Don't run changelog-d in the build

This way we lose the preview of release notes on master, as well
as on https://nixos.org/manual/nix/unstable/release-notes/rl-next
but we can come back to this.

doc/manual/local.mk

@@ -146,7 +146,13 @@ $(d)/language.json: $(bindir)/nix
 
 # Generate "Upcoming release" notes (or clear it and remove from menu)
 $(d)/src/release-notes/rl-next.md: $(d)/rl-next $(d)/rl-next/*
-	$(trace-gen) changelog-d doc/manual/rl-next > $@
+	@if type -p changelog-d > /dev/null; then \
+		echo "  GEN   " $@; \
+		changelog-d doc/manual/rl-next > $@; \
+	else \
+		echo "  NULL  " $@; \
+		true > $@; \
+	fi
 
 $(d)/src/SUMMARY-rl-next.md: $(d)/src/release-notes/rl-next.md
 	$(trace-gen) true

doc/manual/src/contributing/hacking.md

@@ -257,4 +257,4 @@ See also the [format documentation](https://github.com/haskell/cabal/blob/master
 ### Build process
 
 Releases have a precomputed `rl-MAJOR.MINOR.md`, and no `rl-next.md`.
-Non-releases build the release notes on the fly.
+Set `buildUnreleasedNotes = true;` in `flake.nix` to build the release notes on the fly.

flake.nix

@@ -14,6 +14,9 @@
 
       officialRelease = false;
 
+      # Set to true to build the release notes for the next release.
+      buildUnreleasedNotes = false;
+
       version = lib.fileContents ./.version + versionSuffix;
       versionSuffix =
         if officialRelease
@@ -196,7 +199,7 @@
           ]
           ++ lib.optionals stdenv.hostPlatform.isLinux [(buildPackages.util-linuxMinimal or buildPackages.utillinuxMinimal)]
           # Official releases don't have rl-next, so we don't need to compile a changelog
-          ++ lib.optional (!officialRelease) changelog-d
+          ++ lib.optional (!officialRelease && buildUnreleasedNotes) changelog-d
           ;
 
         buildDeps =
@@ -734,8 +737,8 @@
               ++ lib.optional
                 (stdenv.cc.isClang && stdenv.hostPlatform == stdenv.buildPlatform)
                 pkgs.buildPackages.clang-tools
-              # We want changelog-d in the shell even if it's an official release
-              ++ lib.optional officialRelease changelog-d
+              # We want changelog-d in the shell even if the current build doesn't need it
+              ++ lib.optional (officialRelease || ! buildUnreleasedNotes) changelog-d
               ;
 
             buildInputs = buildDeps ++ propagatedDeps