Skip external libraries if they are already included in parent project (#1728)

external/CMakeLists.txt

@@ -10,8 +10,10 @@ if (${ENABLE_SPIRV_CODEGEN})
   set(DXC_SPIRV_TOOLS_DIR "${DXC_EXTERNAL_ROOT_DIR}/SPIRV-Tools"
       CACHE STRING "Location of SPIRV-Tools source")
 
-  if (IS_DIRECTORY ${DXC_SPIRV_HEADERS_DIR})
-    add_subdirectory(${DXC_SPIRV_HEADERS_DIR} EXCLUDE_FROM_ALL)
+  if (NOT DEFINED SPIRV-Headers_SOURCE_DIR)
+    if (IS_DIRECTORY ${DXC_SPIRV_HEADERS_DIR})
+      add_subdirectory(${DXC_SPIRV_HEADERS_DIR} EXCLUDE_FROM_ALL)
+    endif()
   endif()
   if (NOT DEFINED SPIRV-Headers_SOURCE_DIR)
     message(FATAL_ERROR "SPIRV-Headers was not found - required for SPIR-V codegen")
@@ -19,11 +21,13 @@ if (${ENABLE_SPIRV_CODEGEN})
     set(SPIRV_HEADER_INCLUDE_DIR ${SPIRV-Headers_SOURCE_DIR}/include PARENT_SCOPE)
   endif()
 
-  if (IS_DIRECTORY ${DXC_SPIRV_TOOLS_DIR})
-    # We only need the library from SPIRV-Tools.
-    set(SPIRV_SKIP_EXECUTABLES ON CACHE BOOL "Skip building SPIRV-Tools executables")
-    set(SPIRV_TOOLS_EXTRA_DEFINITIONS /D_ITERATOR_DEBUG_LEVEL=0)
-    add_subdirectory(${DXC_SPIRV_TOOLS_DIR} EXCLUDE_FROM_ALL)
+  if (NOT TARGET SPIRV-Tools)
+    if (IS_DIRECTORY ${DXC_SPIRV_TOOLS_DIR})
+      # We only need the library from SPIRV-Tools.
+      set(SPIRV_SKIP_EXECUTABLES ON CACHE BOOL "Skip building SPIRV-Tools executables")
+      set(SPIRV_TOOLS_EXTRA_DEFINITIONS /D_ITERATOR_DEBUG_LEVEL=0)
+      add_subdirectory(${DXC_SPIRV_TOOLS_DIR} EXCLUDE_FROM_ALL)
+    endif()
   endif()
   if (NOT TARGET SPIRV-Tools)
     message(FATAL_ERROR "SPIRV-Tools was not found - required for SPIR-V codegen")
@@ -45,12 +49,14 @@ if (${ENABLE_SPIRV_CODEGEN})
   if (${SPIRV_BUILD_TESTS})
     set(DXC_GTEST_DIR "${DXC_EXTERNAL_ROOT_DIR}/googletest"
         CACHE STRING "Location of GoogleTest source")
-    if (IS_DIRECTORY ${DXC_GTEST_DIR})
-      # Configure googletest
-      include(GTestConfig.cmake)
-    endif()
     if (NOT TARGET gtest)
-      message(FATAL_ERROR "GoogleTest was not found - required for SPIR-V codegen")
+      if (IS_DIRECTORY ${DXC_GTEST_DIR})
+        # Configure googletest
+        include(GTestConfig.cmake)
+      endif()
+      if (NOT TARGET gtest)
+        message(FATAL_ERROR "GoogleTest was not found - required for SPIR-V codegen")
+      endif()
     endif()
   endif()
 
@@ -60,28 +66,32 @@ if (${ENABLE_SPIRV_CODEGEN})
     set(DXC_RE2_DIR "${DXC_EXTERNAL_ROOT_DIR}/re2" CACHE STRING "Location of RE2 source")
     set(DXC_EFFCEE_DIR "${DXC_EXTERNAL_ROOT_DIR}/effcee" CACHE STRING "Location of Effcee source")
 
-    if (IS_DIRECTORY ${DXC_RE2_DIR})
-      # Avoid exception handling warning from MSVC.
-      # This add_compile_options() will only affect the current directory and its subdirectories.
-      if (WIN32)
-        add_compile_options(/EHs)
-      else(WIN32)
-        # Disable all warnings in subproject RE2
-        add_compile_options(-w)
-      endif(WIN32)
-      # Don't build/run re2's tests.
-      set(RE2_BUILD_TESTING OFF CACHE BOOL "Skip RE2 tests")
-      add_subdirectory(${DXC_RE2_DIR} EXCLUDE_FROM_ALL)
+    if (NOT TARGET re2)
+      if (IS_DIRECTORY ${DXC_RE2_DIR})
+        # Avoid exception handling warning from MSVC.
+        # This add_compile_options() will only affect the current directory and its subdirectories.
+        if (WIN32)
+          add_compile_options(/EHs)
+        else(WIN32)
+          # Disable all warnings in subproject RE2
+          add_compile_options(-w)
+        endif(WIN32)
+        # Don't build/run re2's tests.
+        set(RE2_BUILD_TESTING OFF CACHE BOOL "Skip RE2 tests")
+        add_subdirectory(${DXC_RE2_DIR} EXCLUDE_FROM_ALL)
+      endif()
     endif()
 
-    if (IS_DIRECTORY ${DXC_EFFCEE_DIR})
-      # Configure effcee
-      set(EFFCEE_RE2_DIR "${DXC_RE2_DIR}" CACHE STRING "Location of RE2 for effcee")
-      set(EFFCEE_ENABLE_SHARED_CRT ON CACHE BOOL "Enable using shared C Runtime")
-      # Don't build/run effcee's tests.
-      set(EFFCEE_BUILD_TESTING OFF CACHE BOOL "Skip effcee tests")
-      set(EFFCEE_BUILD_SAMPLES OFF CACHE BOOL "Skip building effcee examples")
-      add_subdirectory(${DXC_EFFCEE_DIR} EXCLUDE_FROM_ALL)
+    if (NOT TARGET effcee)
+      if (IS_DIRECTORY ${DXC_EFFCEE_DIR})
+        # Configure effcee
+        set(EFFCEE_RE2_DIR "${DXC_RE2_DIR}" CACHE STRING "Location of RE2 for effcee")
+        set(EFFCEE_ENABLE_SHARED_CRT ON CACHE BOOL "Enable using shared C Runtime")
+        # Don't build/run effcee's tests.
+        set(EFFCEE_BUILD_TESTING OFF CACHE BOOL "Skip effcee tests")
+        set(EFFCEE_BUILD_SAMPLES OFF CACHE BOOL "Skip building effcee examples")
+        add_subdirectory(${DXC_EFFCEE_DIR} EXCLUDE_FROM_ALL)
+      endif()
     endif()
 
     # Organize these targets better in Visual Studio