Prevent IllegalArgumentException

[jbonzohln]

When running my tests I get this error:

java.lang.IllegalArgumentException: Count 'n' must be non-negative, but was -5.

	at kotlin.text.StringsKt__StringsJVMKt.repeat(StringsJVM.kt:775)
	at org.jetbrains.kotlinx.lincheck.strategy.managed.TraceNodePrefixFactory.prefixForNode$lambda$5(TraceReporter.kt:628)
	at org.jetbrains.kotlinx.lincheck.strategy.managed.TraceNode.getPrefix(TraceReporter.kt:354)
	at org.jetbrains.kotlinx.lincheck.strategy.managed.TraceLeafEvent.addRepresentationTo(TraceReporter.kt:415)
	at org.jetbrains.kotlinx.lincheck.strategy.managed.TraceReporterKt.traceGraphToRepresentationList(TraceReporter.kt:343)
	at org.jetbrains.kotlinx.lincheck.strategy.managed.TraceReporterKt.appendShortTrace(TraceReporter.kt:43)
	at org.jetbrains.kotlinx.lincheck.strategy.managed.TraceReporterKt.appendTrace(TraceReporter.kt:31)
	at org.jetbrains.kotlinx.lincheck.ReporterKt.appendFailure(Reporter.kt:392)
	at org.jetbrains.kotlinx.lincheck.strategy.LincheckFailure.toString(LincheckFailure.kt:22)
	at java.base/java.lang.StringConcatHelper.stringOf(StringConcatHelper.java:467)
	at java.base/java.lang.StringConcatHelper.simpleConcat(StringConcatHelper.java:422)
	at org.jetbrains.kotlinx.lincheck.LincheckAssertionError.<init>(LincheckAssertionError.kt:17)
	at org.jetbrains.kotlinx.lincheck.LinChecker$check$1.invoke(LinChecker.kt:48)
	at org.jetbrains.kotlinx.lincheck.LinChecker$check$1.invoke(LinChecker.kt:47)
	at org.jetbrains.kotlinx.lincheck.LinChecker.checkImpl$lincheck(LinChecker.kt:67)
	at org.jetbrains.kotlinx.lincheck.LinChecker.check(LinChecker.kt:47)
	at org.jetbrains.kotlinx.lincheck.LinChecker$Companion.check(LinChecker.kt:195)
	at org.jetbrains.kotlinx.lincheck.LinChecker.check(LinChecker.kt)

[eupp]

Could be related to #404

[avpotapov00]

Hi, @jbonzohln
Thanks for the PR!
Could you please provide the test that caused the failure?
Let's fix it a little bit in a different way.

[jbonzohln]

@avpotapov00 No, sorry it's company code I can't share. I believe the cause is a very deep call stack though.

[ndkoval]

Unfortunately, we cannot accept such a PR without tests.

[eupp]

Hi @ndkoval !
Can we please re-open and merge this PR?

I've tested it on #404 (same issue). I've tried to apply this commit on top of master (as of Lincheck-2.34), and with this commit the problem is no longer reproducible.

Also, I've encountered the same bug while working on another feature --- supporting coroutines in GPMC API #411, and with this fix the problem is also fixed there.

The fix in this PR is very simple, it just prevents the negative value to leak into a function not expecting negative value, by simply taking max(0, x).

As for the test, the problem is that the code affected by this fix is deep down the internal logic of constructing trace representation. It is hard to construct an artificial test to trigger this behavior (I've tried).

We can try to port the reproducing test reported by @de-shyt in #404 from her repository. However, this test is quite large and complicated (it includes custom implementation of Channel interface). Besides, this test is also affected by another issue #403, and when #403 is fixed the issue #404 no longer reproduces.
So my point is that trying to adapt this complicated test for this simple one-liner fix probably does not worth the hustle.

[eupp]

I also believe max in this line was simply forgotten initially, because other branches of this function use max to prevent negative values.

[ndkoval]

@eupp I've merged the PR but accidentally did that to master. Please port the fix to develop as well.