Describe active experimental features in the contributing guide

They are put in the manual separate pages under the new overarching
description of experimental features.

The settings page just lists the valid experimental feature names (so
people know what a valid setting entry looks like), with links to those
pages. It doesn't attempt to describe each experimental feature as that
is too much information for the configuration settings section.

.gitignore

@@ -23,7 +23,8 @@ perl/Makefile.config
 /doc/manual/src/SUMMARY.md
 /doc/manual/src/command-ref/new-cli
 /doc/manual/src/command-ref/conf-file.md
-/doc/manual/src/command-ref/experimental-features.md
+/doc/manual/src/command-ref/experimental-features-shortlist.md
+/doc/manual/src/contributing/experimental-features
 /doc/manual/src/language/builtins.md
 
 # /scripts/

doc/manual/generate-xp-features-shortlist.nix

@@ -0,0 +1,9 @@
+with builtins;
+with import ./utils.nix;
+
+let
+  showExperimentalFeature = name: doc:
+    ''
+      - [`${name}`](@docroot@/contributing/experimental-features/${name}.md)
+    '';
+in xps: indent "  " (concatStrings (attrValues (mapAttrs showExperimentalFeature xps)))

doc/manual/generate-xp-features.nix

@@ -1,11 +1,21 @@
+xps:
+
 with builtins;
 with import ./utils.nix;
 
 let
-  showExperimentalFeature = name: doc:
-    squash ''
-      - <span id="xp-feature-${name}">[`${name}`](#xp-feature-${name})</span>
+  makePage = { name, value }:
+    {
+      name = "${name}.md";
+      inherit value;
+      feature = name;
+    };
 
-      ${indent "  " doc}
-    '';
-in xps: indent "  " (concatStringsSep "\n" (attrValues (mapAttrs showExperimentalFeature xps)))
+  featurePages = map makePage (attrsToList xps);
+
+  tableOfContents = let
+    showEntry = page:
+      "    - [${page.feature}](contributing/experimental-features/${page.name})";
+    in concatStringsSep "\n" (map showEntry featurePages) + "\n";
+
+in (listToAttrs featurePages) // { "SUMMARY.md" = tableOfContents; }

doc/manual/local.mk

@@ -81,10 +81,11 @@ $(d)/%.8: $(d)/src/command-ref/%.md
 $(d)/nix.conf.5: $(d)/src/command-ref/conf-file.md
 	@printf "Title: %s\n\n" "$$(basename $@ .5)" > $^.tmp
 	@cat $^ >> $^.tmp
+	@$(call process-includes,$^,$^.tmp)
 	$(trace-gen) lowdown -sT man --nroff-nolinks -M section=5 $^.tmp -o $@
 	@rm $^.tmp
 
-$(d)/src/SUMMARY.md: $(d)/src/SUMMARY.md.in $(d)/src/command-ref/new-cli
+$(d)/src/SUMMARY.md: $(d)/src/SUMMARY.md.in $(d)/src/command-ref/new-cli $(d)/src/contributing/experimental-features
 	@cp $< $@
 	@$(call process-includes,$@,$@)
 
@@ -93,7 +94,7 @@ $(d)/src/command-ref/new-cli: $(d)/nix.json $(d)/utils.nix $(d)/generate-manpage
 	$(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 $(d)/src/command-ref/experimental-features.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-shortlist.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 $@
@@ -106,11 +107,16 @@ $(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 $(bindir)/nix
+$(d)/src/contributing/experimental-features: $(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)/src/command-ref/experimental-features-shortlist.md: $(d)/xp-features.json $(d)/utils.nix $(d)/generate-xp-features-shortlist.nix $(bindir)/nix
+	@rm -rf $@ $@.tmp
+	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-xp-features-shortlist.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 $@
@@ -154,7 +160,7 @@ 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.jq $(d)/custom.css $(d)/src/SUMMARY.md $(d)/src/command-ref/new-cli $(d)/src/command-ref/conf-file.md $(d)/src/language/builtins.md
+$(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/contributing/experimental-features $(d)/src/command-ref/conf-file.md $(d)/src/language/builtins.md
 	$(trace-gen) \
 		tmp="$$(mktemp -d)"; \
 		cp -r doc/manual "$$tmp"; \

doc/manual/src/SUMMARY.md.in

@@ -96,6 +96,7 @@
 - [Contributing](contributing/contributing.md)
   - [Hacking](contributing/hacking.md)
   - [Experimental Features](contributing/experimental-features.md)
+{{#include ./contributing/experimental-features/SUMMARY.md}}
   - [CLI guideline](contributing/cli-guideline.md)
 - [Release Notes](release-notes/release-notes.md)
   - [Release X.Y (202?-??-??)](release-notes/rl-next.md)

doc/manual/utils.nix

@@ -5,6 +5,9 @@ rec {
 
   concatStrings = concatStringsSep "";
 
+  attrsToList = a:
+    map (name: { inherit name; value = a.${name}; }) (builtins.attrNames a);
+
   replaceStringsRec = from: to: string:
     # recursively replace occurrences of `from` with `to` within `string`
     # example:

src/libutil/config.hh

@@ -384,7 +384,7 @@ struct ExperimentalFeatureSettings : Config {
 
           Experimental features available:
 
-          {{#include experimental-features.md}}
+          {{#include experimental-features-shortlist.md}}
 
           Experimental features are [further documented](@docroot@/contributing/experimental-features.md) in the contribution guide.
         )"};

src/libutil/experimental-features.cc

@@ -57,7 +57,7 @@ constexpr std::array<ExperimentalFeatureDetails, 11> xpFeatureDetails = {{
         .name = "flakes",
         .description = R"(
             Enable flakes. See the manual entry for [`nix
-            flake`](../command-ref/new-cli/nix3-flake.md) for details.
+            flake`](@docroot@/command-ref/new-cli/nix3-flake.md) for details.
         )",
     },
     {