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Original file line number | Diff line number | Diff line change |
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#' Block statements like if (!A) x else y | ||
#' | ||
#' `if (!A) x else y` is the same as `if (A) y else x`, but the latter is | ||
#' easier to reason about in the `else` case. The former requires | ||
#' double negation that can be avoided by switching the statement order. | ||
#' | ||
#' This only applies in the simple `if/else` case. Statements like | ||
#' `if (!A) x else if (B) y else z` don't always have a simpler or | ||
#' more readable form. | ||
#' | ||
#' It also applies to [ifelse()] and the package equivalents | ||
#' `dplyr::if_else()` and `data.table::fifelse()`. | ||
#' | ||
#' @param exceptions Character vector of calls to exclude from linting. | ||
#' By default, [is.null()], [is.na()], and [missing()] are excluded | ||
#' given the common idiom `!is.na(x)` as "x is present". | ||
#' | ||
#' @examples | ||
#' # will produce lints | ||
#' lint( | ||
#' text = "if (!A) x else y", | ||
#' linters = if_not_else_linter() | ||
#' ) | ||
#' | ||
#' lint( | ||
#' text = "ifelse(!is_treatment, x, y)", | ||
#' linters = if_not_else_linter() | ||
#' ) | ||
#' | ||
#' lint( | ||
#' text = "if (!is.null(x)) x else 2", | ||
#' linters = if_not_else_linter(exceptions = character()) | ||
#' ) | ||
#' | ||
#' # okay | ||
#' lint( | ||
#' text = "if (A) x else y", | ||
#' linters = if_not_else_linter() | ||
#' ) | ||
#' | ||
#' lint( | ||
#' text = "ifelse(is_treatment, y, x)", | ||
#' linters = if_not_else_linter() | ||
#' ) | ||
#' | ||
#' lint( | ||
#' text = "if (!is.null(x)) x else 2", | ||
#' linters = if_not_else_linter() | ||
#' ) | ||
#' | ||
#' @evalRd rd_tags("if_not_else_linter") | ||
#' @seealso [linters] for a complete list of linters available in lintr. | ||
#' @export | ||
if_not_else_linter <- function(exceptions = c("is.null", "is.na", "missing")) { | ||
if_xpath <- glue(" | ||
//IF[following-sibling::ELSE[not(following-sibling::expr[IF])]] | ||
/following-sibling::expr[1][ | ||
OP-EXCLAMATION | ||
and not(expr[expr[SYMBOL_FUNCTION_CALL[{ xp_text_in_table(exceptions) }]]]) | ||
] | ||
") | ||
|
||
ifelse_xpath <- glue(" | ||
//SYMBOL_FUNCTION_CALL[ {xp_text_in_table(ifelse_funs)} ] | ||
/parent::expr | ||
/parent::expr[expr[ | ||
position() = 2 | ||
and OP-EXCLAMATION | ||
and not(expr[ | ||
OP-EXCLAMATION | ||
or expr/SYMBOL_FUNCTION_CALL[{ xp_text_in_table(exceptions) }] | ||
]) | ||
]] | ||
") | ||
|
||
Linter(function(source_expression) { | ||
if (!is_lint_level(source_expression, "expression")) { | ||
return(list()) | ||
} | ||
|
||
xml <- source_expression$xml_parsed_content | ||
|
||
if_expr <- xml_find_all(xml, if_xpath) | ||
if_lints <- xml_nodes_to_lints( | ||
if_expr, | ||
source_expression = source_expression, | ||
lint_message = paste( | ||
"In a simple if/else statement,", | ||
"prefer `if (A) x else y` to the less-readable `if (!A) y else x`." | ||
), | ||
type = "warning" | ||
) | ||
|
||
ifelse_expr <- xml_find_all(xml, ifelse_xpath) | ||
ifelse_call <- xp_call_name(ifelse_expr) | ||
ifelse_lints <- xml_nodes_to_lints( | ||
ifelse_expr, | ||
source_expression = source_expression, | ||
lint_message = sprintf( | ||
"Prefer `%1$s(A, x, y)` to the less-readable `%1$s(!A, y, x)`.", | ||
ifelse_call | ||
), | ||
type = "warning" | ||
) | ||
|
||
c(if_lints, ifelse_lints) | ||
}) | ||
} |
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Original file line number | Diff line number | Diff line change |
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test_that("if_not_else_linter skips allowed usages", { | ||
linter <- if_not_else_linter() | ||
|
||
# simple if/else statement is fine | ||
expect_lint("if (A) x else y", NULL, linter) | ||
# not plain negation --> OK | ||
expect_lint("if (!A || B) x else y", NULL, linter) | ||
# no else clause --> OK | ||
expect_lint("if (!A) x", NULL, linter) | ||
|
||
# nested statements are also OK | ||
expect_lint("if (!A) x else if (B) y", NULL, linter) | ||
expect_lint("if (!A) x else if (B) y else z", NULL, linter) | ||
|
||
# ! picked up in the evaluation statements is skipped | ||
expect_lint("if (A) !x else y", NULL, linter) | ||
expect_lint("if (A) x else !y", NULL, linter) | ||
}) | ||
|
||
test_that("if_not_else_linter blocks simple disallowed usages", { | ||
linter <- if_not_else_linter() | ||
lint_msg <- rex::rex("In a simple if/else statement, prefer `if (A) x else y`") | ||
|
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expect_lint("if (!A) x else y", lint_msg, linter) | ||
|
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# ditto for more complicated expressions where ! is still the outer operator | ||
expect_lint("if (!x %in% 1:10) y else z", lint_msg, linter) | ||
}) | ||
|
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patrick::with_parameters_test_that( | ||
"if_not_else_linter blocks usages in ifelse() and friends as well", | ||
{ | ||
linter <- if_not_else_linter() | ||
expect_lint(sprintf("%s(!A | B, x, y)", ifelse_fun), NULL, linter) | ||
expect_lint(sprintf("%s(A, !x, y)", ifelse_fun), NULL, linter) | ||
expect_lint( | ||
sprintf("%s(!A, x, y)", ifelse_fun), | ||
sprintf("Prefer `%s[(]A, x, y[)]` to the less-readable", ifelse_fun), | ||
linter | ||
) | ||
# particularly relevant for if_else() | ||
expect_lint(sprintf("%s(!!A, x, y)", ifelse_fun), NULL, linter) | ||
}, | ||
.test_name = c("ifelse", "fifelse", "if_else"), | ||
ifelse_fun = c("ifelse", "fifelse", "if_else") | ||
) | ||
|
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test_that("if_not_else_linter skips negated calls to is.null & similar", { | ||
linter <- if_not_else_linter() | ||
|
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expect_lint("if (!is.null(x)) x else y", NULL, linter) | ||
expect_lint("if (!is.na(x)) x else y", NULL, linter) | ||
expect_lint("if (!missing(x)) x else y", NULL, linter) | ||
expect_lint("ifelse(!is.na(x), x, y)", NULL, linter) | ||
}) | ||
|
||
test_that("multiple lints are generated correctly", { | ||
expect_lint( | ||
trim_some("{ | ||
if (!A) x else B | ||
ifelse(!A, x, y) | ||
fifelse(!A, x, y) | ||
if_else(!A, x, y) | ||
}"), | ||
list( | ||
"In a simple if/else statement", | ||
"Prefer `ifelse", | ||
"Prefer `fifelse", | ||
"Prefer `if_else" | ||
), | ||
if_not_else_linter() | ||
) | ||
}) | ||
|
||
test_that("exceptions= argument works", { | ||
expect_lint( | ||
"if (!is.null(x)) x else y", | ||
"In a simple if/else statement", | ||
if_not_else_linter(exceptions = character()) | ||
) | ||
|
||
expect_lint("if (!foo(x)) y else z", NULL, if_not_else_linter(exceptions = "foo")) | ||
}) | ||
|
||
# TODO(michaelchirico): should if (A != B) be considered as well? |