feat: add ability to override hub name

Author: Finn Ball

python/private/bzlmod/pip.bzl

@@ -427,39 +427,45 @@ def _pip_impl(module_ctx):
     for mod in module_ctx.modules:
         for pip_attr in mod.tags.parse:
             hub_name = pip_attr.hub_name
-            if hub_name not in pip_hub_map:
+            # only override if the module is root.
+            override = mod.is_root and pip_attr.override
+            if hub_name not in pip_hub_map or override:
                 pip_hub_map[pip_attr.hub_name] = struct(
                     module_name = mod.name,
                     python_versions = [pip_attr.python_version],
+                    pip_attr = pip_attr,
+                    override = override
                 )
-            elif pip_hub_map[hub_name].module_name != mod.name:
-                # We cannot have two hubs with the same name in different
-                # modules.
-                fail((
-                    "Duplicate cross-module pip hub named '{hub}': pip hub " +
-                    "names must be unique across modules. First defined " +
-                    "by module '{first_module}', second attempted by " +
-                    "module '{second_module}'"
-                ).format(
-                    hub = hub_name,
-                    first_module = pip_hub_map[hub_name].module_name,
-                    second_module = mod.name,
-                ))
-
-            elif pip_attr.python_version in pip_hub_map[hub_name].python_versions:
-                fail((
-                    "Duplicate pip python version '{version}' for hub " +
-                    "'{hub}' in module '{module}': the Python versions " +
-                    "used for a hub must be unique"
-                ).format(
-                    hub = hub_name,
-                    module = mod.name,
-                    version = pip_attr.python_version,
-                ))
-            else:
-                pip_hub_map[pip_attr.hub_name].python_versions.append(pip_attr.python_version)
-
-            _create_whl_repos(module_ctx, pip_attr, hub_whl_map, whl_overrides, simpleapi_cache)
+            elif not pip_hub_map[hub_name].pip_attr.override:
+                if pip_hub_map[hub_name].module_name != mod.name:
+                    # We cannot have two hubs with the same name in different
+                    # modules.
+                    fail((
+                        "Duplicate cross-module pip hub named '{hub}': pip hub " +
+                        "names must be unique across modules. First defined " +
+                        "by module '{first_module}', second attempted by " +
+                        "module '{second_module}'"
+                    ).format(
+                        hub = hub_name,
+                        first_module = pip_hub_map[hub_name].module_name,
+                        second_module = mod.name,
+                    ))
+
+                elif pip_attr.python_version in pip_hub_map[hub_name].python_versions:
+                    fail((
+                        "Duplicate pip python version '{version}' for hub " +
+                        "'{hub}' in module '{module}': the Python versions " +
+                        "used for a hub must be unique"
+                    ).format(
+                        hub = hub_name,
+                        module = mod.name,
+                        version = pip_attr.python_version,
+                    ))
+                else:
+                    pip_hub_map[pip_attr.hub_name].python_versions.append(pip_attr.python_version)
+
+    for value in pip_hub_map.values():
+        _create_whl_repos(module_ctx, value.pip_attr, hub_whl_map, whl_overrides, simpleapi_cache)
 
     for hub_name, whl_map in hub_whl_map.items():
         pip_repository(
@@ -557,6 +563,12 @@ A dict of labels to wheel names that is typically generated by the whl_modificat
 The labels are JSON config files describing the modifications.
 """,
         ),
+    "override": attr.bool(
+            default = False,
+            doc = """
+If the module is root, this may override any hub_name's listed in the dependencies.
+            """
+        ),
     }, **pip_repository_attrs)
     attrs.update(AUTH_ATTRS)