New parameters for if_switch_linter() to optionally skip lints on "co…

…mplex" if/else usage (#2413)

NEWS.md

@@ -62,7 +62,7 @@
 * `print_linter()` for discouraging usage of `print()` on string literals like `print("Reached here")` or `print(paste("Found", nrow(DF), "rows."))` (#1894, @MichaelChirico).
 * `unnecessary_nesting_linter()` for discouraging overly-nested code where an early return or eliminated sub-expression (inside '{') is preferable (#2317 and part of #884, @MichaelChirico).
 * `consecutive_mutate_linter()` for encouraging consecutive calls to `dplyr::mutate()` to be combined (part of #884, @MichaelChirico).
-* `if_switch_linter()` for encouraging `switch()` over repeated `if`/`else` tests (part of #884, @MichaelChirico).
+* `if_switch_linter()` for encouraging `switch()` over repeated `if`/`else` tests (#2322 and part of #884, @MichaelChirico).
 * `nested_pipe_linter()` for discouraging pipes within pipes, e.g. `df1 %>% inner_join(df2 %>% select(a, b))` (part of #884, @MichaelChirico).
 * `nrow_subset_linter()` for discouraging usage like `nrow(subset(x, conditions))` in favor of something like `with(x, sum(conditions))` which doesn't require a full subset of `x` (#2313, #2314 and part of #884, @MichaelChirico).
 * `pipe_return_linter()` for discouraging usage of `return()` inside a {magrittr} pipeline (part of #884, @MichaelChirico).

R/if_switch_linter.R

@@ -14,13 +14,77 @@
 #'   approach is roughly linear in the number of conditions that need to
 #'   be evaluated, here up to 3 times).
 #'
+#' @param max_branch_lines,max_branch_expressions Integer, default 0 indicates "no maximum".
+#'   If set any `if`/`else if`/.../`else` chain where any branch occupies more than
+#'   this number of lines (resp. expressions) will not be linted. The conjugate
+#'   applies to `switch()` statements -- if these parameters are set, any `switch()`
+#'   statement with any overly-complicated branches will be linted. See examples.
+#'
 #' @examples
 #' # will produce lints
 #' lint(
 #'   text = "if (x == 'a') 1 else if (x == 'b') 2 else 3",
 #'   linters = if_switch_linter()
 #' )
 #'
+#' code <- paste(
+#'   "if (x == 'a') {",
+#'   "  1",
+#'   "} else if (x == 'b') {",
+#'   "  2",
+#'   "} else if (x == 'c') {",
+#'   "  y <- x",
+#'   "  z <- sqrt(match(y, letters))",
+#'   "  z",
+#'   "}",
+#'   sep = "\n"
+#' )
+#' writeLines(code)
+#' lint(
+#'   text = code,
+#'   linters = if_switch_linter()
+#' )
+#'
+#' code <- paste(
+#'   "if (x == 'a') {",
+#'   "  1",
+#'   "} else if (x == 'b') {",
+#'   "  2",
+#'   "} else if (x == 'c') {",
+#'   "  y <- x",
+#'   "  z <- sqrt(",
+#'   "    match(y, letters)",
+#'   "  )",
+#'   "  z",
+#'   "}",
+#'   sep = "\n"
+#' )
+#' writeLines(code)
+#' lint(
+#'   text = code,
+#'   linters = if_switch_linter()
+#' )
+#'
+#' code <- paste(
+#'   "switch(x,",
+#'   "  a = {",
+#'   "    1",
+#'   "    2",
+#'   "    3",
+#'   "  },",
+#'   "  b = {",
+#'   "    1",
+#'   "    2",
+#'   "  }",
+#'   ")",
+#'   sep = "\n"
+#' )
+#' writeLines(code)
+#' lint(
+#'   text = code,
+#'   linters = if_switch_linter(max_branch_lines = 2L)
+#' )
+#'
 #' # okay
 #' lint(
 #'   text = "switch(x, a = 1, b = 2, 3)",
@@ -33,18 +97,105 @@
 #'   linters = if_switch_linter()
 #' )
 #'
+#' code <- paste(
+#'   "if (x == 'a') {",
+#'   "  1",
+#'   "} else if (x == 'b') {",
+#'   "  2",
+#'   "} else if (x == 'c') {",
+#'   "  y <- x",
+#'   "  z <- sqrt(match(y, letters))",
+#'   "  z",
+#'   "}",
+#'   sep = "\n"
+#' )
+#' writeLines(code)
+#' lint(
+#'   text = code,
+#'   linters = if_switch_linter(max_branch_lines = 2L)
+#' )
+#'
+#' code <- paste(
+#'   "if (x == 'a') {",
+#'   "  1",
+#'   "} else if (x == 'b') {",
+#'   "  2",
+#'   "} else if (x == 'c') {",
+#'   "  y <- x",
+#'   "  z <- sqrt(",
+#'   "    match(y, letters)",
+#'   "  )",
+#'   "  z",
+#'   "}",
+#'   sep = "\n"
+#' )
+#' writeLines(code)
+#' lint(
+#'   text = code,
+#'   linters = if_switch_linter(max_branch_expressions = 2L)
+#' )
+#'
+#' code <- paste(
+#'   "switch(x,",
+#'   "  a = {",
+#'   "    1",
+#'   "    2",
+#'   "    3",
+#'   "  },",
+#'   "  b = {",
+#'   "    1",
+#'   "    2",
+#'   "  }",
+#'   ")",
+#'   sep = "\n"
+#' )
+#' writeLines(code)
+#' lint(
+#'   text = code,
+#'   linters = if_switch_linter(max_branch_lines = 3L)
+#' )
+#'
 #' @evalRd rd_tags("if_switch_linter")
 #' @seealso [linters] for a complete list of linters available in lintr.
 #' @export
-if_switch_linter <- function() {
-  equal_str_cond <- "expr[1][EQ and expr[STR_CONST]]"
+if_switch_linter <- function(max_branch_lines = 0L, max_branch_expressions = 0L) {
+  equal_str_cond <- "expr[1][EQ and expr/STR_CONST]"
+
+  if (max_branch_lines > 0L || max_branch_expressions > 0L) {
+    complexity_cond <- xp_or(c(
+      if (max_branch_lines > 0L) paste("OP-RIGHT-BRACE/@line2 - OP-LEFT-BRACE/@line1 > 1 +", max_branch_lines),
+      if (max_branch_expressions > 0L) paste("count(expr) >", max_branch_expressions)
+    ))
+    branch_expr_cond <- xp_and(c(
+      xp_or(
+        # if (x) { <this expr> } ...
+        xp_and("preceding-sibling::IF", "position() = 2"),
+        # if (x) { ... } else { <this expr> }
+        xp_and("preceding-sibling::ELSE", "not(IF)")
+      ),
+      complexity_cond
+    ))
+    max_lines_cond <- glue(".//expr[{branch_expr_cond}]")
+
+    switch_xpath <- glue("
+    parent::expr
+      /parent::expr[expr[
+        position() > 2
+        and {complexity_cond}
+      ]]
+    ")
+  } else {
+    max_lines_cond <- "false"
+
+    switch_xpath <- NULL
+  }
 
   # NB: IF AND {...} AND ELSE/... implies >= 3 equality conditions are present
   # .//expr/IF/...: the expr in `==` that's _not_ the STR_CONST
   # not(preceding::IF): prevent nested matches which might be incorrect globally
   # not(. != .): don't match if there are _any_ expr which _don't_ match the top
   #   expr
-  xpath <- glue("
+  if_xpath <- glue("
   //IF
     /parent::expr[
       not(preceding-sibling::IF)
@@ -58,15 +209,16 @@ if_switch_linter <- function() {
         .//expr/IF/following-sibling::{equal_str_cond}/expr[not(STR_CONST)]
           != expr[1][EQ]/expr[not(STR_CONST)]
       )
+      and not({ max_lines_cond })
     ]
   ")
 
   Linter(linter_level = "expression", function(source_expression) {
     xml <- source_expression$xml_parsed_content
 
-    bad_expr <- xml_find_all(xml, xpath)
+    bad_expr <- xml_find_all(xml, if_xpath)
 
-    xml_nodes_to_lints(
+    lints <- xml_nodes_to_lints(
       bad_expr,
       source_expression = source_expression,
       lint_message = paste(
@@ -76,5 +228,19 @@ if_switch_linter <- function() {
       ),
       type = "warning"
     )
+
+    if (!is.null(switch_xpath)) {
+      xml_calls <- source_expression$xml_find_function_calls("switch")
+      switch_expr <- xml_find_all(xml_calls, switch_xpath)
+
+      lints <- c(lints, xml_nodes_to_lints(
+        switch_expr,
+        source_expression = source_expression,
+        lint_message = "Prefer repeated if/else statements over overly-complicated switch() statements.",
+        type = "warning"
+      ))
+    }
+
+    lints
   })
 }

inst/lintr/linters.csv

@@ -38,7 +38,7 @@ function_argument_linter,style consistency best_practices
 function_left_parentheses_linter,style readability default
 function_return_linter,readability best_practices
 if_not_else_linter,readability consistency configurable
-if_switch_linter,best_practices readability consistency efficiency
+if_switch_linter,best_practices readability consistency efficiency configurable
 ifelse_censor_linter,best_practices efficiency
 implicit_assignment_linter,style best_practices readability configurable
 implicit_integer_linter,style consistency best_practices configurable