detect functional lambdas in object_usage_linter

NEWS.md

@@ -36,6 +36,7 @@
      `R CMD check`, it defaults to `TRUE` (#941, #1458, @IndrajeetPatil).
    + Handles backticked symbols inside {glue} expressions correctly, e.g. ``glue("{`x`}")`` correctly
      determines `x` was used (#1619, @MichaelChirico)
+   + Detects problems inside R4.1.0+ lambda functions (`\(...)`) (#1933, @MichaelChirico)
 
 * `spaces_inside_linter()` allows terminal missing keyword arguments (e.g. `alist(arg = )`; #540, @MichaelChirico)
 

R/object_usage_linter.R

@@ -37,12 +37,12 @@ object_usage_linter <- function(interpret_glue = TRUE, skip_with = TRUE) {
   # TODO(#1106): use //[...] to capture assignments in more scopes
   xpath_function_assignment <- paste(
     # direct assignments
-    "expr[LEFT_ASSIGN or EQ_ASSIGN]/expr[2][FUNCTION]",
-    "expr_or_assign_or_help[EQ_ASSIGN]/expr[2][FUNCTION]",
-    "equal_assign[EQ_ASSIGN]/expr[2][FUNCTION]",
+    "expr[LEFT_ASSIGN or EQ_ASSIGN]/expr[2][FUNCTION or OP-LAMBDA]",
+    "expr_or_assign_or_help[EQ_ASSIGN]/expr[2][FUNCTION or OP-LAMBDA]",
+    "equal_assign[EQ_ASSIGN]/expr[2][FUNCTION or OP-LAMBDA]",
     # assign() and setMethod() assignments
-    "//SYMBOL_FUNCTION_CALL[text() = 'assign']/parent::expr/following-sibling::expr[2][FUNCTION]",
-    "//SYMBOL_FUNCTION_CALL[text() = 'setMethod']/parent::expr/following-sibling::expr[3][FUNCTION]",
+    "//SYMBOL_FUNCTION_CALL[text() = 'assign']/parent::expr/following-sibling::expr[2][FUNCTION or OP-LAMBDA]",
+    "//SYMBOL_FUNCTION_CALL[text() = 'setMethod']/parent::expr/following-sibling::expr[3][FUNCTION or OP-LAMBDA]",
     sep = " | "
   )
 

tests/testthat/test-object_usage_linter.R

@@ -624,3 +624,17 @@ test_that("messages without a quoted name are caught", {
     object_usage_linter()
   )
 })
+
+test_that("functional lambda definitions are also caught", {
+  skip_if_not_r_version("4.1.0")
+
+  expect_lint(
+    trim_some("
+      fun <- \\() {
+        a <- 1
+      }
+    "),
+    rex::rex("local variable", anything, "assigned but may not be used"),
+    object_usage_linter()
+  )
+})