(Prepare for) Handling trailing spaces in multiline strings

[cgrushko]

We ran into this issue with ktfmt, and solved it by replacing the last of the trailing spaces with a special tombstone to prevent GJF from removing all trailing whitespace.

facebook/ktfmt@a4fdd39

I'm filing this issue so ktfmt can revert to using the supported method once it's available in GJF :)
(assuming multiline strings in Java are going to be a thin soon-ish)

[cushon]

I've been looking at supporting Java language features up to 14 recently, including text blocks, but hadn't thought through this yet. It makes sense that we don't want to make non-semantics-preserving changes to multiline strings. OTOH, have you encountered cases where trailing whitespace in multi-line strings is actually desired/useful? It seems like something that might deserve a style rule.

[cgrushko]

Funnily, it tripped our own tests. We have since converted to regular strings to make it more explicit. Do you suggest the formatter refuses to format such files?

…

On Thu, Mar 26, 2020 at 7:28 PM Liam Miller-Cushon ***@***.***> wrote: I've been looking at supporting Java language features up to 14 recently, including text blocks, but hadn't thought through this yet. It makes sense that we don't want to make non-semantics-preserving changes to multiline strings. OTOH, have you encountered cases where trailing whitespace in multi-line strings is actually desired/useful? It seems like something that might deserve a style rule. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#450 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAPH6YP5UK464YKSTXHYWG3RJOGB7ANCNFSM4LUB5ARQ> .

[cushon]

Do you suggest the formatter refuses to format such files?

No, it generally tries to accept anything that's syntactically valid and produce semantically equivalent output, I was just curious. We should probably try to preserve trailing whitespace and discourage it separately (e.g. with a linter).

[cgrushko]

Cool; I didn't see a test for trailing spaces, though?

…

On Tue, Mar 31, 2020 at 2:43 PM Christian Stein ***@***.***> wrote: Closeable due to 4ddb914 <4ddb914> methinks. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#450 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAPH6YM6MBXMKQPG2SHZCVTRKHJO3ANCNFSM4LUB5ARQ> .

[sormuras]

Cool; I didn't see a test for trailing spaces, though?

Dooh. I replied to the wrong issue and deleted my reply in the meanwhile.

[anthonyvdotbe]

Why isn't removing trailing white space correct, since it's removed during compilation anyway?

[cgrushko]

I don't trailing white space is removed from raw (multiline) strings during compilation.

…

On Mon, Jun 1, 2020 at 8:50 AM Anthony Vanelverdinghe < ***@***.***> wrote: Why isn't removing trailing white space correct, since it's removed during compilation anyway? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#450 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAPH6YLLYDCQ6LFN7I4HXSLRUM6QXANCNFSM4LUB5ARQ> .

[anthonyvdotbe]

The algorithm described in the JEP has:

6. Remove all trailing white space [...]

For cases where trailing spaces must be kept, the line can be ended with the new \s escape sequence:

\s can act as fence to prevent the stripping of trailing white space

[cgrushko]

Interesting! makes sense - otherwise removing trailing whitespace from a .java file requires parsing it.
So yeah, looks like no need to handle it in GJF.
(I don't see something similar for Kotlin, which inspired this issue; I imagine that most editors strip trailing whitespace, so in practice Kotlin programs don't have trailing whitespace)

[cushon]

I'm belatedly closing this out. As pointed out in the bug, trailing whitespace is not significant for text blocks, and requires explicit escaping (which g-j-f preserves if it is present):

$ google-java-format  T.java
public class Example {
  private final String test =
      """
      hello\s\s\s
      world
      """;
}