Github user marmbrus commented on the pull request:
https://github.com/apache/spark/pull/9126#issuecomment-148234664
Unfortunately, I think these annotations may not be worthless and we might
be hitting a bug in the scala compiler. Consider the following class: `class
A(a: A) { def b = a }`
While `a` isn't explicitly declared as a `val`, the compiler is still
silently promoting it to a class field so that it can be used both in the
constructor and in function `b`. In Scala 2.10 at least this results in the
following bytecode:
```
...
private final int a;
flags: ACC_PRIVATE, ACC_FINAL
...
```
Where as `class A(@transient a: Int) { def b = a }` results in:
```
...
private final transient int a;
flags: ACC_PRIVATE, ACC_FINAL, ACC_TRANSIENT
...
```
You can play around with this yourself in the REPL:
```scala
$ build/sbt catalyst/console
scala> class A(a: Int) { def b = a }
defined class A
scala> org.apache.spark.sql.catalyst.expressions.codegen.DumpByteCode(new
A(1))
Classfile
/private/var/folders/36/cjkbrr953xg2p_krwrmn8h_r0000gn/T/spark-292994a3-dd85-4f32-bf2e-ba6f1365712e/$line3/$read$$iw$$iw$A.class
Last modified Oct 14, 2015; size 532 bytes
MD5 checksum f2a93222131c1a1c914498fd7d22ec13
Compiled from "<console>"
public class $line3.$read$$iw$$iw$A
SourceFile: "<console>"
InnerClasses:
public static #23= #20 of #22; //$iw$=class $line3/$read$$iw$ of
class $line3/$read
public static #23= #25 of #20; //$iw$=class $line3/$read$$iw$$iw$ of
class $line3/$read$$iw$
public static #26= #2 of #25; //A=class $line3/$read$$iw$$iw$A of
class $line3/$read$$iw$$iw$
Scala: length = 0x0
minor version: 0
major version: 50
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Utf8 $line3/$read$$iw$$iw$A
#2 = Class #1 // $line3/$read$$iw$$iw$A
#3 = Utf8 java/lang/Object
#4 = Class #3 // java/lang/Object
#5 = Utf8 <console>
#6 = Utf8 a
#7 = Utf8 I
#8 = Utf8 b
#9 = Utf8 ()I
#10 = NameAndType #6:#7 // a:I
#11 = Fieldref #2.#10 // $line3/$read$$iw$$iw$A.a:I
#12 = Utf8 this
#13 = Utf8 L$line3/$read$$iw$$iw$A;
#14 = Utf8 <init>
#15 = Utf8 (I)V
#16 = Utf8 ()V
#17 = NameAndType #14:#16 // "<init>":()V
#18 = Methodref #4.#17 // java/lang/Object."<init>":()V
#19 = Utf8 $line3/$read$$iw$
#20 = Class #19 // $line3/$read$$iw$
#21 = Utf8 $line3/$read
#22 = Class #21 // $line3/$read
#23 = Utf8 $iw$
#24 = Utf8 $line3/$read$$iw$$iw$
#25 = Class #24 // $line3/$read$$iw$$iw$
#26 = Utf8 A
#27 = Utf8 Code
#28 = Utf8 LocalVariableTable
#29 = Utf8 LineNumberTable
#30 = Utf8 SourceFile
#31 = Utf8 InnerClasses
#32 = Utf8 Scala
{
private final int a;
flags: ACC_PRIVATE, ACC_FINAL
public int b();
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: getfield #11 // Field a:I
4: ireturn
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this L$line3/$read$$iw$$iw$A;
LineNumberTable:
line 7: 0
public $line3.$read$$iw$$iw$A(int);
flags: ACC_PUBLIC
Code:
stack=2, locals=2, args_size=2
0: aload_0
1: iload_1
2: putfield #11 // Field a:I
5: aload_0
6: invokespecial #18 // Method
java/lang/Object."<init>":()V
9: return
LocalVariableTable:
Start Length Slot Name Signature
0 10 0 this L$line3/$read$$iw$$iw$A;
0 10 1 a I
LineNumberTable:
line 7: 0
}
```
```scala
scala> class A(@transient a: Int) { def b = a }
defined class A
scala> org.apache.spark.sql.catalyst.expressions.codegen.DumpByteCode(new
A(1))
Classfile
/private/var/folders/36/cjkbrr953xg2p_krwrmn8h_r0000gn/T/spark-292994a3-dd85-4f32-bf2e-ba6f1365712e/$line7/$read$$iw$$iw$A.class
Last modified Oct 14, 2015; size 532 bytes
MD5 checksum 0dc1337c7731bd1a88bf8f33bbfb9e4b
Compiled from "<console>"
public class $line7.$read$$iw$$iw$A
SourceFile: "<console>"
InnerClasses:
public static #23= #20 of #22; //$iw$=class $line7/$read$$iw$ of
class $line7/$read
public static #23= #25 of #20; //$iw$=class $line7/$read$$iw$$iw$ of
class $line7/$read$$iw$
public static #26= #2 of #25; //A=class $line7/$read$$iw$$iw$A of
class $line7/$read$$iw$$iw$
Scala: length = 0x0
minor version: 0
major version: 50
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Utf8 $line7/$read$$iw$$iw$A
#2 = Class #1 // $line7/$read$$iw$$iw$A
#3 = Utf8 java/lang/Object
#4 = Class #3 // java/lang/Object
#5 = Utf8 <console>
#6 = Utf8 a
#7 = Utf8 I
#8 = Utf8 b
#9 = Utf8 ()I
#10 = NameAndType #6:#7 // a:I
#11 = Fieldref #2.#10 // $line7/$read$$iw$$iw$A.a:I
#12 = Utf8 this
#13 = Utf8 L$line7/$read$$iw$$iw$A;
#14 = Utf8 <init>
#15 = Utf8 (I)V
#16 = Utf8 ()V
#17 = NameAndType #14:#16 // "<init>":()V
#18 = Methodref #4.#17 // java/lang/Object."<init>":()V
#19 = Utf8 $line7/$read$$iw$
#20 = Class #19 // $line7/$read$$iw$
#21 = Utf8 $line7/$read
#22 = Class #21 // $line7/$read
#23 = Utf8 $iw$
#24 = Utf8 $line7/$read$$iw$$iw$
#25 = Class #24 // $line7/$read$$iw$$iw$
#26 = Utf8 A
#27 = Utf8 Code
#28 = Utf8 LocalVariableTable
#29 = Utf8 LineNumberTable
#30 = Utf8 SourceFile
#31 = Utf8 InnerClasses
#32 = Utf8 Scala
{
private final transient int a;
flags: ACC_PRIVATE, ACC_FINAL, ACC_TRANSIENT
public int b();
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: getfield #11 // Field a:I
4: ireturn
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this L$line7/$read$$iw$$iw$A;
LineNumberTable:
line 7: 0
public $line7.$read$$iw$$iw$A(int);
flags: ACC_PUBLIC
Code:
stack=2, locals=2, args_size=2
0: aload_0
1: iload_1
2: putfield #11 // Field a:I
5: aload_0
6: invokespecial #18 // Method
java/lang/Object."<init>":()V
9: return
LocalVariableTable:
Start Length Slot Name Signature
0 10 0 this L$line7/$read$$iw$$iw$A;
0 10 1 a I
LineNumberTable:
line 7: 0
}
```
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