RFR: 8034066: Incorrect alignment in the "Code" section for "-c -XDdetails" options

[Chen Liang]

On Fri, 25 Oct 2024 03:01:50 GMT, Chen Liang <liach at openjdk.org> wrote:

>> This PR includes changes to ensure `Code:` block indentation in `javap`for the `-verbose` case and non `-verbose` case is the same, which currently does not hold.
>> 
>> Current behaviour of `javap` differs with and without `-verbose` in the following way:
>> **Command**: `javap -c -XDdetails:stackMaps A.class`
>> 
>> Without `-verbose`
>> 
>> 
>> ...
>>   public void a();
>>     Code:
>>        0: iconst_0
>>        1: istore_1
>>     StackMap locals:  this int
>>     StackMap stack:
>> ...
>> 
>> 
>> With `-verbose`
>> 
>> 
>> ...
>>   public void a();
>>     descriptor: ()V
>>     flags: (0x0001) ACC_PUBLIC
>>     Code:
>>       stack=2, locals=2, args_size=1
>>          0: iconst_0
>>          1: istore_1
>>       StackMap locals:  this int
>>       StackMap stack:
>> ...
>> 
>> 
>> With `-verbose` all contents of the `Code:` section include an extra (2 space) indent, which is missing in the non `-verbose` case. This is because the `CodeWriter` is called via `CoderWriter.write(...)` in the `-verbose` case, which wraps the `Code:` block in `indent(+1);...indent(-1)`.
>> 
>> In the non-verbose case this call is circumvented and a simplified version of `CoderWriter.write(...)` is included directly in `ClassWriter.writeMethod`.
>> 
>> ---
>> 
>> Alternatively to keep the logic within `CodeWriter` with the goal of keeping the logic for `-verbose` and non `-verbose` in the same place one could add `CodeWriter.writeSimple(...)`.
>> 
>> 
>> void writeSimple(CodeAttribute attr) {
>>         println("Code:");
>>         indent(+1);
>>         writeInstrs(attr);
>>         writeExceptionTable(attr);
>>         indent(-1);
>>     }
>> 
>> 
>> ---
>> 
>> Note: Test setup is inspired by existing tests: [T6622232.java](https://github.com/openjdk/jdk/blob/master/test/langtools/tools/javap/T6622232.java) and [8244573](https://github.com/openjdk/jdk/blob/master/test/langtools/tools/javap/8244573)
>
> test/langtools/tools/javap/8034066/EmptyLoop.jcod line 26:
> 
>> 24:  /*
>> 25:  * Original source:
>> 26:  * public class EmptyLoop {
> 
> To reduce test file noise, I recommend adding this as a package-private class to the end of your test file (so not a nested class) after it is renamed, like:
> 
> 
> class EmptyLoop {
>     public void emptyLoop() {
>         for (int i = 0; i < 10; i++) {
>         }
>     }
> }
> 
> 
> After that, once your test class is compiled, the `EmptyLoop.class` is available in `test.classes` property directory, so you can remove this jcod and all code that converts the jcod to class.
> 
> You can see UndefinedAccessFlagTest for how we use such tricks.
> 
> Note: since you will only have one test class, you no longer need a dedicated directory; you can just place our `CodeIndentTest.java` in the root javap directory.

Another example of such a trick is available at [test/jdk/jdk/classfile/ClassBuildingTest.java](https://github.com/openjdk/jdk/blob/master/test/jdk/jdk/classfile/ClassBuildingTest.java)

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/21685#discussion_r1815933828