MPS: Skill for Claude Code

MPS Editor — Technical Reference

Loading companion skills

Companion names in this skill are lazy dependencies: load only those relevant to the current task. If this skill came from an MCP server, use the host's skill loader to resolve the companion's unique discovered entry URI on the same host-assigned originating server. If the host has no server-backed skill loader, stop and report that limitation; do not silently fall back to a filesystem copy. If this skill came from a filesystem catalog, load the named sibling from that same catalog at <skills-root>/<skill-name>/SKILL.md, even if remote skill loaders are also available. Do not invent a tool name or server endpoint.

The jetbrains.mps.lang.editor language defines projectional editors as trees of cell models (display elements) with cell layouts and style items. This skill is the technical lookup: concept names, suffixes, style classes, and the rules that decide which cell model to use where.

Critical Directives

• Always use CellModel_RefNodeList for 0..n or 1..n children. CellModel_RefNode is for single cardinality only.
• Use IndentLayoutOnNewLineStyleClassItem (apply to the cell that should start on a new line) instead of the legacy IndentLayoutNewLineStyle (applied to the cell before the break) — the latter is easier to get wrong.
• Reference cells: set the internal CellModel_Property (e.g. name) inside an InlineEditorComponent to readOnly=true so the referenced target cannot be accidentally renamed through the editor.
• Smart references: no wrapping layout cell — just a single CellModel_RefCell whose editorComponent is an InlineEditorComponent with a CellModel_Property (relationDeclaration: name, readOnly: true).
• List empty state: a CellModel_RefNodeList already synthesizes an editable empty cell, shown as << ... >> (caret lands there, Ctrl+Space works). Add an explicit emptyCellModel (e.g. a CellModel_Constant "<no items>") only to customize the empty cell — but a plain constant is read-only and loses the instant-typing, so to keep it, put the hint in the constant's nullText (not text) and add an EditableStyleClassItem (flag=true). See the Editable Empty-List Placeholder pattern in references/editor-patterns.md.
• Inheritance: components can be reused if defined for the concept, its super-concepts, or implemented interfaces.
• Componentize shared cells: when several concept editors repeat the same cell group, factor it into an EditorComponentDeclaration (bound to the most general concept or interface that owns the relations) and reuse it via CellModel_Component. See references/editor-components.md.
• Stylesheets: check for existing style classes in extended languages before creating new ones in a StyleSheet node. Apply a class with the cell's parentStyleClass reference or an ApplyStyleClass style item (references/cell-models.md).