Changes needed for override warn

conan/cli/printers/graph.py

@@ -78,6 +78,8 @@ def _format_resolved(title, reqs_to_print):
         output.info("Overrides", Color.BRIGHT_YELLOW)
         for req, override_info in overrides.serialize().items():
             output.info("    {}: {}".format(req, override_info), Color.BRIGHT_CYAN)
+            if override_info == [None]:
+                output.warning("Unused override")
 
     if deprecated:
         output.info("Deprecated", Color.BRIGHT_YELLOW)

conans/client/graph/graph.py

@@ -313,19 +313,17 @@ def create(nodes):
         overrides = {}
         for n in nodes:
             for r in n.conanfile.requires.values():
-                if r.override and not r.overriden_ref:  # overrides are not real graph edges
-                    continue
-                if r.overriden_ref:
-                    overrides.setdefault(r.overriden_ref, set()).add(r.override_ref)
-                else:
-                    overrides.setdefault(r.ref, set()).add(None)
+                if r.override:
+                    if r.overriden_ref:
+                        overrides.setdefault(r.overriden_ref, set()).add(r.override_ref)
+                    else:
+                        overrides.setdefault(r.ref, set()).add(None)
 
         # reduce, eliminate those overrides definitions that only override to None, that is, not
         # really an override
         result = Overrides()
         for require, override_info in overrides.items():
-            if len(override_info) != 1 or None not in override_info:
-                result._overrides[require] = override_info
+            result._overrides[require] = override_info
         return result
 
     def get(self, require):

test/integration/graph/require_override_test.py

@@ -40,3 +40,8 @@ def test_can_override_even_versions_with_build_metadata(self):
         c.assert_listed_require({"lib/1.0+xyz": "Cache",
                                  "pkg/1.0": "Cache"})
 
+    def test_discarded_override(self):
+        tc = TestClient(light=True)
+        tc.save({"conanfile.py": GenConanfile("lib").with_requirement("pkg/1.0", override=True)})
+        tc.run("graph info .")
+        assert "Unused override" in tc.out