MPS: Skill for Claude Code

MPS TextGen Aspect

TextGen turns a model (usually the output of generation) into plain text files. It is how BaseLanguage becomes .java on disk, and how any text-targeting language serialises its models. Lives in <lang>/languageModels/textGen.mps, language jetbrains.mps.lang.textGen. Rule bodies are BaseLanguage + smodel + textgen-specific statements (append, indent buffer, with indent).

Prerequisite for any insert: the textGen model must exist (mps_mcp_create_model with modelName: "<lang>.textGen" — aspect ID textGen, case-sensitive, no @ suffix; see aspect-model-stereotypes.md) and must import jetbrains.mps.lang.textGen, jetbrains.mps.baseLanguage, and jetbrains.mps.lang.smodel as used languages before the first mps_mcp_insert_root_node_from_json. Missing any of these three causes node inserts to fail with unresolved-concept errors. See step 1 of the Common-Path Workflow.

Critical Directives

• One ConceptTextGenDeclaration root per concept you want to serialise. Only the file-generating root concept needs extension / filename / encoding; structural concepts inside the file need only textGenBlock.
• extension is a function body returning a string, not a literal property. It must return a string.
• TextGen dispatch is concept-exact, not polymorphic. An extending concept that wants the parent's serialisation must declare its own ConceptTextGenDeclaration (even an empty one) — or its output will be silently missing. See references/dispatch-and-base-component.md.
• The indentation buffer is a per-output-file depth counter. with indent / increase depth / decrease depth and the withIndent flag on NodeAppendPart only mutate the counter — whitespace is emitted only when indent buffer is called. Always pair append \n ; with indent buffer ; on the next line that should be indented. See references/indentation-model.md.
• Prefer with indent { ... } over paired increase depth ; … ; decrease depth ; — the block form cannot leak depth on an early return or exception. Use the paired form only when the scope is not a block.
• Use TextGen only when the final artifact is text. If your pipeline ends in a model-to-model transformation targeting another MPS language (e.g. BaseLanguage), you don't need TextGen — that language's own TextGen handles the final step.
• BinaryWriteOperation (write) cannot be mixed with text appends in the same ConceptTextGenDeclaration. A rule emits either text or bytes, not both.
• The older $ref{node.reference<target>} syntax is deprecated. Use a NodeAppendPart over a resolved node (or over .name).
• Edit textGen models through MPS MCP tools (mps_mcp_insert_root_node_from_json, mps_mcp_update_node). Do not hand-edit .mps files.
• After edits run mps_mcp_check_root_node_problems and rebuild the language; regenerate consumers.