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/union_vector/Attacker.kt

@@ -0,0 +1,51 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class Attacker : Table() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : Attacker {
+        __init(_i, _bb)
+        return this
+    }
+    val swordAttackDamage : Int
+        get() {
+            val o = __offset(4)
+            return if(o != 0) bb.getInt(o + bb_pos) else 0
+        }
+    fun mutateSwordAttackDamage(swordAttackDamage: Int) : Boolean {
+        val o = __offset(4)
+        return if (o != 0) {
+            bb.putInt(o + bb_pos, swordAttackDamage)
+            true
+        } else {
+            false
+        }
+    }
+    companion object {
+        fun validateVersion() = Constants.FLATBUFFERS_1_11_1()
+        fun getRootAsAttacker(_bb: ByteBuffer): Attacker = getRootAsAttacker(_bb, Attacker())
+        fun getRootAsAttacker(_bb: ByteBuffer, obj: Attacker): Attacker {
+            _bb.order(ByteOrder.LITTLE_ENDIAN)
+            return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb))
+        }
+        fun createAttacker(builder: FlatBufferBuilder, swordAttackDamage: Int) : Int {
+            builder.startTable(1)
+            addSwordAttackDamage(builder, swordAttackDamage)
+            return endAttacker(builder)
+        }
+        fun startAttacker(builder: FlatBufferBuilder) = builder.startTable(1)
+        fun addSwordAttackDamage(builder: FlatBufferBuilder, swordAttackDamage: Int) = builder.addInt(0, swordAttackDamage, 0)
+        fun endAttacker(builder: FlatBufferBuilder) : Int {
+            val o = builder.endTable()
+            return o
+        }
+    }
+}

tests/union_vector/BookReader.kt

@@ -0,0 +1,27 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class BookReader : Struct() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : BookReader {
+        __init(_i, _bb)
+        return this
+    }
+    val booksRead : Int get() = bb.getInt(bb_pos + 0)
+    fun mutateBooksRead(booksRead: Int) : ByteBuffer = bb.putInt(bb_pos + 0, booksRead)
+    companion object {
+        fun createBookReader(builder: FlatBufferBuilder, booksRead: Int) : Int {
+            builder.prep(4, 4)
+            builder.putInt(booksRead)
+            return builder.offset()
+        }
+    }
+}

tests/union_vector/Character.kt

@@ -0,0 +1,17 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class Character_ private constructor() {
+    companion object {
+        const val NONE: UByte = 0u
+        const val MuLan: UByte = 1u
+        const val Rapunzel: UByte = 2u
+        const val Belle: UByte = 3u
+        const val BookFan: UByte = 4u
+        const val Other: UByte = 5u
+        const val Unused: UByte = 6u
+        val names : Array<String> = arrayOf("NONE", "MuLan", "Rapunzel", "Belle", "BookFan", "Other", "Unused")
+        fun name(e: Int) : String = names[e]
+    }
+}

tests/union_vector/Movie.kt

@@ -0,0 +1,114 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class Movie : Table() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : Movie {
+        __init(_i, _bb)
+        return this
+    }
+    val mainCharacterType : UByte
+        get() {
+            val o = __offset(4)
+            return if(o != 0) bb.get(o + bb_pos).toUByte() else 0u
+        }
+    fun mutateMainCharacterType(mainCharacterType: UByte) : Boolean {
+        val o = __offset(4)
+        return if (o != 0) {
+            bb.put(o + bb_pos, mainCharacterType.toByte())
+            true
+        } else {
+            false
+        }
+    }
+    fun mainCharacter(obj: Table) : Table? {
+        val o = __offset(6); return if (o != 0) __union(obj, o) else null
+    }
+    fun charactersType(j: Int) : UByte {
+        val o = __offset(8)
+        return if (o != 0) {
+            bb.get(__vector(o) + j * 1).toUByte()
+        } else {
+            0u
+        }
+    }
+    val charactersTypeLength : Int
+        get() {
+            val o = __offset(8); return if (o != 0) __vector_len(o) else 0
+        }
+    val charactersTypeAsByteBuffer : ByteBuffer get() = __vector_as_bytebuffer(8, 1)
+    fun charactersTypeInByteBuffer(_bb: ByteBuffer) : ByteBuffer = __vector_in_bytebuffer(_bb, 8, 1)
+    fun mutateCharactersType(j: Int, charactersType: UByte) : Boolean {
+        val o = __offset(8)
+        return if (o != 0) {
+            bb.put(__vector(o) + j * 1, charactersType.toByte())
+            true
+        } else {
+            false
+        }
+    }
+    fun characters(obj: Table, j: Int) : Table? {
+        val o = __offset(10)
+        return if (o != 0) {
+            __union(obj, __vector(o) + j * 4 - bb_pos)
+        } else {
+            null
+        }
+    }
+    val charactersLength : Int
+        get() {
+            val o = __offset(10); return if (o != 0) __vector_len(o) else 0
+        }
+    companion object {
+        fun validateVersion() = Constants.FLATBUFFERS_1_11_1()
+        fun getRootAsMovie(_bb: ByteBuffer): Movie = getRootAsMovie(_bb, Movie())
+        fun getRootAsMovie(_bb: ByteBuffer, obj: Movie): Movie {
+            _bb.order(ByteOrder.LITTLE_ENDIAN)
+            return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb))
+        }
+        fun MovieBufferHasIdentifier(_bb: ByteBuffer) : Boolean = __has_identifier(_bb, "MOVI")
+        fun createMovie(builder: FlatBufferBuilder, mainCharacterType: UByte, mainCharacterOffset: Int, charactersTypeOffset: Int, charactersOffset: Int) : Int {
+            builder.startTable(4)
+            addCharacters(builder, charactersOffset)
+            addCharactersType(builder, charactersTypeOffset)
+            addMainCharacter(builder, mainCharacterOffset)
+            addMainCharacterType(builder, mainCharacterType)
+            return endMovie(builder)
+        }
+        fun startMovie(builder: FlatBufferBuilder) = builder.startTable(4)
+        fun addMainCharacterType(builder: FlatBufferBuilder, mainCharacterType: UByte) = builder.addByte(0, mainCharacterType.toByte(), 0)
+        fun addMainCharacter(builder: FlatBufferBuilder, mainCharacter: Int) = builder.addOffset(1, mainCharacter, 0)
+        fun addCharactersType(builder: FlatBufferBuilder, charactersType: Int) = builder.addOffset(2, charactersType, 0)
+        fun createCharactersTypeVector(builder: FlatBufferBuilder, data: UByteArray) : Int {
+            builder.startVector(1, data.size, 1)
+            for (i in data.size - 1 downTo 0) {
+                builder.addByte(data[i].toByte())
+            }
+            return builder.endVector()
+        }
+        fun startCharactersTypeVector(builder: FlatBufferBuilder, numElems: Int) = builder.startVector(1, numElems, 1)
+        fun addCharacters(builder: FlatBufferBuilder, characters: Int) = builder.addOffset(3, characters, 0)
+        fun createCharactersVector(builder: FlatBufferBuilder, data: IntArray) : Int {
+            builder.startVector(4, data.size, 4)
+            for (i in data.size - 1 downTo 0) {
+                builder.addOffset(data[i])
+            }
+            return builder.endVector()
+        }
+        fun startCharactersVector(builder: FlatBufferBuilder, numElems: Int) = builder.startVector(4, numElems, 4)
+        fun endMovie(builder: FlatBufferBuilder) : Int {
+            val o = builder.endTable()
+            return o
+        }
+        fun finishMovieBuffer(builder: FlatBufferBuilder, offset: Int) = builder.finish(offset, "MOVI")
+        fun finishSizePrefixedMovieBuffer(builder: FlatBufferBuilder, offset: Int) = builder.finishSizePrefixed(offset, "MOVI")
+    }
+}

tests/union_vector/Rapunzel.kt

@@ -0,0 +1,27 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class Rapunzel : Struct() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : Rapunzel {
+        __init(_i, _bb)
+        return this
+    }
+    val hairLength : Int get() = bb.getInt(bb_pos + 0)
+    fun mutateHairLength(hairLength: Int) : ByteBuffer = bb.putInt(bb_pos + 0, hairLength)
+    companion object {
+        fun createRapunzel(builder: FlatBufferBuilder, hairLength: Int) : Int {
+            builder.prep(4, 4)
+            builder.putInt(hairLength)
+            return builder.offset()
+        }
+    }
+}