Raise lints for several common poor usages of paste()

The following issues are linted by default by this linter (see arguments for which can be de-activated optionally):

1. Block usage of paste() with sep = "". paste0() is a faster, more concise alternative.

2. Block usage of paste() or paste0() with collapse = ", ". toString() is a direct wrapper for this, and alternatives like glue::glue_collapse() might give better messages for humans.

3. Block usage of paste0() that supplies sep= – this is not a formal argument to paste0, and is likely to be a mistake.

4. Block usage of paste() / paste0() combined with rep() that could be replaced by strrep(). strrep() can handle the task of building a block of repeated strings (e.g. often used to build "horizontal lines" for messages). This is both more readable and skips the (likely small) overhead of putting two strings into the global string cache when only one is needed.

   Only target scalar usages – strrep can handle more complicated cases (e.g. strrep(letters, 26:1), but those aren't as easily translated from a paste(collapse=) call.

Usage

paste_linter(
  allow_empty_sep = FALSE,
  allow_to_string = FALSE,
  allow_file_path = c("double_slash", "always", "never")
)

Arguments

allow_empty_sep

Logical, default FALSE. If TRUE, usage of paste() with sep = "" is not linted.

allow_to_string

Logical, default FALSE. If TRUE, usage of paste() and paste0() with collapse = ", " is not linted.

allow_file_path

String, one of "never", "double_slash", or "always"; "double_slash" by default. If "never", usage of paste() and paste0() to construct file paths is not linted. If "double_slash", strings containing consecutive forward slashes will not lint. The main use case here is for URLs – "paths" like "https://" will not induce lints, since constructing them with file.path() might be deemed unnatural. Lastly, if "always", strings with consecutive forward slashes will also lint. Note that "//" is never linted when it comes at the beginning or end of the input, to avoid requiring empty inputs like file.path("", ...) or file.path(..., "").

See also

linters for a complete list of linters available in lintr.

Tags

best_practices, configurable, consistency

Examples

# will produce lints
lint(
  text = 'paste("a", "b", sep = "")',
  linters = paste_linter()
)
#> <text>:1:1: warning: [paste_linter] paste0(...) is better than paste(..., sep = "").
#> paste("a", "b", sep = "")
#> ^~~~~~~~~~~~~~~~~~~~~~~~~

lint(
  text = 'paste(c("a", "b"), collapse = ", ")',
  linters = paste_linter()
)
#> <text>:1:1: warning: [paste_linter] toString(.) is more expressive than paste(., collapse = ", "). Note also glue::glue_collapse() and and::and() for constructing human-readable / translation-friendly lists
#> paste(c("a", "b"), collapse = ", ")
#> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lint(
  text = 'paste0(c("a", "b"), sep = " ")',
  linters = paste_linter()
)
#> <text>:1:1: warning: [paste_linter] sep= is not a formal argument to paste0(); did you mean to use paste(), or collapse=?
#> paste0(c("a", "b"), sep = " ")
#> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lint(
  text = 'paste0(rep("*", 10L), collapse = "")',
  linters = paste_linter()
)
#> <text>:1:1: warning: [paste_linter] strrep(x, times) is better than paste0(rep(x, times), collapse = "").
#> paste0(rep("*", 10L), collapse = "")
#> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#> <text>:1:1: warning: [paste_linter] Use paste(), not paste0(), to collapse a character vector when sep= is not used.
#> paste0(rep("*", 10L), collapse = "")
#> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lint(
  text = 'paste0("http://site.com/", path)',
  linters = paste_linter(allow_file_path = "never")
)
#> <text>:1:1: warning: [paste_linter] Construct file paths with file.path(...) instead of paste0(x, "/", y, "/", z). Note that paste() converts empty inputs to "", whereas file.path() leaves it empty.
#> paste0("http://site.com/", path)
#> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lint(
  text = 'paste0(x, collapse = "")',
  linters = paste_linter()
)
#> <text>:1:1: warning: [paste_linter] Use paste(), not paste0(), to collapse a character vector when sep= is not used.
#> paste0(x, collapse = "")
#> ^~~~~~~~~~~~~~~~~~~~~~~~

# okay
lint(
  text = 'paste0("a", "b")',
  linters = paste_linter()
)
#> ℹ No lints found.

lint(
  text = 'paste("a", "b", sep = "")',
  linters = paste_linter(allow_empty_sep = TRUE)
)
#> ℹ No lints found.

lint(
  text = 'toString(c("a", "b"))',
  linters = paste_linter()
)
#> ℹ No lints found.

lint(
  text = 'paste(c("a", "b"), collapse = ", ")',
  linters = paste_linter(allow_to_string = TRUE)
)
#> ℹ No lints found.

lint(
  text = 'paste(c("a", "b"))',
  linters = paste_linter()
)
#> ℹ No lints found.

lint(
  text = 'strrep("*", 10L)',
  linters = paste_linter()
)
#> ℹ No lints found.

lint(
  text = 'paste0(year, "/", month, "/", day)',
  linters = paste_linter(allow_file_path = "always")
)
#> ℹ No lints found.

lint(
  text = 'paste0("http://site.com/", path)',
  linters = paste_linter()
)
#> ℹ No lints found.

lint(
  text = 'paste(x, collapse = "")',
  linters = paste_linter()
)
#> ℹ No lints found.