Build-Time html Template to VDOM Conversion

1. Summary

Implement a build-time process to convert html tagged template literals into JSON-based VDOM structures. This is a critical optimization that removes the need for a client-side HTML parser, leading to smaller bundle sizes and faster initial render times.

2. Rationale

Pre-processing templates at build time is a best practice in modern web development. It shifts the parsing overhead from the user's browser to the developer's machine, resulting in a better user experience. This also opens the door for more advanced static analysis and optimizations in the future. By converting templates to standard JSON VDOM, we align this new syntax with the core rendering engine of Neo.mjs, ensuring consistency and maintainability.

3. Scope & Implementation Plan

1. Isolate Processor Logic: Refactor the template parsing logic out of the client-side HtmlTemplateProcessor and into a dedicated build script utility (buildScripts/util/templateBuildProcessor.mjs).
2. AST-Based Parsing: Use acorn to parse JavaScript files into an Abstract Syntax Tree (AST), providing a robust way to find templates.
3. Find & Process Templates: Traverse the AST to locate all TaggedTemplateExpression nodes tagged with the html identifier.
4. Convert to VDOM: For each found template, use the templateBuildProcessor to convert it into a JSON VDOM object. This process correctly handles nested templates and embedded JavaScript expressions.
5. Rename render to createVdom: While traversing the AST, if an html template is found within a method or object property named render, rename that method/property to createVdom.
6. Replace in AST: Replace the original TaggedTemplateExpression node in the AST with the newly generated VDOM object (represented as an AST ObjectExpression).
7. Generate Final Code: Use astring to generate the final, modified JavaScript code from the updated AST.
8. Integrate into Build: Incorporate this AST-based transformation into the buildSingleFile.mjs and buildESModules.mjs scripts.

4. Definition of Done

• The build process correctly identifies and converts html templates to VDOM objects.
• The render method/property is automatically renamed to createVdom when it contains an html template.
• The final minified output contains JSON VDOM, not template literals.
• The client-side HtmlTemplateProcessor is no longer required for production builds using this feature.
• The logic is cleanly separated, with no build-time code included in client-side bundles.