Add a script to generate links using Agda's HTML output

Signed-off-by: Danila Fedorin <>
This commit is contained in:
Danila Fedorin 2024-05-22 16:28:00 -07:00
parent 76b061d699
commit 032411fe9c

agda.rb Normal file
View File

@ -0,0 +1,262 @@
require "nokogiri"
require "pathname"
files = ARGV[0..-1]
class LineInfo
attr_accessor :links
def initialize
@links = []
class Handler
def initialize
@file_infos = {}
# Traverse the preformatted Agda block in the given Agda HTML file
# and find which textual ranges have IDs and links to other ranges.
# Store this information in a hash, line => LineInfo.
def process_agda_html_file(file)
return @file_infos[file] if @file_infos.include? file
@file_infos[file] = line_infos = {}
unless File.exists?(file)
return line_infos
document = Nokogiri::HTML.parse(
pre_code = document.css("pre.Agda")[0]
# The traversal postorder; we always visit children before their
# parents, and we visit leaves in sequence.
offset = 0
line = 1
pre_code.traverse do |at|
# Text nodes are always leaves; visiting a new leaf means we've advanced
# in the text by the length of that text. However, if there are newlines
# -- since this is a preformatted block -- we also advanced by a line.
# At this time, do not support links that span multiple lines, but
# Agda doesn't produce those either.
if at.text?
if at.content.include? "\n"
# This textual leaf is at least part whitespace. The logic
# assumes that links can't span multiple pages, and that links
# aren't nested, so ensure that the parent of the textual node
# is the preformatted block itself.
raise "unsupported Agda HTML output" if != "pre"
# Increase the line and track the final offset. Written as a loop
# in case we eventually want to add some handling for the pieces
# sandwiched between newlines.
at.content.split("\n", -1).each_with_index do |bit, idx|
line += 1 unless idx == 0
offset = bit.length
# It's not a newline node, so it could be anywhere. All we need to
# do is adjust the offset within the full pre block's text.
offset += at.content.length
elsif == "a"
# We found a link. Agda emits both links and "things to link to" as
# 'a' nodes, so check for either, and record them. Even if
# the link is nested, the .content.length accessor will only
# retrieve the textual content, and thus -- assuming the link
# isn't split across lines -- will find the proper from-to range.
line_info = line_infos.fetch(line) { line_infos[line] = }
href = at.attribute("href")
id = at.attribute("id")
if href or id
new_link = { :from => offset-at.content.length, :to => offset }
new_link[:href] = href if href
new_link[:id] = id if id
line_info.links << new_link
return line_infos
# Given a Hugo HTML file which references potentially several Agda modules
# in code blocks, insert links into the code blocks.
# There are several things we need to take care of:
# 1. Finding the HTML files associated with each referenced Agda module.
# For this, we make use of the data-base-path etc. attributes that
# the vanilla theme inserts.
# 2. "zipping together" the Agda and Hugo HTML representations. Each of
# them encode the code, but they use different HTML elements and structures.
# So, given a Hugo HTML code block, traverse its textual contents
# and find any that are covered by links in the related Agda HTML file.
# 3. Fixing up links: the Agda HTML links assume each module has its own HTML
# file. This isn't true for us: multiple modules are stitched into
# one Hugo HTML file. Also, we don't include the entire Agda HTML
# file in the Hugo HTML, so some links may be broken. So, find IDs
# that are visible in the Hugo file, rename them to be globally unique,
# and re-write cross-file links that reference these IDs to point
# inside the Hugo file.
def process_source_file(file)
nodes_referencing_href = {} # Agda HTML ID -> all (Hugo HTML) nodes that link to it
seen_hrefs = {} # Agda HTML ID -> its new ID in Hugo-land
id_counter = 0
# Process each highlight group that's been marked as an Agda file.
document = Nokogiri::HTML.parse(
document.css('div[data-agda-block]').each do |t|
first_line, last_line = nil, nil
if first_line_attr = t.attribute("data-first-line")
first_line = first_line_attr.to_s.to_i
if last_line_attr = t.attribute("data-last-line")
last_line = last_line_attr.to_s.to_i
# The name of an Agda module is determined from its directory
# structure: A/B/C.agda creates A.B.C.html. Assume that the
# base path is the Agda module root, and use the remaining directories
# to build the HTML file name.
base_path = t.attribute("data-base-path").to_s
base_path_dirs = Pathname(base_path).each_filename.to_a
full_path = t.attribute("data-file-path").to_s
full_path_dirs = Pathname(full_path).each_filename.to_a
dirs_in_base = full_path_dirs[base_path_dirs.length..-1]
html_file = dirs_in_base.join(".").gsub(/\.agda$/, ".html")
html_path = File.join(["code", base_path, "html", html_file])
agda_info = process_agda_html_file(html_path)
# Hugo conveniently generates a bunch of spans, each encoding a line
# of code output. We can iterate over these and match them up with
# the line numbers we got from reading the Agda HTML output.
lines = t.css("pre.chroma code[data-lang] .line") do |line, line_no|
line_info = agda_info[line_no]
next unless line_info
offset = 0
line.traverse do |lt|
if lt.text?
content = lt.content
new_offset = offset + content.length
# The span/a/etc. structure of the Agda and Hugo HTML files
# need not line up; it's possible for there to be a single link
# in the Agda file that's broken up across multiple HTML nodes
# in the Hugo output. For now, just don't link those, since inserting
# such overlapping links is relatively complicated. Instead,
# require links to fit fully within a current text node (and thus,
# not overlap the boundaries of any HTML).
matching_links = line_info.links.filter do |link|
link[:from] >= offset and link[:to] <= new_offset
# A given text node can be broken into any number of sub-nodes,
# where some sub-nodes are still text, and others have been turned
# into links. Store the new pieces in replace_with. E.g.,
# Original:
# abc
# New:
# a<a href="..">b</a>c
# replace_with:
# ["a", <Nokogiri::XML::Node...>, "c"]
# match_offset represents how much of the original text we've
# already converted. The below iteration assumes that matching
# links are in order, and don't overlap.
replace_with = []
replace_offset = 0
matching_links.each do |match|
# The link's range is an offset from the beginning of the line,
# but the text piece we're splitting up might be partway into
# the line. Convert the link coordinates to piece-relative ones.
relative_from = match[:from] - offset
relative_to = match[:to] - offset
# If the previous link ended some time before the new link
# began (or if the current link is the first one, and is not
# at the beginning), ensure that the plain text "in between"
# is kept.
replace_with << content[replace_offset...relative_from]
tag = (match.include? :href) ? 'a' : 'span'
new_link =, document)
if match.include? :href
# For nodes with links, note what they're referring to, so
# we can adjust their hrefs when we assign global IDs.
href = match[:href].to_s
new_link['href'] = href
ref_list = nodes_referencing_href.fetch(href) { nodes_referencing_href[href] = [] }
ref_list << new_link
if match.include? :id
# For nodes with IDs visible in the current Hugo file, we'll
# want to redirect links that previously go to other Agda
# module HTML files. So, note the ID that we want to redirect,
# and pick a new unique ID to replace it with.
id = match[:id].to_s
uniq_id = "agda-unique-ident-#{id_counter}"
id_counter += 1
new_link['id'] = uniq_id
seen_hrefs["#{html_file}##{id}"] = uniq_id
new_link.content = content[relative_from...relative_to]
replace_with << new_link
replace_offset = relative_to
replace_with << content[replace_offset..-1]
# Finally, replace the node under consideration with the new
# pieces.
replace_with.each do |replacement|
lt.add_previous_sibling replacement
offset = new_offset
# Now, we have a complete list of all the IDs visible in scope.
# Redirect relevant links to these IDs. This achieves within-post
# links.
seen_hrefs.each do |agda_id, hugo_id|
nodes_to_rewrite = nodes_referencing_href[agda_id]
next unless nodes_to_rewrite
nodes_to_rewrite.each do |node|
node['href'] = "##{hugo_id}"
nodes_referencing_href.delete agda_id
# The remaining nodes reference symbols not in the current Hugo document,
# so just replace them with their contents for now (we'd need some
# external hosting to make this work otherwise).
nodes_referencing_href.each do |href, nodes|
nodes.each do |node|
node.replace node.content
File.write(file, document.to_html(encoding: 'UTF-8'))
handler =
files.each do |file|
handler.process_source_file file