Fix remaining compiler and VM review findings

lynglib/src/commonTest/kotlin/CompilerVmReviewRegressionTest.kt

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2026 Sergey S. Chernov
+ *
+ * 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.
+ */
+
+import kotlinx.coroutines.test.runTest
+import net.sergeych.lyng.Compiler
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.Script
+import net.sergeych.lyng.ScriptError
+import net.sergeych.lyng.Source
+import net.sergeych.lyng.asFacade
+import net.sergeych.lyng.obj.ObjString
+import net.sergeych.lyng.obj.toInt
+import net.sergeych.lyng.pacman.ImportManager
+import kotlin.test.Test
+import kotlin.test.assertContains
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+
+class CompilerVmReviewRegressionTest {
+
+    @Test
+    fun missingModuleCaptureFailsFastInsteadOfBecomingUnset() = runTest {
+        val manager = ImportManager()
+        manager.addTextPackages(
+            """
+            package foo
+
+            val answer = 42
+            """.trimIndent()
+        )
+        val script = Compiler.compile(
+            Source(
+                "<missing-module-capture>",
+                """
+                import foo
+                fun make() = { answer }
+                make()
+                """.trimIndent()
+            ),
+            manager
+        )
+
+        val prepared = manager.newModule()
+        script.importInto(prepared)
+        val preparedLambda = script.execute(prepared)
+        assertEquals(42, prepared.asFacade().call(preparedLambda).toInt())
+
+        val rawModule = manager.newModule()
+        val hostScope = Scope(parent = rawModule, thisObj = ObjString("receiver"))
+
+        val lambda = script.execute(hostScope)
+        val ex = assertFailsWith<ScriptError> {
+            hostScope.asFacade().call(lambda)
+        }
+        assertContains(ex.errorMessage, "module binding 'answer'")
+    }
+
+    @Test
+    fun subjectlessWhenReportsScriptError() = runTest {
+        val ex = assertFailsWith<ScriptError> {
+            Compiler.compile(
+                Source(
+                    "<when-without-subject>",
+                    """
+                    when {
+                        true -> 1
+                    }
+                    """.trimIndent()
+                ),
+                Script.defaultImportManager
+            )
+        }
+        assertContains(ex.errorMessage, "when without subject")
+    }
+}