BLD: enable building NumPy with Meson

This enables building with NumPy on Linux and macOS. Windows support
should be complete to, but is untested as of now and may need a few
tweaks. This contains:
- A set of `meson.build` files and related code generation script
  tweaks, header templates, etc.
- One CI job on Linux
- Basic docs on using Meson to build NumPy (not yet integrated in the
  html docs, it's too early for that - this is for early adopters right
  now).

The build should be complete, with the major exception of SIMD support.
The full test suite passes. See gh-22546 for the tracking issue with
detailed notes on the plan for switching NumPy to Meson as its build
system.

Co-authored-by: Stefan van der Walt <stefanv@berkeley.edu>

1 files changed, 62 insertions, 0 deletions

diff --git a/numpy/_build_utils/tempita.py b/numpy/_build_utils/tempita.py
new file mode 100755
index 000000000..3bcc789c5
--- /dev/null
+++ b/numpy/_build_utils/tempita.py
@@ -0,0 +1,62 @@
+#!/usr/bin/env python3
+import sys
+import os
+import argparse
+
+from Cython import Tempita as tempita
+
+# XXX: If this import ever fails (does it really?), vendor either
+# cython.tempita or numpy/npy_tempita.
+
+
+def process_tempita(fromfile, outfile=None):
+    """Process tempita templated file and write out the result.
+
+    The template file is expected to end in `.c.in` or `.pyx.in`:
+    E.g. processing `template.c.in` generates `template.c`.
+
+    """
+    if outfile is None:
+        # We're dealing with a distutils build here, write in-place
+        outfile = os.path.splitext(fromfile)[0]
+
+    from_filename = tempita.Template.from_filename
+    template = from_filename(fromfile, encoding=sys.getdefaultencoding())
+
+    content = template.substitute()
+
+    with open(outfile, 'w') as f:
+        f.write(content)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "infile",
+        type=str,
+        help="Path to the input file"
+    )
+    parser.add_argument(
+        "-o",
+        "--outfile",
+        type=str,
+        help="Path to the output file"
+    )
+    parser.add_argument(
+        "-i",
+        "--ignore",
+        type=str,
+        help="An ignored input - may be useful to add a "
+        "dependency between custom targets",
+    )
+    args = parser.parse_args()
+
+    if not args.infile.endswith('.in'):
+        raise ValueError(f"Unexpected extension: {args.infile}")
+
+    outfile_abs = os.path.join(os.getcwd(), args.outfile)
+    process_tempita(args.infile, outfile_abs)
+
+
+if __name__ == "__main__":
+    main()