Increment subsection heading level when nested

Fixes #1377

NEWS.md

@@ -1,5 +1,8 @@
 # pkgdown (development version)
 
+* Nested `\subsection{}`s now generate appropriate heading levels 
+  (h3, h4, h5 etc) (#1377).
+
 * HTML is automatically stripped from the page title (#1318).
 
 * pkgdown now uses the new downlit package for all syntax highlighting and 

R/rd-html.R

@@ -95,10 +95,12 @@ as_html.COMMENT <- function(x, ...) {
 as_html.USERMACRO <-  function(x, ...) ""
 
 #' @export
-as_html.tag_subsection <- function(x, ...) {
+as_html.tag_subsection <- function(x, ..., subsection_level = 3L) {
+
+  h <- paste0("h", subsection_level)
   paste0(
-    "<h3>", flatten_text(x[[1]], ...), "</h3>\n",
-    flatten_para(x[[2]], ...)
+    "<", h, ">", flatten_text(x[[1]], ...), "</", h, ">\n",
+    flatten_para(x[[2]], ..., subsection_level = subsection_level + 1L)
   )
 }
 

tests/testthat/test-rd-html.R

@@ -47,6 +47,12 @@ test_that("subsection generates h3", {
     p2
   }"), c("<h3>A</h3>", "<p>p1</p>", "<p>p2</p>"))
 })
+test_that("nested subsection generates h4", {
+  expect_equal(
+    rd2html("\\subsection{H3}{\\subsection{H4}{}}"),
+    c("<h3>H3</h3>", "<h4>H4</h4>")
+  )
+})
 
 test_that("if generates html", {
   expect_equal(rd2html("\\if{html}{\\bold{a}}"), "<b>a</b>")