diff --git a/maddi-inspection-openjdk/src/test/java/io/codelaser/maddi/inspection/openjdk/TestRemoveAllSourcesWithOneNameInTwoSourceSets.java b/maddi-inspection-openjdk/src/test/java/io/codelaser/maddi/inspection/openjdk/TestRemoveAllSourcesWithOneNameInTwoSourceSets.java
new file mode 100644
index 000000000..7e71edcec
--- /dev/null
+++ b/maddi-inspection-openjdk/src/test/java/io/codelaser/maddi/inspection/openjdk/TestRemoveAllSourcesWithOneNameInTwoSourceSets.java
@@ -0,0 +1,94 @@
+/*
+ * maddi: a modification analyzer for duplication detection and immutability.
+ * Copyright 2020-2026, CodeLaser BV, https://github.com/CodeLaser/maddi
+ *
+ * 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.
+ */
+
+package io.codelaser.maddi.inspection.openjdk;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.net.URI;
+import java.util.List;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import io.codelaser.maddi.cst.api.element.CompilationUnit;
+import io.codelaser.maddi.cst.api.element.SourceSet;
+import io.codelaser.maddi.cst.api.info.TypeInfo;
+import io.codelaser.maddi.cst.api.runtime.Runtime;
+import io.codelaser.maddi.cst.impl.runtime.RuntimeImpl;
+import io.codelaser.maddi.inspection.resource.InfoByFqn;
+import io.codelaser.maddi.inspection.resource.SourceSetImpl;
+
+/**
+ * {@link InfoByFqn#removeAllSources()} forgets every source type, also a name that two source sets both define.
+ *
+ * Where it was found
+ * refactor.codelaser.io, dropping the project hibernate-orm--main (2026-11-13):
+ *
+ * WARN ProjectServiceImpl - Releasing the old model's inspector of hibernate-orm--main failed
+ * java.lang.UnsupportedOperationException
+ * at java.util.ImmutableCollections$AbstractImmutableCollection.removeIf
+ * at io.codelaser.maddi.inspection.resource.InfoByFqn.lambda$removeAllSources$0(InfoByFqn.java:83)
+ * at io.codelaser.maddi.inspection.openjdk.JavaInspectorImpl.invalidateAllSources(JavaInspectorImpl.java:221)
+ *
+ * A name defined in several source sets is registered with a list built by {@code List.of} or
+ * {@code Stream.toList()}, and those lists cannot be changed: {@code removeIf} on them throws. hibernate-orm has 60
+ * source sets and many class names defined in more than one. The exception stops
+ * {@code JavaInspectorImpl.invalidateAllSources()} at its first line, so the javac file managers and the shared jar
+ * archives it should close stay open.
+ */
+public class TestRemoveAllSourcesWithOneNameInTwoSourceSets {
+
+ @DisplayName("a name defined in two source sets is forgotten; a library type with another name stays")
+ @Test
+ public void bothSourceCopiesGoTheLibraryTypeStays() {
+ Runtime runtime = new RuntimeImpl();
+ SourceSet main = sourceSet("core/main");
+ SourceSet test = sourceSet("core/test");
+ SourceSet jar = new SourceSetImpl.Builder().setName("lib-1.0.jar").setUri(URI.create("file:/lib-1.0.jar"))
+ .setLibrary(true).setExternalLibrary(true).build();
+ InfoByFqn registry = new InfoByFqn();
+
+ TypeInfo inMain = type(runtime, main, "a", "Helper");
+ registry.put(inMain.fullyQualifiedName(), inMain, main);
+ TypeInfo inTest = type(runtime, test, "a", "Helper");
+ registry.put(inTest.fullyQualifiedName(), inTest, test);
+ TypeInfo library = type(runtime, jar, "lib", "Thing");
+ registry.put(library.fullyQualifiedName(), library, main);
+ assertEquals(List.of(inMain, inTest), registry.allTypes("a.Helper"),
+ "set-up: both source sets define a.Helper, so the registry holds two copies of that name");
+
+ assertDoesNotThrow(registry::removeAllSources);
+
+ assertEquals(List.of(), registry.allTypes("a.Helper"),
+ "a.Helper is defined only in the source sets core/main and core/test; after removeAllSources the"
+ + " registry must hold no copy of it");
+ assertEquals(List.of(library), registry.allTypes("lib.Thing"),
+ "lib.Thing comes from lib-1.0.jar, which is not a source set; removeAllSources must keep it");
+ }
+
+ private static SourceSet sourceSet(String name) {
+ return new SourceSetImpl.Builder().setName(name).setUri(URI.create("file:/" + name)).build();
+ }
+
+ private static TypeInfo type(Runtime runtime, SourceSet sourceSet, String packageName, String simpleName) {
+ CompilationUnit cu = runtime.newCompilationUnitBuilder().setPackageName(packageName).setSourceSet(sourceSet)
+ .setURI(URI.create("file:/" + sourceSet.name() + "/" + simpleName + ".java")).build();
+ return runtime.newTypeInfo(cu, simpleName);
+ }
+}
diff --git a/maddi-inspection-resource/src/main/java/io/codelaser/maddi/inspection/resource/InfoByFqn.java b/maddi-inspection-resource/src/main/java/io/codelaser/maddi/inspection/resource/InfoByFqn.java
index 6677fb959..b9fa78913 100644
--- a/maddi-inspection-resource/src/main/java/io/codelaser/maddi/inspection/resource/InfoByFqn.java
+++ b/maddi-inspection-resource/src/main/java/io/codelaser/maddi/inspection/resource/InfoByFqn.java
@@ -80,7 +80,8 @@ public synchronized boolean markClassScannerSetupDone(TypeInfo typeInfo) {
public synchronized void removeAllSources() {
singleTypeByFqn.values().removeIf(InfoByFqn::isSourceType);
- multiTypeByFqn.values().forEach(list -> list.removeIf(InfoByFqn::isSourceType));
+ // rebuild: the lists in this map are immutable (List.of/Stream.toList), so removeIf would throw
+ multiTypeByFqn.replaceAll((fqn, list) -> list.stream().filter(ti -> !isSourceType(ti)).toList());
multiTypeByFqn.values().removeIf(List::isEmpty);
classScannerSetupDone.removeIf(InfoByFqn::isSourceType);
}