Fix S4 .local wrapper extraction

I guess this never worked 🤷

Fixes #847

NEWS.md

@@ -1,5 +1,8 @@
 # roxygen2 (development version)
 
+* S4 methods that generate `.local()` wrapper no longer error with obscure
+  error message (#847).
+
 * `@param` containing only whitespce gets a clear warning message (#869).
 
 * A new system for providing custom roxygen2 metadata is now available. When

R/object-from-call.R

@@ -158,3 +158,34 @@ parser_setConstructorS3 <- function(call, env, block) {
   value <- standardise_obj(name, get(name, env), env, block)
   object(value, name)
 }
+
+
+# helpers -----------------------------------------------------------------
+
+# When a generic has ... and a method adds new arguments, the S4 method
+# wraps the definition inside another function which has the same arguments
+# as the generic. This function figures out if that's the case, and extracts
+# the original function if so.
+#
+# It's based on expression processing based on the structure of the
+# constructed method which looks like:
+#
+# function (x, ...) {
+#   .local <- function (x, ..., y = 7) {}
+#   .local(x, ...)
+# }
+extract_method_fun <- function(x) {
+  fun <- x@.Data
+
+  method_body <- body(fun)
+  if (!is_call(method_body)) return(fun)
+  if (length(method_body) == 0) return(fun)
+  if (!identical(method_body[[1]], quote(`{`))) return(fun)
+
+  first_line <- method_body[[2]]
+  if (!is_call(first_line, name = "<-", n = 2)) return(fun)
+  if (!identical(first_line[[2]], quote(`.local`))) return(fun)
+
+  eval(first_line[[3]])
+}
+

R/object.R

@@ -49,33 +49,6 @@ is_generator <- function(x) {
   methods::is(x, "refObjectGenerator") || methods::is(x, "classGeneratorFunction")
 }
 
-# When a generic has ... and a method adds new arguments, the S4 method
-# wraps the definition inside another function which has the same arguments
-# as the generic. This function figures out if that's the case, and extracts
-# the original function if so.
-#
-# It's based on expression processing based on the structure of the
-# constructed method which looks like:
-#
-# function (x, ...) {
-#   .local <- function (x, ..., y = 7) {}
-#   .local(x, ...)
-# }
-extract_method_fun <- function(x) {
-  fun <- x@.Data
-
-  method_body <- body(fun)
-  if (!is.call(method_body)) return(fun)
-  if (!identical(method_body[[1]], quote(`{`))) return(fun)
-
-  first_line <- method_body[[2]]
-  if (!is.call(first_line)) return(fun)
-  if (!identical(first_line[[1]], quote(`<-`))) return(fun)
-  if (!identical(first_line[[2]], quote(`.local`))) return(fun)
-
-  first_line[[3]]
-}
-
 # Consistent naming scheme for R object classes --------------------------------
 # (s3/s4/rc x generic/class/method, function, data)
 

tests/testthat/test-object-from-call.R

@@ -0,0 +1,12 @@
+test_that("finds arguments when S4 method wrapped inside .local()", {
+  env <- pkg_env()
+  setClass("Foo", where = env)
+  call <- quote(
+    setMethod('subset', 'Foo', function(x, foo, ...) {})
+  )
+  eval(call, envir = env)
+
+  obj <- object_from_call(call, env, block = NULL, file = NULL)
+  expect_s3_class(obj, "s4method")
+  expect_named(formals(obj$value@.Data), c("x", "foo", "..."))
+})