Specify clang and clang++ when building nativeruntime

Currently building nativeruntime only works with clang. Using gcc will
result in obscure linker errors related to missing symbols in libstdc++.
While it would be nice to support both, clang is sufficient for now, and
it is fairly easy to obtain on all platforms.

Also add some more error checks for various edge cases.

.github/workflows/tests.yml

@@ -28,7 +28,6 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-gradle-
 
-
       - name: Set up JDK 11.0.8
         uses: actions/setup-java@v1
         with:

nativeruntime/build.gradle

@@ -28,6 +28,10 @@ task cmakeNativeRuntime {
   doLast {
     mkdir "$buildDir/cpp"
     exec {
+      // Building the nativeruntime does not work with GCC due to libstddc++ linker errors.
+      // TODO: figure out which linker args are needed to build with GCC.
+      environment "CC", "clang"
+      environment "CXX", "clang++"
       workingDir "$buildDir/cpp"
       commandLine 'cmake', "-B", ".", "-S","$projectDir/cpp/"
     }
@@ -36,8 +40,8 @@ task cmakeNativeRuntime {
 
 task configureICU {
   onlyIf { !System.getenv('SKIP_ICU_BUILD') }
-  def os = osName()
   doLast {
+    def os = osName()
     if (!file("$projectDir/external/icu/icu4c/source").exists()) {
       throw new GradleException("ICU submodule not detected. Please run `git submodule update --init`")
     }
@@ -61,9 +65,9 @@ task configureICU {
 task buildICU {
   onlyIf { !System.getenv('SKIP_ICU_BUILD') }
   dependsOn configureICU
-  def os = osName()
   doLast {
     exec {
+      def os = osName()
       if (os.contains("linux") || os.contains("mac")) {
         workingDir "$projectDir/external/icu/icu4c/source"
         commandLine 'make', '-j4'

nativeruntime/cpp/CMakeLists.txt

@@ -17,31 +17,36 @@ if(NOT EXISTS "${ANDROID_SQLITE_DIR}/dist/sqlite3.c")
 endif()
 
 if(DEFINED ENV{ICU_ROOT_DIR})
+
+  if(NOT EXISTS "$ENV{ICU_ROOT_DIR}/lib/libicui18n.a")
+    message(FATAL_ERROR "ICU_ROOT_DIR does not contain 'lib/libicui18n.a'")
+  endif()
+
   message(NOTICE "Using $ENV{ICU_ROOT_DIR} as the ICU root dir")
   list(APPEND CMAKE_PREFIX_PATH "$ENV{ICU_ROOT_DIR}")
   find_library(STATIC_ICUI18N_LIBRARY libicui18n.a)
   find_library(STATIC_ICUUC_LIBRARY libicuuc.a)
   find_library(STATIC_ICUDATA_LIBRARY libicudata.a)
   include_directories($ENV{ICU_ROOT_DIR}/include)
 else()
-  set(ICU_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../external/icu")
+  set(ICU_SUBMODULE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../external/icu")
 
-  if(NOT EXISTS "${ICU_DIR}/icu4c/source/i18n/ucol.cpp")
+  if(NOT EXISTS "${ICU_SUBMODULE_DIR}/icu4c/source/i18n/ucol.cpp")
     message(FATAL_ERROR "ICU submodule missing. Please run `git submodule update --init`.")
   endif()
 
-  message(NOTICE "Using ${ICU_DIR} as the ICU root dir")
+  message(NOTICE "Using ${ICU_SUBMODULE_DIR} as the ICU root dir")
 
-  if(NOT EXISTS "${ICU_DIR}/icu4c/source/lib/libicui18n.a")
+  if(NOT EXISTS "${ICU_SUBMODULE_DIR}/icu4c/source/lib/libicui18n.a")
     message(FATAL_ERROR "ICU not built. Please run `./gradlew :nativeruntime:buildICU`.")
   endif()
 
-  list(APPEND CMAKE_PREFIX_PATH "${ICU_DIR}/icu4c/source/")
+  list(APPEND CMAKE_PREFIX_PATH "${ICU_SUBMODULE_DIR}/icu4c/source/")
   find_library(STATIC_ICUI18N_LIBRARY libicui18n.a)
   find_library(STATIC_ICUUC_LIBRARY libicuuc.a)
   find_library(STATIC_ICUDATA_LIBRARY libicudata.a)
-  include_directories(${ICU_DIR}/icu4c/source/i18n)
-  include_directories(${ICU_DIR}/icu4c/source/common)
+  include_directories(${ICU_SUBMODULE_DIR}/icu4c/source/i18n)
+  include_directories(${ICU_SUBMODULE_DIR}/icu4c/source/common)
 endif()
 
 # Build flags derived from