fix(venv_link): Repair venv link munging (#599)

Fixes the #593 report.

Reworks the venv linking script so that we can add tests covering
munging and prevent future regressions.

---

### Changes are visible to end-users: yes

- Searched for relevant documentation and updated as needed: yes/no
- Breaking change (forces users to change their own code or config):
yes/no
- Suggested release notes appear below: yes

Fixed a regression in the naming of virtualenv links.

### Test plan

- New test cases added

Author: arrdem

py/private/py_venv/BUILD.bazel

@@ -1,4 +1,5 @@
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
+load(":defs.bzl", "py_venv_test")
 
 package(default_visibility = [
     "//docs:__pkg__",
@@ -33,3 +34,13 @@ bzl_library(
         "@aspect_bazel_lib//lib:paths",
     ],
 )
+
+py_venv_test(
+    name = "test_link",
+    srcs = [
+        "link.py",
+        "test_link.py",
+    ],
+    imports = ["."],
+    main = "test_link.py",
+)

py/private/py_venv/link.py

@@ -11,34 +11,43 @@
 import site
 from pathlib import Path
 
-virtualenv_home = os.path.realpath(os.environ["VIRTUAL_ENV"])
-virtualenv_name = os.path.basename(virtualenv_home)
-runfiles_dir = os.path.realpath(os.environ["RUNFILES_DIR"])
-builddir = os.path.realpath(os.environ["BUILD_WORKING_DIRECTORY"])
-target_package, target_name = os.environ["BAZEL_TARGET"].split("//", 1)[1].split(":")
-
-PARSER = argparse.ArgumentParser(
-    prog="link",
-    usage=__doc__,
-    formatter_class=argparse.ArgumentDefaultsHelpFormatter,
-)
-
-PARSER.add_argument(
-    "--dest",
-    dest="dest",
-    default=builddir,
-    help="Dir to link the virtualenv into. Default is $BUILD_WORKING_DIRECTORY.",
-)
-
-PARSER.add_argument(
-    "--name",
-    dest="name",
-    default=".{}+{}".format(target_package.replace("/", "+"), virtualenv_name.lstrip(".")),
-    help="Name to link the virtualenv as.",
-)
 
+def munge_venv_name(target_package, virtualenv_name):
+    acc = (target_package or "").replace("/", "+")
+    if acc:
+        acc += "+"
+    acc += virtualenv_name.lstrip(".")
+    return "." + acc
+    
 
 if __name__ == "__main__":
+    virtualenv_home = os.path.realpath(os.environ["VIRTUAL_ENV"])
+    virtualenv_name = os.path.basename(virtualenv_home)
+    runfiles_dir = os.path.realpath(os.environ["RUNFILES_DIR"])
+    builddir = os.path.realpath(os.environ["BUILD_WORKING_DIRECTORY"])
+    target_package, target_name = os.environ["BAZEL_TARGET"].split("//", 1)[1].split(":")
+
+    PARSER = argparse.ArgumentParser(
+        prog="link",
+        usage=__doc__,
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
+    )
+
+    PARSER.add_argument(
+        "--dest",
+        dest="dest",
+        default=builddir,
+        help="Dir to link the virtualenv into. Default is $BUILD_WORKING_DIRECTORY.",
+    )
+
+    PARSER.add_argument(
+        "--name",
+        dest="name",
+        default=munge_venv_name(target_package, virtualenv_name),
+        help="Name to link the virtualenv as.",
+    )
+
+    
     PARSER.print_help(sys.stdout)
     opts = PARSER.parse_args()
     dest = Path(os.path.join(opts.dest, opts.name))

py/private/py_venv/test_link.py

@@ -0,0 +1,7 @@
+#!/usr/bin/env python3
+
+from link import munge_venv_name
+
+assert munge_venv_name("", ".foo_venv") == ".foo_venv"
+assert munge_venv_name("bar", ".foo_venv") == ".bar+foo_venv"
+assert munge_venv_name("bar/baz", ".foo_venv") == ".bar+baz+foo_venv"