Swig error: Syntax error in input(3) with swig < 4.2

[andyneff]

I was able to build successfully on master on the docker image quay.io/pypa/manylinux_2_28_x86_64 (CentOS/Alma/RHEL 8 based), but image python:3.13 (Debian based) errors on one of the swig steps. Reverting to tag v0.11.1 fixed the problem.

I also saw the same failures when building with VS2022 on Windows 11

This seems to have broken some where between commits 7940c9f (works) and 755fe37 (gets the error)

Version

$ git rev-parse HEAD
778502a21eb9c6e813df72ce9518acfdfeb8e966

Compile Error

Linux

[107/109] Swig compile s2.i for python
FAILED: python/CMakeFiles/s2geometry.dir/s2PYTHON_wrap.cxx python/s2.py /s2geometry/build/temp.linux-x86_64-cpython-313_SwigBindings/python/CMakeFiles/s2geometry.dir/s2PYTHON_wrap.cxx /s2geometry/build/temp.linux-x86_64-cpython-313_SwigBindings/python/s2.py
cd /s2geometry/build/temp.linux-x86_64-cpython-313_SwigBindings/python && /tmp/build-env-omsxz4wu/lib/python3.13/site-packages/cmake/data/bin/cmake -E make_directory /s2geometry/build/temp.linux-x86_64-cpython-313_SwigBindings/python/CMakeFiles/s2geometry.dir /s2geometry/build/temp.linux-x86_64-cpython-313_SwigBindings/python /s2geometry/build/temp.linux-x86_64-cpython-313_SwigBindings/python/CMakeFiles/s2geometry.dir && /tmp/build-env-omsxz4wu/lib/python3.13/site-packages/cmake/data/bin/cmake -E env SWIG_LIB=/usr/share/swig4.0 /usr/bin/swig4.0 -python -DSWIGWORDSIZE64 -module s2geometry -outdir /s2geometry/build/temp.linux-x86_64-cpython-313_SwigBindings/python -c++ -interface _s2geometry -I/usr/include -I/usr/local/include/python3.13 -I/s2geometry/src -o /s2geometry/build/temp.linux-x86_64-cpython-313_SwigBindings/python/CMakeFiles/s2geometry.dir/s2PYTHON_wrap.cxx /s2geometry/src/python/s2.i
/s2geometry/src/s2/util/coding/coder.h:54: Warning 362: operator= ignored
/s2geometry/src/s2/s1angle.h:139: Error: Syntax error in input(3).

Windows

[107/109] Swig compile s2.i for python
FAILED: python/CMakeFiles/s2geometry.dir/s2PYTHON_wrap.cxx python/s2.py C:/Users/andy/src/s2geometry/build/temp.win-amd64-cpython-311/Release_SwigBindings/python/CMakeFiles/s2geometry.dir/s2PYTHON_wrap.cxx C:/Users/andy/src/s2geometry/build/temp.win-amd64-cpython-311/Release_SwigBindings/python/s2.py
C:\WINDOWS\system32\cmd.exe /C "cd /D C:\Users\andy\src\s2geometry\build\temp.win-amd64-cpython-311\Release_SwigBindings\python && C:\Users\andy\AppData\Local\Temp\build-env-8i_fir_m\Lib\site-packages\cmake\data\bin\cmake.exe -E make_directory C:/Users/andy/src/s2geometry/build/temp.win-amd64-cpython-311/Release_SwigBindings/python/CMakeFiles/s2geometry.dir C:/Users/andy/src/s2geometry/build/temp.win-amd64-cpython-311/Release_SwigBindings/python C:/Users/andy/src/s2geometry/build/temp.win-amd64-cpython-311/Release_SwigBindings/python/CMakeFiles/s2geometry.dir && C:\Users\andy\AppData\Local\Temp\build-env-8i_fir_m\Lib\site-packages\cmake\data\bin\cmake.exe -E env SWIG_LIB=C:/ProgramData/chocolatey/lib/swig/tools/install/swigwin-4.1.1/Lib C:/ProgramData/chocolatey/bin/swig.exe -python -module s2geometry -outdir C:/Users/andy/src/s2geometry/build/temp.win-amd64-cpython-311/Release_SwigBindings/python -c++ -interface _s2geometry "-IC:/Program Files/OpenSSL-Win64/include" -IC:/Python311/include -IC:/Users/andy/src/s2geometry/src -o C:/Users/andy/src/s2geometry/build/temp.win-amd64-cpython-311/Release_SwigBindings/python/CMakeFiles/s2geometry.dir/s2PYTHON_wrap.cxx C:/Users/andy/src/s2geometry/src/python/s2.i"
C:\Users\andy\src\s2geometry\src\s2\util\coding\coder.h(54) : Warning 362: operator= ignored
C:\Users\andy\src\s2geometry\src\s2\s1angle.h(139) : Error: Syntax error in input(3).

Linux env

docker run -it --rm python:3.13 bash

apt-get update
apt-get install -y swig

python -m venv /venv
pip install cmake_build_extension wheel build -qq

git clone https://github.com/abseil/abseil-cpp.git /absl -b 20240722.0
cd /absl
cmake -B /absl/build \
      -DCMAKE_PREFIX_PATH=/usr/local \
      -DCMAKE_INSTALL_PREFIX=/usr/local \
      -DABSL_ENABLE_INSTALL=ON \
      -DCMAKE_POSITION_INDEPENDENT_CODE=ON \
      -DBUILD_TESTING=OFF \
      -DCMAKE_CXX_STANDARD=20 \
      -DABSL_BUILD_TESTING=OFF; \
cmake --build /absl/build --target install

git clone https://github.com/google/s2geometry /s2geometry
cd /s2geometry
python -m build --wheel . "-C--global-option=build_ext" "-C--global-option=-DBUILD_TESTS=OFF;CMAKE_CXX_STANDARD=20"

Windows env

choco install openssl swig

python -m venv %USERPROFILE%\venv
%USERPROFILE%\venv\Scripts\activate.bat
pip install build cmake_build_extension wheel build

git clone https://github.com/abseil/abseil-cpp.git %USERPROFILE%\src\absl -b 20240722.0
cd %USERPROFILE%\absl
cmake -B %USERPROFILE%\src\absl\build -DCMAKE_PREFIX_PATH=%USERPROFILE%\src\absl\install -DCMAKE_INSTALL_PREFIX=%USERPROFILE%\src\absl\install -DABSL_ENABLE_INSTALL=ON -DCMAKE_POSITION_INDEPENDENT_CODE=ON -DCMAKE_CXX_STANDARD=20 -DBUILD_TESTING=OFF -DABSL_BUILD_TESTING=OFF
cmake --build %USERPROFILE%\src\absl\build --config Release --target install

git clone https://github.com/google/s2geometry %USERPROFILE%\src\s2geometry
cd %USERPROFILE%\src\s2geometry
python -m build --wheel . "-C--global-option=build_ext" "-C--global-option=-DBUILD_TESTS=OFF;CMAKE_CXX_STANDARD=20;CMAKE_PREFIX_PATH=%USERPROFILE%\src\absl\install"

---

Same errors when using C++17

Using C++14 errored with:

/s2geometry/src/s2/util/math/vector.h:103:8: warning: ‘if constexpr’ only available with ‘-std=c++17’ or ‘-std=gnu++17’ [-Wc++17-extensions]
  103 |     if constexpr (I >= 0 && I < SIZE) return AsD().Data()[I];

So either my gcc is picky, or the README is out of date when it says says "A C++ compiler with C++14 support"

[jmr]

This seems to have broken some where between commits 7940c9f (works) and 755fe37 (gets the error)

s2geometry/src/s2/s1angle.h:139 is

s2geometry/src/s2/s1angle.h

Line 139 in 778502a

friend constexpr bool operator==(S1Angle x, S1Angle y);

It's probably the "Remove some old SWIG workarounds" part of 755fe37. Older swig didn't understand constexpr.

Works for me with swig 4.2.1. Can you check the swig versions on the working/non-working systems?

[andyneff]

Versions I've tried:

• 4.0.2 - Works (quay.io/pypa/manylinux_2_28_x86_64)
• 4.1.0 - Fails (python:3.13)
• 4.1.1 - Fails (Windows 11 via choco)

[andyneff]

Just learned pypi has swig.

All failures are the same error.

• 4.0.2 on Windows 11 failed
• 4.2.1 on Windows 11 works
• 4.3.0 on Windows 11 works
• 4.0.2 on python:3.13 fails
• 4.2.1 on python:3.13 works
• 4.0.2 on quay.io/pypa/manylinux_2_28_x86_64 fails. My guess is the 4.0.2 I installed from the package manager must have had some patch that made things not fail.
• 4.2.1 on quay.io/pypa/manylinux_2_28_x86_64 works

[andyneff]

After #390, I could make an edit to the README either saying we need swig 4.2, or remove mentioning SWIG completely, because python -m build will automatically download swig via pip.

[jmr]

Swig 4.2 is only ~1 year old, a bit too new to depend on based on the versions you're seeing. I'll add the constexpr workarounds back.

[jmr]

or remove mentioning SWIG completely, because python -m build will automatically download swig via pip.

What controls the version of swig that will be downloaded?

[b4rdos]

I think the requires section of the [build-system] should help to define the version to use.

[andyneff]

Right. With no version specified, it will download the latest available from pypi with is currently 4.3.0. (With the option of adding a constraint in the future. E.g. 4.4.0 breaks compatibility, so you can say swig<4.4)

[jmr]

That sounds easier. Let's wait until python -m build is working, then update the instructions.