pydrake: Do not import a duplicate of pydrake, but use another module…

… to load `libdrake.so`

bindings/BUILD.bazel

@@ -0,0 +1,30 @@
+# -*- python -*-
+
+load("//tools/lint:lint.bzl", "add_lint_tests")
+load(
+    "//tools/skylark:pybind.bzl",
+    "drake_pybind_library",
+)
+load(
+    ":bazel_workaround_4594_libdrake.bzl",
+    "get_bazel_workaround_4594_libdrake_package_info",
+)
+
+package(default_visibility = [
+    "//bindings/pydrake:__subpackages__",
+])
+
+# This is placed outside of `pydrake` so that we can import this without
+# pulling in an extra copy of `pydrake`. For more information, see
+# `pydrake/__init__.py`.
+drake_pybind_library(
+    name = "bazel_workaround_4594_libdrake_py",
+    add_install = False,
+    cc_so_name = "bazel_workaround_4594_libdrake",
+    cc_srcs = ["bazel_workaround_4594_libdrake_py.cc"],
+    # Since `package_info` must be a `struct`, we must define this in a `*.bzl`
+    # file.
+    package_info = get_bazel_workaround_4594_libdrake_package_info(),
+)
+
+add_lint_tests()

bindings/bazel_workaround_4594_libdrake.bzl

@@ -0,0 +1,8 @@
+# -*- python -*-
+
+def get_bazel_workaround_4594_libdrake_package_info():
+    """Only to be used by //bindings:bazel_workaround_4594_libdrake_py.
+
+    For more information, see `pydrake/__init__.py`.
+    """
+    return struct(py_imports = ["../.."])

bindings/bazel_workaround_4594_libdrake_py.cc

@@ -0,0 +1,12 @@
+#include "pybind11/pybind11.h"
+
+namespace drake {
+namespace pydrake {
+
+PYBIND11_MODULE(bazel_workaround_4594_libdrake, m) {
+  m.doc() = "Consolidated workaround for bazelbuild/bazel#4594 to load "
+            "libdrake.so, to be used by `pydrake/__init__.py`.";
+}
+
+}  // namespace pydrake
+}  // namespace drake

bindings/pydrake/BUILD.bazel

@@ -22,7 +22,7 @@ load(
 )
 
 package(default_visibility = [
-    "//bindings/pydrake:__subpackages__",
+    "//bindings:__subpackages__",
 ])
 
 # This determines how `PYTHONPATH` is configured, and how to install the
@@ -43,6 +43,7 @@ drake_pybind_library(
     package_info = PACKAGE_INFO,
     py_deps = [
         "//bindings/pydrake/util:deprecation_py",
+        "//bindings:bazel_workaround_4594_libdrake_py",
     ],
     py_srcs = [
         "__init__.py",

bindings/pydrake/__init__.py

@@ -6,15 +6,17 @@
 # When importing `pydrake` as an external under Bazel, Bazel will use a shared
 # library whose relative RPATHs are incorrect for `libdrake.so`, and thus will
 # fail to load; this issue is captured in bazelbuild/bazel#4594. As a
-# workaround, we can use this spelling to load a properly-linked version of
-# `libdrake.so`. Once this is loaded, all of the Python C-extension libraries
+# workaround, we can use a library that properly links to `libdrake.so`, but in
+# `{runfiles}/{workspace}/external/drake` rather than `{runfiles}/drake`.
+# Once this is loaded, all of the Python C-extension libraries
 # that depend on it (and its dependencies) will load properly.
 # Please note that this workaround is only important when running under the
 # Bazel runfiles tree. Installed `pydrake` should not have this issue.
-# N.B. This will actually import a second copy of `pydrake` in the path below;
-# however, we should be able to ignore this as users should not be using it.
+# N.B. We do not import `external.drake.bindings.pydrake` as this may cause
+# duplicate classes to be loaded (#8810). This will not be a problem once #7912
+# is resolved.
 try:
-    import external.drake.bindings.pydrake
+    import external.drake.bindings.bazel_workaround_4594_libdrake
 except ImportError:
     pass
 

tools/install/libdrake/BUILD.bazel

@@ -109,7 +109,7 @@ cc_library(
     include_prefix = "drake",
     strip_include_prefix = "/",
     visibility = [
-        "//bindings/pydrake:__subpackages__",
+        "//bindings:__subpackages__",
         "//examples:__subpackages__",
     ],
     deps = [