refactor: replace SubProject inheritance with has-a Fetcher composition

SubProject was an ABC mixing VCS-specific capabilities with domain
orchestration. Archive fetching has no concept of branches/tags/revisions,
so forcing it to implement VCS-shaped stubs was a design smell.

New domain model:
- Fetcher (Protocol): minimal common contract (fetch, freeze, wanted_version,
  latest_available_version, list_tool_info)
- VcsFetcher(Fetcher, Protocol): VCS additions (branches, tags, revisions,
  browse_tree, patch_type) — git and svn only
- AbstractVcsFetcher(ABC): shared latest_available_version + freeze logic,
  eliminating duplication between GitFetcher and SvnFetcher
- ArchiveFetcher: implements Fetcher only — no VCS methods
- SubProject: concrete domain aggregate composed with a Fetcher; single
  dispatch point via as_vcs() -> VcsFetcher | None

All cyclomatic complexity kept ≤ 6. Pylint 10.00/10. All 569 unit tests
pass. Feature tests pass for git; SVN failures are environmental (no svn).

https://claude.ai/code/session_01BMSF8XFAxV6hABQgL7RZ3z

Author: claude

dfetch/commands/add.py

@@ -29,10 +29,8 @@
 from dfetch.manifest.remote import Remote
 from dfetch.manifest.version import Version
 from dfetch.project import create_sub_project, create_super_project
-from dfetch.project.gitsubproject import GitSubProject
 from dfetch.project.subproject import SubProject
 from dfetch.project.superproject import SuperProject
-from dfetch.project.svnsubproject import SvnSubProject
 from dfetch.terminal import Entry, LsFunction
 from dfetch.terminal.tree_browser import (
     BrowserConfig,
@@ -86,9 +84,9 @@ def browse_tree(subproject: SubProject, version: str = "") -> Generator[LsFuncti
     Adds '.' as the first entry to allow selecting the repo root (which is
     treated as empty src).
     """
-    if isinstance(subproject, (GitSubProject, SvnSubProject)):
-        remote = subproject.remote_repo
-        with remote.browse_tree(version) as vcs_ls:
+    vcs = subproject.as_vcs()
+    if vcs is not None:
+        with vcs.browse_tree(version) as vcs_ls:
 
             def ls(path: str = "") -> list[Entry]:
                 entries = [

dfetch/commands/environment.py

@@ -16,7 +16,7 @@
 
 import dfetch.commands.command
 from dfetch.log import get_logger
-from dfetch.project import SUPPORTED_SUBPROJECT_TYPES
+from dfetch.project import SUPPORTED_FETCHERS
 
 logger = get_logger(__name__)
 
@@ -37,5 +37,5 @@ def __call__(self, _: argparse.Namespace) -> None:
         logger.print_report_line(
             "platform", f"{platform.system()} {platform.release()}"
         )
-        for project_type in SUPPORTED_SUBPROJECT_TYPES:
-            project_type.list_tool_info()
+        for fetcher_type in SUPPORTED_FETCHERS:
+            fetcher_type.list_tool_info()

dfetch/commands/format_patch.py

@@ -34,9 +34,7 @@
 import dfetch.project
 from dfetch.log import get_logger
 from dfetch.project import create_super_project
-from dfetch.project.gitsubproject import GitSubProject
 from dfetch.project.subproject import SubProject
-from dfetch.project.svnsubproject import SvnSubProject
 from dfetch.util.util import (
     catch_runtime_exceptions,
     check_no_path_traversal,
@@ -145,12 +143,6 @@ def __call__(self, args: argparse.Namespace) -> None:
 
 
 def _determine_target_patch_type(subproject: SubProject) -> PatchType:
-    """Determine the subproject type for the patch."""
-    if isinstance(subproject, GitSubProject):
-        required_type = PatchType.GIT
-    elif isinstance(subproject, SvnSubProject):
-        required_type = PatchType.SVN
-    else:
-        required_type = PatchType.PLAIN
-
-    return required_type
+    """Determine the patch format for *subproject*."""
+    vcs = subproject.as_vcs()
+    return vcs.patch_type() if vcs is not None else PatchType.PLAIN

dfetch/project/__init__.py

@@ -7,36 +7,37 @@
 from dfetch.log import get_logger
 from dfetch.manifest.manifest import Manifest
 from dfetch.manifest.parse import find_manifest
-from dfetch.project.archivesubproject import ArchiveSubProject
-from dfetch.project.gitsubproject import GitSubProject
+from dfetch.project.archivesubproject import ArchiveFetcher
+from dfetch.project.gitsubproject import GitFetcher
 from dfetch.project.gitsuperproject import GitSuperProject
 from dfetch.project.subproject import SubProject
 from dfetch.project.superproject import NoVcsSuperProject, SuperProject
-from dfetch.project.svnsubproject import SvnSubProject
+from dfetch.project.svnsubproject import SvnFetcher
 from dfetch.project.svnsuperproject import SvnSuperProject
 from dfetch.util.util import resolve_absolute_path
 
-SUPPORTED_SUBPROJECT_TYPES: list[
-    type[ArchiveSubProject] | type[GitSubProject] | type[SvnSubProject]
-] = [ArchiveSubProject, GitSubProject, SvnSubProject]
+_AnyFetcherType = type[ArchiveFetcher] | type[GitFetcher] | type[SvnFetcher]
+SUPPORTED_FETCHERS: list[_AnyFetcherType] = [ArchiveFetcher, GitFetcher, SvnFetcher]
 SUPPORTED_SUPERPROJECT_TYPES = [GitSuperProject, SvnSuperProject]
 
+# Backward-compatible alias used by environment.py and any external callers.
+SUPPORTED_SUBPROJECT_TYPES = SUPPORTED_FETCHERS
+
 logger = get_logger(__name__)
 
 
 def create_sub_project(
     project_entry: dfetch.manifest.project.ProjectEntry,
 ) -> SubProject:
-    """Create a new SubProject based on a project from the manifest."""
-    for project_type in SUPPORTED_SUBPROJECT_TYPES:
-        if project_type.NAME == project_entry.vcs:
-            return project_type(project_entry)
+    """Create a SubProject by selecting the appropriate fetcher for *project_entry*."""
+    for fetcher_type in SUPPORTED_FETCHERS:
+        if fetcher_type.NAME == project_entry.vcs:
+            return SubProject(project_entry, fetcher_type(project_entry.remote_url))
 
-    for project_type in SUPPORTED_SUBPROJECT_TYPES:
-        project = project_type(project_entry)
+    for fetcher_type in SUPPORTED_FETCHERS:
+        if fetcher_type.handles(project_entry.remote_url):
+            return SubProject(project_entry, fetcher_type(project_entry.remote_url))
 
-        if project.check():
-            return project
     raise RuntimeError("vcs type unsupported")