reject circular self-add

src/poetry/console/commands/add.py

@@ -126,6 +126,7 @@ def handle(self) -> int:
         # dictionary.
         content: dict[str, Any] = self.poetry.file.read()
         poetry_content = content["tool"]["poetry"]
+        project_name = canonicalize_name(poetry_content["name"])
 
         if group == MAIN_GROUP:
             if "dependencies" not in poetry_content:
@@ -223,6 +224,14 @@ def handle(self) -> int:
 
             canonical_constraint_name = canonicalize_name(constraint_name)
 
+            if canonical_constraint_name == project_name:
+                self.line_error(
+                    f"<error>Cannot add dependency on <c1>{_constraint['name']}</c1> to"
+                    " project with the same name."
+                )
+                self.line_error("\nNo changes were applied.")
+                return 1
+
             for key in section:
                 if canonicalize_name(key) == canonical_constraint_name:
                     section[key] = constraint

tests/console/commands/test_add.py

@@ -1057,6 +1057,18 @@ def test_add_should_skip_when_adding_canonicalized_existing_package_with_no_cons
     assert expected in tester.io.fetch_output()
 
 
+def test_add_should_fail_circular_dependency(
+    app: PoetryTestApplication, repo: TestRepository, tester: CommandTester
+) -> None:
+    repo.add_package(get_package("simple-project", "1.1.2"))
+    result = tester.execute("simple-project")
+
+    assert result == 1
+
+    expected = "Cannot add dependency on simple-project to project with the same name."
+    assert expected in tester.io.fetch_error()
+
+
 def test_add_latest_should_not_create_duplicate_keys(
     project_factory: ProjectFactory,
     repo: TestRepository,