rust: add bindgen step as a meson dependency

Add bindings_rs target for generating rust bindings to target-independent
qemu C APIs.

The bindings need be created before any rust crate that uses them is
compiled.

The bindings.rs file will end up in BUILDDIR/bindings.rs and have the
same name as a target:

  ninja bindings.rs

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Link: https://lore.kernel.org/r/1be89a27719049b7203eaf2eca8bbb75b33f18d4.1727961605.git.manos.pitsidianakis@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

scripts/rust/rustc_args.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+
+"""Generate rustc arguments for meson rust builds.
+
+This program generates --cfg compile flags for the configuration headers passed
+as arguments.
+
+Copyright (c) 2024 Linaro Ltd.
+
+Authors:
+ Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""
+
+import argparse
+import logging
+
+from typing import List
+
+
+def generate_cfg_flags(header: str) -> List[str]:
+    """Converts defines from config[..].h headers to rustc --cfg flags."""
+
+    def cfg_name(name: str) -> str:
+        """Filter function for C #defines"""
+        if (
+            name.startswith("CONFIG_")
+            or name.startswith("TARGET_")
+            or name.startswith("HAVE_")
+        ):
+            return name
+        return ""
+
+    with open(header, encoding="utf-8") as cfg:
+        config = [l.split()[1:] for l in cfg if l.startswith("#define")]
+
+    cfg_list = []
+    for cfg in config:
+        name = cfg_name(cfg[0])
+        if not name:
+            continue
+        if len(cfg) >= 2 and cfg[1] != "1":
+            continue
+        cfg_list.append("--cfg")
+        cfg_list.append(name)
+    return cfg_list
+
+
+def main() -> None:
+    # pylint: disable=missing-function-docstring
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-v", "--verbose", action="store_true")
+    parser.add_argument(
+        "--config-headers",
+        metavar="CONFIG_HEADER",
+        action="append",
+        dest="config_headers",
+        help="paths to any configuration C headers (*.h files), if any",
+        required=False,
+        default=[],
+    )
+    args = parser.parse_args()
+    if args.verbose:
+        logging.basicConfig(level=logging.DEBUG)
+    logging.debug("args: %s", args)
+    for header in args.config_headers:
+        for tok in generate_cfg_flags(header):
+            print(tok)
+
+
+if __name__ == "__main__":
+    main()