First draft of Eigen::Tensor support (#4201)

* First draft of Eigen::Tensor support

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* Fix build errors

* Weird allocator stuff?

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* Remove unused + additional allocator junk

* Disable warning

* Use constexpr

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* clang tidy fixes

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* Resolve comments

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* Remove auto constexpr function

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* Try again for older C++

* Oops forgot constexpr

* Move to new files as suggested

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* Fix weird tests

* Fix nits

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* Oops, forgot import

* Fix clang 3.6 bug

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* More comprehensive test suite

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* Refactor allocators to make things more clear

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* Switch to std::copy

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* Switch to DSizes instead of array

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* Address feedback

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* Fix python + dummy c++ change to trigger build

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* Alignment

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* Add include guard

* Forgot inline

* Fix compiler warning

* Remove bad test

* Better type signatures

* Add guards to make compiler requirements more explicit

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* Force rerun of tests due to flake

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* Keep pragmas & all related comments together, add PLEASE KEEP IN SYNC

* Move headers out of detail

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* Fix cmake

* Improve casting

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* Add a ton more tests + refactor

* Improve names

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* Update include/pybind11/eigen/tensor.h

Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>

* Fix tests

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* Update

* Add a test to verify that strange numpy arrays work

* Fix dumb compiler warning

* Better tests

* Better tests

* Fix tests

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* More test fixes

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* A ton more test coverage

* Fix tests

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* Add back constexpr

* Another test

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* Improve tests

* Whoops

* Less magic numbers

* Update tests/test_eigen_tensor.py

Co-authored-by: Sergiu Deitsch <sergiud@users.noreply.github.com>

* Update tests/test_eigen_tensor.py

Co-authored-by: Sergiu Deitsch <sergiud@users.noreply.github.com>

* style: pre-commit fixes

* Fix tests

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* Fix memory leak

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* Fix order

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* Add test to make sure unsafe casts fail

* Minor bug fix to work on 32 bit machines

* Implement convert flag

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* Switch to correct TensorMap const use

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* Support older versions of eigen

* Weird c++ compilers

* Fix Eigen bug

* Fix another eigen bug

* Yet another eigen bug

* Potential flakes?

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* Rerun tests with dummy exception to find out what is going on

* Another dummy test run

* Ablate more

* Found the broken test?

* One step closer

* one step further

* Double check

* one thing at a time

* Give up and disable the test

* Clang lies about being gcc

* Oops, fix matrix test

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* Add tests to verify scalar conversions

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* Fix nits

* Support no_array

* Fix tests

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* Silence compiler warning

* Improve build system for ancient compilers

* Make clang happy

* Make gcc happy

* Implement Skylion's suggestions

* Fix warning

* Inline const pointer check

* Implement suggestions

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* Improve tests

* Typo

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* Support Google's build environment

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* Update include/pybind11/eigen/tensor.h

Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>

* style: pre-commit fixes

* Test cleanup per Skylion

* Switch to remvove_cv_t

* Cleaner test

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* Remove tensor from eigen.h, update tests

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>
Co-authored-by: Aaron Gokaslan <aaronGokaslan@gmail.com>
Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>
Co-authored-by: Sergiu Deitsch <sergiud@users.noreply.github.com>

Author: 5 people

.gitignore

@@ -43,3 +43,4 @@ pybind11Targets.cmake
 /pybind11/share/*
 /docs/_build/*
 .ipynb_checkpoints/
+tests/main.cpp

CMakeLists.txt

@@ -120,6 +120,8 @@ set(PYBIND11_HEADERS
     include/pybind11/complex.h
     include/pybind11/options.h
     include/pybind11/eigen.h
+    include/pybind11/eigen/matrix.h
+    include/pybind11/eigen/tensor.h
     include/pybind11/embed.h
     include/pybind11/eval.h
     include/pybind11/gil.h