#Stencil

#Why this project

• Small API surface: render, compile, and partial-aware rendering helpers.
• Safe-by-default output: {{name}} escapes HTML automatically.
• Practical Mustache coverage: sections, inverted sections, lists, object contexts, comments, raw variables, and partials.
• Predictable edge behavior: standalone control lines, CRLF input, bounded nesting, and deterministic errors.
• MoonBit-first maintenance: tests, CI, changelog, and repository self-checks are part of the project itself.

#Feature Summary

• Escaped variables: {{name}}
• Raw variables: {{{html}}} and {{&html}}
• Sections: {{#items}}...{{/items}}
• Inverted sections: {{^items}}...{{/items}}
• Dotted-path lookup: {{user.profile.name}}
• Implicit iterator for lists: {{.}}
• Partials with standalone indentation propagation
• Comment tags: {{! ignored }}
• Standalone comments and section control lines
• Delimiter changes: {{=<% %>=}}<%name%>
• Bounded parser and partial expansion depth (256 levels)
• Configurable render limits, missing-partial policies, and cycle detection
• PartialStore for reusable partial registries, validation, dependency inspection, and startup compilation
• Diagnostics and structural metrics for editors, CI, and acceptance review
• Compatibility corpus and reproducible HTML catalog benchmark

#Installation

moon add LL124-Arch/stencil

import {
  "LL124-Arch/stencil/src" @stencil,
}

#Quick Start

fn main {
  let template = "Hello {{name}}! Welcome to {{project}}."
  let data : Json = {
    "name": "Developer",
    "project": "Stencil",
  }

  try {
    let result = @stencil.render(template, data)
    println(result)
  } catch {
    @stencil.TemplateError(msg) => println("Template error: \{msg}")
  }
}

Hello Developer! Welcome to Stencil.

#API

#render(template : String, data : Json) -> String raise TemplateError

#compile(source : String) -> Template raise TemplateError

#Template::render(self : Template, data : Json) -> String

#render_with_partials(template : String, data : Json, partials : Map[String, String]) -> String raise TemplateError

#Template::render_with(self : Template, data : Json, partials : Map[String, String]) -> String

#RenderOptions and checked rendering

let options = @stencil.RenderOptions::default()
  .with_max_output_length(1_000_000)
  .with_missing_partial(@stencil.MissingPartialPolicy::Error)
let html = @stencil.render_with_options_and_partials(template, data, partials, options)

#PartialStore

#Diagnostics and analysis

moon run cli -- analyze
moon run cli -- compatibility
moon run cli -- benchmark

#Mustache Compatibility Notes

• Variables and raw variables
• Truthy and falsey section rendering
• List iteration with {{.}}
• Nested object contexts
• Inverted sections
• Partials
• Comments
• Dotted-path lookup
• Standalone comments and section control lines using the default delimiters
• Delimiter changes such as {{=<% %>=}}<%name%>

• Missing keys render as empty strings
• Arrays stringify as [Array] outside section iteration
• Objects stringify as [Object] outside section traversal
• Missing partials render as empty strings only through legacy APIs; configured APIs can error or preserve the tag
• Invalid partial source is ignored by legacy render_with_partials / Template::render_with, while configured APIs report it
• Parser sections and partial expansion default to 256 nested levels; RenderOptions can lower or remove the render-time limits
• Mustache lambdas, expression evaluation, filesystem partial loading, and dynamic partial names are outside the current scope

#Examples

#HTML-safe output

let tpl = "<p>{{content}}</p>"
let result = @stencil.render(tpl, { "content": "<script>alert(1)</script>" })
// <p>&lt;script&gt;alert(1)&lt;/script&gt;</p>

#Reusing a compiled template

let tpl = @stencil.compile("User: {{name}}")
println(tpl.render({ "name": "Alice" }))
println(tpl.render({ "name": "Bob" }))

#Partials with indentation

let template = "items:\n  {{>item}}\ndone"
let partials = {
  "item": "- {{name}}\n- ready",
}
let data : Json = { "name": "Stencil" }
let result = @stencil.render_with_partials(template, data, partials)

items:
  - Stencil
  - ready
done

#Production-style email snippet

let template =
  "Hello {{user.name}},\n" +
  "{{#items}}- {{title}}: {{status}}\n{{/items}}" +
  "{{^items}}No pending tasks.\n{{/items}}"

let data : Json = {
  "user": { "name": "Ops Team" },
  "items": [
    { "title": "CI", "status": "green" },
    { "title": "Release", "status": "pending" },
  ],
}

#CLI Demo

moon run cli

#Development

moon fmt --check
moon check --deny-warn --target all
moon build --target wasm,wasm-gc,js
moon info --target all
git diff --ignore-blank-lines --exit-code
moon test --deny-warn --target wasm,wasm-gc,js

moon test --deny-warn --target native
moon build --target native

#CI and Toolchain Notes

• moon fmt --check src
• moon check --deny-warn --target all
• moon build --target wasm,wasm-gc,js
• moon info --target all
• git diff --ignore-blank-lines --exit-code (interface drift check; ignores toolchain-only blank-line churn)
• moon test --deny-warn --target ...
• moon run cli -- benchmark (deterministic benchmark smoke check)

• GitHub workflow
• GitLink workflow

#OSC2026 Self-Check

powershell -ExecutionPolicy Bypass -File scripts\verify_acceptance.ps1

• repository structure,
• README and license presence,
• GitHub and GitLink CI files,
• commit history summary,
• default branch visibility,
• MoonBit source scale and test-suite floor,
• local verification commands.

#Performance Baseline

powershell -ExecutionPolicy Bypass -File scripts\benchmark.ps1 -Iterations 5

#License