From 3272afa17b68d25c8070e58819f2e56f075c764d Mon Sep 17 00:00:00 2001
From: Jan Tojnar <jtojnar@gmail.com>
Date: Thu, 26 May 2022 16:47:40 +0200
Subject: [PATCH] doc: Port anchors preprocessor to jq script
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Python is only pulled into the build closure by Mercurial, which might end up being removed.
Let’s port the script to jq, which is more likely to stay.
---
 doc/manual/anchors.jq | 31 ++++++++++++++++++++++++
 doc/manual/anchors.py | 56 -------------------------------------------
 doc/manual/book.toml  |  3 ++-
 doc/manual/local.mk   |  2 +-
 flake.nix             |  2 +-
 5 files changed, 35 insertions(+), 59 deletions(-)
 create mode 100755 doc/manual/anchors.jq
 delete mode 100755 doc/manual/anchors.py

diff --git a/doc/manual/anchors.jq b/doc/manual/anchors.jq
new file mode 100755
index 000000000..72309779c
--- /dev/null
+++ b/doc/manual/anchors.jq
@@ -0,0 +1,31 @@
+"\\[\\]\\{#(?<anchor>[^\\}]+?)\\}" as $empty_anchor_regex |
+"\\[(?<text>[^\\]]+?)\\]\\{#(?<anchor>[^\\}]+?)\\}" as $anchor_regex |
+
+
+def transform_anchors_html:
+    . | gsub($empty_anchor_regex; "<a name=\"" + .anchor + "\"></a>")
+      | gsub($anchor_regex; "<a href=\"#" + .anchor + "\" id=\"" + .anchor + "\">" + .text + "</a>");
+
+
+def transform_anchors_strip:
+    . | gsub($empty_anchor_regex; "")
+      | gsub($anchor_regex; .text);
+
+
+def map_contents_recursively(transformer):
+    . + {
+        Chapter: (.Chapter + {
+            content: .Chapter.content | transformer,
+            sub_items: .Chapter.sub_items | map(map_contents_recursively(transformer)),
+        }),
+    };
+
+
+def process_command:
+    .[0] as $context |
+    .[1] as $body |
+    $body + {
+        sections: $body.sections | map(map_contents_recursively(if $context.renderer == "html" then transform_anchors_html else transform_anchors_strip end)),
+    };
+
+process_command
diff --git a/doc/manual/anchors.py b/doc/manual/anchors.py
deleted file mode 100755
index 2a93b2a67..000000000
--- a/doc/manual/anchors.py
+++ /dev/null
@@ -1,56 +0,0 @@
-#!/usr/bin/env python3
-
-import argparse
-import json
-import re
-import sys
-
-
-empty_anchor_regex = re.compile(r"\[\]\{#(?P<anchor>[^\}]+?)\}")
-anchor_regex = re.compile(r"\[(?P<text>[^\]]+?)\]\{#(?P<anchor>[^\}]+?)\}")
-
-
-def transform_anchors_html(content):
-    content = empty_anchor_regex.sub(r'<a name="\g<anchor>"></a>', content)
-    content = anchor_regex.sub(r'<a href="#\g<anchor>" id="\g<anchor>">\g<text></a>', content)
-    return content
-
-
-def transform_anchors_strip(content):
-    content = empty_anchor_regex.sub(r'', content)
-    content = anchor_regex.sub(r'\g<text>', content)
-    return content
-
-
-def map_contents_recursively(transformer, chapter):
-    chapter["Chapter"]["content"] = transformer(chapter["Chapter"]["content"])
-    for sub_item in chapter["Chapter"]["sub_items"]:
-        map_contents_recursively(transformer, sub_item)
-
-
-def supports_command(args):
-    sys.exit(0)
-
-
-def process_command(args):
-    context, book = json.load(sys.stdin)
-    transformer = transform_anchors_html if context["renderer"] == "html" else transform_anchors_strip
-    for section in book["sections"]:
-        map_contents_recursively(transformer, section)
-    print(json.dumps(book))
-
-
-if __name__ == "__main__":
-    parser = argparse.ArgumentParser(
-        description="mdBook preprocessor adding anchors."
-    )
-    parser.set_defaults(command=process_command)
-
-    subparsers = parser.add_subparsers()
-
-    supports_parser = subparsers.add_parser("supports", help="Check if given renderer is supported")
-    supports_parser.add_argument("renderer", type=str)
-    supports_parser.set_defaults(command=supports_command)
-
-    args = parser.parse_args()
-    args.command(args)
diff --git a/doc/manual/book.toml b/doc/manual/book.toml
index 75554d11f..ff6b79c07 100644
--- a/doc/manual/book.toml
+++ b/doc/manual/book.toml
@@ -2,4 +2,5 @@
 additional-css = ["custom.css"]
 
 [preprocessor.anchors]
-command = "python3 doc/manual/anchors.py"
+renderers = ["html"]
+command = "jq --from-file doc/manual/anchors.jq"
diff --git a/doc/manual/local.mk b/doc/manual/local.mk
index 910d0a03b..371ed6f21 100644
--- a/doc/manual/local.mk
+++ b/doc/manual/local.mk
@@ -97,7 +97,7 @@ doc/manual/generated/man1/nix3-manpages: $(d)/src/command-ref/new-cli
 	done
 	@touch $@
 
-$(docdir)/manual/index.html: $(MANUAL_SRCS) $(d)/book.toml $(d)/anchors.py $(d)/custom.css $(d)/src/SUMMARY.md $(d)/src/command-ref/new-cli $(d)/src/command-ref/conf-file.md $(d)/src/expressions/builtins.md $(call rwildcard, $(d)/src, *.md)
+$(docdir)/manual/index.html: $(MANUAL_SRCS) $(d)/book.toml $(d)/anchors.jq $(d)/custom.css $(d)/src/SUMMARY.md $(d)/src/command-ref/new-cli $(d)/src/command-ref/conf-file.md $(d)/src/expressions/builtins.md $(call rwildcard, $(d)/src, *.md)
 	$(trace-gen) RUST_LOG=warn mdbook build doc/manual -d $(DESTDIR)$(docdir)/manual
 
 endif
diff --git a/flake.nix b/flake.nix
index dd3a25e9e..536fcf9fa 100644
--- a/flake.nix
+++ b/flake.nix
@@ -102,7 +102,7 @@
             # Tests
             buildPackages.git
             buildPackages.mercurial # FIXME: remove? only needed for tests
-            buildPackages.jq
+            buildPackages.jq # Also for custom mdBook preprocessor.
           ]
           ++ lib.optionals stdenv.hostPlatform.isLinux [(buildPackages.util-linuxMinimal or buildPackages.utillinuxMinimal)];