add lots of workarounds to handle disabled versions

Author: aignas

python/private/python.bzl

@@ -207,11 +207,15 @@ def parse_modules(*, module_ctx, logger, _fail = fail):
     # "3.X"` transitions work as expected.
     minor_version_toolchains = []
     other_toolchains = []
-    minor_mapping = list(config.minor_mapping.values())
+    minor_mapping = list([minor for minor, full in config.minor_mapping.items() if full])
     for t in toolchains:
         # FIXME @aignas 2025-04-04: How can we unit test that this ordering is
         # consistent with what would actually work?
-        if config.minor_mapping.get(t.python_version, t.python_version) in minor_mapping:
+        py_version = config.minor_mapping.get(t.python_version, t.python_version)
+        if not py_version:
+            # disable version
+            continue
+        elif py_version in minor_mapping:
             minor_version_toolchains.append(t)
         else:
             other_toolchains.append(t)
@@ -840,7 +844,11 @@ def _get_toolchain_config(*, modules, _fail = fail):
 
     return struct(
         kwargs = kwargs,
-        minor_mapping = minor_mapping,
+        # TODO @aignas 2025-11-04: better place for this?
+        minor_mapping = minor_mapping | {
+            # Add unsupported versions here
+            "3.8": "",
+        },
         default = default,
         register_all_versions = register_all_versions,
     )
@@ -940,7 +948,11 @@ def _create_toolchain_attr_structs(*, mod, config, seen_versions):
     if config.register_all_versions:
         arg_structs.extend([
             _create_toolchain_attrs_struct(python_version = v)
-            for v in config.default["tool_versions"].keys() + config.minor_mapping.keys()
+            for v in config.default["tool_versions"].keys() + [
+                minor
+                for minor, full in config.minor_mapping.items()
+                if full
+            ]
             if v not in seen_versions
         ])