Don't list inherited methods if there aren't any (#1387)

Fixes #1371

NEWS.md

@@ -1,5 +1,8 @@
 # roxygen2 (development version)
 
+* R6 documentation no longer shows inherited methods if there aren't any 
+  (#1371).
+
 * If you have a daily build of RStudio, the lists of changed Rd files are
   now clickable so you can immediately see the rendered development
   documentation (#1354).

R/rd-r6.R

@@ -258,9 +258,11 @@ r6_inherited_method_list <- function(block, r6data) {
   self <- r6data$self
   super_meth <- super_meth[! super_meth$name %in% self$name, ]
   super_meth <- super_meth[! duplicated(super_meth$name), ]
+  if (nrow(super_meth) == 0) {
+    return()
+  }
 
   super_meth <- super_meth[rev(seq_len(nrow(super_meth))), ]
-
   details <- paste0(
     "<details",
     if (nrow(super_meth) <= 5) " open",

tests/testthat/_snaps/rd-r6.md

@@ -14,6 +14,32 @@
       Warning:
       [<text>:10] @description Cannot find matching R6 method
 
+# class with no inherited methods
+
+    Code
+      cat(format(rd$get_section("rawRd")))
+    Output
+      \section{Super class}{
+      \code{\link[R_GlobalEnv:C1]{R_GlobalEnv::C1}} -> \code{C2}
+      }
+      \section{Methods}{
+      \subsection{Public methods}{
+      \itemize{
+      \item \href{#method-C2-meth1}{\code{C2$meth1()}}
+      }
+      }
+      \if{html}{\out{<hr>}}
+      \if{html}{\out{<a id="method-C2-meth1"></a>}}
+      \if{latex}{\out{\hypertarget{method-C2-meth1}{}}}
+      \subsection{Method \code{meth1()}}{
+      method1
+      \subsection{Usage}{
+      \if{html}{\out{<div class="r">}}\preformatted{C2$meth1()}\if{html}{\out{</div>}}
+      }
+      
+      }
+      }
+
 # integration test
 
     Code

tests/testthat/test-rd-r6.R

@@ -296,6 +296,33 @@ test_that("warning if no method comes after the docs", {
   doc <- format(rd)
 })
 
+test_that("class with no inherited methods", {
+  text <- "
+    C1 <- R6::R6Class('C1', cloneable = FALSE)
+
+    #' @title Title
+    #' @description Description.
+    #' @details Details.
+    C2 <- R6::R6Class('C2',
+      inherit = C1,
+      cloneable = FALSE,
+      public = list(
+        #' @description method1
+        meth1 = function() 1
+      )
+    )"
+
+  env <- new.env(parent = globalenv())
+
+  eval(parse(text = text, keep.source = TRUE), envir = env)
+  block <- parse_text(text, env = env)[[1]]
+  rd <- RoxyTopic$new()
+
+  topic_add_r6_methods(rd, block, env)
+  expect_snapshot(cat(format(rd$get_section("rawRd"))))
+})
+
+
 test_that("integration test", {
 
   wd <- getwd()