Give a clear error message when adding package with the same name as your local package (#3841)

* give error message when package to be installed is the same as the package name

* handle AssertionError in check_solver_result

* added unit test to check a clear error message when package is a dependence of itself

* fixed message of unit test

* update explanation as in master branch

* added unit test typing hints

src/poetry/mixology/incompatibility.py

@@ -59,7 +59,8 @@ class Incompatibility:
                     # incompatibility irrelevant, since we already know that mutually
                     # exclusive version ranges are incompatible. We should never derive
                     # an irrelevant incompatibility.
-                    assert by_ref[ref] is not None
+                    err_msg = f"Package '{ref}' is listed as a dependency of itself."
+                    assert by_ref[ref] is not None, err_msg
                 else:
                     by_ref[ref] = term
 

tests/mixology/helpers.py

@@ -48,7 +48,6 @@ def check_solver_result(
         locked = {k: DependencyPackage(l.to_dependency(), l) for k, l in locked.items()}
 
     solver = VersionSolver(root, provider, locked=locked, use_latest=use_latest)
-
     try:
         solution = solver.solve()
     except SolveFailure as e:
@@ -61,6 +60,11 @@ def check_solver_result(
             return
 
         raise
+    except AssertionError as e:
+        if error:
+            assert str(e) == error
+            return
+        raise
 
     packages = {}
     for package in solution.packages:

tests/mixology/version_solver/test_unsolvable.py

@@ -110,3 +110,13 @@ Thus, b is forbidden.
 So, because myapp depends on b (*), version solving failed."""
 
     check_solver_result(root, provider, error=error, tries=2)
+
+
+def test_package_with_the_same_name_gives_clear_error_message(
+    root: "ProjectPackage", provider: "Provider", repo: "Repository"
+):
+    pkg_name = "a"
+    root.add_dependency(Factory.create_dependency(pkg_name, "*"))
+    add_to_repo(repo, pkg_name, "1.0.0", deps={pkg_name: "1.0.0"})
+    error = f"Package '{pkg_name}' is listed as a dependency of itself."
+    check_solver_result(root, provider, error=error)