gdbus-codegen: Add an extension system which allows hooking codegen

The extension points are chosen by what libdex needs to generate future
based method calls.

docs/reference/gio/gdbus-codegen.rst

@@ -47,6 +47,7 @@ SYNOPSIS
 |    [--annotate *ELEMENT* *KEY* *VALUE*]…
 |    [--glib-min-required *VERSION*]
 |    [--glib-max-allowed *VERSION*]
+|    [--extension-path *EXTENSION_PATH*]
 |    *FILE*…
 
 DESCRIPTION
@@ -392,6 +393,20 @@ The following options are supported:
   greater than or equal to that passed to ``--glib-min-required``.
   It defaults to the version of GLib which provides this ``gdbus-codegen``.
 
+``--extension-path`` *EXTENSION_PATH*
+
+  Used to load an extension to the codegen. The *EXTENSION_PATH* is a path to
+  a Python file that will be loaded as a module. The extension needs to define
+  at least the function ``def init(args, options)`` where ``args`` is a
+  ``argparse.Namespace`` and ``options`` is a dict containing the key
+  ``version``.
+
+  All other API the extension can use are internal and thus unstable, but effort
+  is made to increase the ``version`` field when those internals change. If you
+  want to use this mechanism, please get in touch by
+  `filing an issue <https://gitlab.gnome.org/GNOME/glib/-/issues>`_. with your
+  use case.
+
 SUPPORTED D-BUS ANNOTATIONS
 ---------------------------
 

gio/gdbus-2.0/codegen/codegen.py

@@ -41,6 +41,54 @@ LICENSE_STR = """/*
 # flake8: noqa: E501
 
 
+def extensionpoint(func):
+    def wrapper(self, *args, **kwargs):
+        # ensures same signature
+        func(*args, **kwargs)
+        if not self._ext:
+            return
+        method = getattr(self._ext, func.__name__, None)
+        if not method:
+            return
+        method(*args, **kwargs)
+
+    return wrapper
+
+
+class ExtensionGenerator:
+    def __init__(self, ext, generator):
+        if self.extending != generator.__class__.__name__:
+            raise Exception("Trying to extend wrong class")
+        self._ext = None
+        klass = getattr(ext, self.extending, None)
+        if klass:
+            self._ext = klass(generator)
+
+
+class ExtensionHeaderCodeGenerator(ExtensionGenerator):
+    extending = "HeaderCodeGenerator"
+
+    @extensionpoint
+    def generate_includes():
+        pass
+
+    @extensionpoint
+    def declare_types():
+        pass
+
+
+class ExtensionCodeGenerator(ExtensionGenerator):
+    extending = "CodeGenerator"
+
+    @extensionpoint
+    def generate_body_preamble():
+        pass
+
+    @extensionpoint
+    def generate():
+        pass
+
+
 def generate_namespace(namespace):
     ns = namespace
     if len(namespace) > 0:
@@ -84,6 +132,7 @@ class HeaderCodeGenerator:
         symbol_decorator,
         symbol_decorator_header,
         outfile,
+        ext,
     ):
         self.ifaces = ifaces
         self.namespace, self.ns_upper, self.ns_lower = generate_namespace(namespace)
@@ -96,6 +145,7 @@ class HeaderCodeGenerator:
         self.symbol_decorator = symbol_decorator
         self.symbol_decorator_header = symbol_decorator_header
         self.outfile = outfile
+        self.ext = ExtensionHeaderCodeGenerator(ext, self)
 
     # ----------------------------------------------------------------------------------------------------
 
@@ -116,6 +166,7 @@ class HeaderCodeGenerator:
 
         self.outfile.write("\n")
         self.outfile.write("#include <gio/gio.h>\n")
+        self.ext.generate_includes()
         self.outfile.write("\n")
         self.outfile.write("G_BEGIN_DECLS\n")
         self.outfile.write("\n")
@@ -360,6 +411,7 @@ class HeaderCodeGenerator:
                         "    GError **error);\n"
                     )
                     self.outfile.write("\n")
+
                 self.outfile.write("\n")
 
             # Then the property accessor declarations
@@ -1014,6 +1066,7 @@ class HeaderCodeGenerator:
     def generate(self):
         self.generate_header_preamble()
         self.declare_types()
+        self.ext.declare_types()
         self.generate_header_postamble()
 
 
@@ -1458,6 +1511,7 @@ class CodeGenerator:
         glib_min_required,
         symbol_decoration_define,
         outfile,
+        ext,
     ):
         self.ifaces = ifaces
         self.namespace, self.ns_upper, self.ns_lower = generate_namespace(namespace)
@@ -1469,6 +1523,7 @@ class CodeGenerator:
         self.symbol_decoration_define = symbol_decoration_define
         self.outfile = outfile
         self.marshallers = set()
+        self.ext = ExtensionCodeGenerator(ext, self)
 
     # ----------------------------------------------------------------------------------------------------
 
@@ -5478,6 +5533,7 @@ class CodeGenerator:
 
     def generate(self):
         self.generate_body_preamble()
+        self.ext.generate_body_preamble()
         for i in self.ifaces:
             self.generate_generic_marshallers(i)
         for i in self.ifaces:
@@ -5496,3 +5552,4 @@ class CodeGenerator:
         if self.generate_objmanager:
             self.generate_object()
             self.generate_object_manager_client()
+        self.ext.generate()

gio/gdbus-2.0/codegen/codegen_main.py

@@ -26,6 +26,8 @@
 import argparse
 import os
 import sys
+import importlib.util
+import traceback
 from contextlib import contextmanager
 
 from . import config
@@ -38,6 +40,16 @@ from . import codegen_rst
 from .utils import print_error, print_warning
 
 
+def import_from_path(module_name, file_path):
+    spec = importlib.util.spec_from_file_location(module_name, file_path)
+    if not spec:
+        raise Exception("Not a Python file")
+    module = importlib.util.module_from_spec(spec)
+    sys.modules[module_name] = module
+    spec.loader.exec_module(module)
+    return module
+
+
 def find_arg(arg_list, arg_name):
     for a in arg_list:
         if a.name == arg_name:
@@ -274,6 +286,12 @@ def codegen_main():
         help="Additional define required for decorator specified by "
         "--symbol-decorator",
     )
+    arg_parser.add_argument(
+        "--extension-path",
+        metavar="EXTENSION_PATH",
+        default="",
+        help="Path to a gdbus-codegen Python extension file (unstable API)",
+    )
 
     group = arg_parser.add_mutually_exclusive_group()
     group.add_argument(
@@ -305,6 +323,20 @@ def codegen_main():
 
     args = arg_parser.parse_args()
 
+    codegen_ext = {}
+    if args.extension_path:
+        try:
+            codegen_ext = import_from_path("GDBusCodegenExt", args.extension_path)
+            codegen_ext.init(
+                args,
+                {
+                    "version": 1,
+                },
+            )
+        except Exception:
+            print_warning(traceback.format_exc())
+            print_error("Loading extension ‘{}’ failed".format(args.extension_path))
+
     if len(args.xml_files) > 0:
         print_warning(
             'The "--xml-files" option is deprecated; use positional arguments instead'
@@ -479,6 +511,7 @@ def codegen_main():
                 args.symbol_decorator,
                 args.symbol_decorator_header,
                 outfile,
+                codegen_ext,
             )
             gen.generate()
 
@@ -494,6 +527,7 @@ def codegen_main():
                 glib_min_required,
                 args.symbol_decorator_define,
                 outfile,
+                codegen_ext,
             )
             gen.generate()