Introspection: Fix running g-ir-scanner 1.80.x+ on Windows

Since we are now building introspection files for GLib while building
GLib, so we want to make sure that we indeed load the freshly-built
DLLs when running g-ir-scanner, so we add the various needed subdirs
(and if needed, subprojects), to set the GI_EXTRA_BASE_DLL_DIRS
envvar so that g-ir-scanner will look for the newly-built GLib DLLs.

Ideally, upstream g-ir-scanner will need to be updated accordingly to do
something similar to what we are doing here, but this is needed until
the time that we require a g-ir-scanner that contains the update.

This will also fix the g-ir-scanner erroring out when there is no
pre-existing GLib on the system, as the needed DLLs are now found.

Related issue: https://gitlab.gnome.org/GNOME/gobject-introspection/-/issues/499
Related MR in G-I:
https://gitlab.gnome.org/GNOME/gobject-introspection/-/merge_requests/458

tools/grab-gio-dll-paths.py

@@ -0,0 +1,68 @@
+#!/usr/bin/env python3
+#
+# Copyright © 2024 Chun-wei Fan.
+#
+# SPDX-License-Identifier: LGPL-2.1-or-later
+#
+# Original author: Chun-wei Fan <fanc999@yahoo.com.tw>
+
+"""
+This script runs pkg-config against the uninstalled pkg-config files to obtain the
+paths where the newly-built GLib and subproject DLLs reside
+"""
+
+import argparse
+import os
+import subprocess
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--build-path", required=True, help="Root build directory")
+    parser.add_argument(
+        "--pkg-config", help="pkg-config or compatible executable", default="pkg-config"
+    )
+    parser.add_argument(
+        "--pkg-config-path",
+        help="Additional paths to look for pkg-config .pc files",
+    )
+    args = parser.parse_args()
+    build_path = args.build_path
+    uninstalled_pc_path = os.path.join(build_path, "meson-uninstalled")
+    if not os.path.isdir(uninstalled_pc_path):
+        raise ValueError("%s is not a valid build path" % build_path)
+
+    additional_pkg_config_paths = [uninstalled_pc_path]
+    if args.pkg_config_path is not None:
+        additional_pkg_config_paths += args.pkg_config_path.split(os.pathsep)
+
+    if "PKG_CONFIG_PATH" in os.environ:
+        additional_pkg_config_paths += os.environ["PKG_CONFIG_PATH"].split(os.pathsep)
+
+    os.environ["PKG_CONFIG_PATH"] = os.pathsep.join(additional_pkg_config_paths)
+
+    # The _giscanner Python module depends on GIO, so use gio-2.0-uninstalled.pc
+    pkg_config_result = subprocess.run(
+        [args.pkg_config, "--libs-only-L", "gio-2.0"],
+        capture_output=True,
+        text=True,
+        check=True,
+    )
+    lib_args = pkg_config_result.stdout.split()
+    libpaths = []
+    for arg in lib_args:
+        # Get rid of the "-L" prefix in the library paths
+        if arg[2:] not in libpaths:
+            libpaths.append(arg[2:])
+
+    # Now append the paths in %PATH%, if the paths exist
+    paths = os.environ["PATH"].split(os.pathsep)
+    for path in paths:
+        if os.path.isdir(path):
+            libpaths.append(path)
+
+    print(os.pathsep.join(libpaths).rstrip())
+
+
+if __name__ == "__main__":
+    main()