Fix C++11 ABI breakage when compiled with C++17 #1668 (#1675)

* ci: suppress Node 20 deprecation and missing python-version warnings

- Injects `FORCE_JAVASCRIPT_ACTIONS_TO_NODE24=true` in all workflows to
  opt-in to Node.js 24 and suppress the deprecation warnings from
  multiple GitHub Actions.
- Specifies `python-version: '3.x'` for `actions/setup-python@v5` in
  `meson.yml` to fix the missing input warning.

* Fix C++11 ABI breakage when compiled with C++17 (#1668)

When JSONCPP_HAS_STRING_VIEW was defined, the library dropped the
`const char*` and `const String&` overloads for `operator[]`, `get`,
`removeMember`, and `isMember`, breaking ABI compatibility for projects
consuming the library with C++11.

This change unconditionally declares and defines the legacy overloads
so they are always exported, restoring compatibility.

* 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.

* fix: inline std::string_view methods to prevent ABI breaks

This commit completely eliminates the ABI breakage that occurs across C++ standard boundaries when using `std::string_view`.

Previously, when the library was built with C++17+, CMake would leak `JSONCPP_HAS_STRING_VIEW=1` as a PUBLIC definition. A C++11 consumer would receive this definition, attempt to parse the header, and fail with compiler errors because `std::string_view` is not available in their environment.

Conversely, if the library was built in C++11 (without `string_view` symbols), a C++17 consumer would naturally define `JSONCPP_HAS_STRING_VIEW` based on `__cplusplus` inside `value.h`. The consumer would then call the declared `string_view` methods, resulting in linker errors because the methods weren't compiled into the library.

By moving all `std::string_view` overloads directly into `value.h` as `inline` methods that delegate to the fundamental `const char*, const char*` methods:
1. The consumer's compiler dictates whether the overloads are visible (via `__cplusplus >= 201703L`).
2. The consumer compiles the inline wrappers locally, removing any reliance on the library's exported symbols for `std::string_view`.
3. CMake no longer needs to pollute the consumer's environment with PUBLIC compile definitions.

* run clang format

* finish clang format

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 <cstdlib>
+#include <iostream>
+
+#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;
+}

include/json/value.h

@@ -357,7 +357,8 @@ class JSON_API Value {
   Value(const StaticString& value);
   Value(const String& value);
 #ifdef JSONCPP_HAS_STRING_VIEW
-  Value(std::string_view value);
+  inline Value(std::string_view value)
+      : Value(value.data(), value.data() + value.length()) {}
 #endif
   Value(bool value);
   Value(std::nullptr_t ptr) = delete;
@@ -405,7 +406,14 @@ class JSON_API Value {
   /** Get string_view of string-value.
    *  \return false if !string. (Seg-fault if str is NULL.)
    */
-  bool getString(std::string_view* str) const;
+  inline bool getString(std::string_view* str) const {
+    char const* begin;
+    char const* end;
+    if (!getString(&begin, &end))
+      return false;
+    *str = std::string_view(begin, static_cast<size_t>(end - begin));
+    return true;
+  }
 #endif
   Int asInt() const;
   UInt asUInt() const;
@@ -496,12 +504,19 @@ class JSON_API Value {
 #ifdef JSONCPP_HAS_STRING_VIEW
   /// Access an object value by name, create a null member if it does not exist.
   /// \param key may contain embedded nulls.
-  Value& operator[](std::string_view key);
+  inline Value& operator[](std::string_view key) {
+    return resolveReference(key.data(), key.data() + key.length());
+  }
   /// Access an object value by name, returns null if there is no member with
   /// that name.
   /// \param key may contain embedded nulls.
-  const Value& operator[](std::string_view key) const;
-#else
+  inline const Value& operator[](std::string_view key) const {
+    Value const* found = find(key.data(), key.data() + key.length());
+    if (!found)
+      return nullSingleton();
+    return *found;
+  }
+#endif
   /// Access an object value by name, create a null member if it does not exist.
   /// \note Because of our implementation, keys are limited to 2^30 -1 chars.
   /// Exceeding that will cause an exception.
@@ -516,7 +531,6 @@ class JSON_API Value {
   /// that name.
   /// \param key may contain embedded nulls.
   const Value& operator[](const String& key) const;
-#endif
   /** \brief Access an object value by name, create a null member if it does not
    * exist.
    *
@@ -533,16 +547,17 @@ class JSON_API Value {
 #ifdef JSONCPP_HAS_STRING_VIEW
   /// Return the member named key if it exist, defaultValue otherwise.
   /// \note deep copy
-  Value get(std::string_view key, const Value& defaultValue) const;
-#else
+  inline Value get(std::string_view key, const Value& defaultValue) const {
+    return get(key.data(), key.data() + key.length(), defaultValue);
+  }
+#endif
   /// Return the member named key if it exist, defaultValue otherwise.
   /// \note deep copy
   Value get(const char* key, const Value& defaultValue) const;
   /// Return the member named key if it exist, defaultValue otherwise.
   /// \note deep copy
   /// \param key may contain embedded nulls.
   Value get(const String& key, const Value& defaultValue) const;
-#endif
   /// Return the member named key if it exist, defaultValue otherwise.
   /// \note deep copy
   /// \note key may contain embedded nulls.
@@ -588,27 +603,29 @@ class JSON_API Value {
   /// \pre type() is objectValue or nullValue
   /// \post type() is unchanged
 #if JSONCPP_HAS_STRING_VIEW
-  void removeMember(std::string_view key);
-#else
+  inline void removeMember(std::string_view key) {
+    removeMember(key.data(), key.data() + key.length(), nullptr);
+  }
+#endif
   void removeMember(const char* key);
   /// Same as removeMember(const char*)
   /// \param key may contain embedded nulls.
   void removeMember(const String& key);
-#endif
   /** \brief Remove the named map member.
    *
    *  Update 'removed' iff removed.
    *  \param key may contain embedded nulls.
    *  \return true iff removed (no exceptions)
    */
 #if JSONCPP_HAS_STRING_VIEW
-  bool removeMember(std::string_view key, Value* removed);
-#else
+  inline bool removeMember(std::string_view key, Value* removed) {
+    return removeMember(key.data(), key.data() + key.length(), removed);
+  }
+#endif
   bool removeMember(String const& key, Value* removed);
   /// Same as removeMember(const char* begin, const char* end, Value* removed),
   /// but 'key' is null-terminated.
   bool removeMember(const char* key, Value* removed);
-#endif
   /// Same as removeMember(String const& key, Value* removed)
   bool removeMember(const char* begin, const char* end, Value* removed);
   /** \brief Remove the indexed array element.
@@ -622,15 +639,16 @@ class JSON_API Value {
 #ifdef JSONCPP_HAS_STRING_VIEW
   /// Return true if the object has a member named key.
   /// \param key may contain embedded nulls.
-  bool isMember(std::string_view key) const;
-#else
+  inline bool isMember(std::string_view key) const {
+    return isMember(key.data(), key.data() + key.length());
+  }
+#endif
   /// Return true if the object has a member named key.
   /// \note 'key' must be null-terminated.
   bool isMember(const char* key) const;
   /// Return true if the object has a member named key.
   /// \param key may contain embedded nulls.
   bool isMember(const String& key) const;
-#endif
   /// Same as isMember(String const& key)const
   bool isMember(const char* begin, const char* end) const;
 

src/lib_json/CMakeLists.txt

@@ -131,9 +131,6 @@ if(BUILD_SHARED_LIBS)
 
     target_compile_features(${SHARED_LIB} PUBLIC ${REQUIRED_FEATURES})
 
-    if(JSONCPP_HAS_STRING_VIEW)
-        target_compile_definitions(${SHARED_LIB} PUBLIC JSONCPP_HAS_STRING_VIEW=1)
-    endif()
 
     target_include_directories(${SHARED_LIB} PUBLIC
         $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
@@ -168,9 +165,6 @@ if(BUILD_STATIC_LIBS)
 
     target_compile_features(${STATIC_LIB} PUBLIC ${REQUIRED_FEATURES})
 
-    if(JSONCPP_HAS_STRING_VIEW)
-        target_compile_definitions(${STATIC_LIB} PUBLIC JSONCPP_HAS_STRING_VIEW=1)
-    endif()
 
     target_include_directories(${STATIC_LIB} PUBLIC
         $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
@@ -198,9 +192,6 @@ if(BUILD_OBJECT_LIBS)
 
     target_compile_features(${OBJECT_LIB} PUBLIC ${REQUIRED_FEATURES})
 
-    if(JSONCPP_HAS_STRING_VIEW)
-        target_compile_definitions(${OBJECT_LIB} PUBLIC JSONCPP_HAS_STRING_VIEW=1)
-    endif()
 
     target_include_directories(${OBJECT_LIB} PUBLIC
         $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>