Java 17 preview switch with exception throw

[wangxufire]

error: expected token: 'case'; generated default instead

example:

  interface Test {}

  static class Test1 implements Test{}
  static class Test2 implements Test{}

  public static void main(String[] args) {
    Test test = new Test1();
    switch (test) {
      case Test1 test1 -> {}
      case Test2 test2 -> {}
      default -> throw new IllegalStateException("Unexpected value: " + test);
    }
  }

[lorenzleutgeb]

Looks like the fix could be similar to #492 which was fixed by @cushon.

An even smaller reproduction (on 1.12.0):

class Preview {
    public static String f(Object o) {
        return switch (o) {
            case String s -> s;
            default -> throw new RuntimeException();
        };
    }
}

> javac --enable-preview -source 17 -Xlint:preview Preview.java
Preview.java:4: warning: [preview] patterns in switch statements are a preview feature and may be removed in a future release.
                        case String s -> s;
                             ^
Preview.java:3: warning: [preview] patterns in switch statements are a preview feature and may be removed in a future release.
                return switch (o) {
                              ^
3 warnings
> test -f Preview.class ; echo $?
0
> java --add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED    \
>      --add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED   \
>      --add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED \
>      --add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED   \
>      --add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED   \
>      -jar google-java-format-1.12.0-all-deps.jar \
>      Preview.java
Preview.java:4:26: error: expected token: 'case'; generated default instead

(Note that presence/absence of -Xlint:preview does not matter.)

In case this is because GJF does not support preview features, then this fact should be documented.

Additional Information

>  uname -sorv
Linux 5.10.75 #1-NixOS SMP Wed Oct 20 09:45:06 UTC 2021 GNU/Linux
> nixos-version
21.11.20211021.34ad3ff (Porcupine)
> javac -version
javac 17.0.1

[diegomrsantos]

@lorenzleutgeb could you please clarify how this issue is different from #492? You said GJF does not support preview features, but isn't #492 already using a preview feature?

The code bellow also fails:

sealed interface MyInterface {}
final class Child implements MyInterface {}

public class A {
    public static MyInterface test(MyInterface o) {
        return switch (o) {
            case Child c -> c;
        };
    }
}

Error:

Caused by: com.google.googlejavaformat.java.FormatterException: 9:14: error: expected token: 'case'; generated default instead
        at com.google.googlejavaformat.java.Formatter.getFormatReplacements(Formatter.java:293)
        at com.google.googlejavaformat.java.Formatter.formatSource(Formatter.java:267)
        at com.google.googlejavaformat.java.Formatter.formatSource(Formatter.java:233)
        ... 142 more

Using:

• spotless 6.0.0
• GJF 1.12.0
• Gradle 7.2
• Java 17.0.1-tem

[lorenzleutgeb]

Right, so this also fails:

class Preview {
    public static String f(Object o) {
        return switch (o) {
            case String s -> s;
        };
    }
}

I thought that it has something to do with throwing an exception, so I missed that the reproduction could be even smaller. Sorry. It appears to really be about patterns.

You said GJF does not support preview features, [...]

That's a misunderstanding. And it's my fault. What I meant to say was that if it is the case that GJF does not support preview features then I think this should be documented, because I did not realize it before (and I am a user and would like to be informed about such constraints).

[...], but isn't #492 already using a preview feature?

No, it's not. It does not use patterns. s is a pattern in my example, and c is a pattern in your example. You can verify that by just executing javac EnumBug.java (without --enable-preview).

[diegomrsantos]

Thanks for the quick and comprehensive answer. I get it now.

You are right, seems that #492 was about switch expressions (which was not a preview feature) and this issue is about pattern matching with a switch expression as you said.

Agree on being more explicit about preview features, I'm still not sure if it is not supported or current issue is a bug.

[cushon]

This has been fixed by 8eb478a

[cushon]

Er, it will be fixed in a moment by #690, which isn't quite submitted yet