Fix hashing completion objects with formatted text

src/prompt_toolkit/completion/base.py

@@ -81,7 +81,9 @@ def __eq__(self, other: object) -> bool:
         )
 
     def __hash__(self) -> int:
-        return hash((self.text, self.start_position, self.display, self._display_meta))
+        # Display and metadata may contain unhashable formatted text. These
+        # two fields alone still guarantee equal completions have equal hashes.
+        return hash((self.text, self.start_position))
 
     @property
     def display_text(self) -> str:

tests/test_completion.py

@@ -8,6 +8,7 @@
 
 from prompt_toolkit.completion import (
     CompleteEvent,
+    Completion,
     FuzzyWordCompleter,
     NestedCompleter,
     PathCompleter,
@@ -467,3 +468,39 @@ def create_completer(deduplicate: bool):
         )
     )
     assert len(completions) == 5
+
+
+def test_completion_hash_default_display():
+    first = Completion("example", start_position=-2)
+    equal = Completion("example", start_position=-2)
+    different = Completion("other", start_position=-2)
+    assert first == equal
+    assert hash(first) == hash(equal)
+    assert {first, equal, different} == {first, different}
+    assert {first: "cached"}[equal] == "cached"
+
+
+def test_completion_hash_formatted_display_and_metadata():
+    first = Completion(
+        "example", display=[("class:name", "Example")], display_meta=[("", "meta")]
+    )
+    equal = Completion(
+        "example", display=[("class:name", "Example")], display_meta=[("", "meta")]
+    )
+    different = Completion(
+        "example", display=[("class:name", "Other")], display_meta=[("", "meta")]
+    )
+    assert first == equal
+    assert hash(first) == hash(equal)
+    assert len({first, equal, different}) == 2
+
+
+def test_completion_hash_does_not_evaluate_lazy_metadata():
+    def metadata():
+        raise AssertionError("Metadata should remain lazy")
+
+    first = Completion("example", display_meta=metadata)
+    equal = Completion("example", display_meta=metadata)
+    assert first == equal
+    assert hash(first) == hash(equal)
+    assert len({first, equal}) == 1