Assemble experimental feature docs outside of Nix itself

Instead of constructing a markdown list in C++ (which involved all sorts
of nasty string literals), export some JSON and assemble it with the
manual build system.

Besides following the precedent set with other dumped data, this is a
better separate of content and presentation; if we decide for example we
want to display this information in a different way, or in a different
section of the manual, it will become much easier to do so.

3 files changed, 25 insertions, 5 deletions

diff --git a/doc/manual/generate-xp-features.nix b/doc/manual/generate-xp-features.nix
new file mode 100644
index 000000000..db1ba6092
--- /dev/null
+++ b/doc/manual/generate-xp-features.nix
@@ -0,0 +1,11 @@
+with builtins;
+with import ./utils.nix;
+
+let
+  showExperimentalFeature = name: doc:
+    squash ''
+      - <span id="xp-feature-${name}">[`${name}`](#xp-feature-${name})</span>
+
+      ${indent "  " doc}
+    '';
+in xps: indent "  " (concatStringsSep "\n" (attrValues (mapAttrs showExperimentalFeature xps)))
diff --git a/doc/manual/local.mk b/doc/manual/local.mk
index df941d460..0d4b9d640 100644
--- a/doc/manual/local.mk
+++ b/doc/manual/local.mk
@@ -88,12 +88,12 @@ $(d)/src/SUMMARY.md: $(d)/src/SUMMARY.md.in $(d)/src/command-ref/new-cli
 	@cp $< $@
 	@$(call process-includes,$@,$@)
 
-$(d)/src/command-ref/new-cli: $(d)/nix.json $(d)/generate-manpage.nix $(bindir)/nix
+$(d)/src/command-ref/new-cli: $(d)/nix.json $(d)/utils.nix $(d)/generate-manpage.nix $(bindir)/nix
 	@rm -rf $@ $@.tmp
 	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-manpage.nix (builtins.readFile $<)'
 	@mv $@.tmp $@
 
-$(d)/src/command-ref/conf-file.md: $(d)/conf-file.json $(d)/utils.nix $(d)/src/command-ref/conf-file-prefix.md $(bindir)/nix
+$(d)/src/command-ref/conf-file.md: $(d)/conf-file.json $(d)/utils.nix $(d)/src/command-ref/conf-file-prefix.md $(d)/src/command-ref/experimental-features.md $(bindir)/nix
 	@cat doc/manual/src/command-ref/conf-file-prefix.md > $@.tmp
 	$(trace-gen) $(nix-eval) --expr '(import doc/manual/utils.nix).showSettings { useAnchors = true; } (builtins.fromJSON (builtins.readFile $<))' >> $@.tmp;
 	@mv $@.tmp $@
@@ -106,6 +106,15 @@ $(d)/conf-file.json: $(bindir)/nix
 	$(trace-gen) $(dummy-env) $(bindir)/nix show-config --json --experimental-features nix-command > $@.tmp
 	@mv $@.tmp $@
 
+$(d)/src/command-ref/experimental-features.md: $(d)/xp-features.json $(d)/utils.nix $(d)/generate-xp-features.nix $(bindir)/nix
+	@rm -rf $@ $@.tmp
+	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-xp-features.nix (builtins.fromJSON (builtins.readFile $<))'
+	@mv $@.tmp $@
+
+$(d)/xp-features.json: $(bindir)/nix
+	$(trace-gen) $(dummy-env) NIX_PATH=nix/corepkgs=corepkgs $(bindir)/nix __dump-xp-features > $@.tmp
+	@mv $@.tmp $@
+
 $(d)/src/language/builtins.md: $(d)/builtins.json $(d)/generate-builtins.nix $(d)/src/language/builtins-prefix.md $(bindir)/nix
 	@cat doc/manual/src/language/builtins-prefix.md > $@.tmp
 	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-builtins.nix (builtins.fromJSON (builtins.readFile $<))' >> $@.tmp;
diff --git a/doc/manual/utils.nix b/doc/manual/utils.nix
index 5eacce0dd..f78e6bb02 100644
--- a/doc/manual/utils.nix
+++ b/doc/manual/utils.nix
@@ -74,10 +74,10 @@ rec {
           if aliases == [] then "" else
             "**Deprecated alias:** ${(concatStringsSep ", " (map (s: "`${s}`") aliases))}";
 
-      indent = prefix: s:
-        concatStringsSep "\n" (map (x: if x == "" then x else "${prefix}${x}") (splitLines s));
-
     in result;
 
+  indent = prefix: s:
+    concatStringsSep "\n" (map (x: if x == "" then x else "${prefix}${x}") (splitLines s));
+
   showSettings = args: settingsInfo: concatStrings (attrValues (mapAttrs (showSetting args) settingsInfo));
 }