From b3af0c176161b7520653f138dfd213529eb84772 Mon Sep 17 00:00:00 2001
From: Marco Barbone <mbarbone@flatironinstitute.org>
Date: Tue, 10 Nov 2026 10:19:57 -0500
Subject: [PATCH] Document FetchContent usage and test it

Show how to consume xsimd with FetchContent. Drop the CPM.cmake
section, as the reviewer asked.

The recipe is a small project under .github/cmake-test-fetchcontent.
The docs include its CMakeLists.txt with literalinclude, so the page
and the test cannot drift. The cmake.yml workflow builds the recipe
on each push and pull request, using the checkout as the xsimd source
through FETCHCONTENT_SOURCE_DIR_XSIMD.

Assisted-by: Hermes Agent
---
 .github/cmake-test-fetchcontent/CMakeLists.txt | 11 +++++++++++
 .github/cmake-test-fetchcontent/main.cpp       | 15 +++++++++++++++
 .github/workflows/cmake.yml                    |  7 +++++++
 docs/source/installation.rst                   | 15 +++++++++++++++
 4 files changed, 48 insertions(+)
 create mode 100644 .github/cmake-test-fetchcontent/CMakeLists.txt
 create mode 100644 .github/cmake-test-fetchcontent/main.cpp

diff --git a/.github/cmake-test-fetchcontent/CMakeLists.txt b/.github/cmake-test-fetchcontent/CMakeLists.txt
new file mode 100644
index 000000000..3234625bf
--- /dev/null
+++ b/.github/cmake-test-fetchcontent/CMakeLists.txt
@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 3.19)
+project(fetchcontent-test VERSION 0.0.1)
+
+include(FetchContent)
+FetchContent_Declare(xsimd
+    GIT_REPOSITORY https://github.com/xtensor-stack/xsimd.git
+    GIT_TAG 14.3.0)
+FetchContent_MakeAvailable(xsimd)
+
+add_executable(app main.cpp)
+target_link_libraries(app PRIVATE xsimd)
diff --git a/.github/cmake-test-fetchcontent/main.cpp b/.github/cmake-test-fetchcontent/main.cpp
new file mode 100644
index 000000000..6307a5f9b
--- /dev/null
+++ b/.github/cmake-test-fetchcontent/main.cpp
@@ -0,0 +1,15 @@
+#include "xsimd/xsimd.hpp"
+
+#include <cstdio>
+
+int main()
+{
+    xsimd::batch<double> a(1.0), b(2.0);
+    double res = (a + b).get(0);
+    if (res != 3.0)
+    {
+        std::fprintf(stderr, "check failed: got %f, expected 3\n", res);
+        return 1;
+    }
+    return 0;
+}
diff --git a/.github/workflows/cmake.yml b/.github/workflows/cmake.yml
index 0ff2cd0a4..9d1771feb 100644
--- a/.github/workflows/cmake.yml
+++ b/.github/workflows/cmake.yml
@@ -23,4 +23,11 @@ jobs:
         ls $PWD/../_install/share/cmake/xsimd
         cmake . -DCMAKE_PREFIX_PATH=$PWD/../_install/share/cmake/xsimd
         cmake --build .
+    - name: Check FetchContent
+      run: |
+        cmake -S ${{ github.workspace }}/.github/cmake-test-fetchcontent \
+          -B _fetchcontent_build \
+          -D FETCHCONTENT_SOURCE_DIR_XSIMD=${{ github.workspace }}
+        cmake --build _fetchcontent_build
+        ./_fetchcontent_build/app
 
diff --git a/docs/source/installation.rst b/docs/source/installation.rst
index 63e4fe5ba..87a51a654 100644
--- a/docs/source/installation.rst
+++ b/docs/source/installation.rst
@@ -87,3 +87,18 @@ as forward other xsimd requirements (minimum C++ version for instance).
 
     find_package(xsimd REQUIRED)
     target_link_libraries(myproject PRIVATE xsimd)
+
+Using FetchContent
+~~~~~~~~~~~~~~~~~~
+
+CMake can download `xsimd` at configure time with `FetchContent <https://cmake.org/cmake/help/latest/module/FetchContent.html>`_. The recipe below is the ``CMakeLists.txt`` of ``.github/cmake-test-fetchcontent``. CI builds it on every pull request:
+
+.. literalinclude:: ../../.github/cmake-test-fetchcontent/CMakeLists.txt
+    :language: cmake
+
+The ``xsimd`` target requires C++17. The program in ``main.cpp`` uses ``xsimd::batch``. From the ``.github/cmake-test-fetchcontent`` directory, build the recipe with:
+
+.. code:: bash
+
+    cmake -B build/
+    cmake --build build/