Put extensions in Lua module instead of sneaking them in environment

Note that neither .cache/config.lua nor .cache/site-tree.json get
updated when EXTENSIONS changes.  This could be hacked as follows:

    config = EXTENSIONS="$(EXTENSIONS)"

    ifneq "$(shell test -f $(config_token) && cat $(config_token))"     \
    "$(shell ./generate-config-token.py $(config))"

    .PHONY: $(lua_config) $(site_tree) $(config_token)
    endif

Plus a recipe for config_token, and some dependencies on it.

4 files changed, 46 insertions, 12 deletions

diff --git a/repo/www/Makefile b/repo/www/Makefile
index f88672c..aa48971 100644
--- a/repo/www/Makefile
+++ b/repo/www/Makefile
@@ -23,6 +23,8 @@ cache = .cache
 title = $(cache)/title
 # Maps folders to their contents (files and subfolders).
 site_tree = $(cache)/site-tree.json
+# Lua module to let filters know about the configuration.
+lua_config = $(cache)/config.lua
 # Defines $(pages) and $(indices).
 dependencies = $(cache)/deps.mk
 
@@ -32,6 +34,9 @@ $(title): $(top_readme) | $(cache)
 $(site_tree): $(page_folders) | $(cache)
 	./generate-tree.py -o $@ $(EXTENSIONS)
 
+$(lua_config): | $(cache)
+	./generate-lua-config.py EXTENSIONS="$(EXTENSIONS)" > $@
+
 $(dependencies): $(site_tree) | $(cache)
 	./generate-deps.py $< $@ $(OUT_DIR)
 
@@ -49,10 +54,10 @@ $(html_folders) $(cache):
 
 $(pages) $(subindices): $(title)
 
-$(pages) $(indices): $(html_template)
+$(pages) $(indices): $(html_template) $(lua_filters) $(lua_config)
 
 $(pages): $(OUT_DIR)/%.html:
-	$(call v,PAGE,$*) EXTENSIONS="$(EXTENSIONS)"                    \
+	$(call v,PAGE,$*)                                               \
 	./generate-page.py --site-title="$$(cat $(title))" --title="$*" \
 		$(foreach f,$(lua_filters),--lua-filter $(f))           \
 		--template=$(html_template) $< $@
@@ -66,7 +71,7 @@ $(subindices): index_options = --site-title="$$(cat $(title))"
 # ⚠ When tweaking this rule, check whether it still works for the
 #   top-level index.html.
 $(indices): $(OUT_DIR)/%index.html:
-	$(call v,INDEX,$*) EXTENSIONS="$(EXTENSIONS)"                           \
+	$(call v,INDEX,$*)                                                      \
 	./generate-index.py $(index_options) --template=$(html_template)        \
 		$(foreach f,$(lua_filters),--lua-filter $(f))                   \
 		$(site_tree) "$(patsubst %/,%,$*)" $@
diff --git a/repo/www/convert-internal-links.lua b/repo/www/convert-internal-links.lua
index e50352a..21054d1 100644
--- a/repo/www/convert-internal-links.lua
+++ b/repo/www/convert-internal-links.lua
@@ -1,10 +1,4 @@
-EXTENSIONS = {}
-
-string.gsub(
-  os.getenv("EXTENSIONS"),
-  "[^%s]+",
-  function (ext) EXTENSIONS[#EXTENSIONS+1] = ext end
-)
+local config = require 'config'
 
 function Link(link)
   if link.target:match("^[%w]+://")
@@ -12,7 +6,7 @@ function Link(link)
     return link
   end
 
-  for _, ext in pairs(EXTENSIONS)
+  for _, ext in pairs(config.EXTENSIONS)
   do
     link.target = link.target:gsub("%."..ext.."$", ".html")
   end
diff --git a/repo/www/generate-lua-config.py b/repo/www/generate-lua-config.py
new file mode 100755
index 0000000..0a00443
--- /dev/null
+++ b/repo/www/generate-lua-config.py
@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+
+from sys import argv
+
+
+TEMPLATE = '''\
+local config = {{}}
+
+config.EXTENSIONS = {{ {EXTENSIONS} }}
+
+return config
+'''
+
+
+def _quote(s):
+    return f"'{s}'"
+
+
+def main(arguments):
+    pairs = (arg.split('=') for arg in arguments)
+
+    formatters = {
+        'EXTENSIONS': lambda v: ', '.join(map(_quote, v.split()))
+    }
+
+    parameters = {
+        key: formatters[key](value) for (key, value) in pairs
+    }
+
+    print(TEMPLATE.format_map(parameters), end='')
+
+
+if __name__ == '__main__':
+    main(argv[1:])
diff --git a/repo/www/helpers.py b/repo/www/helpers.py
index 434ef6c..f76fa02 100644
--- a/repo/www/helpers.py
+++ b/repo/www/helpers.py
@@ -1,7 +1,7 @@
 from collections import defaultdict
 from dataclasses import dataclass, field
 from itertools import chain
-from os import path
+from os import environ, path
 from subprocess import run
 from typing import Iterator
 
@@ -67,4 +67,5 @@ def pandoc(page, output, template, filters, title=None, site_title=None):
     if site_title is not None:
         cmd += ('-T', site_title)
 
+    environ['LUA_PATH'] = '.cache/?.lua;;'
     run(cmd, check=True)