Add a Valgrind build on debug Python 3.9 (#2746)

* Adding a valgrind build on debug Python 3.9

Co-authored-by: Boris Staletic <boris.staletic@gmail.com>

* Add Valgrind suppression files

- Introduce suppression file, populate it with a first suppression taken from CPython, and fix one leak in the tests
- Suppress leak in NumPy
- More clean tests!
- Tests with names a-e passing (except for test_buffer)
- Suppress multiprocessing errors
- Merge multiprocessing suppressions into other suppression files
- Numpy seems to be spelled with a big P
- Append single entry from valgrind-misc.supp to valgrind-python.supp, and make clear valgrind-python.supp is only CPython

Co-authored-by: Boris Staletic <boris.staletic@gmail.com>

* Enable test_virtual_functions with a workaround

* Add a memcheck cmake target

- Add a memcheck cmake target
- Reformat cmake
- Appease the formatting overlords - they are angry
- Format CMake valgrind target decently

* Update CI config to new action versions

* fix: separate memcheck from pytest

* ci: cleanup

* Merge Valgrind and other deadsnakes builds

Co-authored-by: Boris Staletic <boris.staletic@gmail.com>
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>

tests/CMakeLists.txt

@@ -370,12 +370,17 @@ endif()
 string(REPLACE "test_" "${CMAKE_CURRENT_SOURCE_DIR}/test_" PYBIND11_ABS_PYTEST_FILES
                "${PYBIND11_PYTEST_FILES}")
 
+set(PYBIND11_TEST_PREFIX_COMMAND
+    ""
+    CACHE STRING "Put this before pytest, use for checkers and such")
+
 # A single command to compile and run the tests
 add_custom_target(
   pytest
-  COMMAND ${PYTHON_EXECUTABLE} -m pytest ${PYBIND11_ABS_PYTEST_FILES}
+  COMMAND ${PYBIND11_TEST_PREFIX_COMMAND} ${PYTHON_EXECUTABLE} -m pytest
+          ${PYBIND11_ABS_PYTEST_FILES}
   DEPENDS ${test_targets}
-  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+  WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
   USES_TERMINAL)
 
 if(PYBIND11_TEST_OVERRIDE)
@@ -386,6 +391,27 @@ if(PYBIND11_TEST_OVERRIDE)
             "Note: not all tests run: -DPYBIND11_TEST_OVERRIDE is in effect")
 endif()
 
+# cmake-format: off
+add_custom_target(
+  memcheck
+  COMMAND
+    PYTHONMALLOC=malloc
+    valgrind
+    --leak-check=full
+    --show-leak-kinds=definite,indirect
+    --errors-for-leak-kinds=definite,indirect
+    --error-exitcode=1
+    --read-var-info=yes
+    --track-origins=yes
+    --suppressions="${CMAKE_CURRENT_SOURCE_DIR}/valgrind-python.supp"
+    --suppressions="${CMAKE_CURRENT_SOURCE_DIR}/valgrind-numpy-scipy.supp"
+    --gen-suppressions=all
+    ${PYTHON_EXECUTABLE} -m pytest ${PYBIND11_ABS_PYTEST_FILES}
+  DEPENDS ${test_targets}
+  WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
+  USES_TERMINAL)
+# cmake-format: on
+
 # Add a check target to run all the tests, starting with pytest (we add dependencies to this below)
 add_custom_target(check DEPENDS pytest)