Provide the header bit in the table_cell callback

As the same callback is used to render header and body cells, there
is an extra bit needed to check in which one we are currently
rendering the content.

Fixes #604.

CHANGELOG.md

@@ -1,5 +1,14 @@
 # Changelog
 
+* Properly provide a third argument to the `table_cell` callback indicating
+  whether the current cell is part of the header or not.
+
+  The previous implementation with two parameters is still supported.
+
+  Fixes #604, Refs #605.
+
+  *Mark Lambley*
+
 * Fix anchor generation on titles with ampersands.
 
   Fixes #696.

README.markdown

@@ -258,7 +258,7 @@ end
 * paragraph(text)
 * table(header, body)
 * table_row(content)
-* table_cell(content, alignment)
+* table_cell(content, alignment, header)
 
 ### Span-level calls
 

ext/redcarpet/rc_render.c

@@ -113,9 +113,10 @@ rndr_tablerow(struct buf *ob, const struct buf *text, void *opaque)
 static void
 rndr_tablecell(struct buf *ob, const struct buf *text, int align, void *opaque)
 {
-	VALUE rb_align;
+	VALUE rb_align, rb_header;
+	VALUE rb_callback, rb_callback_arity;
 
-	switch (align) {
+	switch (align & MKD_TABLE_ALIGNMASK) {
 	case MKD_TABLE_ALIGN_L:
 		rb_align = CSTR2SYM("left");
 		break;
@@ -133,7 +134,25 @@ rndr_tablecell(struct buf *ob, const struct buf *text, int align, void *opaque)
 		break;
 	}
 
-	BLOCK_CALLBACK("table_cell", 2, buf2str(text), rb_align);
+	if (align & MKD_TABLE_HEADER) {
+		rb_header = Qtrue;
+	} else {
+		rb_header = Qfalse;
+	}
+
+	struct redcarpet_renderopt *opt = opaque;
+
+	rb_callback = rb_funcall(opt->self, rb_intern("method"), 1, CSTR2SYM("table_cell"));
+
+	rb_callback_arity = rb_funcall(rb_callback, rb_intern("arity"), 0);
+
+	/* For backward compatibility, let's ensure that the erasure with
+	   only two parameters is still supported. */
+	if (FIX2SHORT(rb_callback_arity) == 3) {
+		BLOCK_CALLBACK("table_cell", 3, buf2str(text), rb_align, rb_header);
+	} else {
+		BLOCK_CALLBACK("table_cell", 2, buf2str(text), rb_align);
+	}
 }
 
 static void

test/custom_render_test.rb

@@ -64,4 +64,43 @@ def test_base_render_without_quote_callback
 
     assert_equal "", parser.render(%(a "quote"))
   end
+
+  def test_table_cell_callback_having_either_two_or_three_args
+    two = Class.new(Redcarpet::Render::HTML) do
+      def table_cell(content, alignment)
+        %(<td>#{content}</td>)
+      end
+    end
+
+    three = Class.new(Redcarpet::Render::HTML) do
+      def table_cell(content, alignment, header)
+        tag = header ? "th" : "td"
+
+        %(<#{tag}>#{content}</#{tag}>)
+      end
+    end
+
+    markdown = <<-Md.chomp.strip_heredoc
+      | A | B |
+      |---|---|
+      | C | D |
+    Md
+
+    first_parser = Redcarpet::Markdown.new(two.new, tables: true)
+    second_parser = Redcarpet::Markdown.new(three.new, tables: true)
+
+    first_output = first_parser.render(markdown)
+    second_output = second_parser.render(markdown)
+
+    assert { first_output.include?("<td>A</td>") }
+    assert { first_output.include?("<td>B</td>") }
+
+    assert { second_output.include?("<th>A</th>") }
+    assert { second_output.include?("<th>B</th>") }
+
+    [first_output, second_output].each do |output|
+      assert { output.include?("<td>C</td>") }
+      assert { output.include?("<td>D</td>") }
+    end
+  end
 end