sys-apps/nix: restore doc part of DESTDIR patch

Without the change the install fails to access generated man-pages in
$WORKDIR while the build process targeted #DESTDIR.

Reported-by: UnwhiteCat
Issue: #54

sys-apps/nix/files/nix-2.24-doc-destdir.patch

@@ -0,0 +1,43 @@
+Fix DESTDIR handling for USE=doc case.
+
+The build system does not support a separate install phase and fails
+to create man pages locally: always attempts to write to $(DESTDIR).
+--- a/doc/manual/local.mk
++++ b/doc/manual/local.mk
+@@ -183,26 +183,26 @@ install: $(docdir)/manual/index.html
+
+ # Generate 'nix' manpages.
+ .PHONY: manpages
+-manpages: $(mandir)/man1/nix3-manpages
+-install: $(mandir)/man1/nix3-manpages
+-man: doc/manual/generated/man1/nix3-manpages
+-all: doc/manual/generated/man1/nix3-manpages
++manpages: $(DESTDIR)$(mandir)/man1/nix3-manpages
++install: $(DESTDIR)$(mandir)/man1/nix3-manpages
++man: $(DESTDIR)doc/manual/generated/man1/nix3-manpages
++all: $(DESTDIR)doc/manual/generated/man1/nix3-manpages
+
+ # FIXME: unify with how the other man pages are generated.
+ # this one works differently and does not use any of the amenities provided by `/mk/lib.mk`.
+-$(mandir)/man1/nix3-manpages: doc/manual/generated/man1/nix3-manpages
+-	@mkdir -p $(DESTDIR)$$(dirname $@)
+-	$(trace-install) install -m 0644 $$(dirname $<)/* $(DESTDIR)$$(dirname $@)
++$(DESTDIR)$(mandir)/man1/nix3-manpages: $(DESTDIR)doc/manual/generated/man1/nix3-manpages
++	@mkdir -p $$(dirname $@)
++	$(trace-install) install -m 0644 $$(dirname $<)/* $$(dirname $@)
+
+-doc/manual/generated/man1/nix3-manpages: $(d)/src/command-ref/new-cli
+-	@mkdir -p $(DESTDIR)$$(dirname $@)
++$(DESTDIR)doc/manual/generated/man1/nix3-manpages: $(d)/src/command-ref/new-cli
++	@mkdir -p $$(dirname $@)
+ 	$(trace-gen) for i in doc/manual/src/command-ref/new-cli/*.md; do \
+ 		name=$$(basename $$i .md); \
+ 		tmpFile=$$(mktemp); \
+ 		if [[ $$name = SUMMARY ]]; then continue; fi; \
+ 		printf "Title: %s\n\n" "$$name" > $$tmpFile; \
+ 		cat $$i >> $$tmpFile; \
+-		lowdown -sT man --nroff-nolinks -M section=1 $$tmpFile -o $(DESTDIR)$$(dirname $@)/$$name.1; \
++		lowdown -sT man --nroff-nolinks -M section=1 $$tmpFile -o $$(dirname $@)/$$name.1; \
+ 		rm $$tmpFile; \
+ 	done
+ 	@touch $@

sys-apps/nix/nix-2.24.10-r1.ebuild

@@ -83,6 +83,7 @@ PATCHES=(
 	"${FILESDIR}"/${PN}-2.10-libpaths.patch
 	"${FILESDIR}"/${PN}-2.16-no-sandbox-fallback.patch
 	"${FILESDIR}"/${PN}-2.22-no-sandbox-fallback-README.patch
+	"${FILESDIR}"/${PN}-2.24-doc-destdir.patch
 )
 
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