[sergej-koscejev]

Summary

Solutions created with a generated usage preset (text, java, java-tests, java-mps-plugin) now get the default output root ${module}/source_gen, like languages already did. MPS then writes no generatorOutputPath attribute, so their models generate.

 createSolutionModule(name, descriptor, preset)
   add facets for preset
+  if preset != NOT_GENERATED
+    outputRoot = "${module}/source_gen"

Why: SolutionDescriptorPersistence (checked on MPS 2024.1 and 2026.1) saves a null output root as generatorOutputPath="", which means "no output path". An output root equal to ${module}/source_gen is saved as no attribute, which MPS reads back as the default.

Sibling paths: mops create solution and Code Mode project.createSolution both go through ModuleCreator.createSolution, so both get the fix. Edit batches do not create modules.

Left as is:

• not-generated keeps generatorOutputPath="" (see make: a not-generated solution is still generated and fails, sometimes with no message #226).
• The descriptor still has <sourceRoot path="${module}/models" /> where MPS writes <sourceRoot location="models" />. MPS loads both. Changing it means replacing the DefaultModelRoot.createDescriptor call for languages and solutions, so it is not a one-line change and is not in this PR.

Evidence

On MPS 2024.1.6 with _theSimplestLanguage:

• Before: mops create solution repro.java --usage-preset java writes <solution … moduleVersion="0" generatorOutputPath="">; mops make module repro.java after adding a class fails with No output location specified for model repro.java.main. mops test on a java-tests solution reports BUILD_FAILED.

  After: the .msd has no generatorOutputPath for all four generated presets; make module reports success and writes source_gen/…/Example.java and classes_gen/…/Example.class; mops test on a java-tests solution with a JUnit 3 test reports SUCCESS: 1 passed.

New tests:

• ModuleCreationSemanticsTest: solution of a generated preset keeps the default generator output path, one case per generated preset. Failed for all four before the fix.
• CreatedSolutionIntegrationTest: creates a java-tests solution with mops create solution, adds a model with a JUnit 3 test, then make module succeeds and mops test --no-build passes. Without the fix it fails at make with "no output location".

Merge Danger

Blast Radius: small. Only descriptors of newly created solutions change.

Fixes #199