RFR: JDK-8215482: check for cycles in type variables can provoke NPE

[Maurizio Cimadamore]

Looks good!

Maurizio

On 11/01/2019 22:11, Vicente Romero wrote:
>
>
> On 1/11/19 2:13 PM, Maurizio Cimadamore wrote:
>>
>> As per my suggestion to split into multiple stages, it was mostly a 
>> suggestion to take full advantage of the tiered architecture of 
>> TypeEnter. You are basically caching some types in a 'todo later' 
>> list, and then you are coming back at them - avoiding these kind of 
>> queuing is what the (relatively) new TypeEnter code is for.
>>
>> If the cyclic check is moved to a later phase, then I think you just 
>> need to fetch the type variables from the symbol/type/tree and check 
>> them; the types will be already set, no need to stash them into a 
>> map. At least in theory :-)
>>
>
> right thanks for the suggestion, that's a better option, please see:
>
> http://cr.openjdk.java.net/~vromero/8215482/webrev.01/
>
> Vicente
>>
>> Maurizio
>>
>> On 11/01/2019 18:05, Vicente Romero wrote:
>>> I have realized that cloning the type variable is not necessary as 
>>> the Pair<JCTypeParameter, TypeVar> element in the table will keep a 
>>> reference to the type variable
>>>
>>> Vicente
>>>
>>>
>>> On 1/11/19 12:29 PM, Vicente Romero wrote:
>>>>
>>>>
>>>> On 1/11/19 12:21 PM, Maurizio Cimadamore wrote:
>>>>>
>>>>> It seems that another thing that your path is doing is storing all 
>>>>> the type vars to check keyed by outermost class, so that only when 
>>>>> you have finished entering the outermost symbol you actually start 
>>>>> checking all pending typevars for cycles. I guess this delay is 
>>>>> necessary otherwise you would hit a problem anyway when checking 
>>>>> Bc for cyclicity?
>>>>>
>>>>
>>>> correct
>>>>
>>>>> Have you consider moving the attribution and cyclicity check in 
>>>>> different type enter phases? For instance, leave attribution in 
>>>>> HeaderPhase, but move the cycle check in MembersPhase ?
>>>>>
>>>>
>>>> I didn't try, but why would this be preferable? also as annotation 
>>>> processing can nuke the type we would have to make sure that the 
>>>> types are there before doing the cycle check which is something we 
>>>> can guarantee now by keeping the check for cycles in the Header phase
>>>>
>>>>> Maurizio
>>>>>
>>>>
>>>> Vicente
>>>>
>>>>> On 11/01/2019 16:47, Vicente Romero wrote:
>>>>>> Please review the fix for [1] at [2]. The NPE showed up in code like:
>>>>>>
>>>>>> class Outer<A extends Outer.Inner, B> {
>>>>>>     class Inner<Bc extends B> {}
>>>>>> }
>>>>>>
>>>>>> here attribution of type variable `A` during type enter phase 
>>>>>> will trigger attribution of class `Inner` while type variable `B` 
>>>>>> hasn't been attributed yet and thus its bound is still set to 
>>>>>> null. A similar problem arose a while ago see [3]. The issue 
>>>>>> provoking the current bug is that checks for cycles in type 
>>>>>> variables are done as soon as the type variable is attributed but 
>>>>>> in cases like the one above we can't do that until the type 
>>>>>> variable for the outer class has been attributed too.
>>>>>>
>>>>>> My first try was to create a fixup table that maps the outer type 
>>>>>> to the list of type variables defined by it or its members that 
>>>>>> happen to be types too, and once the compiler finish entering the 
>>>>>> outer class it would be safe to check for cycles in all the 
>>>>>> concerning type variables. I had a mild success here as there 
>>>>>> were some trivial cases that were working before that started 
>>>>>> failing. I realized that it was because the annotation processing 
>>>>>> phase was setting all the types to null, no bueno. So I decided 
>>>>>> to clone the type variables to be stored in the fixup table and 
>>>>>> do the cycle check on the clones which is what the current patch 
>>>>>> is doing.
>>>>>>
>>>>>> Thanks,
>>>>>> Vicente
>>>>>>
>>>>>> [1] https://bugs.openjdk.java.net/browse/JDK-8215482
>>>>>> [2] http://cr.openjdk.java.net/~vromero/8215482/
>>>>>> [3] https://bugs.openjdk.java.net/browse/JDK-6660289
>>>>
>>>
>
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