Type inference bug with method references in OpenJDK 16+ discovered

[Guoxiong Li]

Hi Michael,

Thanks for reporting this bug.

I reproduced this bug on linux by using the following commands
and the error messages are similar to yours.

```
java -m jdk.compiler/com.sun.tools.javac.Main $(find src/main/java -name
"*.java")
java -classpath src/main/java net.mirwaldt.bug.Main
```

And I also reproduced it by using the maven to compile.(also on linux)

```
mvn clean compile
java -classpath target/classes/ net.mirwaldt.bug.Main
```

It seems that you misuse some commands.

Anyway, it is a reproduced bug.
Filed https://bugs.openjdk.java.net/browse/JDK-8269121 in the JBS.

Best Regards,
-- Guoxiong


On Mon, Jun 21, 2021 at 5:49 AM Michael Mirwaldt <michael.mirwaldt at gmx.de>
wrote:

> Hi,
> I wanted to report a bug in the type inference with references in
> OpenJDK 16 and 17-ea.
> I have created a sample project on
> https://github.com/mmirwaldt/TypeInferenceBugOfMethodReferences/
> <https://github.com/mmirwaldt/TypeInferenceBugOfMethodReferences/>
> to reproduce the bug. Just run Main and notice the exception.
> However, a friend told me that the bug only occurs with compiling
> directly by javac but not by maven compile.
> We don't know why. Moreover, it seems to be dependent on the operating
> system:
> I haven't been able to reproduce the bug on linux (CentOS 7, OpenJDK
> 16.0.1) yet. Windows 10 and Mac show that bug, though.
> Can you please have a look on it, try it out and help me creating a bug
> ticket if you can confirm it's a bug?
> I mean it must be a bug if the type inference somehow infers the wrong
> type of a method reference which leads to an exception at runtime,
> doesn't it?
> Type inference should either infer the right type or cause a compiler
> error if it cannot infer the type or isn't sure about it in order to ask
> the developer for an explicit declaration. Is that right?
> I am sorry I cannot help you finding the bug in the code of the compiler
> which infers types. I would if I could.
> All the best,
> Michael Mirwaldt
>
>
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