ci: add ABI compatibility matrix workflow

This adds a new GitHub Actions workflow to verify ABI compatibility across C++ standard boundaries. It explicitly tests the scenario where JsonCpp is built with one standard (e.g., C++11) and consumed by an application built with a newer one (e.g., C++23), and vice versa.

To facilitate testing the specific `std::string_view` boundary that is conditionally compiled, a new `stringView` demo application has been added to the `example/` directory and is consumed directly by the CI matrix to ensure standard library symbols link correctly across standard versions, build types (shared/static), and operating systems.

Author: baylesj

.github/workflows/abi-compatibility.yml

@@ -0,0 +1,79 @@
+name: ABI Compatibility
+
+on: [check_run, push, pull_request]
+
+env:
+  FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
+
+jobs:
+  abi-compatibility:
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+        shared_libs: [ON, OFF]
+        include:
+          - jsoncpp_std: 11
+            app_std: 23
+          - jsoncpp_std: 23
+            app_std: 11
+
+    steps:
+      - name: checkout project
+        uses: actions/checkout@v4
+
+      - name: build and install JsonCpp (C++${{ matrix.jsoncpp_std }})
+        shell: bash
+        run: |
+          mkdir build-jsoncpp
+          cd build-jsoncpp
+          cmake .. -DCMAKE_CXX_STANDARD=${{ matrix.jsoncpp_std }} \
+                   -DCMAKE_CXX_STANDARD_REQUIRED=ON \
+                   -DCMAKE_INSTALL_PREFIX=$GITHUB_WORKSPACE/install-jsoncpp \
+                   -DBUILD_SHARED_LIBS=${{ matrix.shared_libs }} \
+                   -DJSONCPP_WITH_TESTS=OFF
+          cmake --build . --config Release
+          cmake --install . --config Release
+
+      - name: create example app
+        shell: bash
+        run: |
+          mkdir example-app
+          cat << 'EOF' > example-app/CMakeLists.txt
+          cmake_minimum_required(VERSION 3.10)
+          project(abi_test)
+
+          find_package(jsoncpp REQUIRED CONFIG)
+
+          add_executable(abi_test stringView.cpp)
+          target_link_libraries(abi_test PRIVATE JsonCpp::JsonCpp)
+          EOF
+
+          cp $GITHUB_WORKSPACE/example/stringView/stringView.cpp example-app/stringView.cpp
+
+      - name: build example app (C++${{ matrix.app_std }})
+        shell: bash
+        run: |
+          cd example-app
+          mkdir build
+          cd build
+          cmake .. -DCMAKE_CXX_STANDARD=${{ matrix.app_std }} \
+                   -DCMAKE_CXX_STANDARD_REQUIRED=ON \
+                   -DCMAKE_PREFIX_PATH=$GITHUB_WORKSPACE/install-jsoncpp
+          cmake --build . --config Release
+
+      - name: run example app
+        shell: bash
+        run: |
+          if [ "$RUNNER_OS" == "Windows" ]; then
+            export PATH=$GITHUB_WORKSPACE/install-jsoncpp/bin:$PATH
+            ./example-app/build/Release/abi_test.exe
+          elif [ "$RUNNER_OS" == "macOS" ]; then
+            export DYLD_LIBRARY_PATH=$GITHUB_WORKSPACE/install-jsoncpp/lib:$DYLD_LIBRARY_PATH
+            ./example-app/build/abi_test
+          else
+            export LD_LIBRARY_PATH=$GITHUB_WORKSPACE/install-jsoncpp/lib:$LD_LIBRARY_PATH
+            ./example-app/build/abi_test
+          fi

example/BUILD.bazel

@@ -33,3 +33,9 @@ cc_binary(
     srcs = ["stringWrite/stringWrite.cpp"],
     deps = ["//:jsoncpp"],
 )
+
+cc_binary(
+    name = "stringView",
+    srcs = ["stringView/stringView.cpp"],
+    deps = ["//:jsoncpp"],
+)

example/CMakeLists.txt

@@ -4,6 +4,7 @@ set(EXAMPLES
     readFromStream
     stringWrite
     streamWrite
+    stringView
 )
 add_definitions(-D_GLIBCXX_USE_CXX11_ABI)
 

example/stringView/stringView.cpp

@@ -0,0 +1,29 @@
+#include "json/json.h"
+#include <iostream>
+#include <cstdlib>
+
+#if defined(JSONCPP_HAS_STRING_VIEW)
+#include <string_view>
+#endif
+
+/**
+ * \brief Example using std::string_view with JsonCpp.
+ */
+int main() {
+  Json::Value root;
+  root["key"] = "value";
+
+#if defined(JSONCPP_HAS_STRING_VIEW)
+  std::cout << "Has string_view support" << std::endl;
+  std::string_view sv("key");
+  if (root.isMember(sv)) {
+    std::cout << root[sv].asString() << std::endl;
+  }
+#else
+  std::cout << "No string_view support" << std::endl;
+  if (root.isMember("key")) {
+    std::cout << root["key"].asString() << std::endl;
+  }
+#endif
+  return EXIT_SUCCESS;
+}