encoding info, and occurrence statistics tabs.
• Previews DisplayList frames inside draggable iPhone presets or a custom-size Window frame, with zoom, fit, actual-size controls, a point ruler, resolved content, effects, and payload placeholders.
• Highlights every matching source range when a statistics row is hovered or focused.
• Copies compact, self-contained links that reopen a shared minimalDescription.
• Runs entirely in the browser; pasted descriptions are not uploaded.
• Tests the conversion engine natively with SwiftPM before every deployment.

Reverse conversion

The direction control can use the current output as the next input. Because minimalDescription intentionally omits rendering details, reconstructed descriptions mark an unknown scalar or identifier with ? and an unrecoverable payload or effect kind with *. Converting the reconstructed description forward again preserves the original minimalDescription.

Shared links

Copy link stores the canonical minimalDescription, rather than the much larger source description, as versioned UTF-8 Base64URL in the URL fragment. Opening the link decodes that value and starts in reverse-conversion mode. Fragments are not included in HTTP requests, so shared DisplayList data is only decoded in the browser.

The mapping follows OpenSwiftUI's DisplayListPrinter.swift, audited for SwiftUI 6.5.4. The interaction model is inspired by SwiftFiddle/swiftregex. The CodeMirror decoration and statistics interaction patterns are adapted from SwiftFiddle/swift-ast-explorer; see THIRD_PARTY_NOTICES.md.

Known ambiguity

DisplayList.description prints identity effects, empty property effects, and platform effects with the same empty (effect …) form, while minimalDescription encodes them differently. Because the source text has already discarded that distinction, the converter renders an empty effect as identity and calls out the ambiguity in the interface.

Local development

Prerequisites:

• Swift 6.2.3 with its matching WebAssembly SDK
• A matching wasm32-unknown-wasip1 Swift SDK
• Node.js 24 or newer

Build the Swift package for WebAssembly, install the web dependencies, and start Vite:

swift package --swift-sdk "$SWIFT_SDK_ID" js
npm ci
npm run dev

Opening index.html through a file:// URL cannot run the ES Module and WebAssembly bundle. To build with the GitHub Pages base path and launch the production preview in one step, run:

npm run preview

Then open http://127.0.0.1:4173/DisplayListExplorer/.

Run the native converter tests with:

swift test

GitHub Pages

The Pages workflow deploys every push to main and can also be run manually from any branch through workflow_dispatch. It tests the converter, builds the SwiftWasm package, bundles the site with the repository's Pages base path, and deploys the dist artifact to https://openswiftuiproject.github.io/DisplayListExplorer/.

Pull request previews

Pull requests opened from branches in this repository are deployed to an isolated Cloudflare Pages preview after CI succeeds. Each pull request receives a stable branch alias such as https://pr-42.display-list-explorer.pages.dev, while every update also creates an immutable deployment URL. GitHub attaches the resulting URL to the pull request as a deployment and maintains a single bot comment containing the stable URL and a commit-by-commit table of immutable snapshots.

The workflow expects a CLOUDFLARE_API_TOKEN repository secret with Cloudflare Pages edit access and a CLOUDFLARE_ACCOUNT_ID repository variable. Pull requests from forks still run the converter and site build, but skip deployment because repository secrets are not exposed to fork workflows.

License

DisplayList Explorer is available under the MIT License. Third-party attributions are listed in THIRD_PARTY_NOTICES.md.