Add param function_braces to brace_linter()

NEWS.md

@@ -55,6 +55,7 @@
 * `todo_comment_linter()` has a new argument `except_regex` for setting _valid_ TODO comments, e.g. for forcing TODO comments to be linked to GitHub issues like `TODO(#154)` (#2047, @MichaelChirico).
 * `vector_logic_linter()` is extended to recognize incorrect usage of scalar operators `&&` and `||` inside subsetting expressions like `dplyr::filter(x, A && B)` (#2166, @MichaelChirico).
 * `any_is_na_linter()` is extended to catch the unusual usage `NA %in% x` (#2113, @MichaelChirico).
+* `brace_linter()`' has a new argument `function_bodies` (default `"multi_line"`) which controls whether to require function bodies to be wrapped in curly braces, with the options `"always"`, `"multi_line"` (only require curly braces when a function body spans multiple lines), `"not_inline"` (only require curly braces when a function body starts on a new line) and `"never"` (#1807, #2240, @salim-b).
 * `make_linter_from_xpath()` errors up front when `lint_message` is missing (instead of delaying this error until the linter is used, #2541, @MichaelChirico).
 * `paste_linter()` is extended to recommend using `paste()` instead of `paste0()` for simply aggregating a character vector with `collapse=`, i.e., when `sep=` is irrelevant (#1108, @MichaelChirico).
 * `expect_no_lint()` was added as new function to cover the typical use case of expecting no lint message, akin to the recent {testthat} functions like `expect_no_warning()` (#2580, @F-Noelle).

R/brace_linter.R

@@ -8,9 +8,14 @@
 #'  - Closing curly braces in `if` conditions are on the same line as the corresponding `else`.
 #'  - Either both or neither branch in `if`/`else` use curly braces, i.e., either both branches use `{...}` or neither
 #'    does.
-#'  - Functions spanning multiple lines use curly braces.
+#'  - Function bodies are wrapped in curly braces.
 #'
-#' @param allow_single_line if `TRUE`, allow an open and closed curly pair on the same line.
+#' @param allow_single_line If `TRUE`, allow an open and closed curly pair on the same line.
+#' @param function_bodies Whether to require function bodies to be wrapped in curly braces. One of
+#'   - `"always"` to require braces for all function definitions, including inline functions,
+#'   - `"not_inline"` to require braces when a function body does not start on the same line as its signature,
+#'   - `"multi_line"` (the default) to require braces when a function definition spans multiple lines,
+#'   - `"never"` to never require braces in function bodies.
 #'
 #' @examples
 #' # will produce lints
@@ -50,7 +55,10 @@
 #' - <https://style.tidyverse.org/syntax.html#indenting>
 #' - <https://style.tidyverse.org/syntax.html#if-statements>
 #' @export
-brace_linter <- function(allow_single_line = FALSE) {
+brace_linter <- function(allow_single_line = FALSE,
+                         function_bodies = c("multi_line", "always", "not_inline", "never")) {
+  function_bodies <- match.arg(function_bodies)
+
   xp_cond_open <- xp_and(c(
     # matching } is on same line
     if (isTRUE(allow_single_line)) {
@@ -124,7 +132,25 @@ brace_linter <- function(allow_single_line = FALSE) {
   # TODO(#1103): if c_style_braces is TRUE, this needs to be @line2 + 1
   xp_else_same_line <- glue("//ELSE[{xp_else_closed_curly} and @line1 != {xp_else_closed_curly}/@line2]")
 
-  xp_function_brace <- "(//FUNCTION | //OP-LAMBDA)/parent::expr[@line1 != @line2 and not(expr[OP-LEFT-BRACE])]"
+  if (function_bodies != "never") {
+    xp_cond_function_brace <- switch(
+      function_bodies,
+      always = "1",
+      multi_line = "@line1 != @line2",
+      not_inline = "@line1 != expr/@line1"
+    )
+
+    xp_function_brace <- glue(
+      "(//FUNCTION | //OP-LAMBDA)/parent::expr[{xp_cond_function_brace} and not(expr[OP-LEFT-BRACE])]"
+    )
+
+    msg_function_brace <- switch(
+      function_bodies,
+      always = "Wrap function bodies in curly braces.",
+      multi_line = "Wrap multi-line function bodies in curly braces.",
+      not_inline = "Wrap function bodies starting on a new line in curly braces."
+    )
+  }
 
   # if (x) { ... } else if (y) { ... } else { ... } is OK; fully exact pairing
   #   of if/else would require this to be
@@ -188,15 +214,16 @@ brace_linter <- function(allow_single_line = FALSE) {
         lint_message = "`else` should come on the same line as the previous `}`."
       )
     )
-
-    lints <- c(
-      lints,
-      xml_nodes_to_lints(
-        xml_find_all(xml, xp_function_brace),
-        source_expression = source_expression,
-        lint_message = "Use curly braces for any function spanning multiple lines."
+    if (function_bodies != "never") {
+      lints <- c(
+        lints,
+        xml_nodes_to_lints(
+          xml_find_all(xml, xp_function_brace),
+          source_expression = source_expression,
+          lint_message = msg_function_brace
+        )
       )
-    )
+    }
 
     lints <- c(
       lints,

tests/testthat/test-brace_linter.R

@@ -299,25 +299,62 @@ test_that("brace_linter lints else correctly", {
 })
 
 test_that("brace_linter lints function expressions correctly", {
-  linter <- brace_linter()
-  expect_lint("function(x) 4", NULL, linter)
+  msg_always <- rex::rex("Wrap function bodies in curly braces.")
+  msg_multi_line <- rex::rex("Wrap multi-line function bodies in curly braces.")
+  msg_not_inline <- rex::rex("Wrap function bodies starting on a new line in curly braces.")
+
+  linter_always <- brace_linter(function_bodies = "always")
+  linter_multi_line <- brace_linter(function_bodies = "multi_line")
+  linter_not_inline <- brace_linter(function_bodies = "not_inline")
+  linter_never <- brace_linter(function_bodies = "never")
 
   lines <- trim_some("
     function(x) {
       x + 4
     }
   ")
-  expect_lint(lines, NULL, linter)
+  expect_lint(lines, NULL, linter_always)
+  expect_lint(lines, NULL, linter_multi_line)
+  expect_lint(lines, NULL, linter_not_inline)
+  expect_lint(lines, NULL, linter_never)
+
+  lints_single_line <- list(
+    rex::rex("Opening curly braces should never go on their own line and should always be followed by a new line."),
+    rex::rex("Closing curly-braces should always be on their own line, unless they are followed by an else.")
+  )
+  expect_lint("function(x) { x + 4 }", lints_single_line, linter_always)
+  expect_lint("function(x) { x + 4 }", lints_single_line, linter_multi_line)
+  expect_lint("function(x) { x + 4 }", lints_single_line, linter_not_inline)
+  expect_lint("function(x) { x + 4 }", lints_single_line, linter_never)
+  # using function_bodies = "always" without allow_single_line = TRUE prohibits inline function definitions:
+  expect_lint(
+    "function(x) { x + 4 }",
+    NULL,
+    brace_linter(allow_single_line = TRUE, function_bodies = "always")
+  )
+
+  expect_lint("function(x) x + 4", msg_always, linter_always)
+  expect_lint("function(x) x + 4", NULL, linter_multi_line)
+  expect_lint("function(x) x + 4", NULL, linter_not_inline)
+  expect_lint("function(x) x + 4", NULL, linter_never)
+
+  lines <- trim_some("
+    function(x) x +
+      4
+  ")
+  expect_lint(lines, msg_always, linter_always)
+  expect_lint(lines, msg_multi_line, linter_multi_line)
+  expect_lint(lines, NULL, linter_not_inline)
+  expect_lint(lines, NULL, linter_never)
 
   lines <- trim_some("
     function(x)
-      x+4
+      x + 4
   ")
-  expect_lint(
-    lines,
-    rex::rex("Use curly braces for any function spanning multiple lines."),
-    linter
-  )
+  expect_lint(lines, msg_always, linter_always)
+  expect_lint(lines, msg_multi_line, linter_multi_line)
+  expect_lint(lines, msg_not_inline, linter_not_inline)
+  expect_lint(lines, NULL, linter_never)
 })
 
 test_that("brace_linter lints if/else matching braces correctly", {