RFR: JDK-8211102: Crash with -XDfind=lambda and -source 7

[Jan Lahoda]

Hi,

I'd like to ask for a review of changes that relate to code like:
---
import java.util.*;

public class AnalyzerBug {
     private void t(boolean b) {
         (b ? Collections.emptyList() : new Iterable<String>() { public 
Iterator<String> iterator() { return null; } }).toString();
     }
}
---

When this code is compiled like:
$ javac -XDfind=lambda -source 7 /tmp/AnalyzerBug.java

javac crashes in Analyzer. There are two immediate causes for the crash:
a) when AnalyzerModes are read form -XDfind, if an analyzer key is 
explicitly mentioned there, the source level is not checked, and the 
analyzer is enabled. So, in the case above, the analyzer with try to 
convert the Iterable<String> to a lambda and process the source, despite 
the -source 7. I suspect this is not intended, so proposing to always 
disable an analyzer if it does not have a meaning in the current source 
level.

b) if there's a lambda in a standalone conditional (i.e. without a 
target), in JDK 12 we try to attribute it anyway, but as a result, the 
type of the lambda will be the recovery type. And the computation of the 
type of the standalone conditional chokes on that, as the recovery type 
does not have a Symbol. So proposing to make the lambda's type an 
erroneous type in such cases (as was before 12), while still attributing it.

There's also related problem, when (very broken) code like this:
         int j = i instanceof ArrayList ? (ArrayList<String>) i : () -> 
{ return null; };

is attributed, visitLambda will keep JCFunctionalExpression.target 
unfilled, which seems fine as JCFunctionalExpression.getDescriptorType 
is prepared for that (and there indeed is no reasonable). But 
Attr.postAttr will fill it with unknownType, and then calls to 
getDescriptorType (e.g. from Flow.FlowAnalyzer.visitLambda) lead to 
FunctionDescriptorLookupError. Seems it might be better to keep the 
field unfilled, which is what the proposed patch is doing. (This is 
somewhat less important, as I am not aware of a way to reproduce this 
without -XDshould-stop.at=FLOW.)

JBS: https://bugs.openjdk.java.net/browse/JDK-8211102
Webrev: http://cr.openjdk.java.net/~jlahoda/8211102/webrev.00/

Any feedback is welcome!

Thanks,
     Jan