Add support for number_offset metadata with number-sections.lua

NEWS.md

@@ -9,6 +9,8 @@ rmarkdown 2.7
 
 - Automatically exclude renv directory for `render_site()` (thanks, @jmbuhr, #1996)
 
+- Number offset for section headers can be set via the `number_offset` top-level option of the YAML front matter. This feature supports variety of formats including those without native `--number-sections` option (e.g.,  `md_document`) (thanks, @atusy, #1999).
+
 rmarkdown 2.6
 ================================================================================
 

R/render.R

@@ -875,6 +875,13 @@ render <- function(input,
 
       pandoc_args <- output_format$pandoc$args
 
+      # let number_offset in metadata be an alternative of --number-offset option
+      if (("--number-sections" %in% pandoc_args) && !is.null(env$metadata$number_offset)) {
+          pandoc_args <- c(
+            pandoc_args, paste0("--number-offset=", env$metadata$number_offset)
+          )
+      }
+
       # if Lua filters are provided, add the command line switch
       if (!is.null(lua_filters <- output_format$pandoc$lua_filters)) {
         lua_filters <- pandoc_lua_filter_args(lua_filters)

inst/rmarkdown/lua/number-sections.lua

@@ -21,6 +21,18 @@ if FORMAT == "docx" then -- to be consistent with Pandoc >= 2.10.1
   separator = pandoc.Str("\t")
 end
 
+function Meta(meta)
+  local offset = meta.number_offset
+  if offset then
+    offset = (type(offset) == "table") and (pandoc.utils.stringify(offset)) or offset
+    local i = 0
+    for int in string.gmatch(offset, "[0-9]+") do
+      i = i + 1
+      section_number_table[i] = tonumber(int)
+    end
+  end
+end
+
 function Header(elem)
   -- If unnumbered
   if (elem.classes:find("unnumbered")) then
@@ -51,3 +63,8 @@ function Header(elem)
 
   return elem
 end
+
+return {
+  {Meta = Meta},
+  {Header = Header}
+}

tests/testthat/test-lua-filters.R

@@ -27,14 +27,28 @@ test_that("pagebreak Lua filters works", {
 })
 
 test_that("number_sections Lua filter works", {
-  numbers <- c("1", "1.1", "2", "2.1")
-  headers <- c("#", "##", "#", "##")
-  rmd <- paste0(headers, " ", numbers, "\n\n")
-  result <- .generate_md_and_convert(rmd, md_document(number_sections = TRUE))
-  expected <- paste(numbers, numbers)
-  # pandoc 2.11.2 default to atx headers
-  if (pandoc_available("2.11.2")) expected <- paste(headers, expected)
-  expect_identical(result[result %in% expected], expected)
+  test_number_sections <- function(number_offset = 0L) {
+      numbers <- paste0(
+        c(1L, 1L, 2L, 2L) + number_offset,
+        c("", ".1", "", ".1")
+      )
+      headers <- c("#", "##", "#", "##")
+      result <- .generate_md_and_convert(
+        paste0(headers, " ", numbers, "\n\n"),
+        md_document(
+          number_sections = TRUE,
+          pandoc_args = if (number_offset > 0) {
+            sprintf("--metadata=number_offset:%s", number_offset)
+          }
+        )
+      )
+      expected <- paste(numbers, numbers)
+      # pandoc 2.11.2 default to atx headers
+      if (pandoc_available("2.11.2")) expected <- paste(headers, expected)
+      expect_identical(result[result %in% expected], expected)
+  }
+  test_number_sections(1L)
+  test_number_sections(2L)
 })
 
 test_that("formats have the expected Lua filter", {