fix rstudio#832: remove attributes on headers <h1>...<h6> since Pandoc 2.8 may add them, e.g., <h1 number="1"> (jgm/pandoc#5944), which will make bookdown fail to parse things like section numbers

yihui · yihui · commit a07ae075a92b · 2019-12-05T11:17:07.000-06:00
also merge the 'class' attribute of &lt;h1&gt; into its parent div's class
diff --git a/NEWS.md b/NEWS.md
@@ -6,6 +6,8 @@
 
 ## BUG FIXES
 
+- Fixed cross-reference issues with Pandoc 2.8 (thanks, @N0rbert @RLesur, #832).
+
 - For output formats like `pdf_book`, unused arguments passed to `base_format` will be discarded (thanks, @jooyoungseo, #790).
 
 - For the sake of backward-compatibility, prevent the commands `\frontmatter`, `\mainmatter`, and `\backmatter` from being automatically added to the LaTeX output when the Pandoc version is higher than 2.7, because **bookdown** users may have added these commands by themselves (thanks, @remlapmot, rstudio/rmarkdown#1721).
diff --git a/R/html.R b/R/html.R
@@ -132,6 +132,7 @@ html_document2 = function(
   config$post_processor = function(metadata, input, output, clean, verbose) {
     if (is.function(post)) output = post(metadata, input, output, clean, verbose)
     x = read_utf8(output)
+    x = clean_html_tags(x)
     x = restore_appendix_html(x, remove = FALSE)
     x = restore_part_html(x, remove = FALSE)
     x = resolve_refs_html(x, global = !number_sections)
@@ -249,7 +250,7 @@ split_chapters = function(output, build = build_chapter, number_sections, split_
   if (!(split_level %in% 0:2)) stop('split_level must be 0, 1, or 2')
 
   x = read_utf8(output)
-  x = clean_meta_tags(x)
+  x = clean_html_tags(x)
 
   i1 = find_token(x, '<!--bookdown:title:start-->')
   i2 = find_token(x, '<!--bookdown:title:end-->')
@@ -448,6 +449,30 @@ clean_meta_tags = function(x) {
   x
 }
 
+# remove extra attributes on headers (Pandoc 2.8+), and merge the 'class' of a
+# header into its parent div: https://github.com/rstudio/bookdown/issues/832
+clean_header_tags = function(x) {
+  r1 = '^(<div [^>]*class="section level[1-6][^"]*)(">)$'
+  r2 = '^(<h[1-6])([^>]+)(>.+</h[1-6]>.*)$'
+  i = grep(r2, x)
+  i = i[grep(r1, x[i - 1])]  # the line above <h1> should be <div>
+  if (length(i) == 0) return(x)
+
+  a = gsub(r2, '\\2', x[i])  # attributes of <h1>
+  j = grep(r3 <- '(.* class=")([^"]+)(".*)', a)
+  a = gsub(r3, ' \\2', a[j])  # extract the 'class' attribute of <h1>
+  k = i[j] - 1  # add the 'class' attribute of <h1> to its parent <div>
+  x[k] = paste0(gsub(r1, '\\1', x[k]), a, gsub(r1, '\\2', x[k]))
+  x[i] = gsub(r2, '\\1\\3', x[i])  # remove attributes on <h1>
+  x
+}
+
+clean_html_tags = function(x) {
+  x = clean_meta_tags(x)
+  x = clean_header_tags(x)
+  x
+}
+
 # move files to output dir if specified
 move_to_output_dir = function(files) {
   files2 = output_path(files)
