From 7f2cac3c7af319964d943a6f349593608dcd6d45 Mon Sep 17 00:00:00 2001
From: Joel Wilcox <jwilcox@squareup.com>
Date: Thu, 15 Dec 2022 16:54:37 -0800
Subject: [PATCH] Update error message when there are no supertypes for the
 binding parameter.

---
 .../codegen/dagger/BindsMethodValidator.kt    |  9 +++--
 .../dagger/BindsMethodValidatorTest.kt        | 36 +++++++++++++++++--
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/compiler/src/main/java/com/squareup/anvil/compiler/codegen/dagger/BindsMethodValidator.kt b/compiler/src/main/java/com/squareup/anvil/compiler/codegen/dagger/BindsMethodValidator.kt
index 30e4d279f..67db5c504 100644
--- a/compiler/src/main/java/com/squareup/anvil/compiler/codegen/dagger/BindsMethodValidator.kt
+++ b/compiler/src/main/java/com/squareup/anvil/compiler/codegen/dagger/BindsMethodValidator.kt
@@ -81,10 +81,15 @@ internal class BindsMethodValidator : PrivateCodeGenerator() {
         .map { it.shortName }
         .toList()
 
+      val superTypesMessage = if (paramSuperTypes.size == 1) {
+        "has no supertypes."
+      } else {
+        "only has the following supertypes: ${paramSuperTypes.drop(1)}"
+      }
       throw AnvilCompilationExceptionFunctionReference(
         message = "@Binds methods' parameter type must be assignable to the return type. " +
-          "Expected return type of $returnType but impl parameter of type " +
-          "${paramSuperTypes.first()} only has the following supertypes: $paramSuperTypes",
+          "Expected binding of type $returnType but impl parameter of type " +
+          "${paramSuperTypes.first()} $superTypesMessage",
         functionReference = function
       )
     }
diff --git a/compiler/src/test/java/com/squareup/anvil/compiler/dagger/BindsMethodValidatorTest.kt b/compiler/src/test/java/com/squareup/anvil/compiler/dagger/BindsMethodValidatorTest.kt
index 63c369bd5..f64a20c41 100644
--- a/compiler/src/test/java/com/squareup/anvil/compiler/dagger/BindsMethodValidatorTest.kt
+++ b/compiler/src/test/java/com/squareup/anvil/compiler/dagger/BindsMethodValidatorTest.kt
@@ -55,8 +55,40 @@ class BindsMethodValidatorTest(
       )
       if (!useDagger) {
         assertThat(messages).contains(
-          "Expected return type of Bar but impl parameter of type Foo only has the following " +
-            "supertypes: [Foo, Ipsum, Lorem]"
+          "Expected binding of type Bar but impl parameter of type Foo only has the following " +
+            "supertypes: [Ipsum, Lorem]"
+        )
+      }
+    }
+  }
+
+  @Test
+  fun `a binding with an incompatible parameter type with no supertypes fails to compile`() {
+    compile(
+      """
+      package com.squareup.test
+ 
+      import dagger.Binds
+      import dagger.Module
+      import javax.inject.Inject
+
+      class Foo @Inject constructor()
+      interface Bar
+
+      @Module
+      abstract class BarModule {
+        @Binds
+        abstract fun bindsBar(impl: Foo): Bar
+      }
+      """
+    ) {
+      assertThat(exitCode).isError()
+      assertThat(messages).contains(
+        "@Binds methods' parameter type must be assignable to the return type"
+      )
+      if (!useDagger) {
+        assertThat(messages).contains(
+          "Expected binding of type Bar but impl parameter of type Foo has no supertypes."
         )
       }
     }