Allow passing Range objects to the nesting_level option

In order to have a higher level of customization for tables of
contents, it is possible to pass a `Range` object (e.g. 2..5) as the
nesting_level option of `HTML_TOC` objects.

Fixes #519

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Changelog
 
+* Allow passing `Range` objects to the `nesting_level` option to have
+  a higher level of customization for table of contents:
+
+  ~~~ruby
+  Redcarpet::Render::HTML_TOC.new(nesting_level: 2..5)
+  ~~~
+
 ## Version 3.4.0
 
 * Rely on djb2 hashing generating anchors with non-ASCII chars.

README.markdown

@@ -182,8 +182,8 @@ which will output a table of contents in HTML based on the headers of the
 Markdown document.
 
 When instantiating this render object, you can optionally pass a `nesting_level`
-option which takes an integer and allows you to make it render only headers
-until a specific level.
+option which takes an integer or a range and allows you to make it render only
+headers at certain levels.
 
 Redcarpet also includes a plaintext renderer, `Redcarpet::Render::StripDown`, that
 strips out all the formatting:

ext/redcarpet/html.c

@@ -326,7 +326,8 @@ rndr_header(struct buf *ob, const struct buf *text, int level, void *opaque)
 	if (ob->size)
 		bufputc(ob, '\n');
 
-	if ((options->flags & HTML_TOC) && (level <= options->toc_data.nesting_level)) {
+	if ((options->flags & HTML_TOC) && level >= options->toc_data.nesting_bounds[0] &&
+	     level <= options->toc_data.nesting_bounds[1]) {
 		bufprintf(ob, "<h%d id=\"", level);
 		rndr_header_anchor(ob, text);
 		BUFPUTSL(ob, "\">");
@@ -675,7 +676,8 @@ toc_header(struct buf *ob, const struct buf *text, int level, void *opaque)
 {
 	struct html_renderopt *options = opaque;
 
-	if (level <= options->toc_data.nesting_level) {
+	if (level >= options->toc_data.nesting_bounds[0] &&
+	    level <= options->toc_data.nesting_bounds[1]) {
 		/* set the level offset if this is the first header
 		 * we're parsing for the document */
 		if (options->toc_data.current_level == 0)
@@ -824,7 +826,8 @@ sdhtml_renderer(struct sd_callbacks *callbacks, struct html_renderopt *options,
 	/* Prepare the options pointer */
 	memset(options, 0x0, sizeof(struct html_renderopt));
 	options->flags = render_flags;
-	options->toc_data.nesting_level = 99;
+	options->toc_data.nesting_bounds[0] = 1;
+	options->toc_data.nesting_bounds[1] = 6;
 
 	/* Prepare the callbacks */
 	memcpy(callbacks, &cb_default, sizeof(struct sd_callbacks));

ext/redcarpet/html.h

@@ -35,7 +35,7 @@ struct html_renderopt {
 	struct {
 		int current_level;
 		int level_offset;
-		int nesting_level;
+		int nesting_bounds[2];
 	} toc_data;
 
 	unsigned int flags;

ext/redcarpet/rc_render.c

@@ -511,10 +511,22 @@ static VALUE rb_redcarpet_htmltoc_init(int argc, VALUE *argv, VALUE self)
 	sdhtml_toc_renderer(&rndr->callbacks, (struct html_renderopt *)&rndr->options.html, render_flags);
 	rb_redcarpet__overload(self, rb_cRenderHTML_TOC);
 
-	if (!(NIL_P(nesting_level)))
-		rndr->options.html.toc_data.nesting_level = NUM2INT(nesting_level);
-	else
-		rndr->options.html.toc_data.nesting_level = 6;
+	/* Check whether we are dealing with a Range object by
+	   checking whether the object responds to min and max */
+	if (rb_respond_to(nesting_level, rb_intern("min")) &&
+	    rb_respond_to(nesting_level, rb_intern("max"))) {
+		int min = NUM2INT(rb_funcall(nesting_level, rb_intern("min"), 0));
+		int max = NUM2INT(rb_funcall(nesting_level, rb_intern("max"), 0));
+
+		rndr->options.html.toc_data.nesting_bounds[0] = min;
+		rndr->options.html.toc_data.nesting_bounds[1] = max;
+	} else if (FIXNUM_P(nesting_level)) {
+		rndr->options.html.toc_data.nesting_bounds[0] = 1;
+		rndr->options.html.toc_data.nesting_bounds[1] = NUM2INT(nesting_level);
+	} else {
+		rndr->options.html.toc_data.nesting_bounds[0] = 1;
+		rndr->options.html.toc_data.nesting_bounds[1] = 6;
+	}
 
 	return Qnil;
 }

test/html_toc_render_test.rb

@@ -33,6 +33,20 @@ def test_granular_toc_render
     assert !output.include?("A sub-sub title")
   end
 
+  def test_granular_toc_render_with_range
+    output = render(@markdown, with: { nesting_level: 2..5 }).strip
+
+    assert output.start_with?("<ul>")
+    assert output.end_with?("</ul>")
+
+    assert output.match("Another one")
+    assert output.match("A sub-sub-title")
+    assert output.match("見出し")
+
+    refute output.match("A title")
+    refute output.match("A really tiny title")
+  end
+
   def test_toc_heading_id
     output = render(@markdown)