MPS: Skill for Claude Code

MPS Actions Aspect

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 actions aspect customizes how new nodes of a concept are constructed by the MPS editor — typically during substitution, side transformations, right-transform/<ctrl-space> replacement, or auto-replace. The framework produces an empty instance of the target concept; the setup function then populates it, often copying fields from the node it is replacing (sampleNode). Lives in <lang>/models/<lang>.actions.mps, language jetbrains.mps.lang.actions. The aspect also hosts copy/paste handlers and paste wrappers (see references/copy-paste-and-paste-wrappers.md).

Critical Directives

• One NodeFactories root per actions model; add per-concept NodeFactory children to it. Do not create one root per concept.
• One NodeFactory per applicableConcept. Multiple factories for the same concept are not merged.
• The setup function runs before newNode is attached to the model. newNode.parent, ancestors, and model-wide queries return null/empty. Use the enclosingNode implicit parameter when you need the would-be parent.
• sampleNode is typed as node<BaseConcept>. Always narrow with ifInstanceOf (sampleNode is <Concept> original) before accessing fields — direct dereference will NPE or fail to compile.
• Use SPropertyAccess (ref property → PropertyDeclaration) for properties; use SLinkAccess (ref link → LinkDeclaration) for both containment and reference child roles.
• Factories do not fire for quotations <C()>, model.add root(<C()>), model.add new root(C), or pure rendering. If you need factory-initialised nodes in generator code, use new node<C>() with explicit property assignments or route creation through an intention that calls add new initialized.
• Edit factories through MPS MCP tools (mps_mcp_insert_root_node_from_json, mps_mcp_update_node, optionally mps_mcp_parse_java_and_insert with featureKind: "STATEMENTS" for the body). Do not hand-edit .mps files.
• After editing, validate with mps_mcp_check_root_node_problems on the NodeFactories root and rebuild the language.