use FetchContent instead of submodules

.appveyor.yml

@@ -22,7 +22,6 @@ environment:
 clone_depth: 5
 
 install:
-  - git submodule update --init --recursive  # get `external_libs` folder
   - set PATH=C:\mingw-w64\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\bin;%PATH%
   - set PYTHON_VERSION=%CONFIGURATION%
   - set CONDA_ENV="test-env"

.ci/lint-cpp.sh

@@ -9,8 +9,7 @@ echo "done running cpplint"
 
 echo "running cmakelint"
 cmake_files=$(
-    find . -name CMakeLists.txt -o -path "./cmake/*.cmake" \
-    | grep -v external_libs
+    find . -name CMakeLists.txt -o -path "./cmake/*.cmake"
 )
 cmakelint \
     --linelength=120 \

.editorconfig

@@ -10,7 +10,6 @@ indent_size = 2
 [*.{py,sh,js}]
 indent_size = 4
 line_length = 120
-skip = external_libs
 known_first_party = lightgbm
 
 # Placeholder files

.pre-commit-config.yaml

@@ -1,7 +1,6 @@
 exclude: |
   (?x)^(
       build|
-      external_libs|
       lightgbm-python|
       lightgbm_r|
   )$

CMakeLists.txt

@@ -31,6 +31,21 @@ cmake_minimum_required(VERSION 3.18)
 
 project(lightgbm LANGUAGES C CXX)
 
+include(FetchContent)
+FetchContent_Declare(
+  fast_double_parser
+  GIT_REPOSITORY https://github.com/lemire/fast_double_parser.git
+  GIT_TAG efec03532ef65984786e5e32dbc81f6e6a55a115
+)
+FetchContent_Declare(
+  fmt
+  GIT_REPOSITORY https://github.com/fmtlib/fmt.git
+  GIT_TAG f5e54359df4c26b6230fc61d38aa294581393084
+)
+FetchContent_MakeAvailable(fast_double_parser fmt)
+include_directories(${fast_double_parser_SOURCE_DIR}/include)
+include_directories(${fmt_SOURCE_DIR}/include/fmt)
+
 if(BUILD_CPP_TEST)
   set(CMAKE_CXX_STANDARD 14)
 else()
@@ -111,8 +126,13 @@ if(USE_SWIG)
   endif()
 endif()
 
-set(EIGEN_DIR "${PROJECT_SOURCE_DIR}/external_libs/eigen")
-include_directories(${EIGEN_DIR})
+FetchContent_Declare(
+  eigen
+  GIT_REPOSITORY https://gitlab.com/libeigen/eigen.git
+  GIT_TAG 3147391d946bb4b6c68edd901f2add6ac1f31f8c
+)
+FetchContent_MakeAvailable(eigen)
+include_directories(${eigen_SOURCE_DIR})
 
 # See https://gitlab.com/libeigen/eigen/-/blob/master/COPYING.README
 add_definitions(-DEIGEN_MPL2_ONLY)
@@ -171,8 +191,13 @@ if(USE_OPENMP)
 endif()
 
 if(USE_GPU)
-    set(BOOST_COMPUTE_HEADER_DIR ${PROJECT_SOURCE_DIR}/external_libs/compute/include)
-    include_directories(${BOOST_COMPUTE_HEADER_DIR})
+    FetchContent_Declare(
+      compute
+      GIT_REPOSITORY https://github.com/boostorg/compute.git
+      GIT_TAG 36350b7de849300bd3d72a05d8bf890ca405a014
+    )
+    FetchContent_MakeAvailable(compute)
+    include_directories(${compute_SOURCE_DIR}/include)
     find_package(OpenCL REQUIRED)
     include_directories(${OpenCL_INCLUDE_DIRS})
     message(STATUS "OpenCL include directory: " ${OpenCL_INCLUDE_DIRS})

build-python.sh

@@ -211,85 +211,6 @@ create_isolated_source_dir() {
     cp -R ./src ./lightgbm-python
     cp -R ./swig ./lightgbm-python
     cp -R ./windows ./lightgbm-python
-
-    # include only specific files from external_libs, to keep the package
-    # small and avoid redistributing code with licenses incompatible with
-    # LightGBM's license
-
-    ######################
-    # fast_double_parser #
-    ######################
-    mkdir -p ./lightgbm-python/external_libs/fast_double_parser
-    cp \
-        external_libs/fast_double_parser/CMakeLists.txt \
-        ./lightgbm-python/external_libs/fast_double_parser/CMakeLists.txt
-    cp \
-        external_libs/fast_double_parser/LICENSE* \
-        ./lightgbm-python/external_libs/fast_double_parser/
-
-    mkdir -p ./lightgbm-python/external_libs/fast_double_parser/include/
-    cp \
-        external_libs/fast_double_parser/include/fast_double_parser.h \
-        ./lightgbm-python/external_libs/fast_double_parser/include/
-
-    #######
-    # fmt #
-    #######
-    mkdir -p ./lightgbm-python/external_libs/fmt
-    cp \
-        external_libs/fast_double_parser/CMakeLists.txt \
-        ./lightgbm-python/external_libs/fmt/CMakeLists.txt
-    cp \
-        external_libs/fmt/LICENSE* \
-        ./lightgbm-python/external_libs/fmt/
-
-    mkdir -p ./lightgbm-python/external_libs/fmt/include/fmt
-    cp \
-        external_libs/fmt/include/fmt/*.h \
-        ./lightgbm-python/external_libs/fmt/include/fmt/
-
-    #########
-    # Eigen #
-    #########
-    mkdir -p ./lightgbm-python/external_libs/eigen/Eigen
-    cp \
-        external_libs/eigen/CMakeLists.txt \
-        ./lightgbm-python/external_libs/eigen/CMakeLists.txt
-
-    modules="Cholesky Core Dense Eigenvalues Geometry Householder Jacobi LU QR SVD"
-    for eigen_module in ${modules}; do
-        cp \
-            external_libs/eigen/Eigen/${eigen_module} \
-            ./lightgbm-python/external_libs/eigen/Eigen/${eigen_module}
-        if [ ${eigen_module} != "Dense" ]; then
-            mkdir -p ./lightgbm-python/external_libs/eigen/Eigen/src/${eigen_module}/
-            cp \
-                -R \
-                external_libs/eigen/Eigen/src/${eigen_module}/* \
-                ./lightgbm-python/external_libs/eigen/Eigen/src/${eigen_module}/
-        fi
-    done
-
-    mkdir -p ./lightgbm-python/external_libs/eigen/Eigen/misc
-    cp \
-        -R \
-        external_libs/eigen/Eigen/src/misc \
-        ./lightgbm-python/external_libs/eigen/Eigen/src/misc/
-
-    mkdir -p ./lightgbm-python/external_libs/eigen/Eigen/plugins
-    cp \
-        -R \
-        external_libs/eigen/Eigen/src/plugins \
-        ./lightgbm-python/external_libs/eigen/Eigen/src/plugins/
-
-    ###################
-    # compute (Boost) #
-    ###################
-    mkdir -p ./lightgbm-python/external_libs/compute
-    cp \
-        -R \
-        external_libs/compute/include \
-        ./lightgbm-python/external_libs/compute/include/
 }
 
 create_isolated_source_dir
@@ -305,7 +226,6 @@ if test "${INSTALL}" = true; then
         rm -rf \
             ./cmake \
             ./CMakeLists.txt \
-            ./external_libs \
             ./include \
             ./src \
             ./swig \

include/LightGBM/utils/common.h

@@ -30,8 +30,8 @@
 #include <vector>
 
 #define FMT_HEADER_ONLY
-#include "../../../external_libs/fast_double_parser/include/fast_double_parser.h"
-#include "../../../external_libs/fmt/include/fmt/format.h"
+#include "fast_double_parser.h"
+#include "format.h"
 
 #ifdef _MSC_VER
 #include <intrin.h>

python-package/pyproject.toml

@@ -83,19 +83,17 @@ minimum-version = "0.4.4"
 [tool.isort]
 line_length = 120
 skip_glob = [
-    "*/external_libs/*",
     "*/lightgbm-python/*"
 ]
 
 [tool.mypy]
-exclude = 'build/*|compile/*|docs/*|examples/*|external_libs/*|lightgbm-python/*|tests/*'
+exclude = 'build/*|compile/*|docs/*|examples/*|lightgbm-python/*|tests/*'
 ignore_missing_imports = true
 
 [tool.ruff]
 exclude = [
     "build",
     "compile",
-    "external_libs",
     "lightgbm-python",
 ]
 line-length = 120
@@ -109,7 +107,6 @@ exclude = [
     "build/*.py",
     "compile/*.py",
     "examples/*.py",
-    "external_libs/*.py",
     "lightgbm-python/*.py",
     "python-package/*.py",
     "tests/*.py"

python-package/setup.cfg

@@ -12,7 +12,6 @@ ignore =
     W503
 exclude =
     ./.nuget,
-    ./external_libs,
     ./lightgbm-python,
     ./python-package/build,
     ./python-package/compile