python,runfiles: runfiles library in @bazel_tools

Also update the Python stub script template to set
$RUNFILES_MANIFEST_FILE or $RUNFILES_DIR so the
runfiles library only needs to look for those.

See https://github.com/bazelbuild/bazel/issues/4460

RELNOTES[NEW]: python,runfiles: You can now depend on `@bazel_tools//tools/runfiles:py-runfiles` to get a platform-independent runfiles library for Python. See DocString of https://github.com/bazelbuild/bazel/blob/master/src/tools/runfiles/runfiles.py for usage information.

Change-Id: I4f68a11cb59f2782e5203e39fe60cc66b46023a2
PiperOrigin-RevId: 184515490

1 files changed, 31 insertions, 0 deletions

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 84dd571afa..d2cdccc6fd 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
@@ -100,6 +100,34 @@ def GetRepositoriesImports(module_space, import_all):
     return [d for d in repo_dirs if os.path.isdir(d)]
   return [os.path.join(module_space, "%workspace_name%")]
 
+# Finds the runfiles manifest or the runfiles directory.
+def RunfilesEnvvar(module_space):
+  # If this binary is the data-dependency of another one, the other sets
+  # RUNFILES_MANIFEST_FILE or RUNFILES_DIR for our sake.
+  runfiles = os.environ.get('RUNFILES_MANIFEST_FILE', None)
+  if runfiles:
+    return ('RUNFILES_MANIFEST_FILE', runfiles)
+
+  runfiles = os.environ.get('RUNFILES_DIR', None)
+  if runfiles:
+    return ('RUNFILES_DIR', runfiles)
+
+  # If running from a zip, there's no manifest file.
+  if IsRunningFromZip():
+    return ('RUNFILES_DIR', module_space)
+
+  # Look for the runfiles "output" manifest, argv[0] + ".runfiles_manifest"
+  runfiles = module_space + '_manifest'
+  if os.path.exists(runfiles):
+    return ('RUNFILES_MANIFEST_FILE', runfiles)
+
+  # Look for the runfiles "input" manifest, argv[0] + ".runfiles/MANIFEST"
+  runfiles = os.path.join(module_space, 'MANIFEST')
+  if os.path.exists(runfiles):
+    return ('RUNFILES_DIR', runfiles)
+
+  return (None, None)
+
 def Main():
   args = sys.argv[1:]
 
@@ -125,6 +153,9 @@ def Main():
     python_path = python_path.replace("/", os.sep)
 
   new_env['PYTHONPATH'] = python_path
+  runfiles_envkey, runfiles_envvalue = RunfilesEnvvar(module_space)
+  if runfiles_envkey:
+    new_env[runfiles_envkey] = runfiles_envvalue
 
   # Now look for my main python source file.
   # The magic string percent-main-percent is replaced with the filename of the