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]

4 files changed, 256 insertions, 129 deletions

diff --git a/doc/release/upcoming_changes/22769.improvement.rst b/doc/release/upcoming_changes/22769.improvement.rst
new file mode 100644
index 000000000..3566648ac
--- /dev/null
+++ b/doc/release/upcoming_changes/22769.improvement.rst
@@ -0,0 +1,5 @@
+`np.show_config` uses information from Meson
+--------------------------------------------
+Build and system information now contains information from Meson.
+`np.show_config` now has a new optional parameter ``mode`` to help
+customize the output.
diff --git a/numpy/__config__.py.in b/numpy/__config__.py.in
index cda615904..659a09b26 100644
--- a/numpy/__config__.py.in
+++ b/numpy/__config__.py.in
@@ -1,52 +1,136 @@
 # This file is generated by numpy's build process
 # It contains system_info results at the time of building this package.
-__all__ = ["get_info", "show"]
-
-import os
-import sys
-
-extra_dll_dir = os.path.join(os.path.dirname(__file__), '.libs')
-
-if sys.platform == 'win32' and os.path.isdir(extra_dll_dir):
-    os.add_dll_directory(extra_dll_dir)
-
-blas_armpl_info={}
-blas_mkl_info={}
-blis_info={}
-openblas_info={}
-accelerate_info={}
-atlas_3_10_blas_threads_info={}
-atlas_3_10_blas_info={}
-atlas_blas_threads_info={}
-atlas_blas_info={}
-blas_info={}
-blas_src_info={}
-blas_opt_info={}
-lapack_armpl_info={}
-lapack_mkl_info={}
-openblas_lapack_info={}
-openblas_clapack_info={}
-flame_info={}
-atlas_3_10_threads_info={}
-atlas_3_10_info={}
-atlas_threads_info={}
-atlas_info={}
-lapack_info={}
-lapack_src_info={}
-lapack_opt_info={}
-numpy_linalg_lapack_lite={}
-
-def get_info(name):
-    g = globals()
-    return g.get(name, g.get(name + "_info", {}))
-
-def show():
+from enum import Enum
+from numpy.core._multiarray_umath import (
+    __cpu_features__,
+    __cpu_baseline__,
+    __cpu_dispatch__,
+)
+
+__all__ = ["show"]
+_built_with_meson = True
+
+
+class DisplayModes(Enum):
+    stdout = "stdout"
+    dicts = "dicts"
+
+
+def _cleanup(d):
     """
-    Show libraries in the system on which NumPy was built.
+    Removes empty values in a `dict` recursively
+    This ensures we remove values that Meson could not provide to CONFIG
+    """
+    if type(d) is dict:
+        return dict(
+            (k, _cleanup(v)) for k, v in d.items() if v and _cleanup(v)
+        )
+    else:
+        return d
+
+
+CONFIG = _cleanup(
+    {
+        "Compilers": {
+            "c": {
+                "name": "@C_COMP@",
+                "linker": "@C_COMP_LINKER_ID@",
+                "version": "@C_COMP_VERSION@",
+                "commands": "@C_COMP_CMD_ARRAY@",
+            },
+            "cython": {
+                "name": "@CYTHON_COMP@",
+                "linker": "@CYTHON_COMP_LINKER_ID@",
+                "version": "@CYTHON_COMP_VERSION@",
+                "commands": "@CYTHON_COMP_CMD_ARRAY@",
+            },
+            "c++": {
+                "name": "@CPP_COMP@",
+                "linker": "@CPP_COMP_LINKER_ID@",
+                "version": "@CPP_COMP_VERSION@",
+                "commands": "@CPP_COMP_CMD_ARRAY@",
+            },
+        },
+        "Machine Information": {
+            "host": {
+                "cpu": "@HOST_CPU@",
+                "family": "@HOST_CPU_FAMILY@",
+                "endian": "@HOST_CPU_ENDIAN@",
+                "system": "@HOST_CPU_SYSTEM@",
+            },
+            "build": {
+                "cpu": "@BUILD_CPU@",
+                "family": "@BUILD_CPU_FAMILY@",
+                "endian": "@BUILD_CPU_ENDIAN@",
+                "system": "@BUILD_CPU_SYSTEM@",
+            },
+            "cross-compiled": "@CROSS_COMPILED@",
+        },
+        "Build Dependencies": {
+            "blas": {
+                "name": "@BLAS_NAME@",
+                "found": "@BLAS_FOUND@",
+                "version": "@BLAS_VERSION@",
+                "detection method": "@BLAS_TYPE_NAME@",
+                "include directory": "@BLAS_INCLUDEDIR@",
+                "lib directory": "@BLAS_LIBDIR@",
+                "openblas configuration": "@BLAS_OPENBLAS_CONFIG@",
+                "pc file directory": "@BLAS_PCFILEDIR@",
+            },
+            "lapack": {
+                "name": "@LAPACK_NAME@",
+                "found": "@LAPACK_FOUND@",
+                "version": "@LAPACK_VERSION@",
+                "detection method": "@LAPACK_TYPE_NAME@",
+                "include directory": "@LAPACK_INCLUDEDIR@",
+                "lib directory": "@LAPACK_LIBDIR@",
+                "openblas configuration": "@LAPACK_OPENBLAS_CONFIG@",
+                "pc file directory": "@LAPACK_PCFILEDIR@",
+            },
+        },
+        "Python Information": {
+            "path": "@PYTHON_PATH@",
+            "version": "@PYTHON_VERSION@",
+        },
+        "SIMD Extensions": {
+            "baseline": __cpu_baseline__,
+            "found": [
+                feature
+                for feature in __cpu_dispatch__
+                if __cpu_features__[feature]
+            ],
+            "not found": [
+                feature
+                for feature in __cpu_dispatch__
+                if not __cpu_features__[feature]
+            ],
+        },
+    }
+)
+
+
+def _check_pyyaml():
+    import yaml
+
+    return yaml
+
+
+def show(mode=DisplayModes.stdout.value):
+    """
+    Show libraries and system information on which NumPy was built
+    and is being used
+
+    Parameters
+    ----------
+    mode : {`'stdout'`, `'dicts'`}, optional.
+        Indicates how to display the config information.
+        `'stdout'` prints to console, `'dicts'` returns a dictionary
+        of the configuration.
 
-    Print information about various resources (libraries, library
-    directories, include directories, etc.) in the system on which
-    NumPy was built.
+    Returns
+    -------
+    out : {`dict`, `None`}
+        If mode is `'dicts'`, a dict is returned, else None
 
     See Also
     --------
@@ -55,80 +139,24 @@ def show():
 
     Notes
     -----
-    1. Classes specifying the information to be printed are defined
-       in the `numpy.distutils.system_info` module.
-
-       Information may include:
-
-       * ``language``: language used to write the libraries (mostly
-         C or f77)
-       * ``libraries``: names of libraries found in the system
-       * ``library_dirs``: directories containing the libraries
-       * ``include_dirs``: directories containing library header files
-       * ``src_dirs``: directories containing library source files
-       * ``define_macros``: preprocessor macros used by
-         ``distutils.setup``
-       * ``baseline``: minimum CPU features required
-       * ``found``: dispatched features supported in the system
-       * ``not found``: dispatched features that are not supported
-         in the system
-
-    2. NumPy BLAS/LAPACK Installation Notes
-
-       Installing a numpy wheel (``pip install numpy`` or force it
-       via ``pip install numpy --only-binary :numpy: numpy``) includes
-       an OpenBLAS implementation of the BLAS and LAPACK linear algebra
-       APIs. In this case, ``library_dirs`` reports the original build
-       time configuration as compiled with gcc/gfortran; at run time
-       the OpenBLAS library is in
-       ``site-packages/numpy.libs/`` (linux), or
-       ``site-packages/numpy/.dylibs/`` (macOS), or
-       ``site-packages/numpy/.libs/`` (windows).
-
-       Installing numpy from source
-       (``pip install numpy --no-binary numpy``) searches for BLAS and
-       LAPACK dynamic link libraries at build time as influenced by
-       environment variables NPY_BLAS_LIBS, NPY_CBLAS_LIBS, and
-       NPY_LAPACK_LIBS; or NPY_BLAS_ORDER and NPY_LAPACK_ORDER;
-       or the optional file ``~/.numpy-site.cfg``.
-       NumPy remembers those locations and expects to load the same
-       libraries at run-time.
-       In NumPy 1.21+ on macOS, 'accelerate' (Apple's Accelerate BLAS
-       library) is in the default build-time search order after
-       'openblas'.
-
-    Examples
-    --------
-    >>> import numpy as np
-    >>> np.show_config()
-    blas_opt_info:
-        language = c
-        define_macros = [('HAVE_CBLAS', None)]
-        libraries = ['openblas', 'openblas']
-        library_dirs = ['/usr/local/lib']
+    1. The `'stdout'` mode will give more readable
+       output if ``pyyaml`` is installed
+
     """
-    from numpy.core._multiarray_umath import (
-        __cpu_features__, __cpu_baseline__, __cpu_dispatch__
-    )
-    for name,info_dict in globals().items():
-        if name[0] == "_" or type(info_dict) is not type({}): continue
-        print(name + ":")
-        if not info_dict:
-            print("  NOT AVAILABLE")
-        for k,v in info_dict.items():
-            v = str(v)
-            if k == "sources" and len(v) > 200:
-                v = v[:60] + " ...\n... " + v[-60:]
-            print("    %s = %s" % (k,v))
-
-    features_found, features_not_found = [], []
-    for feature in __cpu_dispatch__:
-        if __cpu_features__[feature]:
-            features_found.append(feature)
-        else:
-            features_not_found.append(feature)
-
-    print("Supported SIMD extensions in this NumPy install:")
-    print("    baseline = %s" % (','.join(__cpu_baseline__)))
-    print("    found = %s" % (','.join(features_found)))
-    print("    not found = %s" % (','.join(features_not_found)))
+    if mode == DisplayModes.stdout.value:
+        try:  # Non-standard library, check import
+            yaml = _check_pyyaml()
+
+            print(yaml.dump(CONFIG))
+        except ModuleNotFoundError:
+            import warnings
+            import json
+
+            warnings.warn("Install `pyyaml` for better output", stacklevel=1)
+            print(json.dumps(CONFIG, indent=2))
+    elif mode == DisplayModes.dicts.value:
+        return CONFIG
+    else:
+        raise AttributeError(
+            f"Invalid `mode`, use one of: {', '.join([e.value for e in DisplayModes])}"
+        )
diff --git a/numpy/meson.build b/numpy/meson.build
index 23bd83a04..ec131ebb5 100644
--- a/numpy/meson.build
+++ b/numpy/meson.build
@@ -66,15 +66,17 @@ endif
 blas = dependency(blas_name, required: false)
 lapack = dependency(lapack_name, required: false)
 
+dependency_map = {
+  'BLAS': blas,
+  'LAPACK': lapack,
+}
+
 # BLAS and LAPACK are optional dependencies for NumPy. We can only use a BLAS
 # which provides a CBLAS interface.
 # TODO: add ILP64 support
 have_blas = blas.found() # TODO: and blas.has_cblas()
 have_lapack = lapack.found()
 
-
-# TODO: generate __config__.py (see scipy/meson.build)
-
 # Copy the main __init__.py|pxd files to the build dir (needed for Cython)
 __init__py = fs.copyfile('__init__.py')
 __init__pxd = fs.copyfile('__init__.pxd')
@@ -143,12 +145,60 @@ foreach subdir: pure_subdirs
   install_subdir(subdir, install_dir: np_dir)
 endforeach
 
-custom_target('__config__.py',
-  output: '__config__.py',
+compilers = {
+  'C': cc,
+  'CPP': cpp,
+  'CYTHON': meson.get_compiler('cython')
+}
+
+machines = {
+  'HOST': host_machine,
+  'BUILD': build_machine,
+}
+
+conf_data = configuration_data()
+
+# Set compiler information
+foreach name, compiler : compilers
+  conf_data.set(name + '_COMP', compiler.get_id())
+  conf_data.set(name + '_COMP_LINKER_ID', compiler.get_linker_id())
+  conf_data.set(name + '_COMP_VERSION', compiler.version())
+  conf_data.set(name + '_COMP_CMD_ARRAY', compiler.cmd_array())
+endforeach
+
+# Machines CPU and system information
+foreach name, machine : machines
+  conf_data.set(name + '_CPU', machine.cpu())
+  conf_data.set(name + '_CPU_FAMILY', machine.cpu_family())
+  conf_data.set(name + '_CPU_ENDIAN', machine.endian())
+  conf_data.set(name + '_CPU_SYSTEM', machine.system())
+endforeach
+
+conf_data.set('CROSS_COMPILED', meson.is_cross_build())
+
+# Python information
+conf_data.set('PYTHON_PATH', py.full_path())
+conf_data.set('PYTHON_VERSION', py.language_version())
+
+# Dependencies information
+foreach name, dep : dependency_map
+  conf_data.set(name + '_NAME', dep.name())
+  conf_data.set(name + '_FOUND', dep.found())
+  if dep.found()
+    conf_data.set(name + '_VERSION', dep.version())
+    conf_data.set(name + '_TYPE_NAME', dep.type_name())
+    conf_data.set(name + '_INCLUDEDIR', dep.get_variable('includedir'))
+    conf_data.set(name + '_LIBDIR', dep.get_variable('libdir'))
+    conf_data.set(name + '_OPENBLAS_CONFIG', dep.get_variable('openblas_config'))
+    conf_data.set(name + '_PCFILEDIR', dep.get_variable('pcfiledir'))
+  endif
+endforeach
+
+configure_file(
   input: '__config__.py.in',
-  command: [tempita_cli, '@INPUT@', '-o', '@OUTPUT@'],
-  install: true,
-  install_dir: np_dir
+  output: '__config__.py',
+  configuration : conf_data,
+  install_dir: np_dir,
 )
 
 subdir('core')
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"
+        )