Only attempt to link to igraph if it can be found.

This allows us to handle situations where igraph is being made available
outside of Cmake, e.g., by manual addition of -I directories.

.github/workflows/check-install.yaml

@@ -16,26 +16,6 @@ jobs:
     - name: Get latest CMake
       uses: lukka/get-cmake@latest
 
-    - name: Cache installed igraph
-      id: cache-igraph
-      uses: actions/cache@v4
-      with:
-        path: _deps
-        key: libigraph
-
-    - name: Make and install igraph
-      if: ${{ steps.cache-igraph.outputs.cache-hit != 'true' }}
-      run: |
-        version=0.10.13
-        path=$(pwd)
-        wget https://github.com/igraph/igraph/releases/download/${version}/igraph-${version}.tar.gz
-        tar -xf igraph-${version}.tar.gz
-        cd igraph-${version}
-        mkdir build && cd build
-        cmake .. -DCMAKE_INSTALL_PREFIX=${path}/_deps
-        cmake --build .
-        sudo cmake --install .
-
     - name: Configure the build
       run: cmake -S . -B build -DSCRAN_GRAPH_CLUSTER_TESTS=OFF -DCMAKE_PREFIX_PATH=_deps
 

CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.14)
 
 project(scran_graph_cluster
-    VERSION 0.1.1
+    VERSION 0.1.2
     DESCRIPTION "Cluster cells using graph-based methods"
     LANGUAGES CXX)
 
@@ -19,22 +19,22 @@ target_compile_features(scran_graph_cluster INTERFACE cxx_std_17)
 
 # Dependencies
 option(SCRAN_GRAPH_CLUSTER_FETCH_EXTERN "Automatically fetch scran_graph_cluster's external dependencies (except for igraph)." ON)
-option(SCRAN_GRAPH_CLUSTER_FETCH_EXTERN_IGRAPH "Automatically fetch scran_graph_cluster's external igraph dependency." OFF)
-
-if (NOT SCRAN_GRAPH_CLUSTER_FETCH_EXTERN_IGRAPH)
-    # igraph needs compilation so we just try to get it from the system by
-    # default, rather than pulling it down and building the whole thing.
-    find_package(igraph 0.10.0 CONFIG REQUIRED)
-endif()
-
 if(SCRAN_GRAPH_CLUSTER_FETCH_EXTERN)
     add_subdirectory(extern)
 else()
     find_package(ltla_raiigraph 1.1.0 CONFIG REQUIRED)
     find_package(knncolle_knncolle 2.0.0 CONFIG REQUIRED)
 endif()
 
-target_link_libraries(scran_graph_cluster INTERFACE igraph::igraph ltla::raiigraph knncolle::knncolle)
+target_link_libraries(scran_graph_cluster INTERFACE ltla::raiigraph knncolle::knncolle)
+
+option(SCRAN_GRAPH_CLUSTER_FIND_IGRAPH "Search for the igraph package." ON)
+if(SCRAN_GRAPH_CLUSTER_FIND_IGRAPH)
+    find_package(igraph 0.10.0 CONFIG)
+    if (igraph_FOUND)
+        target_link_libraries(scran_graph_cluster INTERFACE igraph::igraph)
+    endif()
+endif()
 
 # Tests
 if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)

README.md

@@ -78,8 +78,9 @@ target_link_libraries(myexe libscran::scran_graph_cluster)
 target_link_libraries(mylib INTERFACE libscran::scran_graph_cluster)
 ```
 
-This will fetch all external dependencies except for [**igraph**](https://igraph.org), which should already be installed.
-We can instruct CMake to fetch and build **igraph** by setting `-DSCRAN_GRAPH_CLUSTER_FETCH_EXTERN_IGRAPH=ON`.
+This will fetch all external dependencies except for [**igraph**](https://igraph.org), which should already be installed and available via `find_package()`.
+Users can set the `SCRAN_GRAPH_CLUSTER_FIND_IGRAPH` option to disable **igraph** discovery (e.g., to supply a custom **igraph** installation),
+in which case they will need to link to **igraph** manually in their `target_link_libraries()` call.
 
 ### CMake with `find_package()`
 
@@ -99,8 +100,9 @@ cmake --build . --target install
 By default, this will use `FetchContent` to fetch all external dependencies.
 If you want to install them manually, use `-DSCRAN_GRAPH_CLUSTER_FETCH_EXTERN=OFF`.
 See the tags in [`extern/CMakeLists.txt`](extern/CMakeLists.txt) to find compatible versions of each dependency.
+Again, **igraph** is assumed to be installed and available via `find_package()`.
 
 ### Manual
 
 If you're not using CMake, the simple approach is to just copy the files in `include/` - either directly or with Git submodules - and include their path during compilation with, e.g., GCC's `-I`.
-This requires the external dependencies listed in [`extern/CMakeLists.txt`](extern/CMakeLists.txt), which also need to be made available during compilation.
+This requires the external dependencies listed in [`extern/CMakeLists.txt`](extern/CMakeLists.txt) as well as the **igraph** library.

cmake/Config.cmake.in

@@ -2,7 +2,12 @@
 
 include(CMakeFindDependencyMacro)
 find_dependency(knncolle_knncolle 2.0.0 CONFIG REQUIRED)
-find_dependency(igraph 0.10.0 CONFIG REQUIRED)
 find_dependency(ltla_raiigraph 1.1.0 CONFIG REQUIRED)
 
+if(@SCRAN_GRAPH_CLUSTER_FIND_IGRAPH@)
+    # Not REQUIRED, so don't use find_dependency according to
+    # https://stackoverflow.com/questions/64846805/how-do-i-specify-an-optional-dependency-in-a-cmake-package-configuration-file
+    find_package(igraph 0.10.0 CONFIG)
+endif()
+
 include("${CMAKE_CURRENT_LIST_DIR}/libscran_scran_graph_clusterTargets.cmake")

extern/CMakeLists.txt

@@ -1,13 +1,5 @@
 include(FetchContent)
 
-if (SCRAN_MARKERS_FETCH_EXTERN_IGRAPH)
-    FetchContent_Declare(
-      igraph
-      GIT_REPOSITORY https://github.com/igraph/igraph
-      GIT_TAG master # ^0.10.0
-    )
-endif()
-
 FetchContent_Declare(
   knncolle
   GIT_REPOSITORY https://github.com/knncolle/knncolle
@@ -21,10 +13,5 @@ FetchContent_Declare(
 )
 
 FetchContent_MakeAvailable(knncolle)
-
-if (SCRAN_MARKERS_FETCH_EXTERN_IGRAPH)
-    FetchContent_MakeAvailable(igraph)
-endif()
-
 FetchContent_MakeAvailable(raiigraph)