From 9a9015190ca3a4832dcbe8cb104491d4c496e209 Mon Sep 17 00:00:00 2001
From: Brad Corso <bcorso@google.com>
Date: Thu, 28 Jan 2021 14:05:13 -0800
Subject: [PATCH] Fail fast with better error message when trying to use a type
 parameter with the @AssistedFactory creator method.

We're considering supporting this feature in the future, but until then we're adding a better error message.

See https://github.com/google/dagger/issues/2279

RELNOTES=Issue #2279: Adds better error message when trying to use a type parameter with @AssistedFactory creator method.
PiperOrigin-RevId: 354389636
---
 .../AssistedFactoryProcessingStep.java        |  6 ++++
 .../codegen/AssistedFactoryErrorsTest.java    | 30 +++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/java/dagger/internal/codegen/AssistedFactoryProcessingStep.java b/java/dagger/internal/codegen/AssistedFactoryProcessingStep.java
index 32b1019366c..b687b6b18d4 100644
--- a/java/dagger/internal/codegen/AssistedFactoryProcessingStep.java
+++ b/java/dagger/internal/codegen/AssistedFactoryProcessingStep.java
@@ -160,6 +160,12 @@ ValidationReport<TypeElement> validate(TypeElement factory) {
                   methodType.getReturnType()),
               method);
         }
+        if (!method.getTypeParameters().isEmpty()) {
+          report.addError(
+              "@AssistedFactory does not currently support type parameters in the creator "
+                  + "method. See https://github.com/google/dagger/issues/2279",
+              method);
+        }
       }
 
       if (abstractFactoryMethods.size() > 1) {
diff --git a/javatests/dagger/internal/codegen/AssistedFactoryErrorsTest.java b/javatests/dagger/internal/codegen/AssistedFactoryErrorsTest.java
index 0c22875342a..ec18cada26e 100644
--- a/javatests/dagger/internal/codegen/AssistedFactoryErrorsTest.java
+++ b/javatests/dagger/internal/codegen/AssistedFactoryErrorsTest.java
@@ -772,4 +772,34 @@ public void testInaccessibleFoo() {
       assertThat(compilation).succeeded();
     }
   }
+
+  @Test
+  public void testAssistedFactoryMethodWithTypeParametersFails() {
+    JavaFileObject foo =
+        JavaFileObjects.forSourceLines(
+            "test.Foo",
+            "package test;",
+            "",
+            "import dagger.assisted.AssistedInject;",
+            "import dagger.assisted.AssistedFactory;",
+            "",
+            "class Foo<T> {",
+            "  @AssistedInject",
+            "  Foo() {}",
+            "",
+            "  @AssistedFactory",
+            "  interface FooFactory {",
+            "    <T> Foo<T> create();",
+            "  }",
+            "}");
+
+    Compilation compilation = compilerWithOptions(compilerMode.javacopts()).compile(foo);
+    assertThat(compilation).failed();
+    assertThat(compilation).hadErrorCount(1);
+    assertThat(compilation)
+        .hadErrorContaining(
+            "@AssistedFactory does not currently support type parameters in the creator method.")
+        .inFile(foo)
+        .onLine(12);
+  }
 }