[20] Switch pattern dominance: redundant ECJ compiler errors

[kriegaex]

@jarthana, @mpalat: The current batch compiler for Java 20 shows the behaviour described in the Javadoc comment of this sample class:

/**
 * This used to work up to preview 3 (Java 19), but no longer in preview 4 (Java 20).
 * Now, the default case seems to need to be the last one in the list.
 *
 * Javac says 4x: "this case label is dominated by a preceding case label"
 *
 * ECJ/AJC says 11x: "This case label is dominated by one of the preceding case label" (yes, "label" singular)
 */
public class SwitchPatternPreview4Error {
  static void defaultCanAppearBeforePattern(Integer i) {
    switch (i) {
      case null -> System.out.println("value unavailable: " + i);
      case -1, 1 -> System.out.println("absolute value 1: " + i);
      default -> System.out.println("other integer: " + i);
      case Integer value when value > 0 -> System.out.println("positive integer: " + i);
    }
  }

  static void defaultCanAppearBeforeNull(Integer i) {
    switch (i) {
      case -1, 1 -> System.out.println("absolute value 1: " + i);
      default -> System.out.println("other integer: " + i);
      case null -> System.out.println("value unavailable: " + i);
      case Integer value when value > 0 -> System.out.println("positive integer: " + i);
    }
  }

  static void defaultCanAppearBeforeConstantLabel(Integer i) {
    switch (i) {
      case null -> System.out.println("value unavailable: " + i);
      default -> System.out.println("other integer: " + i);
      case -1, 1 -> System.out.println("absolute value 1: " + i);
      case Integer value when value > 0 -> System.out.println("positive integer: " + i);
    }
  }
}

Some logs for you to compare:

$ javac -J-Duser.language=en --enable-preview --release 20 SwitchPatternPreview4Error.java

SwitchPatternPreview4Error.java:15: error: this case label is dominated by a preceding case label
      case Integer value when value > 0 -> System.out.println("positive integer: " + i);
           ^
SwitchPatternPreview4Error.java:23: error: this case label is dominated by a preceding case label
      case null -> System.out.println("value unavailable: " + i);
           ^
SwitchPatternPreview4Error.java:24: error: this case label is dominated by a preceding case label
      case Integer value when value > 0 -> System.out.println("positive integer: " + i);
           ^
SwitchPatternPreview4Error.java:33: error: this case label is dominated by a preceding case label
      case Integer value when value > 0 -> System.out.println("positive integer: " + i);
           ^
Note: SwitchPatternPreview4Error.java uses preview features of Java SE 20.
Note: Recompile with -Xlint:preview for details.
4 errors

$ java -jar org.eclipse.jdt.core.compiler.batch_3.34.0.v20230327-1130.jar --enable-preview --release 20 -nowarn SwitchPatternPreview4Error.java

----------
1. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 15)
        case Integer value when value > 0 -> System.out.println("positive integer: " + i);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This case label is dominated by one of the preceding case label
----------
2. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 15)
        case Integer value when value > 0 -> System.out.println("positive integer: " + i);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This case label is dominated by one of the preceding case label
----------
3. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 15)
        case Integer value when value > 0 -> System.out.println("positive integer: " + i);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This case label is dominated by one of the preceding case label
----------
4. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 23)
        case null -> System.out.println("value unavailable: " + i);
             ^^^^
This case label is dominated by one of the preceding case label
----------
5. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 23)
        case null -> System.out.println("value unavailable: " + i);
             ^^^^
This case label is dominated by one of the preceding case label
----------
6. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 24)
        case Integer value when value > 0 -> System.out.println("positive integer: " + i);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This case label is dominated by one of the preceding case label
----------
7. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 24)
        case Integer value when value > 0 -> System.out.println("positive integer: " + i);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This case label is dominated by one of the preceding case label
----------
8. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 24)
        case Integer value when value > 0 -> System.out.println("positive integer: " + i);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This case label is dominated by one of the preceding case label
----------
9. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 33)
        case Integer value when value > 0 -> System.out.println("positive integer: " + i);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This case label is dominated by one of the preceding case label
----------
10. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 33)
        case Integer value when value > 0 -> System.out.println("positive integer: " + i);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This case label is dominated by one of the preceding case label
----------
11. ERROR in C:\Users\Alexander\Documents\java-src\AspectJ\tests\features1920\java20\SwitchPatternPreview4Error.java (at line 33)
        case Integer value when value > 0 -> System.out.println("positive integer: " + i);
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This case label is dominated by one of the preceding case label
----------
11 problems (11 errors)

You see that ECJ reports the same 4 error types, but 1x2 + 3x3 = 11 times instead of 4x1 times.

The source for the batch compiler was I20230327-1800, more exactly org.eclipse.jdt.core.compiler.batch_3.34.0.v20230327-1130.jar

[mpalat]

@jarthana this may be same as #881 - so please enable RPT._test26 also and check when this is fixed

[jarthana]

@jarthana this may be same as #881 - so please enable RPT._test26 also and check when this is fixed

Nope, that one is different. Closing this one as fixed.

[kriegaex]

Thanks for fixing this, I successfully retested it in AspectJ after my merge.

Do you think it would be possible to also fix this message, as mentioned above, and add a plural "s"?

This case label is dominated by one of the preceding case labels
                                                               ^
                                                           plural "s"