Don't bake env into binary (aspect-build#464)

This mirrors the behavior of rules_python's py_binary, and other
*_binary rules. Previously any env set on the binary was baked into the
script, and therefore included if the script was run with --run_under,
or through a genrule. Now this env is passed through to
RunEnvironmentInfo so it only applies in the default cases.

py/private/py_binary.bzl

@@ -1,8 +1,8 @@
 """Implementation for the py_binary and py_test rules."""
 
-load("@rules_python//python:defs.bzl", "PyInfo")
-load("@aspect_bazel_lib//lib:paths.bzl", "BASH_RLOCATION_FUNCTION", "to_rlocation_path")
 load("@aspect_bazel_lib//lib:expand_make_vars.bzl", "expand_locations", "expand_variables")
+load("@aspect_bazel_lib//lib:paths.bzl", "BASH_RLOCATION_FUNCTION", "to_rlocation_path")
+load("@rules_python//python:defs.bzl", "PyInfo")
 load("//py/private:py_library.bzl", _py_library = "py_library_utils")
 load("//py/private:py_semantics.bzl", _py_semantics = "semantics")
 load("//py/private/toolchain:types.bzl", "PY_TOOLCHAIN", "VENV_TOOLCHAIN")
@@ -49,14 +49,15 @@ def _py_binary_rule_impl(ctx):
         content = pth_lines,
     )
 
-    env = dict({
+    default_env = {
         "BAZEL_TARGET": str(ctx.label).lstrip("@"),
         "BAZEL_WORKSPACE": ctx.workspace_name,
         "BAZEL_TARGET_NAME": ctx.attr.name,
-    }, **ctx.attr.env)
+    }
 
-    for k, v in env.items():
-        env[k] = expand_variables(
+    passed_env = dict(ctx.attr.env)
+    for k, v in passed_env.items():
+        passed_env[k] = expand_variables(
             ctx,
             expand_locations(ctx, v, ctx.attr.data),
             attribute_name = "env",
@@ -75,7 +76,7 @@ def _py_binary_rule_impl(ctx):
             "{{ARG_VENV_NAME}}": ".{}.venv".format(ctx.attr.name),
             "{{ARG_PTH_FILE}}": to_rlocation_path(ctx, site_packages_pth_file),
             "{{ENTRYPOINT}}": to_rlocation_path(ctx, ctx.file.main),
-            "{{PYTHON_ENV}}": "\n".join(_dict_to_exports(env)).strip(),
+            "{{PYTHON_ENV}}": "\n".join(_dict_to_exports(default_env)).strip(),
             "{{EXEC_PYTHON_BIN}}": "python{}".format(
                 py_toolchain.interpreter_version_info.major,
             ),
@@ -123,6 +124,9 @@ def _py_binary_rule_impl(ctx):
             uses_shared_libraries = False,
         ),
         instrumented_files_info,
+        RunEnvironmentInfo(
+            environment = passed_env,
+        ),
     ]
 
 _attrs = dict({