Implement support for taking over library prefix of deprecated compon…

…ents

Commodore will verify that either the component who's prefix we're
trying to take over isn't present in the cluster configuration (in this
case the alias is just a regular alias) or that the component is
deprecated, and has nominated us as their replacement component. Library
prefixes of non-deprecated components, or deprecated components which
don't specify a replacement can't be taken over.

commodore/dependency_mgmt/component_library.py

@@ -21,8 +21,16 @@ def validate_component_library_name(cname: str, lib: Path) -> Path:
     return lib
 
 
-def _check_library_alias_prefixes(libalias: str, cn: str, component_prefixes: set[str]):
-    for p in component_prefixes - {cn}:
+def _check_library_alias_prefixes(
+    libalias: str,
+    cn: str,
+    component_prefixes: set[str],
+    additional_cname: str,
+):
+    prefixes = component_prefixes - {cn}
+    if additional_cname:
+        prefixes = prefixes - {additional_cname}
+    for p in prefixes:
         if libalias.startswith(p):
             raise click.ClickException(
                 f"Invalid alias prefix '{p}' "
@@ -40,8 +48,27 @@ def _check_library_alias_collisions(cfg: Config, cluster_params: dict[str, Any])
     for cn, component in components.items():
         cmeta = cluster_params[component.parameters_key].get("_metadata", {})
         aliases = cmeta.get("library_aliases", {})
+        # If component replaces another component, and wants to use the old component's
+        # library prefix, it should set `_metadata.replaces` to the old component name.
+        additional_cname = cmeta.get("replaces", "")
+        if additional_cname and additional_cname in components:
+            ometa = cluster_params[components[additional_cname].parameters_key].get(
+                "_metadata", {}
+            )
+            odeprecated = ometa.get("deprecated", False)
+            if not odeprecated:
+                click.secho(
+                    f" > Ignoring additional library prefix '{additional_cname}' "
+                    + f"requested by '{cn}', component with requested name is "
+                    + "also deployed on the cluster.",
+                    fg="yellow",
+                )
+                additional_cname = ""
+
         for libalias in aliases.keys():
-            _check_library_alias_prefixes(libalias, cn, component_prefixes)
+            _check_library_alias_prefixes(
+                libalias, cn, component_prefixes, additional_cname
+            )
             collisions.setdefault(libalias, set()).add(cn)
 
     for libalias, cnames in collisions.items():
@@ -56,7 +83,9 @@ def _check_library_alias_collisions(cfg: Config, cluster_params: dict[str, Any])
 def create_component_library_aliases(cfg: Config, cluster_params: dict[str, Any]):
     _check_library_alias_collisions(cfg, cluster_params)
 
-    for _, component in cfg.get_components().items():
+    components = cfg.get_components()
+
+    for cn, component in components.items():
         cmeta = cluster_params[component.parameters_key].get("_metadata", {})
         aliases = cmeta.get("library_aliases", {}).items()