2 files changed, 23 insertions, 6 deletions
diff --git a/custom/extensions/about-render.lua b/custom/extensions/about-render.lua
index 03c17d8..af4f0df 100644
--- a/custom/extensions/about-render.lua
+++ b/custom/extensions/about-render.lua
@@ -38,8 +38,9 @@ local max_depth = 24
 
 local filename, tree_base, tree_query, chunks = "", "", "", {}
 
--- How often each heading anchor has been handed out. The ids already on the
--- page around the readme start at one, so no heading takes them.
+-- The heading anchors handed out so far, each with the count its next
+-- repeat takes. The ids already on the page around the readme are in it
+-- from the start, so no heading takes them.
 local id_counts = {}
 
 
@@ -259,10 +260,16 @@ local function emit_id(nodes)
 	if base == "" then
 		return
 	end
-	local count = id_counts[base] or 0
-	id_counts[base] = count + 1
+	-- A count can land on an anchor a heading already took, as "Twice 1"
+	-- does after two of "Twice", so it goes on up until the anchor is free.
+	local id = base
+	while id_counts[id] do
+		id_counts[base] = id_counts[base] + 1
+		id = base .. "-" .. id_counts[base]
+	end
+	id_counts[id] = 0
 	html(" id='")
-	html_attr(count > 0 and base .. "-" .. count or base)
+	html_attr(id)
 	html("'")
 end
 
@@ -972,7 +979,7 @@ function filter_open(name, base, query)
 	tree_base = base or ""
 	tree_query = query or ""
 	chunks = {}
-	id_counts = { cgit = 1, header = 1, about = 1 }
+	id_counts = { cgit = 0, header = 0, about = 0 }
 end
 
 function filter_write(str)
diff --git a/tests/extensions/test-about-render.lua b/tests/extensions/test-about-render.lua
index b9284c4..6f54805 100644
--- a/tests/extensions/test-about-render.lua
+++ b/tests/extensions/test-about-render.lua
@@ -86,6 +86,16 @@ h.contains("a repeated anchor is counted", out, "<h1 id='twice'>Twice</h1><h1 id
 out = render("README.md", "# About")
 h.contains("no heading takes an id of the page", out, "<h1 id='about-1'>")
 
+out = render("README.md", "# Cgit\n# Header")
+h.contains("nor any other id of the page", out, "<h1 id='cgit-1'>Cgit</h1><h1 id='header-1'>Header</h1>")
+
+out = render("README.md", "# Twice\n# Twice\n# Twice 1")
+h.contains("a count never gives an anchor a heading already took", out,
+	"<h1 id='twice-1'>Twice</h1><h1 id='twice-1-1'>Twice 1</h1>")
+
+out = render("README.md", "# About\n# About 1")
+h.contains("and the same holds past an id of the page", out, "<h1 id='about-1'>About</h1><h1 id='about-1-1'>About 1</h1>")
+
 out = render("README.md", "# ???")
 h.contains("a heading of punctuation gets no anchor", out, "<h1>???</h1>")
-rw-r--r--	custom/extensions/about-render.lua	19
-rw-r--r--	tests/extensions/test-about-render.lua	10