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

girepository/introspection/meson.build

@@ -14,6 +14,30 @@ if 'address' in glib_sanitizers
     'ASAN_OPTIONS', 'verify_asan_link_order=0', separator: ',')
 endif
 
+if host_system == 'windows'
+  # Use gio-2.0-uninstalled.pc to find the paths where the GLib DLLs (and their dependent non-system
+  # DLLs that are built as subprojects) are located
+  check_built_dll_paths_cmd = [get_dll_paths_script, '--build-path=@0@'.format(meson.project_build_root())]
+  meson_pkgconfig_paths = get_option('pkg_config_path')
+  if meson_pkgconfig_paths.length() > 0
+    check_built_dll_paths_cmd += '--pkg-config-path=@0@'.format(''.join(meson_pkgconfig_paths))
+  endif
+  check_built_dll_paths = run_command(
+    check_built_dll_paths_cmd,
+	capture: true,
+    check: true,
+  )
+  # hmm, no os.pathsep in Meson to make this more portable, if needed?
+  gi_scanner_dll_paths = check_built_dll_paths.stdout().strip().split(';')
+
+  # Also assume the existing paths in %PATH% to be considered for DLLs
+  message('Ensure that all of GLib\'s dependent non-system DLLs that are not built')
+  message('alongside with GLib can be found in paths in %PATH%')
+  message('Check this if building .gir files fail due to \'ImportError: DLL load failed while importing _giscanner\'')
+
+  gi_gen_env_variables.set('GI_EXTRA_BASE_DLL_DIRS', gi_scanner_dll_paths)
+endif
+
 # GLib
 glib_gir_sources = [
   gi_gen_shared_sources,
@@ -314,6 +338,12 @@ libgirepository_gir_args = [
   '--identifier-prefix=GI',
 ]
 
+gi_libgirepository_gen_env_variables = environment()
+
+if host_system == 'windows'
+  gi_libgirepository_gen_env_variables.set('GI_EXTRA_BASE_DLL_DIRS', gi_scanner_dll_paths)
+endif
+
 girepository_gir = gnome.generate_gir(libgirepository,
   sources: libgirepository_gir_sources,
   namespace: 'GIRepository',
@@ -327,5 +357,6 @@ girepository_gir = gnome.generate_gir(libgirepository,
   install_dir_gir: glib_girdir,
   dependencies: [ libglib_dep, libgobject_dep, libgmodule_dep, libgio_dep ],
   extra_args: gir_args + libgirepository_gir_args,
+  env: gi_libgirepository_gen_env_variables,
 )
 

meson.build

@@ -236,8 +236,16 @@ if host_system == 'qnx'
   add_project_arguments('-D_QNX_SOURCE', language: 'c')
 endif
 
+# dummy/empty dependency() object to declare fallbacks and simpler dependencies
+not_found = dependency('', required: false)
+
+get_dll_paths_script = not_found
+
 if host_system == 'windows'
   add_project_arguments(['-DUNICODE', '-D_UNICODE'], language: 'c')
+
+  # Script to obtain paths where the DLLs that we will reside for g-ir-scanner
+  get_dll_paths_script = find_program('tools/grab-gio-dll-paths.py', native: true)
 endif
 
 # Disable strict aliasing;
@@ -246,9 +254,6 @@ if cc.has_argument('-fno-strict-aliasing')
   add_project_arguments('-fno-strict-aliasing', language: 'c')
 endif
 
-# dummy/empty dependency() object to declare fallbacks and simpler dependencies
-not_found = dependency('', required: false)
-
 ########################
 # Configuration begins #
 ########################

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()