fixed_regex_linter incorrectly suggest that my regex with "\>" is static

[dschlaep]

My code removes some text from the end of some other text using sub().

fixed_regex_linter() (incorrectly) suggests that my regular expression is static (example 1 below) if I use the symbol "\>" to match the empty string at end of a word. The suggestion with fixed = TRUE does not reproduce my desired outcome. However, fixed_regex_linter() correctly recognizes that regular expressions with "$" and "\b" are not static (examples 2 and 3) - obviously, I could use one of those instead.

I am not sure whether this has anything to do with the fact that regular expressions with "$" and "\b" work for both perl = FALSE and perl = TRUE while those with "\>" work only for perl = FALSE (?regex).

Example: trim "_stuff" only from end of "name_stuff_more_stuff" with desired result "name_stuff_more"

# 1) Approach "\>"
print(sub("_stuff\\>", "", "name_stuff_more_stuff"))
#> [1] "name_stuff_more"

# Lint
lintr::lint(
  text = 'sub("_stuff\\\\>", "", "name_stuff_more_stuff")',
  linters = lintr::fixed_regex_linter()
)
#> <text>:1:5: warning: [fixed_regex_linter] This regular expression is static, i.e., its matches can be expressed as a fixed substring expression, which is faster to compute. Here, you can use "_stuff>" with fixed = TRUE.
#> sub("_stuff\\>", "", "name_stuff_more_stuff")
#>     ^~~~~~~~~~~

# Suggestion by `fixed_regex_linter()` is incorrect
print(sub("_stuff>", "", "name_stuff_more_stuff", fixed = TRUE))
#> [1] "name_stuff_more_stuff"

^{Created on 2022-07-27 by the reprex package (v2.0.1)}

# 2) Approach "$"
print(sub("_stuff$", "", "name_stuff_more_stuff"))
#> [1] "name_stuff_more"

# No lint
lintr::lint(
  text = 'sub("_stuff$", "", "name_stuff_more_stuff")',
  linters = lintr::fixed_regex_linter()
)

^{Created on 2022-07-27 by the reprex package (v2.0.1)}

# 3) Approach "\b"
print(sub("_stuff\\b", "", "name_stuff_more_stuff"))
#> [1] "name_stuff_more"

# No lint
lintr::lint(
  text = 'sub("_stuff\\\\b", "", "name_stuff_more_stuff")',
  linters = lintr::fixed_regex_linter()
)

^{Created on 2022-07-27 by the reprex package (v2.0.1)}

print(packageVersion("lintr"))
#> [1] '3.0.0.9000'

[MichaelChirico]

Note some discussion here BTW:

#1032 (comment)

I think at root we want to detect the value of perl= and tweak the logic for what's a fixed regex or not accordingly. There are very subtle (and rare! \< is almost unheard of 😸) differences.

[janlimbeck]

Any updates on when this issue might be resolved?

[MichaelChirico]

Hi @janlimbeck, we're all volunteers to if this affects you a lot, feel free to take it up & go for a fix! PRs welcome; happy to help you along if you're stuck.