Debugger: improving kotlin support and fixing #220

This post continues series of debugger rework, refer to previous post. Today changes are focused around #220 Exception in Lambda transformation using modified soot:

Root case

Soot was crashing as it was not able to solve local variables type constraints as same variable was assigned with diffirent type values. E.g. with integer and Object.
Soot performs local split run on each local assignment so each assignment produces new variable and with uniq value and type. Then locals variables of same type are get packet to revert split and minimize variable count.
As result Soot not always can pack splited locals into one variable. This was a problem for debugger before variable resolution rework.

What wrong with kotlin, again

#220 was crashing on following case:

class: kotlinx.coroutines.scheduling.WorkQueue: 
method: kotlinx.coroutines.scheduling.Task pollExternal$default(kotlinx.coroutines.scheduling.WorkQueue,kotlin.jvm.functions.Function1,int,java.lang.Object)>

0 = {JIdentityStmt@1008} "l0: index=0 := @parameter0: kotlinx.coroutines.scheduling.WorkQueue"
1 = {JIdentityStmt@1009} "l1: index=1 := @parameter1: kotlin.jvm.functions.Function1"
2 = {JIdentityStmt@1010} "l2: index=2 := @parameter2: int"
3 = {JIdentityStmt@1011} "l3: index=3 := @parameter3: java.lang.Object"
4 = {JAssignStmt@1012} "$stack0#2: = l2:, index=2 & 1"
5 = {JIfStmt@1013} "if $stack0#2: == 0 goto l3:, index=3 = l0:, index=0.<kotlinx.coroutines.scheduling.WorkQueue: int consumerIndex>"
6 = {JAssignStmt@1014} "$stack0#3: = <kotlinx.coroutines.scheduling.WorkQueue$pollExternal$1: kotlinx.coroutines.scheduling.WorkQueue$pollExternal$1 INSTANCE>"
7 = {JAssignStmt@1015} "l1:, index=1 = (kotlin.jvm.functions.Function1) $stack0#3:"
8 = {JAssignStmt@1016} "l3:, index=3 = l0:, index=0.<kotlinx.coroutines.scheduling.WorkQueue: int consumerIndex>"
...

Problem here is that l3: index=3 is being assigned with java.lang.Object value(line 3) and int value(line 8). This happend as variable was not split in two locals.
Why? RoboVM was preventing spliting variables that were passed as parameter(here is slot 3 is a parameter).
Why? Java compiler reserved these slots for parameters and it was one time during entire method space so RoboVM was minimizing split effect by forbiding splitting slot variables used by parameters.
But kotlin reuses these slots for local variables.

So parameter slots are also has to be allowed for split.

The fix

Is allow to split parameter slots. These changes are applied to soot branch. Also RoboVM debugger code was changed to allow the fact that parameter variable is not persistent during method.

Code

All changes are present in debugger_local_resolution branch. Also PR349 was created.

Idea build for testing

test build for 2.3.6-SNAPSHOT available at google drive