Change the Python binary find runfiles algorithm to match the one use?

?d by Java.

Closes #6228.

PiperOrigin-RevId: 219766676

src/main/java/com/google/devtools/build/lib/bazel/rules/python/python_stub_template.txt

diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/python/python_stub_template.txt b/src/main/java/com/google/devtools/build/lib/bazel/rules/python/python_stub_template.txt
index d5fb78f..129ce90 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/python/python_stub_template.txt
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/python/python_stub_template.txt
@@ -71,17 +71,27 @@
 
 # Find the runfiles tree
 def FindModuleSpace():
-  stub_filename = os.path.abspath(sys.argv[0])
-  module_space = stub_filename + ('.exe' if IsWindows() else '') + '.runfiles'
-  if os.path.isdir(module_space):
-    return module_space
+  stub_filename = sys.argv[0]
+  if not os.path.isabs(stub_filename):
+    stub_filename = os.path.join(os.getcwd(), stub_filename)
 
-  runfiles_pattern = "(.*\.runfiles)/.*"
-  if IsWindows():
-    runfiles_pattern = "(.*\.runfiles)\\.*"
-  matchobj = re.match(runfiles_pattern, os.path.abspath(sys.argv[0]))
-  if matchobj:
-    return matchobj.group(1)
+  while True:
+    module_space = stub_filename + ('.exe' if IsWindows() else '') + '.runfiles'
+    if os.path.isdir(module_space):
+      return module_space
+
+    runfiles_pattern = r'(.*\.runfiles)' + (r'\\' if IsWindows() else '/') + '.*'
+    matchobj = re.match(runfiles_pattern, stub_filename)
+    if matchobj:
+      return matchobj.group(1)
+
+    if not os.path.islink(stub_filename):
+      break
+    target = os.readlink(stub_filename)
+    if os.path.isabs(target):
+      stub_filename = target
+    else:
+      stub_filename = os.path.join(os.path.dirname(stub_filename), target)
 
   raise AssertionError('Cannot find .runfiles directory for %s' % sys.argv[0])