Adjust CMake minimal version

.github/workflows/ubuntu.yml

@@ -23,7 +23,7 @@ jobs:
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@56d043d188c3612951d8755da8f4b709ec951ad6 # v3.31.6
+        uses: lukka/get-cmake@28983e0d3955dba2bb0a6810caae0c6cf268ec0c # v4.0.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -54,7 +54,7 @@ jobs:
         run: sudo apt-get update ; sudo apt-get install -y valgrind
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@56d043d188c3612951d8755da8f4b709ec951ad6 # v3.31.6
+        uses: lukka/get-cmake@28983e0d3955dba2bb0a6810caae0c6cf268ec0c # v4.0.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -71,7 +71,7 @@ jobs:
         run: apt-get update ; apt-get install -y git clang-tools iwyu unzip
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@56d043d188c3612951d8755da8f4b709ec951ad6 # v3.31.6
+        uses: lukka/get-cmake@28983e0d3955dba2bb0a6810caae0c6cf268ec0c # v4.0.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -85,10 +85,10 @@ jobs:
         target: [ci_cmake_flags, ci_test_diagnostics, ci_test_diagnostic_positions, ci_test_noexceptions, ci_test_noimplicitconversions, ci_test_legacycomparison, ci_test_noglobaludls]
     steps:
       - name: Install build-essential
-        run: apt-get update ; apt-get install -y build-essential unzip wget git
+        run: apt-get update ; apt-get install -y build-essential unzip wget git libssl-dev
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@56d043d188c3612951d8755da8f4b709ec951ad6 # v3.31.6
+        uses: lukka/get-cmake@28983e0d3955dba2bb0a6810caae0c6cf268ec0c # v4.0.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -148,7 +148,7 @@ jobs:
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@56d043d188c3612951d8755da8f4b709ec951ad6 # v3.31.6
+        uses: lukka/get-cmake@28983e0d3955dba2bb0a6810caae0c6cf268ec0c # v4.0.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -165,7 +165,7 @@ jobs:
         run: apt-get update ; apt-get install -y unzip git
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@56d043d188c3612951d8755da8f4b709ec951ad6 # v3.31.6
+        uses: lukka/get-cmake@28983e0d3955dba2bb0a6810caae0c6cf268ec0c # v4.0.0
       - name: Set env FORCE_STDCPPFS_FLAG for clang 7 / 8 / 9 / 10
         run: echo "JSON_FORCED_GLOBAL_COMPILE_OPTIONS=-DJSON_HAS_FILESYSTEM=0;-DJSON_HAS_EXPERIMENTAL_FILESYSTEM=0" >> "$GITHUB_ENV"
         if: ${{ matrix.compiler == '7' || matrix.compiler == '8' || matrix.compiler == '9' || matrix.compiler == '10' }}
@@ -183,7 +183,7 @@ jobs:
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@56d043d188c3612951d8755da8f4b709ec951ad6 # v3.31.6
+        uses: lukka/get-cmake@28983e0d3955dba2bb0a6810caae0c6cf268ec0c # v4.0.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -201,7 +201,7 @@ jobs:
         run: apt-get update ; apt-get install -y git unzip
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@56d043d188c3612951d8755da8f4b709ec951ad6 # v3.31.6
+        uses: lukka/get-cmake@28983e0d3955dba2bb0a6810caae0c6cf268ec0c # v4.0.0
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build with libc++

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.1...3.14)
+cmake_minimum_required(VERSION 3.5...4.0)
 
 ##
 ## PROJECT

README.md

@@ -1144,7 +1144,7 @@ The library is used in multiple projects, applications, operating systems, etc.
 Though it's 2025 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work:
 
 - GCC 4.8 - 14.2 (and possibly later)
-- Clang 3.4 - 20.0 (and possibly later)
+- Clang 3.4 - 21.0 (and possibly later)
 - Apple Clang 9.1 - 16.0 (and possibly later)
 - Intel C++ Compiler 17.0.2 (and possibly later)
 - Nvidia CUDA Compiler 11.0.221 (and possibly later)

cmake/ci.cmake

@@ -541,33 +541,42 @@ add_custom_target(ci_benchmarks
 # CMake flags
 ###############################################################################
 
+# we test the project with different CMake versions:
+# - CMake 3.5 (the earliest supported)
+# - CMake 3.31.6 (the latest 3.x release)
+# - CMake 4.0.0 (the latest release)
+
 function(ci_get_cmake version var)
     set(${var} ${PROJECT_BINARY_DIR}/cmake-${version}/bin/cmake)
     add_custom_command(
         OUTPUT ${${var}}
         COMMAND wget -nc https://github.com/Kitware/CMake/releases/download/v${version}/cmake-${version}.tar.gz
         COMMAND tar xfz cmake-${version}.tar.gz
         COMMAND rm cmake-${version}.tar.gz
-        COMMAND ${CMAKE_COMMAND} -S cmake-${version} -B cmake-${version}
-        COMMAND ${CMAKE_COMMAND} --build cmake-${version} --parallel 10
+        # -DCMAKE_POLICY_VERSION_MINIMUM=3.5 required to compile older CMake versions with CMake 4.0.0
+        COMMAND cmake -S cmake-${version} -B cmake-${version} -DCMAKE_POLICY_VERSION_MINIMUM=3.5
+        COMMAND cmake --build cmake-${version} --parallel 10
         WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
         COMMENT "Download CMake ${version}"
     )
     set(${var} ${${var}} PARENT_SCOPE)
 endfunction()
 
-ci_get_cmake(3.1.0 CMAKE_3_1_0_BINARY)
-ci_get_cmake(3.13.0 CMAKE_3_13_0_BINARY)
+ci_get_cmake(3.5.0  CMAKE_3_5_0_BINARY)
+ci_get_cmake(3.31.6 CMAKE_3_31_6_BINARY)
+ci_get_cmake(4.0.0  CMAKE_4_0_0_BINARY)
 
-set(JSON_CMAKE_FLAGS_3_1_0 JSON_Diagnostics JSON_Diagnostic_Positions JSON_GlobalUDLs JSON_ImplicitConversions JSON_DisableEnumSerialization
+# the tests require CMake 3.13 or later, so they are excluded for CMake 3.5.0
+set(JSON_CMAKE_FLAGS_3_5_0 JSON_Diagnostics JSON_Diagnostic_Positions JSON_GlobalUDLs JSON_ImplicitConversions JSON_DisableEnumSerialization
     JSON_LegacyDiscardedValueComparison JSON_Install JSON_MultipleHeaders JSON_SystemInclude JSON_Valgrind)
-set(JSON_CMAKE_FLAGS_3_13_0 JSON_BuildTests)
+set(JSON_CMAKE_FLAGS_3_31_6 JSON_BuildTests ${JSON_CMAKE_FLAGS_3_31_6})
+set(JSON_CMAKE_FLAGS_4_0_0 JSON_BuildTests ${JSON_CMAKE_FLAGS_3_5_0})
 
 function(ci_add_cmake_flags_targets flag min_version)
     string(TOLOWER "ci_cmake_flag_${flag}" flag_target)
     string(REPLACE . _ min_version_var ${min_version})
     set(cmake_binary ${CMAKE_${min_version_var}_BINARY})
-    add_custom_target(${flag_target}
+    add_custom_target(${flag_target}_${min_version}_2
         COMMENT "Check CMake flag ${flag} (CMake ${CMAKE_VERSION})"
         COMMAND ${CMAKE_COMMAND}
             -Werror=dev
@@ -587,12 +596,16 @@ function(ci_add_cmake_flags_targets flag min_version)
     set(JSON_CMAKE_FLAG_BUILD_DIRS ${JSON_CMAKE_FLAG_BUILD_DIRS} PARENT_SCOPE)
 endfunction()
 
-foreach(JSON_CMAKE_FLAG ${JSON_CMAKE_FLAGS_3_1_0})
-    ci_add_cmake_flags_targets(${JSON_CMAKE_FLAG} 3.1.0)
+foreach(JSON_CMAKE_FLAG ${JSON_CMAKE_FLAGS_3_5_0})
+    ci_add_cmake_flags_targets(${JSON_CMAKE_FLAG} 3.5.0)
+endforeach()
+
+foreach(JSON_CMAKE_FLAG ${JSON_CMAKE_FLAGS_3_31_6})
+    ci_add_cmake_flags_targets(${JSON_CMAKE_FLAG} 3.31.6)
 endforeach()
 
-foreach(JSON_CMAKE_FLAG ${JSON_CMAKE_FLAGS_3_13_0})
-    ci_add_cmake_flags_targets(${JSON_CMAKE_FLAG} 3.13.0)
+foreach(JSON_CMAKE_FLAG ${JSON_CMAKE_FLAGS_4_0_0})
+    ci_add_cmake_flags_targets(${JSON_CMAKE_FLAG} 4.0.0)
 endforeach()
 
 add_custom_target(ci_cmake_flags
@@ -695,6 +708,6 @@ add_custom_target(ci_test_build_documentation
 ###############################################################################
 
 add_custom_target(ci_clean
-    COMMAND rm -fr ${PROJECT_BINARY_DIR}/build_* cmake-3.1.0-Darwin64 ${JSON_CMAKE_FLAG_BUILD_DIRS} ${single_binaries}
+    COMMAND rm -fr ${PROJECT_BINARY_DIR}/build_* cmake-3.5.0-Darwin64 ${JSON_CMAKE_FLAG_BUILD_DIRS} ${single_binaries}
     COMMENT "Clean generated directories"
 )

docs/mkdocs/docs/community/quality_assurance.md

@@ -208,4 +208,7 @@ violations will result in a failed build.
     All library functions are exposed and usable by CMake.
 
 - [x] All library options are exposed as [CMake options](https://json.nlohmann.me/integration/cmake/) and tested.
-- [x] The library is tested against the earliest supported CMake version.
+- [x] The library is tested against relevant CMake versions:
+  - CMake 3.5 (the earliest supported)
+  - CMake 3.31.6 (the latest 3.x release)
+  - CMake 4.0.0 (a very recent release)

docs/mkdocs/docs/home/customers.md

@@ -111,6 +111,7 @@ the result of an internet search. If you know further customers of the library,
 - [**Autodesk Desktop**](https://damassets.autodesk.net/content/dam/autodesk/www/Company/legal-notices-trademarks/autodesk-desktop-platform-components/internal-autodesk-components-web-page-2023.pdf), a software platform developed by Autodesk for creating and managing desktop applications and services
 - [**Check Point**](https://www.checkpoint.com/about-us/copyright-and-trademarks/): a cybersecurity company specializing in threat prevention and network security solutions, offering a range of products designed to protect enterprises from cyber threats and ensure data integrity
 - [**Microsoft Office for Mac**](https://officecdnmac.microsoft.com/pr/legal/mac/OfficeforMacAttributions.html), a suite of productivity applications developed by Microsoft for macOS, including tools for word processing, spreadsheets, and presentations
+- [**Microsoft Teams**](https://www.microsoft.com/microsoft-teams/), a team collaboration application offering workspace chat and video conferencing, file storage, and integration of proprietary and third-party applications and services
 - [**Nexthink Infinity**](https://docs.nexthink.com/legal/services-terms/experience-open-source-software-licenses/infinity-2022.8-software-licenses): a digital employee experience management platform for monitoring and improving IT performance
 - [**Sophos Connect Client**](https://docs.sophos.com/nsg/licenses/SophosConnect/SophosConnectAttribution.html): a secure VPN client from Sophos that allows remote users to connect to their corporate network, ensuring secure access to resources and data
 - [**Stonebranch**](https://stonebranchdocs.atlassian.net/wiki/spaces/UA77/pages/799545647/Licenses+for+Third-Party+Libraries): a cloud-based cybersecurity solution that integrates backup, disaster recovery, and cybersecurity features to protect data and ensure business continuity for organizations

docs/mkdocs/docs/integration/cmake.md

@@ -15,7 +15,7 @@ and use the namespaced imported target from the generated package configuration:
 !!! example
 
     ```cmake title="CMakeLists.txt"
-    cmake_minimum_required(VERSION 3.1)
+    cmake_minimum_required(VERSION 3.5)
     project(ExampleProject LANGUAGES CXX)
 
     find_package(nlohmann_json 3.11.3 REQUIRED)
@@ -35,7 +35,7 @@ To embed the library directly into an existing CMake project, place the entire s
 !!! example
 
     ```cmake title="CMakeLists.txt"
-    cmake_minimum_required(VERSION 3.1)
+    cmake_minimum_required(VERSION 3.5)
     project(ExampleProject LANGUAGES CXX)
 
     # If you only include this third party in PRIVATE source files, you do not need to install it

tests/cmake_add_subdirectory/project/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.1...3.14)
+cmake_minimum_required(VERSION 3.5...3.14)
 
 project(DummyImport CXX)
 

tests/cmake_import/project/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.1...3.14)
+cmake_minimum_required(VERSION 3.5...3.14)
 
 project(DummyImport CXX)
 

tests/cmake_import_minver/project/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.1...3.14)
+cmake_minimum_required(VERSION 3.5...3.14)
 
 project(DummyImportMinVer CXX)
 

tests/cmake_target_include_directories/project/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.1...3.14)
+cmake_minimum_required(VERSION 3.5...3.14)
 
 project(DummyImport CXX)