fix(mps-model-adapters): return null when resolving project module in an unresolvable project

Previously, the method failed while trying to cast null to a non-null type.

Author: Oleksandr Dzhychko

mps-model-adapters-plugin/src/test/kotlin/org/modelix/model/mpsadapters/MPSAreaTest.kt

@@ -0,0 +1,38 @@
+package org.modelix.model.mpsadapters
+
+import org.modelix.model.api.BuiltinLanguages
+import org.modelix.model.api.INode
+
+/*
+ * Copyright (c) 2023.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+class MPSAreaTest : MpsAdaptersTestBase("SimpleProject") {
+
+    fun testResolveModuleInNonExistingProject() {
+        val repositoryNode: INode = MPSRepositoryAsNode(mpsProject.repository)
+        val area = repositoryNode.getArea()
+        readAction {
+            val nonExistingProject = MPSProjectReference("nonExistingProject")
+            val module = repositoryNode.getChildren(BuiltinLanguages.MPSRepositoryConcepts.Repository.modules)
+                .single { it.getPropertyValue(BuiltinLanguages.jetbrains_mps_lang_core.INamedConcept.name) == "Solution1" }
+            val projectModuleReference = MPSProjectModuleReference((module.reference as MPSModuleReference).moduleReference, nonExistingProject)
+
+            val resolutionResult = area.resolveNode(projectModuleReference)
+
+            assertNull(resolutionResult)
+        }
+    }
+}

mps-model-adapters/src/main/kotlin/org/modelix/model/mpsadapters/MPSArea.kt

@@ -306,13 +306,24 @@ data class MPSArea(val repository: SRepository) : IArea, IAreaReference {
         val projectRef = if (ref is MPSProjectModuleReference) {
             ref.projectRef
         } else {
+            // XXX Prefix of `projectRef` is not checked.
+            // `projectRef` might actually be a ref to anything.
+            // This might trigger unexpected resolution results and undefined behavior.
+            // Similar missing checks exist for other references in `MPSArea`.
+            // See https://issues.modelix.org/issue/MODELIX-923
             val projectRef = serialized.substringAfter(MPSProjectModuleReference.SEPARATOR)
             NodeReference(projectRef)
         }
 
+        val resolvedNodeForProject = resolveNode(projectRef) ?: return null
+        check(resolvedNodeForProject is MPSProjectAsNode) {
+            "Resolved node `$resolvedNodeForProject` does not represent a project."
+        }
+        val resolvedProject = resolvedNodeForProject.project
+
         return moduleRef.resolve(repository)?.let {
             MPSProjectModuleAsNode(
-                project = (resolveNode(projectRef) as MPSProjectAsNode).project,
+                project = resolvedProject,
                 module = it,
             )
         }