tp: fix metrics and stdlib on Android builds

Bug: 264711057
Change-Id: Ib66087e4aaaf294038539015785f0ea599824e5a

tools/gen_stdlib_docs_json.py

diff --git a/tools/gen_stdlib_docs_json.py b/tools/gen_stdlib_docs_json.py
index e6953d0..c89b7a7 100755
--- a/tools/gen_stdlib_docs_json.py
+++ b/tools/gen_stdlib_docs_json.py
@@ -30,7 +30,6 @@
   parser = argparse.ArgumentParser()
   parser.add_argument('--json-out', required=True)
   parser.add_argument('--input-list-file')
-  parser.add_argument('--root-dir', required=True)
   parser.add_argument('sql_files', nargs='*')
   args = parser.parse_args()
 
@@ -46,11 +45,23 @@
   else:
     sql_files = args.sql_files
 
+  # Unfortunately we cannot pass this in as an arg as soong does not provide
+  # us a way to get the path to the Perfetto source directory. This fails on
+  # empty path but it's a price worth paying to have to use gross hacks in
+  # Soong.
+  root_dir = os.path.commonpath(sql_files)
+
   # Extract the SQL output from each file.
   sql_outputs: Dict[str, str] = {}
   for file_name in sql_files:
     with open(file_name, 'r') as f:
-      relpath = os.path.relpath(file_name, args.root_dir)
+      relpath = os.path.relpath(file_name, root_dir)
+
+      # We've had bugs (e.g. b/264711057) when Soong's common path logic breaks
+      # and ends up with a bunch of ../ prefixing the path: disallow any ../
+      # as this should never be a valid in our C++ output.
+      assert '../' not in relpath
+
       sql_outputs[relpath] = f.read()
 
   modules = defaultdict(list)