feat(cmake): Use modern FetchContent approaches when available

.appveyor.yml

@@ -26,7 +26,9 @@ build_script:
 - cmake -G "%CMAKE_GENERATOR%" -A "%CMAKE_ARCH%"
     -DCMAKE_CXX_STANDARD=14
     -DPYBIND11_WERROR=ON
+    -DPYBIND11_CATCH_TESTS=ON
     -DDOWNLOAD_CATCH=ON
+    -DPYBIND11_EIGEN_TESTS=ON
     -DCMAKE_SUPPRESS_REGENERATION=1
     .
 - set MSBuildLogger="C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll"

.github/CONTRIBUTING.md

@@ -87,7 +87,7 @@ system with CMake 3.15+:
 python3 -m venv .venv
 source .venv/bin/activate
 pip install -r tests/requirements.txt
-cmake -S . -B build -DDOWNLOAD_CATCH=ON -DDOWNLOAD_EIGEN=ON
+cmake -S . -B build -DPYBIND11_CATCH_TESTS=ON -DPYBIND11_EIGEN_TESTS=ON
 cmake --build build -j4
 ```
 
@@ -149,8 +149,10 @@ The valid options are:
   classic, deprecated, custom FindPythonLibs
 * `-DPYBIND11_NOPYTHON=ON`: Disable all Python searching (disables tests)
 * `-DBUILD_TESTING=ON`: Enable the tests
-* `-DDOWNLOAD_CATCH=ON`: Download catch to build the C++ tests
-* `-DDOWNLOAD_EIGEN=ON`: Download Eigen for the NumPy tests
+* `-DPYBIND11_CATCH_TESTS=ON`: Enable tests using catch
+  (Fetched automatically if missing)
+* `-DPYBIND11_EIGEN_TESTS=ON`: Enable testing of Eigen for the NumPy tests
+  (Fetched automatically if missing)
 * `-DPYBIND11_INSTALL=ON/OFF`: Enable the install target (on by default for the
   master project)
 * `-DUSE_PYTHON_INSTALL_DIR=ON`: Try to install into the python dir
@@ -295,7 +297,7 @@ recent CMake and Python):
 python3 -m venv venv
 . venv/bin/activate
 pip install pytest
-cmake -S . -B build-intel -DCMAKE_CXX_COMPILER=$(which icpc) -DDOWNLOAD_CATCH=ON -DDOWNLOAD_EIGEN=ON -DPYBIND11_WERROR=ON
+cmake -S . -B build-intel -DCMAKE_CXX_COMPILER=$(which icpc) -DPYBIND11_CATCH_TESTS=ON -DPYBIND11_EIGEN_TESTS=ON -DPYBIND11_WERROR=ON
 ```
 
 This will test the PGI compilers:

.github/workflows/ci.yml

@@ -205,8 +205,8 @@ jobs:
         -DPYBIND11_WERROR=ON
         -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON
         -DPYBIND11_PYTEST_ARGS=-v
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         -DCMAKE_CXX_STANDARD=14
         -DPYBIND11_INTERNALS_VERSION=10000000
 
@@ -308,9 +308,11 @@ jobs:
       run: >
         cmake -S . -B build
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
+        -DPYBIND11_CATCH_TESTS=ON
         -DCMAKE_CXX_STANDARD=${{ matrix.std }}
         -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}"
+        -DPYBIND11_EIGEN_TESTS=ON
+        -DCMAKE_REQUIRE_FIND_PACKAGE_Eigen3=ON
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 
     - name: Build
@@ -344,7 +346,7 @@ jobs:
       run: apt-get update && DEBIAN_FRONTEND="noninteractive" apt-get install -y cmake git python3-dev python3-pytest python3-numpy
 
     - name: Configure
-      run: cmake -S . -B build -DPYBIND11_CUDA_TESTS=ON -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
+      run: cmake -S . -B build -DPYBIND11_CUDA_TESTS=ON -DPYBIND11_WERROR=ON -DPYBIND11_CATCH_TESTS=ON
 
     - name: Build
       run: cmake --build build -j2 --verbose
@@ -382,7 +384,7 @@ jobs:
 #      run: |
 #        source /etc/profile.d/modules.sh
 #        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/20.11
-#        cmake -S . -B build -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_STANDARD=14 -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
+#        cmake -S . -B build -DPYBIND11_CATCH_TESTS=ON -DCMAKE_CXX_STANDARD=14 -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 #
 #    - name: Build
 #      run: cmake --build build -j 2 --verbose
@@ -437,7 +439,7 @@ jobs:
       run: |
         source /etc/profile.d/modules.sh
         module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/25.11
-        cmake -S . -B build -DDOWNLOAD_CATCH=ON \
+        cmake -S . -B build -DPYBIND11_CATCH_TESTS=ON \
                             -DCMAKE_CXX_STANDARD=17 \
                             -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") \
                             -DCMAKE_CXX_FLAGS="-Wc,--pending_instantiations=0" \
@@ -493,9 +495,11 @@ jobs:
       run: >
         cmake -S . -B build
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
+        -DPYBIND11_CATCH_TESTS=ON
         -DCMAKE_CXX_STANDARD=${{ matrix.std }}
         -DCMAKE_CXX_FLAGS="${{ matrix.cxx_flags }}"
+        -DPYBIND11_EIGEN_TESTS=ON
+        -DCMAKE_REQUIRE_FIND_PACKAGE_Eigen3=ON
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 
     - name: Build
@@ -520,7 +524,7 @@ jobs:
       run: >
         cmake -S . -B build_partial
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
+        -DPYBIND11_CATCH_TESTS=ON
         -DCMAKE_CXX_STANDARD=${{ matrix.std }}
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
         "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
@@ -570,8 +574,8 @@ jobs:
         set +e; source /opt/intel/oneapi/setvars.sh; set -e
         cmake -S . -B build-11     \
         -DPYBIND11_WERROR=ON    \
-        -DDOWNLOAD_CATCH=ON     \
-        -DDOWNLOAD_EIGEN=OFF    \
+        -DPYBIND11_CATCH_TESTS=ON     \
+        -DPYBIND11_EIGEN_TESTS=OFF  \
         -DCMAKE_CXX_STANDARD=11             \
         -DCMAKE_CXX_COMPILER=$(which icpc)  \
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
@@ -608,8 +612,8 @@ jobs:
         set +e; source /opt/intel/oneapi/setvars.sh; set -e
         cmake -S . -B build-17     \
         -DPYBIND11_WERROR=ON    \
-        -DDOWNLOAD_CATCH=ON     \
-        -DDOWNLOAD_EIGEN=OFF    \
+        -DPYBIND11_CATCH_TESTS=ON     \
+        -DPYBIND11_EIGEN_TESTS=OFF  \
         -DCMAKE_CXX_STANDARD=17             \
         -DCMAKE_CXX_COMPILER=$(which icpc)  \
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
@@ -686,8 +690,8 @@ jobs:
         cmake -S . -B build
         -DCMAKE_BUILD_TYPE=MinSizeRel
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         -DCMAKE_CXX_STANDARD=11
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 
@@ -744,8 +748,10 @@ jobs:
     - name: Configure tests
       run: >
         cmake ../pybind11-tests
-        -DDOWNLOAD_CATCH=ON
+        -DPYBIND11_CATCH_TESTS=ON
         -DPYBIND11_WERROR=ON
+        -DPYBIND11_EIGEN_TESTS=ON
+        -DCMAKE_REQUIRE_FIND_PACKAGE_Eigen3=ON
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
       working-directory: /build-tests
 
@@ -838,8 +844,8 @@ jobs:
         cmake -S . -B build
         -G "Visual Studio 17 2022" -A Win32
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         ${{ matrix.args }}
     - name: Build C++11
       run: cmake --build build -j 2
@@ -889,8 +895,8 @@ jobs:
         -G "Visual Studio 17 2022" -A Win32
         -DCMAKE_BUILD_TYPE=Debug
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         ${{ matrix.args }}
     - name: Build C++11
       run: cmake --build build --config Debug -j 2
@@ -929,8 +935,8 @@ jobs:
       run: >
         cmake -S . -B build
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         -DCMAKE_CXX_STANDARD=20
 
     - name: Build C++20
@@ -953,8 +959,8 @@ jobs:
       run: >
         cmake -S . -B build_partial
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         -DCMAKE_CXX_STANDARD=20
         "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
 
@@ -1006,7 +1012,7 @@ jobs:
       # LTO leads to many undefined reference like
       # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
       run: >-
-        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
+        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -DPYBIND11_WERROR=ON -DPYBIND11_CATCH_TESTS=ON
         -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
         -S . -B build
 
@@ -1031,7 +1037,7 @@ jobs:
 
     - name: Configure C++14
       run: >-
-        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
+        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -DPYBIND11_WERROR=ON -DPYBIND11_CATCH_TESTS=ON
         -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
         -S . -B build2
 
@@ -1056,7 +1062,7 @@ jobs:
 
     - name: Configure C++17
       run: >-
-        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
+        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DPYBIND11_WERROR=ON -DPYBIND11_CATCH_TESTS=ON
         -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
         -S . -B build3
 
@@ -1124,8 +1130,8 @@ jobs:
           cmake -G Ninja -S . -B .
           -DPYBIND11_WERROR=OFF
           -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
-          -DDOWNLOAD_CATCH=ON
-          -DDOWNLOAD_EIGEN=ON
+          -DPYBIND11_CATCH_TESTS=ON
+          -DPYBIND11_EIGEN_TESTS=ON
           -DCMAKE_CXX_COMPILER=clang++
           -DCMAKE_CXX_STANDARD=17
 
@@ -1192,8 +1198,8 @@ jobs:
           cmake -G Ninja -S . -B . `
             -DPYBIND11_WERROR=OFF `
             -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF `
-            -DDOWNLOAD_CATCH=ON `
-            -DDOWNLOAD_EIGEN=ON `
+            -DPYBIND11_CATCH_TESTS=ON `
+            -DPYBIND11_EIGEN_TESTS=ON `
             -DCMAKE_CXX_COMPILER=clang++ `
             -DCMAKE_CXX_STANDARD=20 `
             -DPython_EXECUTABLE="$pythonExecutable" `
@@ -1267,8 +1273,8 @@ jobs:
       run: >-
         cmake -S . -B build
         -DPYBIND11_WERROR=OFF
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         -DCMAKE_CXX_COMPILER=clang++
         -DCMAKE_CXX_STANDARD=20
         -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")

.github/workflows/configure.yml

@@ -71,7 +71,7 @@ jobs:
     # These steps use a directory with a space in it intentionally
     - name: Configure
       shell: bash
-      run: cmake -S. -B"build dir" -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
+      run: cmake -S. -B"build dir" -DPYBIND11_WERROR=ON -DPYBIND11_CATCH_TESTS=ON
 
     # Only build and test if this was manually triggered in the GitHub UI
     - name: Build

.github/workflows/reusable-standard.yml

@@ -72,8 +72,8 @@ jobs:
           cmake -S. -Bbuild -Werror=dev
           -DPYBIND11_WERROR=ON
           -DPYBIND11_PYTEST_ARGS=-v
-          -DDOWNLOAD_CATCH=ON
-          -DDOWNLOAD_EIGEN=ON
+          -DPYBIND11_CATCH_TESTS=ON
+          -DPYBIND11_EIGEN_TESTS=ON
           ${{ inputs.cmake-args }}
 
       - name: Build

.github/workflows/upstream.yml

@@ -54,8 +54,8 @@ jobs:
       run: >
         cmake -S . -B build11
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         -DCMAKE_CXX_STANDARD=11
         -DCMAKE_BUILD_TYPE=Debug
 
@@ -77,8 +77,8 @@ jobs:
       run: >
         cmake -S . -B build17
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         -DCMAKE_CXX_STANDARD=17
 
     - name: Build C++17
@@ -96,8 +96,8 @@ jobs:
       run: >
         cmake -S . -B build17max
         -DPYBIND11_WERROR=ON
-        -DDOWNLOAD_CATCH=ON
-        -DDOWNLOAD_EIGEN=ON
+        -DPYBIND11_CATCH_TESTS=ON
+        -DPYBIND11_EIGEN_TESTS=ON
         -DCMAKE_CXX_STANDARD=17
         -DPYBIND11_INTERNALS_VERSION=10000000
 

CMakePresets.json

@@ -13,8 +13,8 @@
       "cacheVariables": {
         "CMAKE_BUILD_TYPE": "Debug",
         "CMAKE_EXPORT_COMPILE_COMMANDS": true,
-        "DOWNLOAD_CATCH": true,
-        "DOWNLOAD_EIGEN": true,
+        "PYBIND11_CATCH_TESTS": true,
+        "PYBIND11_EIGEN_TESTS": true,
         "PYBIND11_FINDPYTHON": "NEW",
         "PYBIND11_WERROR": true,
         "CMAKE_COLOR_DIAGNOSTICS": true

noxfile.py

@@ -43,8 +43,8 @@ def tests(session: nox.Session) -> None:
         "-S.",
         f"-B{tmpdir}",
         "-DPYBIND11_WERROR=ON",
-        "-DDOWNLOAD_CATCH=ON",
-        "-DDOWNLOAD_EIGEN=ON",
+        "-DPYBIND11_CATCH_TESTS=ON",
+        "-DPYBIND11_EIGEN_TESTS=ON",
         *session.posargs,
     )
     session.run("cmake", "--build", tmpdir)