Add basic Kotlin support (#5409)

* [Kotlin] Add kotlin generate code for tests and add
kotlin test to TestAll.sh

* [Kotlin] Add Kotlin generator

This change adds support for generating Kotlin classes.

The approach of this generator is to keep it as close
as possible to the java generator for now, in order
to keep the change simple.

It uses the already implemented java runtime,
so we don't support cross-platform nor js Kotlin yet.

Kotlin tests are just a copy of the java tests.

* Add optional ident support for CodeWriter

Identation is important for some languages and
different projects have different ways of ident
code, e.g. tabs vs spaces, so we are adding optional
support on CodeWriter for identation.

* [Kotlin] Add Documentation for Kotlin

* [Kotlin] Modify generated code to use experimental Unsigned types.

tests/namespace_test/NamespaceA/NamespaceB/EnumInNestedNS.kt

@@ -0,0 +1,15 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+package NamespaceA.NamespaceB
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class EnumInNestedNS private constructor() {
+    companion object {
+        const val A: Byte = 0
+        const val B: Byte = 1
+        const val C: Byte = 2
+        val names : Array<String> = arrayOf("A", "B", "C")
+        fun name(e: Int) : String = names[e]
+    }
+}

tests/namespace_test/NamespaceA/NamespaceB/StructInNestedNS.kt

@@ -0,0 +1,32 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+package NamespaceA.NamespaceB
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class StructInNestedNS : Struct() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : StructInNestedNS {
+        __init(_i, _bb)
+        return this
+    }
+    val a : Int get() = bb.getInt(bb_pos + 0)
+    fun mutateA(a: Int) : ByteBuffer = bb.putInt(bb_pos + 0, a)
+    val b : Int get() = bb.getInt(bb_pos + 4)
+    fun mutateB(b: Int) : ByteBuffer = bb.putInt(bb_pos + 4, b)
+    companion object {
+        fun createStructInNestedNS(builder: FlatBufferBuilder, a: Int, b: Int) : Int {
+            builder.prep(4, 8)
+            builder.putInt(b)
+            builder.putInt(a)
+            return builder.offset()
+        }
+    }
+}

tests/namespace_test/NamespaceA/NamespaceB/TableInNestedNS.kt

@@ -0,0 +1,53 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+package NamespaceA.NamespaceB
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class TableInNestedNS : Table() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : TableInNestedNS {
+        __init(_i, _bb)
+        return this
+    }
+    val foo : Int
+        get() {
+            val o = __offset(4)
+            return if(o != 0) bb.getInt(o + bb_pos) else 0
+        }
+    fun mutateFoo(foo: Int) : Boolean {
+        val o = __offset(4)
+        return if (o != 0) {
+            bb.putInt(o + bb_pos, foo)
+            true
+        } else {
+            false
+        }
+    }
+    companion object {
+        fun validateVersion() = Constants.FLATBUFFERS_1_11_1()
+        fun getRootAsTableInNestedNS(_bb: ByteBuffer): TableInNestedNS = getRootAsTableInNestedNS(_bb, TableInNestedNS())
+        fun getRootAsTableInNestedNS(_bb: ByteBuffer, obj: TableInNestedNS): TableInNestedNS {
+            _bb.order(ByteOrder.LITTLE_ENDIAN)
+            return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb))
+        }
+        fun createTableInNestedNS(builder: FlatBufferBuilder, foo: Int) : Int {
+            builder.startTable(1)
+            addFoo(builder, foo)
+            return endTableInNestedNS(builder)
+        }
+        fun startTableInNestedNS(builder: FlatBufferBuilder) = builder.startTable(1)
+        fun addFoo(builder: FlatBufferBuilder, foo: Int) = builder.addInt(0, foo, 0)
+        fun endTableInNestedNS(builder: FlatBufferBuilder) : Int {
+            val o = builder.endTable()
+            return o
+        }
+    }
+}

tests/namespace_test/NamespaceA/SecondTableInA.kt

@@ -0,0 +1,48 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+package NamespaceA
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class SecondTableInA : Table() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : SecondTableInA {
+        __init(_i, _bb)
+        return this
+    }
+    val referToC : NamespaceC.TableInC? get() = referToC(NamespaceC.TableInC())
+    fun referToC(obj: NamespaceC.TableInC) : NamespaceC.TableInC? {
+        val o = __offset(4)
+        return if (o != 0) {
+            obj.__assign(__indirect(o + bb_pos), bb)
+        } else {
+            null
+        }
+    }
+    companion object {
+        fun validateVersion() = Constants.FLATBUFFERS_1_11_1()
+        fun getRootAsSecondTableInA(_bb: ByteBuffer): SecondTableInA = getRootAsSecondTableInA(_bb, SecondTableInA())
+        fun getRootAsSecondTableInA(_bb: ByteBuffer, obj: SecondTableInA): SecondTableInA {
+            _bb.order(ByteOrder.LITTLE_ENDIAN)
+            return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb))
+        }
+        fun createSecondTableInA(builder: FlatBufferBuilder, referToCOffset: Int) : Int {
+            builder.startTable(1)
+            addReferToC(builder, referToCOffset)
+            return endSecondTableInA(builder)
+        }
+        fun startSecondTableInA(builder: FlatBufferBuilder) = builder.startTable(1)
+        fun addReferToC(builder: FlatBufferBuilder, referToC: Int) = builder.addOffset(0, referToC, 0)
+        fun endSecondTableInA(builder: FlatBufferBuilder) : Int {
+            val o = builder.endTable()
+            return o
+        }
+    }
+}

tests/namespace_test/NamespaceA/TableInFirstNS.kt

@@ -0,0 +1,68 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+package NamespaceA
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class TableInFirstNS : Table() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : TableInFirstNS {
+        __init(_i, _bb)
+        return this
+    }
+    val fooTable : NamespaceA.NamespaceB.TableInNestedNS? get() = fooTable(NamespaceA.NamespaceB.TableInNestedNS())
+    fun fooTable(obj: NamespaceA.NamespaceB.TableInNestedNS) : NamespaceA.NamespaceB.TableInNestedNS? {
+        val o = __offset(4)
+        return if (o != 0) {
+            obj.__assign(__indirect(o + bb_pos), bb)
+        } else {
+            null
+        }
+    }
+    val fooEnum : Byte
+        get() {
+            val o = __offset(6)
+            return if(o != 0) bb.get(o + bb_pos) else 0
+        }
+    fun mutateFooEnum(fooEnum: Byte) : Boolean {
+        val o = __offset(6)
+        return if (o != 0) {
+            bb.put(o + bb_pos, fooEnum)
+            true
+        } else {
+            false
+        }
+    }
+    val fooStruct : NamespaceA.NamespaceB.StructInNestedNS? get() = fooStruct(NamespaceA.NamespaceB.StructInNestedNS())
+    fun fooStruct(obj: NamespaceA.NamespaceB.StructInNestedNS) : NamespaceA.NamespaceB.StructInNestedNS? {
+        val o = __offset(8)
+        return if (o != 0) {
+            obj.__assign(o + bb_pos, bb)
+        } else {
+            null
+        }
+    }
+    companion object {
+        fun validateVersion() = Constants.FLATBUFFERS_1_11_1()
+        fun getRootAsTableInFirstNS(_bb: ByteBuffer): TableInFirstNS = getRootAsTableInFirstNS(_bb, TableInFirstNS())
+        fun getRootAsTableInFirstNS(_bb: ByteBuffer, obj: TableInFirstNS): TableInFirstNS {
+            _bb.order(ByteOrder.LITTLE_ENDIAN)
+            return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb))
+        }
+        fun startTableInFirstNS(builder: FlatBufferBuilder) = builder.startTable(3)
+        fun addFooTable(builder: FlatBufferBuilder, fooTable: Int) = builder.addOffset(0, fooTable, 0)
+        fun addFooEnum(builder: FlatBufferBuilder, fooEnum: Byte) = builder.addByte(1, fooEnum, 0)
+        fun addFooStruct(builder: FlatBufferBuilder, fooStruct: Int) = builder.addStruct(2, fooStruct, 0)
+        fun endTableInFirstNS(builder: FlatBufferBuilder) : Int {
+            val o = builder.endTable()
+            return o
+        }
+    }
+}

tests/namespace_test/NamespaceC/TableInC.kt

@@ -0,0 +1,59 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+package NamespaceC
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class TableInC : Table() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : TableInC {
+        __init(_i, _bb)
+        return this
+    }
+    val referToA1 : NamespaceA.TableInFirstNS? get() = referToA1(NamespaceA.TableInFirstNS())
+    fun referToA1(obj: NamespaceA.TableInFirstNS) : NamespaceA.TableInFirstNS? {
+        val o = __offset(4)
+        return if (o != 0) {
+            obj.__assign(__indirect(o + bb_pos), bb)
+        } else {
+            null
+        }
+    }
+    val referToA2 : NamespaceA.SecondTableInA? get() = referToA2(NamespaceA.SecondTableInA())
+    fun referToA2(obj: NamespaceA.SecondTableInA) : NamespaceA.SecondTableInA? {
+        val o = __offset(6)
+        return if (o != 0) {
+            obj.__assign(__indirect(o + bb_pos), bb)
+        } else {
+            null
+        }
+    }
+    companion object {
+        fun validateVersion() = Constants.FLATBUFFERS_1_11_1()
+        fun getRootAsTableInC(_bb: ByteBuffer): TableInC = getRootAsTableInC(_bb, TableInC())
+        fun getRootAsTableInC(_bb: ByteBuffer, obj: TableInC): TableInC {
+            _bb.order(ByteOrder.LITTLE_ENDIAN)
+            return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb))
+        }
+        fun createTableInC(builder: FlatBufferBuilder, referToA1Offset: Int, referToA2Offset: Int) : Int {
+            builder.startTable(2)
+            addReferToA2(builder, referToA2Offset)
+            addReferToA1(builder, referToA1Offset)
+            return endTableInC(builder)
+        }
+        fun startTableInC(builder: FlatBufferBuilder) = builder.startTable(2)
+        fun addReferToA1(builder: FlatBufferBuilder, referToA1: Int) = builder.addOffset(0, referToA1, 0)
+        fun addReferToA2(builder: FlatBufferBuilder, referToA2: Int) = builder.addOffset(1, referToA2, 0)
+        fun endTableInC(builder: FlatBufferBuilder) : Int {
+            val o = builder.endTable()
+            return o
+        }
+    }
+}