Inconsistency between sub and gsub

[prfss]

I'm not sure if this is a bug.

Passing an empty string as the third argument, sub returns the replacement string.

λ> sub [re|^$|] "replacement" ""
"replacement"
λ> sub [re|.*|] "replacement" ""
"replacement"

But gsub returns an empty string for the same input.

λ> gsub [re|^$|] "replacement" ""
""
λ> gsub [re|.*|] "replacement" ""
""

[valpackett]

That does look strange indeed… any idea why it could happen?

[prfss]

Please forgive my poor English...

The immediate cause is the gusb0.loop's first guard (offset >= l). offset and l are both 0.
However, without the guard gsub0 loops forever because any string has empty substring at its right end that matches the regex.

I think that the root of the problem is that gsub0 cannot determine whether the empty string is consumed or not from the value of offset.