[Buildroot] [PATCH] pkg-infra: allow dumping reverse dependencies of a package

[Yann E. MORIN]

Finding the packages that select another one in a specific configuration
is not very trivial:

  - when optional, the dependency is not expressed in Kconfig

  - looking at the .mk files is not very nice.

Introduce a way to dump reverse dependencies of packages, i.e. the list
of packages that directly depend on that package. Like for direct
dependencies, we limit the list to the first-order reverse dependencies.

Document it in the main help; use the opportunity to also docuemnt
foo-show-depends.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
---
 Makefile               | 2 ++
 package/pkg-generic.mk | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/Makefile b/Makefile
index 5e4daef..3039983 100644
--- a/Makefile
+++ b/Makefile
@@ -943,6 +943,8 @@ help:
 	@echo '  <pkg>-depends          - Build <pkg>'\''s dependencies'
 	@echo '  <pkg>-configure        - Build <pkg> up to the configure step'
 	@echo '  <pkg>-build            - Build <pkg> up to the build step'
+	@echo '  <pkg>-show-depends     - List packages on which <pkg> depends'
+	@echo '  <pkg>-show-rdepends    - List packages which have <pkg> as a dependency'
 	@echo '  <pkg>-graph-depends    - Generate a graph of <pkg>'\''s dependencies'
 	@echo '  <pkg>-dirclean         - Remove <pkg> build directory'
 	@echo '  <pkg>-reconfigure      - Restart the build from the configure step'
diff --git a/package/pkg-generic.mk b/package/pkg-generic.mk
index 68ead3d..779f294 100644
--- a/package/pkg-generic.mk
+++ b/package/pkg-generic.mk
@@ -523,6 +523,10 @@ $(2)_FINAL_DEPENDENCIES = $$(sort $$($(2)_DEPENDENCIES))
 $(2)_FINAL_PATCH_DEPENDENCIES = $$(sort $$($(2)_PATCH_DEPENDENCIES))
 $(2)_FINAL_ALL_DEPENDENCIES = $$(sort $$($(2)_FINAL_DEPENDENCIES) $$($(2)_FINAL_PATCH_DEPENDENCIES))
 
+# Register package as a reverse-dependencies of all its dependencies
+$$(eval $$(foreach p,$$($(2)_FINAL_ALL_DEPENDENCIES),\
+	$$(call UPPERCASE,$$(p))_RDEPENDENCIES += $(1)$$(sep)))
+
 $(2)_INSTALL_STAGING		?= NO
 $(2)_INSTALL_IMAGES		?= NO
 $(2)_INSTALL_TARGET		?= YES
@@ -698,6 +702,9 @@ $(1)-show-version:
 $(1)-show-depends:
 			@echo $$($(2)_FINAL_ALL_DEPENDENCIES)
 
+$(1)-show-rdepends:
+			@echo $$($(2)_RDEPENDENCIES)
+
 $(1)-graph-depends: graph-depends-requirements
 			@$$(INSTALL) -d $$(GRAPHS_DIR)
 			@cd "$$(CONFIG_DIR)"; \
-- 
2.7.4