Require usage of fixed=TRUE in regular expressions where appropriate

Invoking a regular expression engine is overkill for cases when the search pattern only involves static patterns.

Usage

fixed_regex_linter(allow_unescaped = FALSE, check_file_listing = TRUE)

Arguments

allow_unescaped

Logical, default FALSE. If TRUE, only patterns that require regex escapes (e.g. "\\$" or "[$]") will be linted. See examples.

check_file_listing

Logical, default TRUE, governing whether to require list.files() and dir() to use fixed = TRUE for non-regex pattern=. Note that fixed = TRUE is only available from R 4.6.0.

Details

NB: for stringr functions, that means wrapping the pattern in stringr::fixed().

NB: this linter is likely not able to distinguish every possible case when a fixed regular expression is preferable, rather it seeks to identify likely cases. It should never report false positives, however; please report false positives as an error.

See also

linters for a complete list of linters available in lintr.

Tags

best_practices, configurable, efficiency, readability, regex

Examples

# will produce lints
code_lines <- 'gsub("\\\\.", "", x)'
writeLines(code_lines)
#> gsub("\\.", "", x)
lint(
  text = code_lines,
  linters = fixed_regex_linter()
)
#> <text>:1:6: warning: [fixed_regex_linter] Use "." with fixed = TRUE here. This regular expression is static, i.e., its matches can be expressed as a fixed substring expression, which is faster to compute.
#> gsub("\\.", "", x)
#>      ^~~~~

lint(
  text = 'grepl("a[*]b", x)',
  linters = fixed_regex_linter()
)
#> <text>:1:7: warning: [fixed_regex_linter] Use "a*b" with fixed = TRUE here. This regular expression is static, i.e., its matches can be expressed as a fixed substring expression, which is faster to compute.
#> grepl("a[*]b", x)
#>       ^~~~~~~

lint(
  text = 'grepl("a[*]b", x)',
  linters = fixed_regex_linter(allow_unescaped = TRUE)
)
#> <text>:1:7: warning: [fixed_regex_linter] Use "a*b" with fixed = TRUE here. This regular expression is static, i.e., its matches can be expressed as a fixed substring expression, which is faster to compute.
#> grepl("a[*]b", x)
#>       ^~~~~~~

code_lines <- 'stringr::str_subset(x, "\\\\$")'
writeLines(code_lines)
#> stringr::str_subset(x, "\\$")
lint(
  text = code_lines,
  linters = fixed_regex_linter()
)
#> <text>:1:24: warning: [fixed_regex_linter] Use stringr::fixed("$") as the pattern here. This regular expression is static, i.e., its matches can be expressed as a fixed substring expression, which is faster to compute.
#> stringr::str_subset(x, "\\$")
#>                        ^~~~~

lint(
  text = 'grepl("Munich", address)',
  linters = fixed_regex_linter()
)
#> <text>:1:7: warning: [fixed_regex_linter] Use "Munich" with fixed = TRUE here. This regular expression is static, i.e., its matches can be expressed as a fixed substring expression, which is faster to compute.
#> grepl("Munich", address)
#>       ^~~~~~~~

lint(
  text = 'list.files(pattern = "RDS")',
  linters = fixed_regex_linter(check_file_listing = TRUE)
)
#> <text>:1:22: warning: [fixed_regex_linter] Use "RDS" with fixed = TRUE here. This regular expression is static, i.e., its matches can be expressed as a fixed substring expression, which is faster to compute.
#> list.files(pattern = "RDS")
#>                      ^~~~~

# okay
code_lines <- 'gsub("\\\\.", "", x, fixed = TRUE)'
writeLines(code_lines)
#> gsub("\\.", "", x, fixed = TRUE)
lint(
  text = code_lines,
  linters = fixed_regex_linter()
)
#> ℹ No lints found.

lint(
  text = 'grepl("a*b", x, fixed = TRUE)',
  linters = fixed_regex_linter()
)
#> ℹ No lints found.

lint(
  text = 'stringr::str_subset(x, stringr::fixed("$"))',
  linters = fixed_regex_linter()
)
#> ℹ No lints found.

lint(
  text = 'grepl("Munich", address, fixed = TRUE)',
  linters = fixed_regex_linter()
)
#> ℹ No lints found.

lint(
  text = 'grepl("Munich", address)',
  linters = fixed_regex_linter(allow_unescaped = TRUE)
)
#> ℹ No lints found.

lint(
  text = 'list.files(pattern = "RDS", fixed = TRUE)',
  linters = fixed_regex_linter(check_file_listing = TRUE)
)
#> ℹ No lints found.