lister: Allow lister to build url out of the instance parameter

This pushes the rather elementary logic within the lister's scope. This will simplify
and unify cli call between lister and scheduler clis. This will also allow to reduce
erroneous operations which can happen for example in the add-forge-now.

With the following, we will only have to provide the type and the instance, then
everything will be scheduled properly.

Refs. swh/devel/swh-lister#4693

swh/lister/gitlab/lister.py

@@ -99,7 +99,7 @@ class GitLabLister(Lister[GitLabListerState, PageResult]):
     def __init__(
         self,
         scheduler,
-        url: str,
+        url: Optional[str] = None,
         name: Optional[str] = "gitlab",
         instance: Optional[str] = None,
         credentials: Optional[CredentialsType] = None,
@@ -113,7 +113,8 @@ class GitLabLister(Lister[GitLabListerState, PageResult]):
             self.LISTER_NAME = name
         super().__init__(
             scheduler=scheduler,
-            url=url.rstrip("/"),
+            # if url is not provided, url will be built in the `build_url` method
+            url=url.rstrip("/") if url else None,
             instance=instance,
             credentials=credentials,
             max_origins_per_page=max_origins_per_page,
@@ -138,6 +139,11 @@ class GitLabLister(Lister[GitLabListerState, PageResult]):
             if api_token:
                 self.session.headers["Authorization"] = f"Bearer {api_token}"
 
+    def build_url(self, instance: str) -> str:
+        """Build gitlab api url."""
+        prefix_url = super().build_url(instance)
+        return f"{prefix_url}/api/v4"
+
     def state_from_dict(self, d: Dict[str, Any]) -> GitLabListerState:
         return GitLabListerState(**d)
 

swh/lister/gitlab/tests/test_lister.py

@@ -22,17 +22,30 @@ logger = logging.getLogger(__name__)
 
 
 def api_url(instance: str) -> str:
-    return f"https://{instance}/api/v4/"
+    return f"https://{instance}/api/v4"
 
 
 def _match_request(request, lister_name="gitlab"):
     return request.headers.get("User-Agent") == USER_AGENT_TEMPLATE % lister_name
 
 
+def test_lister_gitlab_fail_to_instantiate(swh_scheduler):
+    """Build a lister without its url nor its instance should raise"""
+    # while instantiating a gitlab lister is fine with the url or the instance...
+    assert GitLabLister(swh_scheduler, url="https://gitlab.com/api/v4") is not None
+    assert GitLabLister(swh_scheduler, instance="gitlab.fr") is not None
+
+    # ... It will raise without any of those
+    with pytest.raises(ValueError, match="'url' or 'instance'"):
+        GitLabLister(swh_scheduler)
+
+
 def test_lister_gitlab(datadir, swh_scheduler, requests_mock):
     """Gitlab lister supports full listing"""
     instance = "gitlab.com"
-    lister = GitLabLister(swh_scheduler, url=api_url(instance), instance=instance)
+    lister = GitLabLister(swh_scheduler, instance=instance)
+
+    assert lister.url == api_url(instance)
 
     response = gitlab_page_response(datadir, instance, 1)