[Records] Unhelpful warning "Empty block should be documented" for records without components

[jubax]

When you have

sealed interface Foo {
    record Bar1WithParameter(String parameter) implements Foo {
    }
    record Bar2WithoutParameter() implements Foo {
    }
    record Bar3WithParameter(String parameter) implements Foo {
    }
}

Then you get the "empty block" warning for the seconds record (probably because the record has no parameters):

This warning should not be shown.

[srikanth-sankaran]

I'll take a look.

I have never programmed with records so a naive question. Does a record with no data make sense ? Are there valid use cases for such ??

[jubax]

I'll take a look.

I have never programmed with records so a naive question. Does a record with no data make sense ? Are there valid use cases for such ??

Yes, it is useful for more functional-style result values. E.g. consider

ParseLogFileResult parseLogFileAndExtractErrorLevelMessages(File file) {}

sealed interface ParseLogFileResult {
  record Success(List<String> messagesWithErrorLevel) implements ParseLogFileResult {}
  record NotApplicable_FileDoesNotExist() {}
  record NotApplicable_InvalidLogFileFormat() {}
  record Failure(Exception exception) {}
}

So we are using records as markers here.

[iloveeclipse]

Oftopic: why not use enums instead?

[jubax]

Oftopic: why not use enums instead?

Because enums are static. But in the example above I want to return the actual values. With the structure above I can write

    sealed interface ParseLogFileResult {
      record Success(List<String> messagesWithErrorLevel) implements ParseLogFileResult {}
      record NotApplicable_FileDoesNotExist() implements ParseLogFileResult {}
      record NotApplicable_InvalidLogFileFormat() implements ParseLogFileResult {}
      record Failure(Exception exception) implements ParseLogFileResult {}
    }
    
    ParseLogFileResult parseLogFileAndExtractErrorLevelMessages(File file) {
	return new ParseLogFileResult.Success(List.of("a", "b"));
    }
    
    public void test() {
	ParseLogFileResult result = parseLogFileAndExtractErrorLevelMessages(new File("x.log"));
	switch (result) {
        	case ParseLogFileResult.Success(List<String> messagesWithErrorLevel) -> {
        	    System.out.println(messagesWithErrorLevel);
        	}
        	case ParseLogFileResult.NotApplicable_FileDoesNotExist() -> {}
        	case ParseLogFileResult.NotApplicable_InvalidLogFileFormat() -> {}
        	case ParseLogFileResult.Failure(Exception ex) -> { ex.printStackTrace(); }
	}
    }

[srikanth-sankaran]

Thanks for the example. Thought provoking (at least for me.)

[srikanth-sankaran]

See https://bugs.eclipse.org/bugs/show_bug.cgi?id=576806#c1

@MaisiKoleni writes there: The question is if it should make a difference whether a record has at least one component or not. My intuition says that a record without record components (like shown below) should still be considered empty and require a comment explaining what its purpose is.

In the present ticket, we have examples of legitimate use case - so we will course correct on that account.