New linter for complex conditional expressions

DESCRIPTION

@@ -76,6 +76,7 @@ Collate:
     'commas_linter.R'
     'commented_code_linter.R'
     'comparison_negation_linter.R'
+    'complex_conditional_linter.R'
     'condition_call_linter.R'
     'condition_message_linter.R'
     'conjunct_test_linter.R'

NAMESPACE

@@ -31,6 +31,7 @@ export(closed_curly_linter)
 export(commas_linter)
 export(commented_code_linter)
 export(comparison_negation_linter)
+export(complex_conditional_linter)
 export(condition_call_linter)
 export(condition_message_linter)
 export(conjunct_test_linter)

R/complex_conditional_linter.R

@@ -0,0 +1,105 @@
+#' Complex Conditional Expressions Linter
+#'
+#' Detects complex conditional expressions and suggests extracting
+#' them into Boolean functions or variables for improved readability and reusability.
+#'
+#' For example, if you have a conditional expression with more than two logical operands,
+#'
+#' ```
+#' if (looks_like_a_duck(x) &&
+#'     swims_like_a_duck(x) &&
+#'     quacks_like_a_duck(x)) {
+#'     ...
+#' }
+#' ````
+#'
+#' to improve its readability and reusability, you can extract the conditional expression.
+#'
+#' You can either extract it into a Boolean function:
+#'
+#' ```
+#' is_duck <- function(x) {
+#'   looks_like_a_duck(x) &&
+#'     swims_like_a_duck(x) &&
+#'     quacks_like_a_duck(x)
+#' }
+#'
+#' if (is_duck(x)) {
+#'   ...
+#' }
+#' ```
+#'
+#' or into a Boolean variable:
+#'
+#' ```
+#' is_duck <- looks_like_a_duck(x) &&
+#'    swims_like_a_duck(x) &&
+#'    quacks_like_a_duck(x)
+#'
+#' if (is_duck) {
+#'  ...
+#' }
+#' ```
+#'
+#' In addition to improving code readability, extracting complex conditional expressions
+#' has the added benefit of introducing a reusable abstraction.
+#'
+#' @param threshold Integer. The maximum number of logical operators (`&&` or `||`)
+#'   allowed in a conditional expression. The default is `1L`, meaning any conditional expression
+#'   with more than one logical operator will be flagged.
+#'
+#' @examples
+#' # will produce lints
+#' code <- "if (a && b && c) { do_something() }"
+#' writeLines(code)
+#' lint(
+#'   text = code,
+#'   linters = complex_conditional_linter()
+#' )
+#'
+#' # okay
+#' ready_to_do_something <- a && b && c
+#' code <- "if (ready_to_do_something) { do_something() }"
+#' writeLines(code)
+#' lint(
+#'   text = code,
+#'   linters = complex_conditional_linter()
+#' )
+#'
+#' @evalRd rd_tags("complex_conditional_linter")
+#' @seealso [linters] for a complete list of linters available in lintr.
+#' @export
+complex_conditional_linter <- function(threshold = 1L) {
+  stopifnot(is.numeric(threshold), length(threshold) == 1L, threshold >= 1L)
+  threshold <- as.integer(threshold)
+
+  xpath <- glue::glue("//expr[
+    parent::expr[IF or WHILE]
+    and
+    preceding-sibling::*[1][self::OP-LEFT-PAREN]
+    and
+    following-sibling::*[1][self::OP-RIGHT-PAREN]
+    and
+    count(descendant-or-self::*[AND2 or OR2]) > {threshold}
+  ]")
+
+
+  Linter(linter_level = "expression", function(source_expression) {
+    xml <- source_expression$xml_parsed_content
+
+    nodes <- xml2::xml_find_all(xml, xpath)
+
+    lints <- xml_nodes_to_lints(
+      nodes,
+      source_expression = source_expression,
+      lint_message = paste0(
+        "Complex conditional with more than ",
+        threshold,
+        " logical operator(s). Consider extracting into a boolean function or variable for readability and reusability."
+      ),
+      type = "warning"
+    )
+
+    lints
+  })
+}

R/unnecessary_nesting_linter.R

@@ -238,7 +238,7 @@ unnecessary_nesting_linter <- function(
     unnecessary_else_brace_lints <- xml_nodes_to_lints(
       unnecessary_else_brace_expr,
       source_expression = source_expression,
-      lint_message = "Simplify this condition by using 'else if' instead of 'else { if.",
+      lint_message = "Simplify this condition by using 'else if' instead of 'else { if'.",
       type = "warning"
     )
 

inst/lintr/linters.csv

@@ -11,6 +11,7 @@ closed_curly_linter,defunct
 commas_linter,style readability default configurable
 commented_code_linter,style readability best_practices default
 comparison_negation_linter,readability consistency
+complex_conditional_linter,style readability best_practices configurable
 condition_call_linter,style tidy_design best_practices configurable
 condition_message_linter,best_practices consistency
 conjunct_test_linter,package_development best_practices readability configurable pkg_testthat