Check types parameter size in init (#1063)

* Add types size check in code gen

Resolves #932

* Add more useful message for mismatched generics lookup

* Add tests

* Style

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/api/AdapterGenerator.kt

@@ -18,6 +18,7 @@ package com.squareup.moshi.kotlin.codegen.api
 import com.squareup.kotlinpoet.ARRAY
 import com.squareup.kotlinpoet.AnnotationSpec
 import com.squareup.kotlinpoet.CodeBlock
+import com.squareup.kotlinpoet.CodeBlock.Companion
 import com.squareup.kotlinpoet.FileSpec
 import com.squareup.kotlinpoet.FunSpec
 import com.squareup.kotlinpoet.INT
@@ -158,6 +159,22 @@ internal class AdapterGenerator(
 
     if (typeVariables.isNotEmpty()) {
       result.addTypeVariables(typeVariables.map { it.stripTypeVarVariance() as TypeVariableName })
+      // require(types.size == 1) {
+      //   "TypeVariable mismatch: Expecting 1 type(s) for generic type variables [T], but received ${types.size} with values $types"
+      // }
+      result.addInitializerBlock(CodeBlock.builder()
+          .beginControlFlow("require(types.size == %L)", typeVariables.size)
+          .addStatement(
+              "buildString·{·append(%S).append(%L).append(%S).append(%S).append(%S).append(%L)·}",
+              "TypeVariable mismatch: Expecting ",
+              typeVariables.size,
+              " ${if (typeVariables.size == 1) "type" else "types"} for generic type variables [",
+              typeVariables.joinToString(", ") { it.name },
+              "], but received ",
+              "${typesParam.name}.size"
+          )
+          .endControlFlow()
+          .build())
     }
 
     // TODO make this configurable. Right now it just matches the source model

kotlin/tests/src/test/kotlin/com/squareup/moshi/kotlin/codegen/GeneratedAdaptersTest.kt

@@ -1220,6 +1220,30 @@ class GeneratedAdaptersTest {
       val propertyWithAnnotatedType: @TypeAnnotation String = "",
       val generic: List<@TypeAnnotation String>
   )
+
+  @Test fun typesSizeCheckMessages_noArgs() {
+    try {
+      moshi.adapter(MultipleGenerics::class.java)
+      fail("Should have failed to construct the adapter due to missing generics")
+    } catch (e: RuntimeException) {
+      assertThat(e).hasMessage("Failed to find the generated JsonAdapter constructor for 'class com.squareup.moshi.kotlin.codegen.GeneratedAdaptersTest\$MultipleGenerics'. Suspiciously, the type was not parameterized but the target class 'com.squareup.moshi.kotlin.codegen.GeneratedAdaptersTest_MultipleGenericsJsonAdapter' is generic. Consider using Types#newParameterizedType() to define these missing type variables.")
+    }
+  }
+
+  @Test fun typesSizeCheckMessages_wrongNumberOfArgs() {
+    try {
+      GeneratedAdaptersTest_MultipleGenericsJsonAdapter<String, Any, Any, Any>(
+          moshi,
+          arrayOf(String::class.java)
+      )
+      fail("Should have failed to construct the adapter due to wrong number of generics")
+    } catch (e: IllegalArgumentException) {
+      assertThat(e).hasMessage("TypeVariable mismatch: Expecting 4 types for generic type variables [A, B, C, D], but received 1")
+    }
+  }
+
+  @JsonClass(generateAdapter = true)
+  data class MultipleGenerics<A, B, C, D>(val prop: String)
 }
 
 // Regression test for https://github.com/square/moshi/issues/1022

moshi/src/main/java/com/squareup/moshi/internal/Util.java

@@ -517,9 +517,10 @@ public final class Util {
       return null;
     }
     String adapterClassName = Types.generatedJsonAdapterName(rawType.getName());
+    Class<? extends JsonAdapter<?>> adapterClass = null;
     try {
-      @SuppressWarnings("unchecked") // We generate types to match.
+      //noinspection unchecked - We generate types to match.
-          Class<? extends JsonAdapter<?>> adapterClass = (Class<? extends JsonAdapter<?>>)
+      adapterClass = (Class<? extends JsonAdapter<?>>)
           Class.forName(adapterClassName, true, rawType.getClassLoader());
       Constructor<? extends JsonAdapter<?>> constructor;
       Object[] args;
@@ -547,16 +548,24 @@ public final class Util {
       return constructor.newInstance(args).nullSafe();
     } catch (ClassNotFoundException e) {
       throw new RuntimeException(
-          "Failed to find the generated JsonAdapter class for " + rawType, e);
+          "Failed to find the generated JsonAdapter class for " + type, e);
     } catch (NoSuchMethodException e) {
-      throw new RuntimeException(
+      if (!(type instanceof ParameterizedType) && adapterClass.getTypeParameters().length != 0) {
-          "Failed to find the generated JsonAdapter constructor for " + rawType, e);
+        throw new RuntimeException(
+            "Failed to find the generated JsonAdapter constructor for '" + type
+            + "'. Suspiciously, the type was not parameterized but the target class '"
+            + adapterClass.getCanonicalName() + "' is generic. Consider using "
+            + "Types#newParameterizedType() to define these missing type variables.", e);
+      } else {
+        throw new RuntimeException(
+            "Failed to find the generated JsonAdapter constructor for " + type, e);
+      }
     } catch (IllegalAccessException e) {
       throw new RuntimeException(
-          "Failed to access the generated JsonAdapter for " + rawType, e);
+          "Failed to access the generated JsonAdapter for " + type, e);
     } catch (InstantiationException e) {
       throw new RuntimeException(
-          "Failed to instantiate the generated JsonAdapter for " + rawType, e);
+          "Failed to instantiate the generated JsonAdapter for " + type, e);
     } catch (InvocationTargetException e) {
       throw rethrowCause(e);
     }