linux-kernel - Re: [PATCH 17/26] rv/rvgen: fix possibly unbound variable in ltl2k

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Message-ID: <aW9oj7-iagg2-VF_@fedora>
Date: Tue, 20 Jan 2026 08:37:05 -0300
From: Wander Lairson Costa <wander@...hat.com>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, Nam Cao <namcao@...utronix.de>, 
	open list <linux-kernel@...r.kernel.org>, 
	"open list:RUNTIME VERIFICATION (RV)" <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH 17/26] rv/rvgen: fix possibly unbound variable in ltl2k

On Tue, Jan 20, 2026 at 09:59:11AM +0100, Gabriele Monaco wrote:
> On Mon, 2026-01-19 at 17:45 -0300, Wander Lairson Costa wrote:
> > Initialize loop variable `i` before the for loop in abbreviate_atoms
> > function to fix pyright static type checker error. The previous code
> > left `i` potentially unbound in edge cases where the range could be
> > empty, though this would not occur in practice since the loop always
> > executes at least once with the given range parameters.
> > 
> > The initialization to zero ensures that `i` has a defined value before
> > entering the loop scope, satisfying static analysis requirements
> > while preserving the existing logic. The for loop immediately assigns
> > i to the first value from the range, so the initialization value is
> > never actually used in normal execution paths.
> > 
> > This change resolves the pyright reportPossiblyUnbound error without
> > altering the function's behavior or performance characteristics.
> 
> So are we just pleasing the tool or is there a real implication of this?
> 
> Apparently code like
> 
> for i in range(len([]), -1, -1):
>     pass
> print(i)
> 
> works just fine since range() returns at least 0 (as you mentioned in the commit
> message) and i is not used before assignation in the loop, so I don't really see
> a problem.
> 
> Apparently pyright devs don't want ([1]) to implement a logic to sort out the
> /possibly/ unbound error here.
> 
> From what I understand, this code is already not pythonic, so rather than
> silence the warning to please this tool I'd just refactor the code not to use i
> after the loop (or leave it as it is, since it works fine).
> 
> What do you think?

You're right, I could have done:

for atom in reversed(atoms): ...

I will modify it in v2.

> 
> Thanks,
> Gabriele
> 
> [1] - https://github.com/microsoft/pyright/issues/844
> 
> > 
> > Signed-off-by: Wander Lairson Costa <wander@...hat.com>
> > ---
> >  tools/verification/rvgen/rvgen/ltl2k.py | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/tools/verification/rvgen/rvgen/ltl2k.py
> > b/tools/verification/rvgen/rvgen/ltl2k.py
> > index fa9ea6d597095..94dc64af1716d 100644
> > --- a/tools/verification/rvgen/rvgen/ltl2k.py
> > +++ b/tools/verification/rvgen/rvgen/ltl2k.py
> > @@ -45,6 +45,7 @@ def abbreviate_atoms(atoms: list[str]) -> list[str]:
> >  
> >      abbrs = []
> >      for atom in atoms:
> > +        i = 0
> >          for i in range(len(atom), -1, -1):
> >              if sum(a.startswith(atom[:i]) for a in atoms) > 1:
> >                  break
>