add support for Java 15

[monperrus]

See feature list at https://openjdk.java.net/projects/jdk/15/

[MartinWitt]

For more details read https://www.oracle.com/java/technologies/javase/15-relnote-issues.html

[LakshyAAAgrawal]

Going through the above release notes, I could identify the following changes that will need to be incorporated into Spoon:

• Text Blocks

Preview features:

• Records(Second preview)
• Sealed Classes(Preview)
• Pattern Matching for instanceof(Second Preview)

I think that preview and second preview will not need to be incorporated. Is that right?

[monperrus]

I think that preview and second preview will not need to be incorporated. Is that right?

I would say yes, it's not needed for now.

[MartinWitt]

Looking at the current jdt version 3.23 we cant implement any feature expect java 14 record preview. Is there a way to use a nighty/weekly version of jdt? Otherwise we would need to wait for the next release. And we really should add some test cases for textblocks. After a first look they are working, but maybe some tests wouldn't harm.
Implementing a preview version could speed up development for features, when they leave preview.
Edit: I believe we should look at https://openjdk.java.net/jeps/371. I'm unsure if we need to handle this and/or could deliver an API/Refactoring supporting this.

[LakshyAAAgrawal]

As mentioned in #3627 (comment), need to work on a way to preserve the origin of a string as either a textblock or a single qoute string in Java.

[monperrus]

FTR #3627 is one important step for this issue.

What remains to be done is pretty-printing of text blocks.

[MartinWitt]

Looking at the printing problem, i see 2 potential solutions. Either create a flag in Literal isTextblock or create a class TextblockLiteral extends Literal. Wdyt about the solutions?

[LakshyAAAgrawal]

Hey, I have been taking a look at this. Was going through the relevant source code. I think creating a class extending Literal would be more general? But that would break the existing pattern followed by Literal. My thought was to go ahead with extending the class and likewise in the future creating other classes for various types of literals like numeric and singly qouted strings.

[monperrus]

Agree, extending CtLiteral seems a better option.

[MartinWitt]

My thought was to go ahead with extending the class and likewise in the future creating other classes for various types of literals like numeric

I would prefer the KISS solution and create only TextblockLiteral class.
A potential feature for a refactoring could be the conversion from textblock to string and string to textblock. But for now 1 new class does it and spoon supports java 15.