Allow mapping scalars to simple generic types

libraries/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/codegen/java/JavaResolver.kt

@@ -10,6 +10,7 @@ import com.apollographql.apollo.compiler.codegen.ResolverClassName
 import com.apollographql.apollo.compiler.codegen.ResolverEntry
 import com.apollographql.apollo.compiler.codegen.ResolverKey
 import com.apollographql.apollo.compiler.codegen.ResolverKeyKind
+import com.apollographql.apollo.compiler.codegen.java.helpers.bestGuess
 import com.apollographql.apollo.compiler.codegen.java.helpers.singletonAdapterInitializer
 import com.apollographql.apollo.compiler.ir.IrCatchTo
 import com.apollographql.apollo.compiler.ir.IrCompositeType2
@@ -245,22 +246,6 @@ internal class JavaResolver(
     }
   }
 
-  /**
-   * Best guess a type name. Handles simple generics like `Map<String, Integer>`, but no variance or wildcards.
-   */
-  private fun bestGuess(name: String): TypeName? {
-    val className = ClassName.bestGuess(name.substringBefore('<'))
-    val typeArgs = name.substringAfter('<', "").substringBefore('>', "")
-        .split(',')
-        .filterNot { it.isEmpty() }
-        .map { it.trim() }
-    return if (typeArgs.isEmpty()) {
-      className
-    } else {
-      ParameterizedTypeName.get(className, *typeArgs.map { bestGuess(it) }.toTypedArray())
-    }
-  }
-
   fun resolveCompiledType(name: String): CodeBlock {
     return CodeBlock.of("$T.$type", resolveAndAssert(ResolverKeyKind.SchemaType, name))
   }

libraries/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/codegen/java/helpers/bestGuess.kt

@@ -0,0 +1,51 @@
+package com.apollographql.apollo.compiler.codegen.java.helpers
+
+import com.squareup.javapoet.ClassName
+import com.squareup.javapoet.ParameterizedTypeName
+import com.squareup.javapoet.TypeName
+
+/**
+ * Best guess a type name. Handles simple generics like `Map<String, Integer>`, but no variance or wildcards.
+ */
+internal fun bestGuess(name: String): TypeName? {
+  val className = ClassName.bestGuess(name.substringBefore('<').withPackage())
+  val typeArgs = name.substringAfter('<', "").substringBefore('>', "")
+      .split(',')
+      .filterNot { it.isEmpty() }
+      .map { it.trim() }
+  return if (typeArgs.isEmpty()) {
+    className
+  } else {
+    ParameterizedTypeName.get(className, *typeArgs.map { bestGuess(it) }.toTypedArray())
+  }
+}
+
+private fun String.withPackage(): String {
+  return if (this in commonJavaTypes) {
+    "java.lang.${this}"
+  } else if (this in commonJavaCollectionsTypes) {
+    "java.util.${this}"
+  } else {
+    this
+  }
+}
+
+private val commonJavaTypes = setOf(
+    "Boolean",
+    "Byte",
+    "Character",
+    "Double",
+    "Float",
+    "Integer",
+    "Iterable",
+    "Long",
+    "Short",
+    "String",
+)
+
+private val commonJavaCollectionsTypes = setOf(
+    "Collection",
+    "List",
+    "Map",
+    "Set",
+)

libraries/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/codegen/kotlin/KotlinResolver.kt

@@ -9,6 +9,7 @@ import com.apollographql.apollo.compiler.codegen.ResolverClassName
 import com.apollographql.apollo.compiler.codegen.ResolverEntry
 import com.apollographql.apollo.compiler.codegen.ResolverKey
 import com.apollographql.apollo.compiler.codegen.ResolverKeyKind
+import com.apollographql.apollo.compiler.codegen.kotlin.helpers.bestGuess
 import com.apollographql.apollo.compiler.codegen.kotlin.helpers.obj
 import com.apollographql.apollo.compiler.ir.IrCatchTo
 import com.apollographql.apollo.compiler.ir.IrCompositeType2
@@ -148,24 +149,6 @@ internal class KotlinResolver(
     }
   }
 
-  /**
-   * Best guess a type name. Handles simple generics like `Map<String, Int?>`, but no variance or wildcards.
-   */
-  private fun bestGuess(name: String): TypeName {
-    val isNullable = name.endsWith('?')
-    val className = ClassName.bestGuess(name.substringBeforeLast('?').substringBefore('<'))
-    val typeArgs = name.substringAfter('<', "").substringBefore('>', "")
-        .split(',')
-        .filterNot { it.isEmpty() }
-        .map { it.trim() }
-    return if (typeArgs.isEmpty()) {
-      className
-    } else {
-      className.parameterizedBy(typeArgs.map { bestGuess(it) })
-    }
-        .copy(nullable = isNullable)
-  }
-
   internal fun resolveIrType2(type: IrType2): TypeName {
     return when (type) {
       is IrNonNullType2 -> resolveIrType2(type.ofType).copy(nullable = false)

libraries/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/codegen/kotlin/helpers/bestGuess.kt

@@ -0,0 +1,63 @@
+package com.apollographql.apollo.compiler.codegen.kotlin.helpers
+
+import com.squareup.kotlinpoet.ClassName
+import com.squareup.kotlinpoet.ParameterizedTypeName.Companion.parameterizedBy
+import com.squareup.kotlinpoet.TypeName
+
+/**
+ * Best guess a type name. Handles simple generics like `Map<String, Int?>`, but no variance or wildcards.
+ * Common types such as `String`, `List`, `Map` are automatically prefixed with `kotlin.` or `kotlin.collections.`.
+ */
+internal fun bestGuess(name: String): TypeName {
+  val isNullable = name.endsWith('?')
+  val className = ClassName.bestGuess(name.substringBeforeLast('?').substringBefore('<').withPackage())
+  val typeArgs = name.substringAfter('<', "").substringBefore('>', "")
+      .split(',')
+      .filterNot { it.isEmpty() }
+      .map { it.trim() }
+  return if (typeArgs.isEmpty()) {
+    className
+  } else {
+    className.parameterizedBy(typeArgs.map { bestGuess(it) })
+  }
+      .copy(nullable = isNullable)
+}
+
+private fun String.withPackage(): String {
+  return if (this in commonKotlinTypes) {
+    "kotlin.${this}"
+  } else if (this in commonKotlinCollectionsTypes) {
+    "kotlin.collections.${this}"
+  } else {
+    this
+  }
+}
+
+private val commonKotlinTypes = setOf(
+    "Any",
+    "Boolean",
+    "Byte",
+    "Char",
+    "CharSequence",
+    "Double",
+    "Float",
+    "Int",
+    "Long",
+    "Number",
+    "Short",
+    "String",
+    "UByte",
+    "UInt",
+    "ULong",
+    "Unit",
+    "UShort",
+)
+
+private val commonKotlinCollectionsTypes = setOf(
+    "Array",
+    "Collection",
+    "Iterable",
+    "List",
+    "Map",
+    "Set",
+)

libraries/apollo-compiler/src/test/kotlin/com/apollographql/apollo/compiler/CodegenTest.kt

@@ -305,15 +305,15 @@ class CodegenTest {
               "URL" to ScalarInfo("java.lang.String", ExpressionAdapterInitializer("com.example.UrlAdapter.INSTANCE")),
               "ID" to ScalarInfo("java.lang.Long"),
               "String" to ScalarInfo("java.lang.String", ExpressionAdapterInitializer("new com.example.MyStringAdapter()")),
-              "ListOfString" to ScalarInfo("java.util.List<java.lang.String>"),
+              "ListOfString" to ScalarInfo("List<String>"),
           )
         } else {
           mapOf(
               "Date" to ScalarInfo("java.util.Date"),
               "URL" to ScalarInfo("kotlin.String", ExpressionAdapterInitializer("com.example.UrlAdapter")),
               "ID" to ScalarInfo("kotlin.Long"),
               "String" to ScalarInfo("kotlin.String", ExpressionAdapterInitializer("com.example.MyStringAdapter()")),
-              "ListOfString" to ScalarInfo("kotlin.collections.List<kotlin.String?>"),
+              "ListOfString" to ScalarInfo("List<String?>"),
           )
         }
       } else {