Minor crimes to deal with platform-variable pythons

WORKSPACE

@@ -53,7 +53,7 @@ load("@rules_python//python:pip.bzl", "pip_parse")
 pip_parse(
     name = "arrdem_source_pypi",
     requirements_lock = "//tools/python:requirements.txt",
-    python_interpreter = "/usr/bin/python3.10"
+    python_interpreter_target = "//tools/python:pythonshim",
 )
 
 # Load the starlark macro which will define your dependencies.
@@ -62,13 +62,14 @@ load("@arrdem_source_pypi//:requirements.bzl", "install_deps")
 # Call it to define repos for your requirements.
 install_deps()
 
-# git_repository(
+git_repository(
-#     name = "rules_zapp",
-#     remote = "https://github.com/arrdem/rules_zapp.git",
-#     tag = "0.1.2",
-# )
-
-local_repository(
     name = "rules_zapp",
-    path = "/home/arrdem/doc/hobby/programming/lang/python/rules_zapp",
+    remote = "https://github.com/arrdem/rules_zapp.git",
+    commit = "d7a0382927fb8a68115b560f4fee7dca743068f8",
+    # tag = "0.1.2",
 )
+
+# local_repository(
+#     name = "rules_zapp",
+#     path = "/home/arrdem/doc/hobby/programming/lang/python/rules_zapp",
+# )

tools/python/BUILD

@@ -12,12 +12,13 @@ exports_files([
     "defs.bzl",
     "bzl_pytest_shim.py",
     "bzl_unittest_shim.py",
+    "pythonshim",
 ])
 
 py_runtime(
     name = "python3_runtime",
     files = [],
-    interpreter_path = "/usr/bin/python3.10",
+    interpreter = ":pythonshim",
     python_version = "PY3",
     visibility = ["//visibility:public"],
 )

tools/python/pythonshim

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+# Bazel STRONGLY disapproves of linking dynamically to a Python interpreter.
+# But ... that's exactly what we want to do.
+# So this script exists to find a 'compliant' Python install and use that.
+
+PYTHONREV="3.10"
+CMD="python${PYTHONREV}"
+
+if [ -x "$(command -v "$CMD")" ]; then
+    exec "$(which "$CMD")" "$@"
+else
+    case "$(uname)" in
+        Darwin)
+            # FIXME: What if it isn't there?
+            exec /opt/homebrew/bin/"$CMD" "$@"
+            ;;
+    esac
+    echo "Error: Unable to find a viable Python executable" >&2
+    exit 1
+fi