JDK-8189335: NPE in Lower due to class name clash

B. Blaser bsrbnd at gmail.com
Wed Feb 21 15:58:34 UTC 2018

On 19 February 2018 at 15:53, B. Blaser <bsrbnd at gmail.com> wrote:
> On 19 February 2018 at 00:42, B. Blaser <bsrbnd at gmail.com> wrote:
>> Hi,
>> As explained in JDK-8189335, the following example crashes javac with
>> a NPE in Lower:
>> class R {
>>     private class R$1 {}
>>     void f() {
>>         new R$1();
>>     }
>> }
>> class R$1 {}

Some precisions related to my laconic explanation about the problem and the fix.

All starts in 'Lower.accessConstructorTag()' when searching for the
anonymous class 'R$1':


The top level class 'R$1' (not anonymous) is found and wrongly added
to 'accessConstrTags'.

Then, when checking the access constructor tags in
'Lower.checkAccessConstructorTags()', the 'outermostClass()' of the
top level class 'R$1' is requested:


'R$1' being a top level class, its outermost class doesn't exist,
causing the NPE in 'Lower.makeEmptyClass()'.

The fix I suggested two days ago (here under) is then quite
straightforward. If a class 'R$1' exists but isn't anonymous, it has
to be skipped and a fresh anonymous class 'R$2' has to be created as
access constructor tag:


Nothing seems to be broken and the provided example compiles successfully.

What do you think (I hope this is clearer)?


> diff --git a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Lower.java
> b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Lower.java
> --- a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Lower.java
> +++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Lower.java
> @@ -1236,7 +1236,7 @@
>                                           target.syntheticNameChar() +
>                                           "1");
>          ClassSymbol ctag = chk.getCompiled(topModle, flatname);
> -        if (ctag == null)
> +        if (ctag == null || !ctag.isAnonymous())
>              ctag = makeEmptyClass(STATIC | SYNTHETIC, topClass).sym;
>          // keep a record of all tags, to verify that all are
> generated as required
>          accessConstrTags = accessConstrTags.prepend(ctag);

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