Allow plugins to add pkg-config dependencies to rocksdb.pc (#9198)

Summary:
This patch fixes an issue that occur when dependencies of plugins are not
installed to the same prefix as librocksdb. Because plugin dependencies are
declared in the `Libs` field of rocksdb.pc, programs that link against
librocksdb with `pkg-config --libs rocksdb` will link with `-L` flag for the
path of librocksdb only. This patch allows plugin dependencies to be declared in
the `Requires` field of rocksdb.pc, so that pkg-config will correctly provide
`-L` flags for dependencies of plugins that are installed in other locations.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9198

Reviewed By: akankshamahajan15

Differential Revision: D32596620

Pulled By: ajkr

fbshipit-source-id: e17b2b6452b5f2e955b430140197c57e26a4a518

Makefile

@@ -249,8 +249,20 @@ ROCKSDB_PLUGIN_MKS = $(foreach plugin, $(ROCKSDB_PLUGINS), plugin/$(plugin)/*.mk
 include $(ROCKSDB_PLUGIN_MKS)
 ROCKSDB_PLUGIN_SOURCES = $(foreach plugin, $(ROCKSDB_PLUGINS), $(foreach source, $($(plugin)_SOURCES), plugin/$(plugin)/$(source)))
 ROCKSDB_PLUGIN_HEADERS = $(foreach plugin, $(ROCKSDB_PLUGINS), $(foreach header, $($(plugin)_HEADERS), plugin/$(plugin)/$(header)))
+ROCKSDB_PLUGIN_PKGCONFIG_REQUIRES = $(foreach plugin, $(ROCKSDB_PLUGINS), $($(plugin)_PKGCONFIG_REQUIRES))
 PLATFORM_LDFLAGS += $(foreach plugin, $(ROCKSDB_PLUGINS), $($(plugin)_LDFLAGS))
 
+ifneq ($(ROCKSDB_PLUGIN_PKGCONFIG_REQUIRES),)
+LDFLAGS := $(LDFLAGS) $(shell pkg-config --libs $(ROCKSDB_PLUGIN_PKGCONFIG_REQUIRES))
+ifneq ($(.SHELLSTATUS),0)
+$(error pkg-config failed)
+endif
+CXXFLAGS := $(CXXFLAGS) $(shell pkg-config --cflags $(ROCKSDB_PLUGIN_PKGCONFIG_REQUIRES))
+ifneq ($(.SHELLSTATUS),0)
+$(error pkg-config failed)
+endif
+endif
+
 export JAVAC_ARGS
 CLEAN_FILES += make_config.mk rocksdb.pc
 
@@ -2011,6 +2023,7 @@ gen-pc:
 	-echo 'Libs: -L$${libdir} $(EXEC_LDFLAGS) -lrocksdb' >> rocksdb.pc
 	-echo 'Libs.private: $(PLATFORM_LDFLAGS)' >> rocksdb.pc
 	-echo 'Cflags: -I$${includedir} $(PLATFORM_CXXFLAGS)' >> rocksdb.pc
+	-echo 'Requires: $(subst ",,$(ROCKSDB_PLUGIN_PKGCONFIG_REQUIRES))' >> rocksdb.pc
 
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