clang-format adds new line between semicolon and body-less loop

[Jorengarenar]

I'm gonna borrow example from this SO question (and here's a similar one):

I want to configure clang-format that it leaves single-line while-statement without adding a line break for the trailing semicolon.
For example, clang-format should just leave a "one-liner" as it is:

while (checkWaitCondition() != true);

But unfortunately it adds by default a line break (plus an indentation):

while (checkWaitCondition() != true)
  ;

[llvmbot]

@llvm/issue-subscribers-clang-format

[gedare]

Steps to reproduce:

$ echo "while(1);" | clang-format -style=LLVM
while (1)
  ;

I have this behavior on 16.0.0 and 17.0.0. I do not have an older version to test or bisect setup at the moment.

[rymiel]

I do not have an older version to test or bisect setup at the moment.

That's fine, this is clang-format's behavior since its inception (i think) and definitely intended. Question is, do we want this to be configurable

[gedare]

I do not have an older version to test or bisect setup at the moment.

That's fine, this is clang-format's behavior since its inception (i think) and definitely intended. Question is, do we want this to be configurable

I would like to make this configurable. Any suggestions are welcome, otherwise I may try to bring a proposal. Maybe BreakBeforeEmptyLoopBody or AllowEmptyLoopsOnASingleLine

[owenca]

Steps to reproduce:

$ echo "while(1);" | clang-format -style=LLVM
while (1)
  ;

The default value of AllowShortLoopsOnASingleLine for LLVM is false. To demonstrate that the loop is not merged despite that AllowShortLoopsOnASingleLine is changed to true:

 $ echo "while(1);" | clang-format -style='{AllowShortLoopsOnASingleLine: true}'
while (1)
  ;

[owenca]

https://reviews.llvm.org/D154550

[HazardyKnusperkeks]

I do not have an older version to test or bisect setup at the moment.

That's fine, this is clang-format's behavior since its inception (i think) and definitely intended. Question is, do we want this to be configurable

I'd say this should not be formatted on a single line. I'd change AllowShortLoopsOnASingleLine to Never, NonEmpty (this is the old true) and Always, or something like that.

[owenca]

See the discussion from here and onward.

[prj-]

@owenca, @HazardyKnusperkeks, sorry to bump this old thread, but is there a way to revert to the "old" behavior, i.e., having the semi-colon on a single line? It seems https://reviews.llvm.org/D154550#4526386 never got merged, so I cannot use NonNullStatement.

[owenca]

is there a way to revert to the "old" behavior, i.e., having the semi-colon on a single line?

Yes, by setting AllowShortLoopsOnASingleLine to false.

[prj-]

This, however, introduces a very large number of other white-space changes. Is something like AllowEmptyLoopsOnASingleLine planned at all?

[owenca]

I don't think so, if you mean:

while (i > 0) --i;
while (0)
  ;
while (j > 0) { --j; }
while (1)
{}

Empty loops are short loops and should follow the setting of AllowShortLoopsOnASingleLine.

[prj-]

OK, thanks, no problem.