Mismatching number of %-placeholders in string

[kaddkaka]

Summary

Like #24031.

Incorrect number of format specifies should give error.

There are already many good warnings and tips about using f-strings. Howerever I believe this code does not give any warning about number of arguments:

"" % banana

Since there is 0 placeholders in the string, there should be no reason to use % at all.

Cases to solve for(?) :

"hello" % x  # string literal
f"world" % y  # f-string? (maybe not because f-string interpolation could produce placeholders) 
"hello " * 3 % z  # can this be solved for free? 

Any more cases that are possible to solve? Easily?

Notes: x could be a tuple with 0 elements, but I can't see any meaningful value in code like that. But does that fact mean this should be it's own lint rule separate from F507?

Related:

• Mismatching number of %-placeholders in string formatting #24031
• F507: Fix false negative for non-tuple RHS in %-formatting #24142

[MichaReiser]

Extending F507 to also catch "" % banana where banana is known to not be a zero length tuple (use Ruff's type inference) does make sense to me.

f"world" % y # f-string? (maybe not because f-string interpolation could produce placeholders)
"hello " * 3 % z # can this be solved for free?

Let's ignore f-strings and multiplications in this issue.

[kaddkaka]

Could we also catch "" % banana even if banana has unknown value? Or should that be a new separate rule that says: "usage of % with string without placeholders"?

[MichaReiser]

Could we also catch "" % banana even if banana has unknown value?

I guess we could. The chance where this is intentional is very low

[spider-yamet]

@MichaReiser @ntBre May I work on this issue? then, please feel free the assign this for me.
Thanks

[spider-yamet]

I think F507 is designed for runtime-mismatch checker, but for this issue, we have to catch weird style pattern as well.
Like in "hello" % banana, banana is unknown at lint time, so it is skipped to avoid false positives.
So the problem is rule mismatch, I think. Would appreciate your feedback, Thanks