Return None instead of "" for empty hover results

Summary:
Empty hover results have historically been returning the empty string. This is ok for the UX and our telemetry metrics, but not ideal for chronicle metrics as they count this as a successful response. By sending `null` instead of the empty string, we fix  these metrics.

See the [LSP spec](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#languageServerProtocol) for more details.

The special casing in pyre_language_server is necessary because my testing of [exclude](lidatong/dataclasses-json#187) seems to not work. It still encodes as {} instead of `None`.

| Why not make an alias for `LspHoverResponse` = `NonEmptyLspHoverResponse | None`?
This isn't ideal for usability since our static method `from_pyre_hover_responses` would be on the `NonEmptyLspHoverResponse`.

Reviewed By: grievejia

Differential Revision: D48253814

fbshipit-source-id: 358ae59e3172dd7566e4806730a0cee72b0746d5

client/commands/daemon_querier.py

@@ -71,7 +71,7 @@ class GetDefinitionLocationsResponse:
 @dataclasses.dataclass(frozen=True)
 class GetHoverResponse:
     source: DaemonQuerierSource
-    data: lsp.LspHoverResponse
+    data: Optional[lsp.LspHoverResponse]
 
 
 def file_not_typechecked_coverage_result() -> lsp.TypeCoverageResponse:

client/commands/pyre_language_server.py

@@ -616,7 +616,7 @@ async def process_hover_request(
                 json_rpc.SuccessResponse(
                     id=request_id,
                     activity_key=activity_key,
-                    result=lsp.LspHoverResponse.empty().to_dict(),
+                    result=None,
                 ),
             )
         daemon_status_before = self.server_state.status_tracker.get_status()
@@ -636,10 +636,14 @@ async def process_hover_request(
             raw_result = None
             empty = True
         else:
-            raw_result = lsp.LspHoverResponse.cached_schema().dump(
-                result.data,
+            empty = result.data is None
+            raw_result = (
+                None
+                if empty
+                else lsp.LspHoverResponse.cached_schema().dump(
+                    result.data,
+                )
             )
-            empty = len(result.data.contents) == 0
 
         await lsp.write_json_rpc(
             self.output_channel,

client/commands/tests/language_server_test.py

@@ -1887,9 +1887,7 @@ async def test_hover__unopened(self) -> None:
             output_writer,
             [
                 self._expect_success_message(
-                    result=lsp.LspHoverResponse.cached_schema().dump(
-                        lsp.LspHoverResponse.empty()
-                    ),
+                    result=None,
                 )
             ],
         )

client/language_server/protocol.py

@@ -563,17 +563,20 @@ class LspHoverResponse(json_mixins.CamlCaseAndExcludeJsonMixin):
 
     contents: str
 
-    @staticmethod
-    def empty() -> "LspHoverResponse":
-        return LspHoverResponse(contents="")
-
     @staticmethod
     def from_pyre_hover_responses(
         responses: List["PyreHoverResponse"],
-    ) -> "LspHoverResponse":
-        return LspHoverResponse(
-            "\n".join(
-                [response.to_lsp_hover_response().contents for response in responses]
+    ) -> Optional["LspHoverResponse"]:
+        lsp_hover_responses = [
+            lsp_response
+            for lsp_response in (hover.to_lsp_hover_response() for hover in responses)
+            if lsp_response is not None
+        ]
+        return (
+            None
+            if len(lsp_hover_responses) == 0
+            else LspHoverResponse(
+                "\n".join(response.contents for response in lsp_hover_responses)
             )
         )
 
@@ -584,12 +587,14 @@ class PyreHoverResponse(json_mixins.CamlCaseAndExcludeJsonMixin):
     value: Optional[str] = None
     docstring: Optional[str] = None
 
-    def to_lsp_hover_response(self) -> LspHoverResponse:
+    def to_lsp_hover_response(self) -> Optional[LspHoverResponse]:
         lines = []
         if self.value:
             lines.append(f"```\n{self.value}\n```" if self.value else "")
         if self.docstring:
             lines.append(self.docstring)
+        if len(lines) == 0:
+            return None
         return LspHoverResponse("\n".join(lines))
 
 

client/language_server/remote_index.py

@@ -10,7 +10,7 @@
 
 import abc
 from pathlib import Path
-from typing import List
+from typing import List, Optional
 
 from . import protocol as lsp
 
@@ -30,7 +30,7 @@ async def definition(
     @abc.abstractmethod
     async def hover(
         self, path: Path, position: lsp.PyrePosition
-    ) -> lsp.LspHoverResponse:
+    ) -> Optional[lsp.LspHoverResponse]:
         raise NotImplementedError()
 
     @abc.abstractmethod
@@ -71,8 +71,8 @@ async def references(
 
     async def hover(
         self, path: Path, position: lsp.PyrePosition
-    ) -> lsp.LspHoverResponse:
-        return lsp.LspHoverResponse.empty()
+    ) -> Optional[lsp.LspHoverResponse]:
+        return None
 
     async def prepare_call_hierarchy(
         self,

client/language_server/tests/protocol_test.py

@@ -30,6 +30,7 @@
     Info,
     InitializationOptions,
     InitializeParameters,
+    LspHoverResponse,
     PublishDiagnosticsClientCapabilities,
     PublishDiagnosticsClientTagSupport,
     PyreHoverResponse,
@@ -185,12 +186,29 @@ class LSPHoverResponseTest(testslide.TestCase):
     def test_to_lsp_response(self) -> None:
         result = PyreHoverResponse("type", "docstring").to_lsp_hover_response()
         expected = "```\ntype\n```\ndocstring"
+        self.assertIsNotNone(result)
         self.assertEqual(result.contents, expected)
 
     def test_to_lsp_response_empty(self) -> None:
         result = PyreHoverResponse().to_lsp_hover_response()
-        expected = ""
-        self.assertEqual(result.contents, expected)
+        self.assertIsNone(result)
+
+    def test_from_pyre_hover_responses_all_empty(self) -> None:
+        self.assertIsNone(
+            LspHoverResponse.from_pyre_hover_responses(
+                [PyreHoverResponse(), PyreHoverResponse()]
+            )
+        )
+
+    def test_from_pyre_hover_responses_non_empty(self) -> None:
+        actual = LspHoverResponse.from_pyre_hover_responses(
+            [
+                PyreHoverResponse(),
+                PyreHoverResponse("type", "docstring"),
+            ]
+        )
+        expected = LspHoverResponse("```\ntype\n```\ndocstring")
+        self.assertEqual(actual, expected)
 
 
 class LSPParsingTest(testslide.TestCase):