Implement dependency resolution

Author: Gallaecio

scrapy_poet/_request_fingerprinter.py

@@ -100,16 +100,10 @@ def _get_deps(self, request: Request) -> Optional[List[str]]:
             dependencies requested by the request, or None if dependency injection
             is not required."""
             plan = self._injector.build_plan(request)
-            root_deps = plan[-1][1]
-            if not root_deps:
+            deps = {dep for dep, params in plan[:-1]} - self.IGNORED_UNANNOTATED_DEPS
+            if not deps:
                 return None
-            return sorted(
-                [
-                    _serialize_dep(cls)
-                    for cls in root_deps.values()
-                    if cls not in self.IGNORED_UNANNOTATED_DEPS
-                ]
-            )
+            return sorted([_serialize_dep(cls) for cls in deps])
 
         def get_deps_key(self, request: Request) -> Optional[bytes]:
             """Return a JSON array as bytes that uniquely identifies the

tests/test_request_fingerprinter.py

@@ -305,16 +305,6 @@ async def parse_all(self, response, input_a: input_cls_a, input_b: input_cls_b):
 
 
 def test_dep_resolution():
-    """Currently we do not resolve dependencies, so it is possible to get a
-    different fingerprint for callbacks that resolve to identical
-    dependencies.
-
-    The reason for not resolving dependencies is that it could be hard where
-    items are involved. This might be addressed in the future, in which case
-    we should consider to fingerprint based on leaf dependencies (those with a
-    provider) and not on the root dependencies present in the callback.
-    """
-
     class TestSpider(Spider):
         name = "test_spider"
 
@@ -330,7 +320,7 @@ async def parse_b(self, response, web: WebPage, http_response: HttpResponse):
     fingerprint1 = fingerprinter.fingerprint(request1)
     request2 = Request("https://toscrape.com", callback=crawler.spider.parse_b)
     fingerprint2 = fingerprinter.fingerprint(request2)
-    assert fingerprint1 != fingerprint2
+    assert fingerprint1 == fingerprint2
 
 
 def test_page_params(caplog):