BLD: Meson `__config__` generation (#22769)

Add functionality to autogenerate build information for a Meson-based build.

In order to add new information, do the following:
- Add the information as an argument in `numpy/meson.build`
- Modify `__config__.py.in` to accept the new argument

Note that SIMD information is added to config, but is WIP/empty,
because  `__cpu*` lists are not yet populated as meson does not build
SIMD features yet.

There are two display modes:

    - `stdout`: Uses `PyYaml` to display in a human friendly
       format. Uses `json` if `PyYaml` is not installed
    - `dicts`: Returns a `dict` object

Things will work fine without `pyyaml` installed, an unobtrusive
warning is displayed that the printed output will look better
with `pyyaml`.

[ci skip]

1 files changed, 44 insertions, 0 deletions

diff --git a/numpy/tests/test_numpy_config.py b/numpy/tests/test_numpy_config.py
new file mode 100644
index 000000000..82c1ad70b
--- /dev/null
+++ b/numpy/tests/test_numpy_config.py
@@ -0,0 +1,44 @@
+"""
+Check the numpy config is valid.
+"""
+import numpy as np
+import pytest
+from unittest.mock import Mock, patch
+
+pytestmark = pytest.mark.skipif(
+    not hasattr(np.__config__, "_built_with_meson"),
+    reason="Requires Meson builds",
+)
+
+
+class TestNumPyConfigs:
+    REQUIRED_CONFIG_KEYS = [
+        "Compilers",
+        "Machine Information",
+        "Python Information",
+    ]
+
+    @patch("numpy.__config__._check_pyyaml")
+    def test_pyyaml_not_found(self, mock_yaml_importer):
+        mock_yaml_importer.side_effect = ModuleNotFoundError()
+        with pytest.warns(UserWarning):
+            np.show_config()
+
+    def test_dict_mode(self):
+        config = np.show_config(mode="dicts")
+
+        assert isinstance(config, dict)
+        assert all([key in config for key in self.REQUIRED_CONFIG_KEYS]), (
+            "Required key missing,"
+            " see index of `False` with `REQUIRED_CONFIG_KEYS`"
+        )
+
+    def test_invalid_mode(self):
+        with pytest.raises(AttributeError):
+            np.show_config(mode="foo")
+
+    def test_warn_to_add_tests(self):
+        assert len(np.__config__.DisplayModes) == 2, (
+            "New mode detected,"
+            " please add UT if applicable and increment this count"
+        )