This typically means the Dagger compiler was not applied to the library that defines the
+ * module. Factories for modules in the current compilation are generated by {@code
+ * ModuleProcessingStep} and may not yet be visible via {@link XProcessingEnv#findTypeElement}, so
+ * those modules are skipped.
+ *
+ * @see dagger#5146
+ */
+ public void checkGeneratedFactoriesAvailable(
+ ModuleDescriptor module, ValidationReport.Builder report) {
+ XTypeElement moduleElement = module.moduleElement();
+ if (isModuleFromCurrentCompilation(moduleElement)) {
+ return;
+ }
+ for (ContributionBinding binding : module.bindings()) {
+ if (binding.kind() != PROVISION && binding.kind() != PRODUCTION) {
+ continue;
+ }
+ if (!binding.bindingElement().isPresent()) {
+ continue;
+ }
+ XClassName factoryName = generatedClassNameForBinding(binding);
+ if (processingEnv.findTypeElement(factoryName) == null) {
+ report.addError(
+ String.format(
+ "The Dagger factory type %s is missing. This usually means the Dagger compiler was"
+ + " not applied to the module %s where the binding is defined. Ensure that the"
+ + " dependency that contains that module runs the Dagger annotation processor"
+ + " (or KSP plugin).",
+ factoryName.getCanonicalName(), moduleElement.getQualifiedName()),
+ moduleElement);
+ // One diagnostic per module is enough to point users at the root cause.
+ return;
+ }
+ }
}
/** Returns a validation report for a module type. */
diff --git a/javatests/dagger/internal/codegen/ModuleMissingFactoryErrorTest.java b/javatests/dagger/internal/codegen/ModuleMissingFactoryErrorTest.java
new file mode 100644
index 00000000000..94b97ef46d1
--- /dev/null
+++ b/javatests/dagger/internal/codegen/ModuleMissingFactoryErrorTest.java
@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) 2026 The Dagger Authors.
+ *
+ * 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 dagger.internal.codegen;
+
+import androidx.room3.compiler.processing.util.Source;
+import com.google.common.collect.ImmutableCollection;
+import com.google.common.collect.ImmutableList;
+import dagger.testing.compile.CompilerTests;
+import java.io.File;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
+
+/**
+ * Tests that using a {@code @Module} from a library that was not processed by Dagger yields a
+ * clear error (https://github.com/google/dagger/issues/5146).
+ */
+@RunWith(Parameterized.class)
+public class ModuleMissingFactoryErrorTest {
+ @Parameters(name = "{0}")
+ public static ImmutableCollection