Holo Dev for VS Code

Syntax highlighting, intelligent autocomplete, diagnostics, and Go to Definition for the Hologram framework.

Install

VS Code

Search for "Holo Dev" in the Extensions panel, or install from Marketplace.

Cursor / Open VSX

Search for "Holo Dev" in Cursor's Extensions panel, or install from Open VSX.

Manual Install (VSIX)

If the extension isn't showing in your editor's marketplace yet:

Download the latest .vsix file from GitHub Releases
Open Command Palette (Cmd+Shift+P / Ctrl+Shift+P)
Run "Extensions: Install from VSIX..."
Select the downloaded .vsix file

Setup

All features work out of the box — the extension scans your .ex files to find pages, components, props, actions, commands, and Ash resource fields. No configuration required.

For the most accurate results (especially in projects with custom use wrappers or complex Ash resources), set up the optional Mix introspection task:

Mix Introspection (Optional, Recommended)

The mdis_holo_dev Elixir dependency provides a Mix task that introspects your compiled modules — giving the extension accurate data about pages, components, props, actions, commands, and Ash resource fields.

Add {:mdis_holo_dev, "~> 0.1", only: :dev} to your mix.exs deps
Run mix deps.get
Run the introspection task:

# One-shot — generates .holo_dev/*.json
mix holo_dev.introspect

# Watch mode — re-generates on recompile (run alongside phx.server)
mix holo_dev.introspect --watch

The extension watches .holo_dev/*.json and automatically picks up changes — no restart needed.

.holo_dev/ is automatically added to your .gitignore.

Features

Syntax Highlighting

Full syntax highlighting for .holo template files and ~HOLO""" sigils in Elixir files:

HTML tags and attributes
Hologram control flow: {%if}, {%else if}, {%else}, {%for}, {/if}, {/for}
Raw blocks: {%raw}...{/raw}
Elixir expressions: {expression}
Component tags: <MyComponent>
Event bindings: $click, $change, $submit, etc.
Expression attributes: count={@count}
<slot> tags
Embedded CSS in <style> and JavaScript in <script> blocks

Autocomplete

Event Types

Type $ inside an HTML tag to see all Hologram event types ($click, $change, $submit, etc.) sorted by usage frequency. The list is fully configurable.

Actions & Commands

After selecting an event type and typing =, the extension scans the current module and offers:

Actions without params — inserts text syntax: "my_action"
Actions with params — inserts expression shorthand: {:my_action, key: value}
Actions (longhand) — inserts full syntax with target/params placeholders
Commands — inserts longhand syntax: {command: :my_command}

State & Props

Type @ inside a ~HOLO template to see all available state variables and props from the current module.

Field Access

Type @place. when place is a prop with a known Ash resource type — the extension suggests its attributes (id, title, slug, etc.).

Page Completions

Type to={ inside a <Link> component or use put_page(component, in an action to see all available page modules with their routes.

Diagnostics

Unknown fields — @place.nonexistent warns with "Did you mean?" suggestions and quick fixes
Invalid pages — to={NonExistentPage} warns with similar page suggestions
Missing required props — warns when a required prop is not provided on a component
Unknown props — warns when an attribute doesn't match any declared prop

All diagnostics include quick fix actions (Cmd+.).

Go to Definition

Cmd+click (or Ctrl+click) navigation:

Context	Jumps to
`@variable`	`put_state(...)` or `prop :name` declaration
`$click="action"`	`def action(...)` or `def command(...)`
`<Component>`	Component module (configurable target)
`to={PageModule}`	Page module's template
`@place.title`	`attribute :title` in the Ash resource
`function_call()`	`def`/`defp` definition in the module
`layout ModuleName`	Layout module

Configuration

Setting	Default	Description
`holoDev.defaultJumpTarget`	`template`	Where Cmd+click lands on component tags: `template`, `init`, or `module`
`holoDev.eventTypes`	All 15 event types	Configurable event type list for autocomplete. Order = sort priority.
`holoDev.customComponents`	`[]`	Define additional components from deps with their props for validation.

Custom Components Example

"holoDev.customComponents": [
  {
    "module": "MyLib.Components.Button",
    "props": [
      { "name": "label", "type": "string", "required": true },
      { "name": "variant", "type": "string" }
    ]
  }
]

License

MIT

Holo Dev

MDIS