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
@@ -96,7 +97,7 @@ internal class JavaResolver(
     val result = resolve(ResolverKey(kind, id))
 
     check(result != null) {
-        "Cannot resolve $kind($id). " +
+      "Cannot resolve $kind($id). " +
           "Have you set up an 'opposite link' on the downstream project to the schema module as a isADependencyOf(..)?"
     }
     return result
@@ -239,9 +240,9 @@ internal class JavaResolver(
     }
   }
 
-  private fun resolveScalarTarget(name: String): ClassName? {
+  private fun resolveScalarTarget(name: String): TypeName? {
     return scalarMapping[name]?.targetName?.let {
-      ClassName.bestGuess(it)
+      bestGuess(it)
     }
   }
 
@@ -427,7 +428,8 @@ internal class JavaResolver(
 }
 
 
-internal fun ResolverClassName.toJavaPoetClassName(): ClassName = ClassName.get(packageName, simpleNames[0], *simpleNames.drop(1).toTypedArray())
+internal fun ResolverClassName.toJavaPoetClassName(): ClassName =
+  ClassName.get(packageName, simpleNames[0], *simpleNames.drop(1).toTypedArray())
 
 
 private val primitiveTypeNames = setOf(TypeName.DOUBLE, TypeName.INT, TypeName.BOOLEAN)

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
@@ -43,7 +44,7 @@ internal class KotlinResolver(
     private val scalarMapping: Map<String, ScalarInfo>,
     private val requiresOptInAnnotation: String?,
 ) {
-  fun resolve(key: ResolverKey): ClassName?  {
+  fun resolve(key: ResolverKey): ClassName? {
     return classNames[key] ?: next?.resolve(key)
   }
 
@@ -60,7 +61,7 @@ internal class KotlinResolver(
 
     check(result != null) {
       "Cannot resolve $kind($id). " +
-        "Have you set up an 'opposite link' on the downstream project to the schema module as a isADependencyOf(..)?"
+          "Have you set up an 'opposite link' on the downstream project to the schema module as a isADependencyOf(..)?"
     }
     return result
   }
@@ -85,6 +86,7 @@ internal class KotlinResolver(
       type.optional -> {
         KotlinSymbols.Optional.parameterizedBy(resolveIrType(type.optional(false), jsExport, isInterface))
       }
+
       type.catchTo != IrCatchTo.NoCatch -> {
         resolveIrType(type.catchTo(IrCatchTo.NoCatch), jsExport, isInterface).let {
           when (type.catchTo) {
@@ -94,9 +96,11 @@ internal class KotlinResolver(
           }
         }
       }
+
       type.nullable -> {
         resolveIrType(type.nullable(false), jsExport, isInterface).copy(nullable = true)
       }
+
       else -> {
         when (type) {
           is IrListType -> resolveIrType(type.ofType, jsExport, isInterface).wrapInList(jsExport, isInterface)
@@ -139,9 +143,9 @@ internal class KotlinResolver(
     return listType.parameterizedBy(param)
   }
 
-  private fun resolveScalarTarget(name: String): ClassName? {
+  private fun resolveScalarTarget(name: String): TypeName? {
     return scalarMapping[name]?.targetName?.let {
-      ClassName.bestGuess(it)
+      bestGuess(it)
     }
   }
 
@@ -203,6 +207,7 @@ internal class KotlinResolver(
         val presentFun = MemberName("com.apollographql.apollo.api", "present")
         CodeBlock.of("%L.%M()", adapterInitializer(type.optional(false), requiresBuffering, jsExport), presentFun)
       }
+
       type.catchTo != IrCatchTo.NoCatch -> {
         adapterInitializer(type.catchTo(IrCatchTo.NoCatch), requiresBuffering, jsExport).let {
           val member = when (type.catchTo) {
@@ -213,11 +218,13 @@ internal class KotlinResolver(
           CodeBlock.of("%L.%M()", it, member)
         }
       }
+
       type.maybeError -> {
         adapterInitializer(type.maybeError(false), requiresBuffering, jsExport).let {
           CodeBlock.of("%L.%M()", it, KotlinSymbols.errorAware)
         }
       }
+
       type.nullable -> {
         // Don't hardcode the adapter when the scalar is mapped to a user-defined type
         val scalarWithoutCustomMapping = type is IrScalarType && !scalarMapping.containsKey(type.name)
@@ -237,6 +244,7 @@ internal class KotlinResolver(
           }
         }
       }
+
       else -> {
         when (type) {
           is IrListType -> {

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/graphql/com/example/custom_scalar_type/TestOperation.graphql

@@ -10,3 +10,7 @@ query TestQuery {
     links
   }
 }
+
+query ScalarWithGenericType {
+  listOfString
+}