Improve support for the optional ICU dependency.

For GNU make, conditionally populate the `Requires:` field in `re2.pc`.
Use `pkg-config` to obtain the necessary compiler and linker flags when
building `static-testinstall` and `shared-testinstall`.

For CMake, the dependency has to be expressed to CMake itself, not just
to `pkg-config` as above.

Fixes #407.

Change-Id: Ie5e0ea88e0662f54be011b3bc0c57f2cfa852f88
Reviewed-on: https://code-review.googlesource.com/c/re2/+/60931
Reviewed-by: Paul Wankadia <junyer@google.com>
Reviewed-by: Perry Lorier <perryl@google.com>

CMakeLists.txt

@@ -12,12 +12,18 @@ include(CTest)
 include(GNUInstallDirs)
 
 option(BUILD_SHARED_LIBS "build shared libraries" OFF)
-option(USEPCRE "use PCRE in tests and benchmarks" OFF)
+option(RE2_USE_ICU "build against ICU for full Unicode properties support" OFF)
+
+# For historical reasons, this is just "USEPCRE", not "RE2_USE_PCRE".
+option(USEPCRE "build against PCRE for testing and benchmarking" OFF)
 
 # CMake seems to have no way to enable/disable testing per subproject,
 # so we provide an option similar to BUILD_TESTING, but just for RE2.
 option(RE2_BUILD_TESTING "enable testing for RE2" ON)
 
+# The pkg-config Requires: field.
+set(REQUIRES)
+
 # ABI version
 # http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html
 set(SONAME 10)
@@ -43,11 +49,19 @@ endif()
 if(WIN32)
   add_definitions(-DUNICODE -D_UNICODE -DSTRICT -DNOMINMAX)
   add_definitions(-D_CRT_SECURE_NO_WARNINGS -D_SCL_SECURE_NO_WARNINGS)
-elseif(UNIX)
+endif()
+
+if(UNIX)
   set(THREADS_PREFER_PTHREAD_FLAG ON)
   find_package(Threads REQUIRED)
 endif()
 
+if(RE2_USE_ICU)
+  find_package(ICU REQUIRED COMPONENTS uc)
+  add_definitions(-DRE2_USE_ICU)
+  list(APPEND REQUIRES icu-uc)
+endif()
+
 if(USEPCRE)
   add_definitions(-DUSEPCRE)
   list(APPEND EXTRA_TARGET_LINK_LIBRARIES pcre)
@@ -89,6 +103,10 @@ if(UNIX)
   target_link_libraries(re2 PUBLIC Threads::Threads)
 endif()
 
+if(RE2_USE_ICU)
+  target_link_libraries(re2 PUBLIC ICU::uc)
+endif()
+
 if(RE2_BUILD_TESTING)
   set(TESTING_SOURCES
       re2/testing/backtrack.cc

Makefile

@@ -7,7 +7,7 @@
 # CCICU=$(shell pkg-config icu-uc --cflags) -DRE2_USE_ICU
 # LDICU=$(shell pkg-config icu-uc --libs)
 
-# To build against PCRE for testing or benchmarking,
+# To build against PCRE for testing and benchmarking,
 # uncomment the next two lines:
 # CCPCRE=-I/usr/local/include -DUSEPCRE
 # LDPCRE=-L/usr/local/lib -lpcre
@@ -42,6 +42,12 @@ else
 SED_INPLACE=sed -i
 endif
 
+# The pkg-config Requires: field.
+REQUIRES=
+ifdef LDICU
+REQUIRES+=icu-uc
+endif
+
 # ABI version
 # http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html
 SONAME=10
@@ -320,6 +326,7 @@ common-install:
 	$(INSTALL_DATA) re2.pc.in $(DESTDIR)$(libdir)/pkgconfig/re2.pc
 	$(SED_INPLACE) -e "s#@CMAKE_INSTALL_FULL_INCLUDEDIR@#$(includedir)#" $(DESTDIR)$(libdir)/pkgconfig/re2.pc
 	$(SED_INPLACE) -e "s#@CMAKE_INSTALL_FULL_LIBDIR@#$(libdir)#" $(DESTDIR)$(libdir)/pkgconfig/re2.pc
+	$(SED_INPLACE) -e "s#@REQUIRES@#$(REQUIRES)#" $(DESTDIR)$(libdir)/pkgconfig/re2.pc
 	$(SED_INPLACE) -e "s#@SONAME@#$(SONAME)#" $(DESTDIR)$(libdir)/pkgconfig/re2.pc
 
 .PHONY: testinstall
@@ -329,27 +336,27 @@ testinstall: static-testinstall shared-testinstall
 	@echo
 
 .PHONY: static-testinstall
-static-testinstall: CXXFLAGS:=-pthread -I$(DESTDIR)$(includedir) $(CXXFLAGS)
-static-testinstall: LDFLAGS:=-pthread -L$(DESTDIR)$(libdir) -l:libre2.a $(LDICU) $(LDFLAGS)
 static-testinstall:
-	@mkdir -p obj
-	@cp testinstall.cc obj/static-testinstall.cc
 ifeq ($(shell uname),Darwin)
 	@echo Skipping test for libre2.a on Darwin.
 else ifeq ($(shell uname),SunOS)
 	@echo Skipping test for libre2.a on SunOS.
 else
-	(cd obj && $(CXX) static-testinstall.cc -o static-testinstall $(CXXFLAGS) $(LDFLAGS))
+	@mkdir -p obj
+	@cp testinstall.cc obj/static-testinstall.cc
+	(cd obj && export PKG_CONFIG_PATH=$(DESTDIR)$(libdir)/pkgconfig; \
+	  $(CXX) static-testinstall.cc -o static-testinstall $(CXXFLAGS) $(LDFLAGS) \
+	  $$(pkg-config re2 --cflags --libs | sed -e "s#-lre2#-l:libre2.a#"))
 	obj/static-testinstall
 endif
 
 .PHONY: shared-testinstall
-shared-testinstall: CXXFLAGS:=-pthread -I$(DESTDIR)$(includedir) $(CXXFLAGS)
-shared-testinstall: LDFLAGS:=-pthread -L$(DESTDIR)$(libdir) -lre2 $(LDICU) $(LDFLAGS)
 shared-testinstall:
 	@mkdir -p obj
 	@cp testinstall.cc obj/shared-testinstall.cc
-	(cd obj && $(CXX) shared-testinstall.cc -o shared-testinstall $(CXXFLAGS) $(LDFLAGS))
+	(cd obj && export PKG_CONFIG_PATH=$(DESTDIR)$(libdir)/pkgconfig; \
+	  $(CXX) shared-testinstall.cc -o shared-testinstall $(CXXFLAGS) $(LDFLAGS) \
+	  $$(pkg-config re2 --cflags --libs))
 ifeq ($(shell uname),Darwin)
 	DYLD_LIBRARY_PATH="$(DESTDIR)$(libdir):$(DYLD_LIBRARY_PATH)" obj/shared-testinstall
 else

re2.pc.in

@@ -3,6 +3,7 @@ libdir=@CMAKE_INSTALL_FULL_LIBDIR@
 
 Name: re2
 Description: RE2 is a fast, safe, thread-friendly regular expression engine.
+Requires: @REQUIRES@
 Version: @SONAME@.0.0
 Cflags: -pthread -I${includedir}
 Libs: -pthread -L${libdir} -lre2

re2Config.cmake.in

@@ -13,6 +13,10 @@ if(UNIX)
   find_dependency(Threads REQUIRED)
 endif()
 
+if(@RE2_USE_ICU@)
+  find_dependency(ICU REQUIRED COMPONENTS uc)
+endif()
+
 check_required_components(re2)
 
 if(TARGET re2::re2)