Added downgrading note when updating to an older version (#8176)

src/poetry/installation/executor.py

@@ -461,13 +461,18 @@ class Executor:
             )
 
         if isinstance(operation, Update):
+            initial_version = (initial_pkg := operation.initial_package).version
+            target_version = (target_pkg := operation.target_package).version
+            update_kind = (
+                "Updating" if target_version >= initial_version else "Downgrading"
+            )
             return (
-                f"<{base_tag}>Updating"
-                f" <{package_color}>{operation.initial_package.name}</{package_color}> "
+                f"<{base_tag}>{update_kind}"
+                f" <{package_color}>{initial_pkg.name}</{package_color}> "
                 f"(<{source_operation_color}>"
-                f"{operation.initial_package.full_pretty_version}"
+                f"{initial_pkg.full_pretty_version}"
                 f"</{source_operation_color}> -> <{operation_color}>"
-                f"{operation.target_package.full_pretty_version}</>)</>"
+                f"{target_pkg.full_pretty_version}</>)</>"
             )
         return ""
 

tests/installation/test_executor.py

@@ -246,6 +246,7 @@ def test_execute_executes_a_batch_of_operations(
             Install(Package("pytest", "3.5.1")),
             Uninstall(Package("attrs", "17.4.0")),
             Update(Package("requests", "2.18.3"), Package("requests", "2.18.4")),
+            Update(Package("pytest", "3.5.1"), Package("pytest", "3.5.0")),
             Uninstall(Package("clikit", "0.2.3")).skip("Not currently installed"),
             Install(file_package),
             Install(directory_package),
@@ -254,11 +255,12 @@ def test_execute_executes_a_batch_of_operations(
     )
 
     expected = f"""
-Package operations: 4 installs, 1 update, 1 removal
+Package operations: 4 installs, 2 updates, 1 removal
 
   • Installing pytest (3.5.1)
   • Removing attrs (17.4.0)
   • Updating requests (2.18.3 -> 2.18.4)
+  • Downgrading pytest (3.5.1 -> 3.5.0)
   • Installing demo (0.1.0 {file_package.source_url})
   • Installing simple-project (1.2.3 {directory_package.source_url})
   • Installing demo (0.1.0 master)
@@ -267,9 +269,9 @@ Package operations: 4 installs, 1 update, 1 removal
     expected_lines = set(expected.splitlines())
     output_lines = set(io.fetch_output().splitlines())
     assert output_lines == expected_lines
-    assert wheel_install.call_count == 5
-    # Two pip uninstalls: one for the remove operation one for the update operation
-    assert len(env.executed) == 2
+    assert wheel_install.call_count == 6
+    # 3 pip uninstalls: one for the remove operation and two for the update operations
+    assert len(env.executed) == 3
     assert return_code == 0
 
     assert prepare_spy.call_count == 2