Add --vscode-launch-props to gdbclient.py

The new argument allows the user to pass a JSON of properties to merge
into the generated launch.json config when setting up vscode-lldb
forwarding. This way the user can add pre-build tasks, extra init
commands etc.

Test: atest gdbclient_test
Test: lldbclient.py --setup-forwarding=vscode-lldb
  --vscode-launch-props='{"sourceMap": {"test1": "test2"},
  "postDebugTask": "Stop LLDB client", "processCreateCommands" :
  ["test"]}' -r test
Change-Id: I763dd15dde10421e86bc0a6ddfde974156ef1588
diff --git a/scripts/gdbclient.py b/scripts/gdbclient.py
index 9c602cc..ef32bf0 100755
--- a/scripts/gdbclient.py
+++ b/scripts/gdbclient.py
@@ -28,7 +28,7 @@
 import tempfile
 import textwrap
 
-from typing import BinaryIO
+from typing import BinaryIO, Any
 
 # Shared functions across gdbclient.py and ndk-gdb.py.
 import gdbrunner
@@ -98,8 +98,13 @@
         choices=["lldb", "vscode-lldb"],
         help=("Set up lldb-server and port forwarding. Prints commands or " +
               ".vscode/launch.json configuration needed to connect the debugging " +
-              "client to the server. 'vscode' with llbd and 'vscode-lldb' both " +
+              "client to the server. 'vscode' with lldb and 'vscode-lldb' both " +
               "require the 'vadimcn.vscode-lldb' extension."))
+    parser.add_argument(
+        "--vscode-launch-props", default=None,
+        dest="vscode_launch_props",
+        help=("JSON with extra properties to add to launch parameters when using " +
+              "vscode-lldb forwarding."))
 
     parser.add_argument(
         "--env", nargs=1, action="append", metavar="VAR=VALUE",
@@ -244,7 +249,49 @@
 
     return (binary_file, pid, run_cmd)
 
-def generate_vscode_lldb_script(root: str, sysroot: str, binary_name: str, port: str | int, solib_search_path: list[str]) -> str:
+def merge_launch_dict(base: dict[str, Any], to_add:  dict[str, Any] | None) -> None:
+    """Merges two dicts describing VSCode launch.json properties: base and
+    to_add. Base is modified in-place with items from to_add.
+    Items from to_add that are not present in base are inserted. Items that are
+    present are merged following these rules:
+        - Lists are merged with to_add elements appended to the end of base
+          list. Only a list can be merged with a list.
+        - dicts are merged recursively. Only a dict can be merged with a dict.
+        - Other present values in base get overwritten with values from to_add.
+
+    The reason for these rules is that merging in new values should prefer to
+    expand the existing set instead of overwriting where possible.
+    """
+    if to_add is None:
+        return
+
+    for key, val in to_add.items():
+        if key not in base:
+            base[key] = val
+        else:
+            if isinstance(base[key], list) and not isinstance(val, list):
+                raise ValueError(f'Cannot merge non-list into list at key={key}. ' +
+                'You probably need to wrap your value into a list.')
+            if not isinstance(base[key], list) and isinstance(val, list):
+                raise ValueError(f'Cannot merge list into non-list at key={key}.')
+            if isinstance(base[key], dict) != isinstance(val, dict):
+                raise ValueError(f'Cannot merge dict and non-dict at key={key}')
+
+            # We don't allow the user to overwrite or interleave lists and don't allow
+            # to delete dict entries.
+            # It can be done but would make the implementation a bit more complicated
+            # and provides less value than adding elements.
+            # We expect that the config generated by gdbclient doesn't contain anything
+            # the user would want to remove.
+            if isinstance(base[key], list):
+                base[key] += val
+            elif isinstance(base[key], dict):
+                merge_launch_dict(base[key], val)
+            else:
+                base[key] = val
+
+
+def generate_vscode_lldb_script(root: str, sysroot: str, binary_name: str, port: str | int, solib_search_path: list[str], extra_props: dict[str, Any] | None) -> str:
     # TODO It would be nice if we didn't need to copy this or run the
     #      lldbclient.py program manually. Doing this would probably require
     #      writing a vscode extension or modifying an existing one.
@@ -262,6 +309,7 @@
                                  "target modules search-paths add / {}/".format(sysroot)],
         "processCreateCommands": ["gdb-remote {}".format(str(port))]
     }
+    merge_launch_dict(res, extra_props)
     return json.dumps(res, indent=4)
 
 def generate_lldb_script(root: str, sysroot: str, binary_name: str, port: str | int, solib_search_path: list[str]) -> str:
@@ -278,7 +326,7 @@
     return '\n'.join(commands)
 
 
-def generate_setup_script(sysroot: str, linker_search_dir: str | None, binary_name: str, is64bit: bool, port: str | int, debugger: str) -> str:
+def generate_setup_script(sysroot: str, linker_search_dir: str | None, binary_name: str, is64bit: bool, port: str | int, debugger: str, vscode_launch_props: dict[str, Any] | None) -> str:
     # Generate a setup script.
     root = os.environ["ANDROID_BUILD_TOP"]
     symbols_dir = os.path.join(sysroot, "system", "lib64" if is64bit else "lib")
@@ -294,7 +342,7 @@
 
     if debugger == "vscode-lldb":
         return generate_vscode_lldb_script(
-            root, sysroot, binary_name, port, solib_search_path)
+            root, sysroot, binary_name, port, solib_search_path, vscode_launch_props)
     elif debugger == 'lldb':
         return generate_lldb_script(
             root, sysroot, binary_name, port, solib_search_path)
@@ -332,6 +380,12 @@
     # Fetch binary for -p, -n.
     binary_file, pid, run_cmd = handle_switches(args, sysroot)
 
+    vscode_launch_props = None
+    if args.vscode_launch_props:
+        if args.setup_forwarding != "vscode-lldb":
+            raise ValueError('vscode_launch_props requires --setup-forwarding=vscode-lldb')
+        vscode_launch_props = json.loads(args.vscode_launch_props)
+
     with binary_file:
         if sys.platform.startswith("linux"):
             platform_name = "linux-x86"
@@ -381,7 +435,8 @@
                                                binary_name=binary_file.name,
                                                is64bit=is64bit,
                                                port=args.port,
-                                               debugger=debugger)
+                                               debugger=debugger,
+                                               vscode_launch_props=vscode_launch_props)
 
         if not args.setup_forwarding:
             # Print a newline to separate our messages from the GDB session.