This Stackoverflow question https://stackoverflow.com/q/77036362 turned
up a bug in the R PCRE interface.
The example (currently in an edit to the original question) tried to use
named capture with more than 127 named groups. Here's the code:
append_unique_id <- function(x) {
for (i in seq_along(x)) {
x[i] <- paste0("<", paste(sample(letters, 10), collapse = ""), ">",
x[i])
}
x
}
list_regexes <- sample(letters, 128, TRUE) # <<<<<<<<<<< change this to
# 127 and it works
regex2 <- append_unique_id(list_regexes)
regex2 <- paste0("(?", regex2, ")")
regex2 <- paste(regex2, collapse = "|")
out <- gregexpr(regex2, "Cyprus", perl = TRUE, ignore.case = TRUE)
#> Error in gregexpr(regex2, "Cyprus", perl = TRUE, ignore.case = TRUE):
attempt to set index -129/128 in SET_STRING_ELT
I think the bug is in R, here:
https://github.com/wch/r-source/blob/57d15d68235dd9bcfaa51fce83aaa71163a020e1/src/main/grep.c#L3079
This is the line
int capture_num = (entry[0]<<8) + entry[1] - 1;
where entry is declared as a pointer to a char. What this is doing is
extracting a 16 bit number from the first two bytes of a character
string holding the name of the capture group. Since char is a signed
type, the conversion of bytes to integer gets messed up and the value
comes out wrong.
Duncan Murdoch
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