Reapply "Bug 1967834 - remove the preprocessing scripts in favor of direct changes in gn_processor.py r=ng".

This reverts commit 946f65307b1377e305dbbd65fa43009b34f39604.

UltraBlame original commit: 73cae34a99b20564f13d0eac36c0fb46528bf27b

Author: marco-c

build/gn_processor.py

@@ -10,7 +10,6 @@
 import tempfile
 from collections import defaultdict, deque
 from copy import deepcopy
-from importlib import util
 from pathlib import Path
 from shutil import which
 
@@ -720,7 +719,6 @@ def generate_gn_config(
     input_variables,
     sandbox_variables,
     gn_target,
-    preprocessor,
     moz_build_flag,
 ):
     def str_for_arg(v):
@@ -775,25 +773,19 @@ def str_for_arg(v):
         subprocess.check_call(gen_args, cwd=build_root_dir, stderr=subprocess.STDOUT)
 
         gn_config_file = resolved_tempdir / "project.json"
-        if preprocessor:
-            preprocessor.main(gn_config_file)
-
         with open(gn_config_file) as fh:
-            gn_out = json.load(fh)
-            gn_out = filter_gn_config(
-                resolved_tempdir, gn_out, sandbox_variables, input_variables, gn_target
+            raw_json = fh.read()
+            raw_json = raw_json.replace(f"{target_dir}/", "")
+            raw_json = raw_json.replace(f"{target_dir}:", ":")
+            gn_config = json.loads(raw_json)
+            gn_config = filter_gn_config(
+                resolved_tempdir,
+                gn_config,
+                sandbox_variables,
+                input_variables,
+                gn_target,
             )
-            return gn_out
-
-
-def load_preprocessor(script_name):
-    if script_name and os.path.isfile(script_name):
-        print(f"Loading preprocessor {script_name}")
-        spec = util.spec_from_file_location("preprocess", script_name)
-        module = util.module_from_spec(spec)
-        spec.loader.exec_module(module)
-        return module
-    return None
+            return gn_config
 
 
 def main():
@@ -840,8 +832,6 @@ def main():
                         vars["use_x11"] = True
                     vars_set.append(vars)
 
-    preprocessor = load_preprocessor(config.get("preprocessing_script", None))
-
     gn_configs = []
     for vars in vars_set:
         gn_configs.append(
@@ -852,7 +842,6 @@ def main():
                 vars,
                 config["gn_sandbox_variables"],
                 config["gn_target"],
-                preprocessor,
                 config["moz_build_flag"],
             )
         )

dom/media/webrtc/third_party_build/gn-configs/abseil.json

@@ -1,7 +1,6 @@
 {
   "build_root_dir": "third_party",
   "target_dir": "abseil-cpp",
-  "preprocessing_script": "dom/media/webrtc/third_party_build/gn-configs/abseil_preprocessor.py",
   "moz_build_flag": "build_mozilla_absl",
   "gn_target": "//:absl",
   "gn_sandbox_variables": {

dom/media/webrtc/third_party_build/gn-configs/abseil_preprocessor.py

@@ -1,7 +1,6 @@
 {
   "build_root_dir": "third_party",
   "target_dir": "libwebrtc",
-  "preprocessing_script": "dom/media/webrtc/third_party_build/gn-configs/webrtc_preprocessor.py",
   "moz_build_flag": "build_mozilla_webrtc",
   "gn_target": "//:webrtc",
   "gn_sandbox_variables": {