On Sun, Oct 3, 2021 at 6:38 AM Dwaipayan Ray <dwaipayanray1@xxxxxxxxx> wrote:
>
> On Sat, Oct 2, 2021 at 8:15 PM Utkarsh Verma <utkarshverma294@xxxxxxxxx> wrote:
> >
> > Added and documented UNNECESSARY_ELSE message type.
> >
> > Signed-off-by: Utkarsh Verma <utkarshverma294@xxxxxxxxx>
> > ---
> > Changes in v2:
> > - Included the continue statement.
> >
> > Documentation/dev-tools/checkpatch.rst | 77 ++++++++++++++++++++++++++
> > 1 file changed, 77 insertions(+)
> >
> > diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
> > index f0956e9ea2d8..b7c41e876d1d 100644
> > --- a/Documentation/dev-tools/checkpatch.rst
> > +++ b/Documentation/dev-tools/checkpatch.rst
> > @@ -1166,3 +1166,80 @@ Others
> >
> > **TYPO_SPELLING**
> > Some words may have been misspelled. Consider reviewing them.
> > +
> > + **UNNECESSARY_ELSE**
> > + Using an else statement just after a return/break/continue statement is
> > + unnecessary. For example::
> > +
> > + for (i = 0; i < 100; i++) {
> > + int foo = bar();
> > + if (foo < 1)
> > + break;
> > + else
> > + usleep(1);
> > + }
> > +
> > + is generally better written as::
> > +
> > + for (i = 0; i < 100; i++) {
> > + int foo = bar();
> > + if (foo < 1)
> > + break;
> > + usleep(1);
> > + }
> > +
> > + It helps to reduce the indentation and removes the unnecessary else
> > + statement. But note, there can be some false positives because of the
> > + way it is implemented in the checkpatch script. The checkpatch script
> > + throws this warning message if it finds an else statement and the line
> > + above it is a break/continue/return statement indented at one tab more
> > + than the else statement. So there can be some false positives like::
> > +
> > + int n = 15;
> > + if (n > 10)
> > + n--;
> > + else if (n == 10)
> > + return 0;
> > + else
> > + n++;
> > +
> > + Now the checkpatch will give a warning for the use of else after return
> > + statement. If the else statement is removed then::
> > +
> > + int n = 15;
> > + if (n > 10)
> > + n--;
> > + else if (n == 10)
> > + return 0;
> > + n++;
> > +
> > + Now both the n-- and n++ statements will be executed which is different
> > + from the logic in the first case. As the if block doesn't have a return
> > + statement, so removing the else statement is wrong.
> > +
> > + Always check the previous if/else if blocks, for break/continue/return
> > + statements, and do not blindly follow the checkpatch advice. One
> > + patch (https://lore.kernel.org/all/20200615155131.GA4563@sevic69/)
> > + even made it to the mainline, which was again reverted and fixed.
> > + Commit 98fe05e21a6e ("staging: rtl8712: Remove unnecesary else
>
> s/unnecesary/unnecessary
> > + after return statement.")
> > +
> > + Also, do not change the code if there is only a single return statement
> > + inside if-else block, like::
> > +
> > + if (a > b)
> > + return a;
> > + else
> > + return b;
> > +
> > + now if the else statement is removed::
> > +
> > + if (a > b)
> > + return a;
> > + return b;
> > +
> > + there is no considerable increase in the readability and one can argue
> > + that the first form is more readable because of the indentation. So
> > + do not remove the else statement in case of a single return statement
> > + inside the if-else block.
> > + See: https://lore.kernel.org/lkml/20140925032215.GK7996@xxxxxxxxxxxxxxxxxx/
> > --
> > 2.25.1
> >
>
> I think this message is unnecessarily long for a warning that's understandable
> at best without the verbose part. Try to shorten it up with only what's
> required for a user to understand why the warning is there.
>
Dwaipayan, I actually considered all this interesting information and
all valuable background information on this rule.
Now, I would like to see all this information in the checkpatch
documentation. Maybe here, the expectations for the --verbose option
and the checkpatch documentation are slightly different.
IMHO, the need for the checkpatch documentation beats the --verbose
option. If checkpatch users really ask for --verbose help on this
rule, they are already questioning the value of a rule that is already
quite understandable (as you said). So, then we should convince them
with all background information and known false positives we
encountered.
I vote for keeping all information; wordsmithing and writing more
precisely is certainly doable.
Lukas
