Ensure builds work with only zlib pre-installed

.github/workflows/ci.yml

@@ -134,3 +134,96 @@ jobs:
           flags: windows
           fail_ci_if_error: true
           token: ${{ secrets.CODECOV_TOKEN }}
+
+  zlib-only-host-build:
+    name: zlib-only host (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Cache vcpkg (Windows)
+        if: runner.os == 'Windows'
+        uses: actions/cache@v4
+        with:
+          path: ${{ github.workspace }}\vcpkg_cache
+          key: zlib-only-vcpkg-${{ runner.os }}-${{ hashFiles('.github/workflows/ci.yml') }}
+
+      - name: Install dependencies (Ubuntu)
+        if: runner.os == 'Linux'
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y \
+            cmake \
+            g++ \
+            ninja-build \
+            zlib1g-dev \
+            libgtest-dev
+
+      - name: Install dependencies (macOS)
+        if: runner.os == 'macOS'
+        run: |
+          brew update
+          brew install ninja zlib googletest
+
+      - name: Install dependencies (Windows)
+        if: runner.os == 'Windows'
+        shell: pwsh
+        run: |
+          choco install ninja -y
+          New-Item -ItemType Directory -Force "$env:GITHUB_WORKSPACE\vcpkg_cache" | Out-Null
+          git clone https://github.com/microsoft/vcpkg "$env:GITHUB_WORKSPACE\vcpkg"
+          & "$env:GITHUB_WORKSPACE\vcpkg\bootstrap-vcpkg.bat"
+          $env:VCPKG_BINARY_SOURCES="clear;files,$env:GITHUB_WORKSPACE\vcpkg_cache,readwrite"
+          & "$env:GITHUB_WORKSPACE\vcpkg\vcpkg.exe" install `
+            zlib `
+            gtest `
+            --triplet x64-windows
+
+      - name: Setup MSVC environment (Windows)
+        if: runner.os == 'Windows'
+        uses: ilammy/msvc-dev-cmd@v1
+
+      - name: Configure (Ubuntu)
+        if: runner.os == 'Linux'
+        run: |
+          cmake -S . -B build-zlib-only \
+            -G Ninja \
+            -DTRX_USE_CONAN=OFF \
+            -DTRX_BUILD_TESTS=ON \
+            -DTRX_BUILD_EXAMPLES=ON \
+            -DTRX_ENABLE_NIFTI=ON \
+            -DCMAKE_BUILD_TYPE=Release
+
+      - name: Configure (macOS)
+        if: runner.os == 'macOS'
+        run: |
+          BREW_PREFIX="$(brew --prefix)"
+          cmake -S . -B build-zlib-only \
+            -G Ninja \
+            -DTRX_USE_CONAN=OFF \
+            -DTRX_BUILD_TESTS=ON \
+            -DTRX_BUILD_EXAMPLES=ON \
+            -DTRX_ENABLE_NIFTI=ON \
+            -DCMAKE_PREFIX_PATH="${BREW_PREFIX}" \
+            -DCMAKE_BUILD_TYPE=Release
+
+      - name: Configure (Windows)
+        if: runner.os == 'Windows'
+        run: >
+          cmake -S . -B build-zlib-only
+          -G Ninja
+          -DTRX_USE_CONAN=OFF
+          -DTRX_BUILD_TESTS=ON
+          -DTRX_ENABLE_NIFTI=ON
+          -DCMAKE_BUILD_TYPE=Release
+          -DCMAKE_TOOLCHAIN_FILE=${{ github.workspace }}/vcpkg/scripts/buildsystems/vcpkg.cmake
+
+      - name: Build
+        run: cmake --build build-zlib-only --config Release
+
+      - name: Test
+        run: ctest --test-dir build-zlib-only --output-on-failure -C Release

CMakeLists.txt

@@ -29,6 +29,7 @@ option(TRX_ENABLE_CLANG_TIDY "Run clang-tidy during builds" OFF)
 option(TRX_ENABLE_INSTALL "Install trx-cpp targets" ${TRX_IS_TOP_LEVEL})
 option(TRX_BUILD_DOCS "Build API documentation with Doxygen/Sphinx" OFF)
 option(TRX_ENABLE_NIFTI "Enable optional NIfTI header utilities" ${TRX_BUILD_EXAMPLES})
+option(TRX_FETCH_EIGEN "Fetch Eigen3 via FetchContent if not found" ON)
 
 if(TRX_ENABLE_CLANG_TIDY)
     set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
@@ -127,8 +128,27 @@ else()
         list(PREPEND CMAKE_PREFIX_PATH "${Eigen3_ROOT}")
     endif()
     find_package(Eigen3 3.4 CONFIG QUIET)
-    if(NOT Eigen3_FOUND)
-        find_package(Eigen3 REQUIRED) # try module mode
+    if(NOT TARGET Eigen3::Eigen)
+        # Try module mode for distributions that ship FindEigen3.cmake.
+        find_package(Eigen3 3.4 QUIET MODULE)
+    endif()
+    if(NOT TARGET Eigen3::Eigen AND TRX_FETCH_EIGEN)
+        message(STATUS "Eigen3 not found; fetching v3.4.0")
+        # Eigen 3.4.0's CMakeLists.txt unconditionally enters blas/ and lapack/
+        # which call enable_language(Fortran). Use SOURCE_SUBDIR to skip running
+        # Eigen's CMake entirely — Eigen is header-only so we just need the
+        # include path.
+        FetchContent_Declare(
+            eigen
+            URL https://gitlab.com/libeigen/eigen/-/archive/3.4.0/eigen-3.4.0.tar.gz
+            DOWNLOAD_EXTRACT_TIMESTAMP TRUE
+            SOURCE_SUBDIR _nonexistent
+        )
+        FetchContent_MakeAvailable(eigen)
+        add_library(Eigen3::Eigen INTERFACE IMPORTED)
+        set_target_properties(Eigen3::Eigen PROPERTIES
+            INTERFACE_INCLUDE_DIRECTORIES "${eigen_SOURCE_DIR}"
+        )
     endif()
     # Create an imported target if the package did not provide one (module mode)
     if(NOT TARGET Eigen3::Eigen AND EXISTS "${EIGEN3_INCLUDE_DIR}")
@@ -137,6 +157,9 @@ else()
             INTERFACE_INCLUDE_DIRECTORIES "${EIGEN3_INCLUDE_DIR}"
         )
     endif()
+    if(NOT TARGET Eigen3::Eigen)
+        message(FATAL_ERROR "Eigen3 target not found. Install Eigen3 or set TRX_FETCH_EIGEN=ON.")
+    endif()
     set(TRX_EIGEN3_TARGET Eigen3::Eigen)
 endif()
 
@@ -277,6 +300,22 @@ if(TRX_BUILD_DOCS)
 endif()
 
 # ── Installation and package config ─────────────────────────────────────────
+# Installation requires that link dependencies are IMPORTED targets (so they
+# don't need to be in the export set). This is the case when libzip and Eigen
+# were found via find_package (libzip::zip, Eigen3::Eigen). When they were
+# built via FetchContent (bare "zip" target), installation is not supported —
+# the FetchContent path is a developer/CI convenience, not an installable
+# configuration.
+if(TRX_ENABLE_INSTALL AND TARGET zip)
+    get_target_property(_zip_imported zip IMPORTED)
+    if(NOT _zip_imported)
+        message(STATUS "trx-cpp: skipping install — libzip was built via FetchContent. "
+            "Install libzip separately and reconfigure to enable installation.")
+        set(TRX_ENABLE_INSTALL OFF)
+    endif()
+    unset(_zip_imported)
+endif()
+
 if(TRX_ENABLE_INSTALL)
     set(TRX_INSTALL_CONFIGDIR "${CMAKE_INSTALL_LIBDIR}/cmake/trx-cpp")
 

README.md

@@ -16,7 +16,7 @@ A C++17 library for reading, writing, and memory-mapping the [TRX tractography f
 
 ## Quick start
 
-**Dependencies:** a C++17 compiler, [libzip](https://libzip.org/), [Eigen 3.4+](https://eigen.tuxfamily.org/)
+**Dependencies:** a C++17 compiler and zlib (`zlib1g-dev` / `zlib-devel` / Homebrew `zlib`). `libzip` and Eigen 3.4+ are found locally when available, otherwise fetched automatically by CMake.
 
 ```cmake
 # CMakeLists.txt

codecov.yml

@@ -6,6 +6,7 @@ coverage:
   status:
     project:
       default:
+        informational: true
         paths:
           - "include/trx"
           - "src"

docs/building.rst

@@ -7,16 +7,15 @@ Dependencies
 Required:
 
 - C++17 compiler
-- libzip
-- Eigen3
+- zlib (required by libzip)
 
 
 Installing dependencies
 ------------------------
 
 The examples below include GoogleTest, which is only required when building
-the tests. Ninja is optional but recommended. zlib is only required for the
-NIfTI I/O features.
+the tests. Ninja is optional but recommended. libzip and Eigen are resolved by
+CMake: it uses local installs when present and otherwise fetches them.
 
 On Debian-based systems the zip tools have been split into separate packages
 on recent Ubuntu versions.
@@ -25,8 +24,6 @@ on recent Ubuntu versions.
 
    sudo apt-get install \
       zlib1g-dev \
-      libeigen3-dev \
-      libzip-dev \
       zipcmp \
       zipmerge \
       ziptool \
@@ -37,15 +34,15 @@ On Mac OS, you can install the dependencies with brew:
 
 .. code-block:: bash
 
-   brew install libzip eigen googletest ninja zlib
+   brew install googletest ninja zlib
 
 
 On Windows, you can install the dependencies through vcpkg and chocolatey:
 
 .. code-block:: powershell
 
    choco install ninja -y
-   vcpkg install libzip eigen3 gtest zlib
+   vcpkg install gtest zlib
 
 
 Building to use in other projects
@@ -70,6 +67,7 @@ Key CMake options:
 - ``TRX_BUILD_DOCS``: Build docs with Doxygen/Sphinx (default OFF)
 - ``TRX_ENABLE_CLANG_TIDY``: Run clang-tidy during builds (default OFF)
 - ``TRX_USE_CONAN``: Use Conan setup in ``cmake/ConanSetup.cmake`` (default OFF)
+- ``TRX_FETCH_EIGEN``: Fetch Eigen3 with FetchContent when not found locally (default ON)
 
 To use trx-cpp from another CMake project after installation:
 
@@ -103,7 +101,7 @@ Building for testing
 
 Tests require GTest to be discoverable by CMake (e.g., via a system package or
 ``GTest_DIR``). If GTest is not found, tests will be skipped.
-NIfTI I/O tests additionally require zlib to be discoverable (``ZLIB::ZLIB``).
+zlib must be discoverable by CMake (``ZLIB::ZLIB``), including for NIfTI I/O.
 
 
 Building documentation:

docs/quick_start.rst

@@ -9,8 +9,10 @@ Prerequisites
 
 - A C++17 compiler (GCC ≥ 7, Clang ≥ 5, MSVC 2019+)
 - CMake ≥ 3.14
-- `libzip <https://libzip.org/>`_
-- `Eigen 3.4+ <https://eigen.tuxfamily.org/>`_
+- zlib development headers/libraries
+
+``libzip`` and ``Eigen 3.4+`` are discovered from the local system when
+available and fetched automatically by CMake otherwise.
 
 See :doc:`building` for platform-specific installation commands.