Fix Python interpreter target labels with @@ prefixes. (#940)

ERROR: An error occurred during the fetch of repository 'rules_python~0.16.1~pip~pip':
   Traceback (most recent call last):
	File "/home/miha/.cache/bazel/_bazel_miha/bd93af10788cff1331d75ed739998a3c/external/rules_python~0.16.1/python/pip_install/pip_repository.bzl", line 335, column 63, in _pip_repository_impl
		environment = _create_repository_execution_environment(rctx),
	File "/home/miha/.cache/bazel/_bazel_miha/bd93af10788cff1331d75ed739998a3c/external/rules_python~0.16.1/python/pip_install/pip_repository.bzl", line 210, column 47, in _create_repository_execution_environment
		cppflags.extend(_get_toolchain_unix_cflags(rctx))
	File "/home/miha/.cache/bazel/_bazel_miha/bd93af10788cff1331d75ed739998a3c/external/rules_python~0.16.1/python/pip_install/pip_repository.bzl", line 115, column 37, in _get_toolchain_unix_cflags
		if not is_standalone_interpreter(rctx, rctx.attr.python_interpreter_target):
	File "/home/miha/.cache/bazel/_bazel_miha/bd93af10788cff1331d75ed739998a3c/external/rules_python~0.16.1/python/repositories.bzl", line 64, column 22, in is_standalone_interpreter
		rctx.path(Label("@{}//:WORKSPACE".format(rctx.attr.python_interpreter_target.workspace_name))).dirname,
Error in path: Unable to load package for @[unknown repo 'rules_python~0.16.1~python~python3_10_x86_64-unknown-linux-gnu' requested from @rules_python~0.16.1]//:WORKSPACE: The repository '@[unknown repo 'rules_python~0.16.1~python~python3_10_x86_64-unknown-linux-gnu' requested from @rules_python~0.16.1]' could not be resolved: No repository visible as '@rules_python~0.16.1~python~python3_10_x86_64-unknown-linux-gnu' from repository '@rules_python~0.16.1'

Author: oxidase

python/pip_install/pip_repository.bzl

@@ -1,6 +1,6 @@
 ""
 
-load("//python:repositories.bzl", "is_standalone_interpreter")
+load("//python:repositories.bzl", "get_interpreter_dirname", "is_standalone_interpreter")
 load("//python/pip_install:repositories.bzl", "all_requirements")
 load("//python/pip_install:requirements_parser.bzl", parse_requirements = "parse")
 load("//python/pip_install/private:srcs.bzl", "PIP_INSTALL_PY_SRCS")
@@ -124,7 +124,7 @@ def _get_toolchain_unix_cflags(rctx):
         fail("could not get python version from interpreter (status {}): {}".format(er.return_code, er.stderr))
     _python_version = er.stdout
     include_path = "{}/include/python{}".format(
-        rctx.path(Label("@{}//:WORKSPACE".format(rctx.attr.python_interpreter_target.workspace_name))).dirname.realpath,
+        get_interpreter_dirname(rctx, rctx.attr.python_interpreter_target),
         _python_version,
     )
 

python/repositories.bzl

@@ -58,6 +58,19 @@ def py_repositories():
 
 STANDALONE_INTERPRETER_FILENAME = "STANDALONE_INTERPRETER"
 
+def get_interpreter_dirname(rctx, python_interpreter_target):
+    """Get a python interpreter target dirname.
+
+    Args:
+        rctx (repository_ctx): The repository rule's context object.
+        python_interpreter_target (Target): A target representing a python interpreter.
+
+    Returns:
+        str: The Python interpreter directory.
+    """
+
+    return rctx.path(Label("{}//:WORKSPACE".format(str(python_interpreter_target).split("//")[0]))).dirname
+
 def is_standalone_interpreter(rctx, python_interpreter_target):
     """Query a python interpreter target for whether or not it's a rules_rust provided toolchain
 
@@ -77,7 +90,7 @@ def is_standalone_interpreter(rctx, python_interpreter_target):
     return rctx.execute([
         "ls",
         "{}/{}".format(
-            rctx.path(Label("@{}//:WORKSPACE".format(rctx.attr.python_interpreter_target.workspace_name))).dirname,
+            get_interpreter_dirname(rctx, python_interpreter_target),
             STANDALONE_INTERPRETER_FILENAME,
         ),
     ]).return_code == 0