test: add cppapi test to give TorchCodecConfig.cmake a try

test/cppapi/CMakeLists.txt

@@ -0,0 +1,27 @@
+cmake_minimum_required(VERSION 3.18)
+project(CppApiTest)
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+find_package(Torch REQUIRED)
+find_package(TorchCodec REQUIRED)
+
+function(make_torchcodec_targets torchcodec_variant)
+    set(binname "torchcodec_cppapitest${torchcodec_variant}")
+    set(sources CppApiTest.cpp)
+
+    # Building executable to check the linkage
+    add_executable(${binname} ${sources})
+    # Avoid adding the "lib" prefix which we already add explicitly.
+    set_target_properties(${binname} PROPERTIES PREFIX "")
+    set_target_properties(${binname} PROPERTIES CXX_STANDARD 17)
+    target_link_libraries(${binname}
+      ${TORCH_LIBRARIES}
+      torchcodec::core${torchcodec_variant}
+      torchcodec::ffmpeg${torchcodec_variant}
+    )
+endfunction()
+
+foreach(variant IN LISTS TORCHCODEC_VARIANTS)
+    make_torchcodec_targets(${variant})
+endforeach()

test/cppapi/CppApiTest.cpp

@@ -0,0 +1,38 @@
+#include "DeviceInterface.h"
+#include "FilterGraph.h"
+
+namespace facebook::torchcodec {
+
+class DummyDeviceInterface : public DeviceInterface {
+ public:
+  DummyDeviceInterface(const torch::Device& device) : DeviceInterface(device) {}
+
+  virtual ~DummyDeviceInterface() {}
+
+  void initialize(
+      const AVStream* avStream,
+      const UniqueDecodingAVFormatContext& avFormatCtx,
+      const SharedAVCodecContext& codecContext) override {}
+
+  void convertAVFrameToFrameOutput(
+      UniqueAVFrame& avFrame,
+      FrameOutput& frameOutput,
+      std::optional<torch::Tensor> preAllocatedOutputTensor =
+          std::nullopt) override {}
+
+ private:
+  std::unique_ptr<FilterGraph> filterGraphContext_;
+};
+
+namespace {
+static bool g_dummy = registerDeviceInterface(
+    DeviceInterfaceKey(torch::kPrivateUse1),
+    [](const torch::Device& device) {
+      return new DummyDeviceInterface(device);
+    });
+} // namespace
+} // namespace facebook::torchcodec
+
+int main(int argc, char* argv[]) {
+  return 0;
+}

test/test_cppapi.py

@@ -0,0 +1,80 @@
+import os
+import subprocess
+
+from pathlib import Path
+
+import torch
+import torchcodec
+
+
+def test_cppapi_pkgconfig(tmp_path):
+    cmake_args = [
+        "cmake",
+        "-DCMAKE_BUILD_TYPE=Debug",
+        "-DCMAKE_VERBOSE_MAKEFILE=ON",
+        f"-DCMAKE_PREFIX_PATH={torchcodec.cmake_prefix_path};{torch.utils.cmake_prefix_path}",
+        Path(__file__).parent / "cppapi",
+    ]
+    result = subprocess.run(cmake_args, cwd=tmp_path)
+    assert result.returncode == 0
+
+    result = subprocess.run(["cmake", "--build", "."], cwd=tmp_path)
+    assert result.returncode == 0
+
+    ver = f"{torchcodec.ffmpeg_major_version}"
+    result = subprocess.run([f"./torchcodec_cppapitest{ver}"], cwd=tmp_path)
+    assert result.returncode == 0
+
+
+def test_cppapi_no_ffmpeg(tmp_path):
+    cmake_args = [
+        "cmake",
+        "-DCMAKE_BUILD_TYPE=Debug",
+        "-DCMAKE_VERBOSE_MAKEFILE=ON",
+        f"-DCMAKE_PREFIX_PATH={torchcodec.cmake_prefix_path};{torch.utils.cmake_prefix_path}",
+        Path(__file__).parent / "cppapi",
+    ]
+    ver = f"{torchcodec.ffmpeg_major_version}"
+    my_env = os.environ.copy()
+    my_env[f"TORCHCODEC_FFMPEG{ver}_INSTALL_PREFIX"] = (
+        Path(__file__).parent / "no-such-dir"
+    )
+
+    # cmake config should fail as we've set ffmpeg install prefix to the not existing
+    # directory
+    result = subprocess.run(cmake_args, cwd=tmp_path, env=my_env)
+    assert result.returncode != 0
+
+
+def test_cppapi_with_prefix(tmp_path):
+    cmake_args = [
+        "cmake",
+        "-DCMAKE_BUILD_TYPE=Debug",
+        "-DCMAKE_VERBOSE_MAKEFILE=ON",
+        f"-DCMAKE_PREFIX_PATH={torchcodec.cmake_prefix_path};{torch.utils.cmake_prefix_path}",
+        Path(__file__).parent / "cppapi",
+    ]
+
+    # In this test we are calculating the prefix of installed ffmpeg version from the location
+    # of its libavcodec.pc file. Potentially, on the custom ffmpeg install with custom layout
+    # our calculation can be wrong and test might fail.
+    result = subprocess.run(
+        ["pkg-config", "--path", "libavcodec"], capture_output=True, text=True
+    )
+    assert result.returncode == 0
+
+    ver = f"{torchcodec.ffmpeg_major_version}"
+    my_env = os.environ.copy()
+    my_env[f"TORCHCODEC_FFMPEG{ver}_INSTALL_PREFIX"] = Path(
+        f"{result.stdout}"
+    ).parent.parent.parent
+
+    result = subprocess.run(cmake_args, cwd=tmp_path, env=my_env)
+    assert result.returncode == 0
+
+    result = subprocess.run(["cmake", "--build", "."], cwd=tmp_path)
+    assert result.returncode == 0
+
+    ver = f"{torchcodec.ffmpeg_major_version}"
+    result = subprocess.run([f"./torchcodec_cppapitest{ver}"], cwd=tmp_path)
+    assert result.returncode == 0