1 file changed, 105 insertions, 19 deletions
diff --git a/custom/extensions/about-render.lua b/custom/extensions/about-render.lua
index d7753a3..040768c 100644
--- a/custom/extensions/about-render.lua
+++ b/custom/extensions/about-render.lua
@@ -81,11 +81,36 @@ local function split_lines(text)
 	end
 end
 
+-- A pipe escaped with a backslash belongs to its cell, even inside a code
+-- span, so as on GitHub the backslash goes and the pipe stays. An even run of
+-- backslashes escapes only itself, so the pipe after it still divides.
 local function split_cells(row)
-	row = trim(row):gsub("^|", ""):gsub("|$", "")
-	local cells = {}
-	for cell in (row .. "|"):gmatch("(.-)|") do
-		cells[#cells + 1] = trim(cell)
+	row = trim(row)
+	local cells, parts, start = {}, {}, 1
+	if row:sub(1, 1) == "|" then
+		start = 2
+	end
+	while true do
+		local bar = row:find("|", start, true)
+		if not bar then
+			break
+		end
+		local slashes = 0
+		while row:sub(bar - slashes - 1, bar - slashes - 1) == "\\" do
+			slashes = slashes + 1
+		end
+		if slashes % 2 == 1 then
+			parts[#parts + 1] = row:sub(start, bar - 2) .. "|"
+		else
+			parts[#parts + 1] = row:sub(start, bar - 1)
+			cells[#cells + 1] = trim(table.concat(parts))
+			parts = {}
+		end
+		start = bar + 1
+	end
+	if start <= #row or #parts > 0 then
+		parts[#parts + 1] = row:sub(start)
+		cells[#cells + 1] = trim(table.concat(parts))
 	end
 	return cells
 end
@@ -96,10 +121,11 @@ end
 -- so it is safe on Lua 5.1, where an embedded zero byte ends a pattern.
 local function safe_url(url)
 	url = url:gsub("[%c%s]", "")
-	-- A leading "//" or "/\" is scheme-relative, which a browser
-	-- resolves to another origin, so it is not the local target the
-	-- parser meant to allow.
-	if url:sub(1, 2) == "//" or url:sub(1, 2) == "/\\" then
+	-- A leading "//" is scheme-relative, which a browser resolves to
+	-- another origin, and it reads a backslash there as a slash, so no
+	-- pair of the two is the local target the parser meant to allow.
+	local head = url:sub(1, 2):gsub("\\", "/")
+	if head == "//" then
 		return nil
 	end
 	local scheme = url:match("^(%a[%w%+%.%-]*):")
@@ -316,11 +342,10 @@ end
 
 
 -- Markdown is a deliberate subset rather than CommonMark, leaving out
--- reference links, raw HTML passthrough, nested lists and setext headings,
--- and inline markup does not span the end of a line. Man rendering covers the
--- common macros and drops the rest. Both parse into a node tree before
--- anything is emitted, so a failed parse falls back to plain text without
--- leaving half a page behind.
+-- reference links, raw HTML passthrough and nested lists, and inline markup
+-- does not span the end of a line. Man rendering covers the common macros and
+-- drops the rest. Both parse into a node tree before anything is emitted, so a
+-- failed parse falls back to plain text without leaving half a page behind.
 
 local render_markdown, render_man
 
@@ -428,6 +453,11 @@ if has_lpeg then
 
 	local lang_char = R("az", "AZ", "09") + S("_.+#-")
 	local heading_line = C(P("#") * P("#") ^ -5) * space ^ 1 * C(P(1) ^ 0)
+	-- A run of equals signs or dashes under a paragraph turns it into a
+	-- heading, as on GitHub, rather than reading as more of its text.
+	local setext_line = space ^ 0 * (C(P("=") ^ 1) + C(P("-") ^ 1))
+		* space ^ 0 * eol
+	local code_indent = P("    ") + P("\t")
 	local function thematic(mark)
 		return space ^ 0 * P(mark) * (space ^ 0 * P(mark)) ^ 2 * space ^ 0 * eol
 	end
@@ -454,6 +484,28 @@ if has_lpeg then
 
 	local function ordered(mark) return mark:match("%d") ~= nil end
 
+	local function follows_list(blocks)
+		local last = blocks[#blocks]
+		return last ~= nil and last.kind == "list"
+	end
+
+	-- An indented block runs on through blank lines, and up to four spaces
+	-- or one tab come off each of its lines.
+	local function continues_code(line)
+		return code_indent:match(line) or not line:find("%S")
+	end
+
+	local function unindent(line)
+		return line:match("^\t(.*)$") or line:match("^ ? ? ? ?(.*)$")
+	end
+
+	local function setext_level(line)
+		local run = setext_line:match(line)
+		if run then
+			return run:sub(1, 1) == "=" and 1 or 2
+		end
+	end
+
 	local function table_starts(lines, i)
 		return i < #lines and lines[i]:find("|", 1, true) ~= nil
 			and table_delimiter:match(lines[i + 1]) ~= nil
@@ -589,17 +641,51 @@ if has_lpeg then
 					ordered = is_ordered,
 					items = items,
 				}
+			-- Four spaces or a tab start a code block, except straight
+			-- after a list, where an indented paragraph more likely
+			-- carries an item on.
+			elseif code_indent:match(line) and not follows_list(blocks) then
+				local code = {}
+				while i <= n and continues_code(lines[i]) do
+					code[#code + 1] = unindent(lines[i])
+					i = i + 1
+				end
+				while code[#code]:match("^%s*$") do
+					code[#code] = nil
+				end
+				blocks[#blocks + 1] = {
+					kind = "code",
+					text = table.concat(code, "\n") .. "\n",
+				}
 			else
-				local paragraph = { line }
+				local paragraph, level = { line }, nil
 				i = i + 1
-				while i <= n and not ends_paragraph(lines, i) do
+				while i <= n do
+					level = setext_level(lines[i])
+					if level or ends_paragraph(lines, i)
+						or break_line:match(lines[i]) then
+						break
+					end
 					paragraph[#paragraph + 1] = lines[i]
 					i = i + 1
 				end
-				blocks[#blocks + 1] = {
-					kind = "para",
-					lines = paragraph_lines(paragraph),
-				}
+				if level then
+					local words = {}
+					for k, text in ipairs(paragraph) do
+						words[k] = trim(text)
+					end
+					blocks[#blocks + 1] = {
+						kind = "heading",
+						level = level,
+						kids = parse_inline(table.concat(words, " ")),
+					}
+					i = i + 1
+				else
+					blocks[#blocks + 1] = {
+						kind = "para",
+						lines = paragraph_lines(paragraph),
+					}
+				end
 			end
 		end
 		return blocks