fix out-of-source builds with cmake (#7946)

.github/workflows/build.yml

@@ -76,6 +76,28 @@ jobs:
     - name: build
       run: make -j
 
+  build-linux-out-of-source:    
+    name: Build Linux with out-of-source build location
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - name: make build directory
+      run: mkdir build
+    - name: cmake
+      working-directory: build
+      run: >
+        CXX=clang++-12 cmake .. -G "Unix Makefiles" -DFLATBUFFERS_STRICT_MODE=ON
+        -DFLATBUFFERS_BUILD_CPP17=ON -DFLATBUFFERS_CPP_STD=17
+    - name: build
+      working-directory: build
+      run: make -j
+    - name: test
+      working-directory: build
+      run: pwd && ./flattests
+    - name: test C++17
+      working-directory: build
+      run: ./flattests_cpp17
+
   build-linux-cpp-std:
     name: Build Linux C++
     runs-on: ubuntu-latest

CMakeLists.txt

@@ -516,10 +516,12 @@ function(compile_schema_for_samples SRC_FBS OPT)
 endfunction()
 
 if(FLATBUFFERS_BUILD_TESTS)
-  include_directories(${CMAKE_CURRENT_BINARY_DIR}/tests)
   add_executable(flattests ${FlatBuffers_Tests_SRCS})
   target_link_libraries(flattests PRIVATE $<BUILD_INTERFACE:ProjectConfig>)
-  target_include_directories(flattests PUBLIC src)
+  target_include_directories(flattests PUBLIC src tests)
+
+  # Have tests load data from the source directory, not the build directory.
+  add_definitions(-DFLATBUFFERS_TEST_PATH_PREFIX=${CMAKE_CURRENT_SOURCE_DIR}/)
 
   # The flattest target needs some generated files
   SET(FLATC_OPT --cpp --gen-mutable --gen-object-api --reflect-names)
@@ -552,6 +554,7 @@ if(FLATBUFFERS_BUILD_TESTS)
   if(FLATBUFFERS_BUILD_CPP17)
     add_executable(flattests_cpp17 ${FlatBuffers_Tests_CPP17_SRCS})
     target_link_libraries(flattests_cpp17 PRIVATE $<BUILD_INTERFACE:ProjectConfig>)
+    target_include_directories(flattests_cpp17 PUBLIC src tests)
     target_compile_features(flattests_cpp17 PRIVATE cxx_std_17) # requires cmake 3.8
 
     if(FLATBUFFERS_CODE_SANITIZE)

tests/BUILD.bazel

@@ -71,7 +71,6 @@ cc_test(
     ],
     copts = [
         "-DFLATBUFFERS_TRACK_VERIFIER_BUFFER_SIZE",
-        "-DBAZEL_TEST_DATA_PATH",
     ],
     data = [
         ":alignment_test.fbs",

tests/test.cpp

@@ -1670,12 +1670,7 @@ int FlatBufferTests(const std::string &tests_data_path) {
 }  // namespace flatbuffers
 
 int main(int argc, const char *argv[]) {
-  std::string tests_data_path =
+  std::string tests_data_path = "tests/";
-#ifdef BAZEL_TEST_DATA_PATH
-      "../com_github_google_flatbuffers/tests/";
-#else
-      "tests/";
-#endif
 
   for (int argi = 1; argi < argc; argi++) {
     std::string arg = argv[argi];