Fix runtime files for python library.

src/generate_python_lib.py

@@ -10,17 +10,15 @@ def main():
 
   library_str = \
 f'''
-import os
+from bazel_tools.tools.python.runfiles import runfiles
 
 from src import py_stuff_sack
 
-# The location of the relative location of the runfiles depends on whether the library is run as a
-# tool or standalone.  We manually prepend the runfiles path to handle both cases.
-workspace = os.path.basename(os.getcwd())
+r = runfiles.Create()
 
 globals().update(py_stuff_sack.get_globals(
-    os.path.join(os.environ['RUNFILES_DIR'], workspace, '{args.lib}'),
-    os.path.join(os.environ['RUNFILES_DIR'], workspace, '{args.spec}')
+    r.Rlocation('{args.lib}'),
+    r.Rlocation('{args.spec}')
 ))
 '''
 

tools/gen_message_def.bzl

@@ -49,8 +49,8 @@ def gen_message_def(name, message_spec, c_deps = None, **kwargs):
         outs = [
             name + ".py",
         ],
-        cmd = ("$(execpath @stuff_sack//src:generate_python_lib) --spec $(rootpath {}) " +
-               "--lib $(rootpath {}) --output $@").format(
+        cmd = ("$(execpath @stuff_sack//src:generate_python_lib) --spec $(rlocationpath {}) " +
+               "--lib $(rlocationpath {}) --output $@").format(
             message_spec,
             ":" + name + "-c-so",
         ),
@@ -63,6 +63,7 @@ def gen_message_def(name, message_spec, c_deps = None, **kwargs):
         srcs = [name + ".py"],
         deps = [
             "@stuff_sack//src:py_stuff_sack",
+            "@bazel_tools//tools/python/runfiles",
         ],
         data = [
             ":" + name + "-c-so",