doc: stub out epub manual

same reasoning as for the nixos manual.

doc/Makefile

@@ -66,18 +66,13 @@ out/html/index.html: doc-support/result manual-full.xml style.css highlightjs
 	cp doc-support/result/xsl/docbook/images/callouts/*.svg out/html/images/callouts/
 	chmod u+w -R out/html/
 
-out/epub/manual.epub: manual-full.xml
+out/epub/manual.epub: epub.xml
 	mkdir -p out/epub/scratch
 	xsltproc --nonet \
 		--output out/epub/scratch/ \
 		doc-support/result/epub.xsl \
-		./manual-full.xml
+		./epub.xml
 
-	cp -r $(pandoc_media_dir) out/epub/scratch/OEBPS
-	cp ./overrides.css out/epub/scratch/OEBPS
-	cp ./style.css out/epub/scratch/OEBPS
-	mkdir -p out/epub/scratch/OEBPS/images/callouts/
-	cp doc-support/result/xsl/docbook/images/callouts/*.svg out/epub/scratch/OEBPS/images/callouts/
 	echo "application/epub+zip" > mimetype
 	zip -0Xq "out/epub/manual.epub" mimetype
 	rm mimetype

doc/default.nix

@@ -20,7 +20,33 @@ in pkgs.stdenv.mkDerivation {
     ln -s ${doc-support} ./doc-support/result
   '';
 
+  epub = ''
+    <book xmlns="http://docbook.org/ns/docbook"
+          xmlns:xlink="http://www.w3.org/1999/xlink"
+          version="5.0"
+          xml:id="nixpkgs-manual">
+      <info>
+        <title>Nixpkgs Manual</title>
+        <subtitle>Version ${pkgs.lib.version}</subtitle>
+      </info>
+      <chapter>
+        <title>Temporarily unavailable</title>
+        <para>
+          The Nixpkgs manual is currently not available in EPUB format,
+          please use the <link xlink:href="https://nixos.org/nixpkgs/manual">HTML manual</link>
+          instead.
+        </para>
+        <para>
+          If you've used the EPUB manual in the past and it has been useful to you, please
+          <link xlink:href="https://github.com/NixOS/nixpkgs/issues/237234">let us know</link>.
+        </para>
+      </chapter>
+    </book>
+  '';
+  passAsFile = [ "epub" ];
+
   preBuild = ''
+    cp $epubPath epub.xml
     make -j$NIX_BUILD_CORES render-md
   '';