cmake/icu.cmake: use pkgconf, if available, to look up system libicu

cmake/icu.cmake

@@ -46,7 +46,9 @@
 # The lowest checked version is 55 on Ubuntu 16.
 SET(MIN_ICU_VERSION_REQUIRED "55")
 
-MACRO(FIND_ICU_VERSION ICU_COMMON_DIR)
+MACRO(FIND_ICU_VERSION ICU_SEARCH_DIRS)
+  FIND_PATH(ICU_COMMON_DIR NAMES unicode/uvernum.h ${ICU_SEARCH_DIRS})
+
   # Extract the version number. Major version information looks like:
   #   #define U_ICU_VERSION_MAJOR_NUM nn
   FILE(STRINGS "${ICU_COMMON_DIR}/unicode/uvernum.h"
@@ -71,13 +73,30 @@ ENDMACRO()
 #
 FUNCTION(FIND_ICU install_root)
   IF("${install_root}" STREQUAL "system")
-    SET(EXTRA_FIND_LIB_ARGS)
-    SET(EXTRA_FIND_INC_ARGS)
-    IF(APPLE)
-      SET(EXTRA_FIND_LIB_ARGS HINTS "${HOMEBREW_HOME}/icu4c"
-        PATH_SUFFIXES "lib")
-      SET(EXTRA_FIND_INC_ARGS HINTS "${HOMEBREW_HOME}/icu4c"
-        PATH_SUFFIXES "include")
+    FIND_PACKAGE(PkgConfig QUIET)
+    IF(PkgConfig_FOUND)
+      PKG_CHECK_MODULES(ICU icu-io)
+    ENDIF()
+
+    IF(ICU_FOUND)
+      SET(ICU_INCLUDE_DIRS ${ICU_INCLUDE_DIRS})
+      IF(BUILD_SHARED_LIBS)
+        SET(ICU_LIBRARIES ${ICU_LIBRARIES})
+      ELSE()
+        SET(ICU_LIBRARIES ${ICU_STATIC_LIBRARIES})
+      ENDIF()
+
+      MESSAGE(STATUS "ICU_INCLUDE_DIRS ${ICU_INCLUDE_DIRS}")
+      MESSAGE(STATUS "ICU_LIBRARIES ${ICU_LIBRARIES}")
+    ELSE()
+      SET(EXTRA_FIND_LIB_ARGS)
+      SET(EXTRA_FIND_INC_ARGS)
+      IF(APPLE)
+        SET(EXTRA_FIND_LIB_ARGS HINTS "${HOMEBREW_HOME}/icu4c"
+          PATH_SUFFIXES "lib")
+        SET(EXTRA_FIND_INC_ARGS HINTS "${HOMEBREW_HOME}/icu4c"
+          PATH_SUFFIXES "include")
+      ENDIF()
     ENDIF()
   ELSE()
     SET(EXTRA_FIND_LIB_ARGS HINTS "${install_root}"
@@ -86,38 +105,41 @@ FUNCTION(FIND_ICU install_root)
       PATH_SUFFIXES "include"     NO_DEFAULT_PATH)
   ENDIF()
 
-  FIND_PATH(ICU_INCLUDE_DIR NAMES unicode/regex.h ${EXTRA_FIND_INC_ARGS})
-  IF (NOT ICU_INCLUDE_DIR)
-    MESSAGE(FATAL_ERROR "Cannot find ICU regular expression headers")
-  ENDIF()
-
-  IF(WIN32)
-    SET(ICU_LIBS icuuc icuio icudt icuin)
-  ELSE()
-    SET(ICU_LIBS icuuc icuio icudata icui18n)
-  ENDIF()
+  IF(NOT ICU_FOUND)
+    FIND_PATH(ICU_INCLUDE_DIR NAMES unicode/regex.h ${EXTRA_FIND_INC_ARGS})
+    IF (NOT ICU_INCLUDE_DIR)
+      MESSAGE(FATAL_ERROR "Cannot find ICU regular expression headers")
+    ENDIF()
 
-  SET(ICU_SYSTEM_LIBRARIES)
-  FOREACH(ICU_LIB ${ICU_LIBS})
-    UNSET(ICU_LIB_PATH CACHE)
-    FIND_LIBRARY(ICU_LIB_PATH NAMES ${ICU_LIB} ${EXTRA_FIND_LIB_ARGS})
-    IF(NOT ICU_LIB_PATH)
-      MESSAGE(FATAL_ERROR "Cannot find the ICU library ${ICU_LIB}")
+    IF(WIN32)
+      SET(ICU_LIBS icuuc icuio icudt icuin)
+    ELSE()
+      SET(ICU_LIBS icuuc icuio icudata icui18n)
     ENDIF()
-    LIST(APPEND ICU_SYSTEM_LIBRARIES ${ICU_LIB_PATH})
-  ENDFOREACH()
 
-  SET(ICU_INCLUDE_DIRS ${ICU_INCLUDE_DIR})
-  SET(ICU_LIBRARIES ${ICU_SYSTEM_LIBRARIES})
+    SET(ICU_SYSTEM_LIBRARIES)
+    FOREACH(ICU_LIB ${ICU_LIBS})
+      UNSET(ICU_LIB_PATH CACHE)
+      FIND_LIBRARY(ICU_LIB_PATH NAMES ${ICU_LIB} ${EXTRA_FIND_LIB_ARGS})
+      IF(NOT ICU_LIB_PATH)
+        MESSAGE(FATAL_ERROR "Cannot find the ICU library ${ICU_LIB}")
+      ENDIF()
+      LIST(APPEND ICU_SYSTEM_LIBRARIES ${ICU_LIB_PATH})
+    ENDFOREACH()
 
-  SET(ICU_COMMON_DIR ${ICU_INCLUDE_DIR})
-  FIND_ICU_VERSION(${ICU_COMMON_DIR})
+    SET(ICU_INCLUDE_DIRS ${ICU_INCLUDE_DIR})
+    SET(ICU_LIBRARIES ${ICU_SYSTEM_LIBRARIES})
+
+    SET(ICU_COMMON_DIR ${ICU_INCLUDE_DIR})
+  ENDIF()
+
+  FIND_ICU_VERSION(${ICU_INCLUDE_DIRS})
 
   ADD_LIBRARY(icu_interface INTERFACE)
   TARGET_LINK_LIBRARIES(icu_interface INTERFACE ${ICU_LIBRARIES})
-  IF(NOT ICU_INCLUDE_DIR STREQUAL "/usr/include")
+  IF(NOT ICU_INCLUDE_DIRS STREQUAL "/usr/include")
     TARGET_INCLUDE_DIRECTORIES(icu_interface SYSTEM INTERFACE
-      ${ICU_INCLUDE_DIR})
+      ${ICU_INCLUDE_DIRS})
   ENDIF()
 ENDFUNCTION(FIND_ICU)