From 0ed683baf91c07354829753195860a53ac35ac9d Mon Sep 17 00:00:00 2001
From: Boris Staletic <boris.staletic@protonmail.com>
Date: Mon, 12 Aug 2024 07:54:00 +0200
Subject: [PATCH] Add support for DocumentSymbol in document outline requests

We are intentionally not advertising the capability.
We do want a flat response, so receiving a DocumentSymbol is a
pessimisation.
Not advertising the capability means that conforming servers take the
faster code path and the likes of OmniSharp, that assume capabilities,
still work.

Yes, it's messy, but so is LSP.
---
 .../language_server_completer.py              | 49 +++++++++++++-
 .../language_server_completer_test.py         | 65 +++++++++++++++++++
 2 files changed, 111 insertions(+), 3 deletions(-)

diff --git a/ycmd/completers/language_server/language_server_completer.py b/ycmd/completers/language_server/language_server_completer.py
index cd2b1317bc..e47dc885e0 100644
--- a/ycmd/completers/language_server/language_server_completer.py
+++ b/ycmd/completers/language_server/language_server_completer.py
@@ -2655,10 +2655,10 @@ def GoToDocumentOutline( self, request_data ):
 
     result = response.get( 'result' ) or []
 
-    # We should only receive SymbolInformation (not DocumentSymbol)
     if any( 'range' in s for s in result ):
-      raise ValueError(
-        "Invalid server response; DocumentSymbol not supported" )
+      LOGGER.debug( 'Hierarchical DocumentSymbol not supported.' )
+      result = _FlattenDocumentSymbolHierarchy( result )
+      return _DocumentSymboListToGoTo( request_data, result )
 
     return _SymbolInfoListToGoTo( request_data, result )
 
@@ -3427,6 +3427,49 @@ def BuildGoToLocationFromSymbol( symbol ):
     return locations
 
 
+def _FlattenDocumentSymbolHierarchy( symbols ):
+  result = []
+  for s in symbols:
+    partial_results = [ s ]
+    if s.get( 'children' ):
+      partial_results.extend(
+        _FlattenDocumentSymbolHierarchy( s[ 'children' ] ) )
+    result.extend( partial_results )
+  return result
+
+
+def _DocumentSymboListToGoTo( request_data, symbols ):
+  """Convert a list of LSP DocumentSymbol into a YCM GoTo response"""
+
+  def BuildGoToLocationFromSymbol( symbol ):
+    symbol[ 'uri' ] = lsp.FilePathToUri( request_data[ 'filepath' ] )
+    location, line_value = _LspLocationToLocationAndDescription(
+      request_data,
+      symbol )
+
+    description = ( f'{ lsp.SYMBOL_KIND[ symbol[ "kind" ] ] }: '
+                    f'{ symbol[ "name" ] }' )
+
+    goto = responses.BuildGoToResponseFromLocation( location,
+                                                    description )
+    goto[ 'extra_data' ] = {
+      'kind': lsp.SYMBOL_KIND[ symbol[ 'kind' ] ],
+      'name': symbol[ 'name' ],
+    }
+    return goto
+
+  locations = [ BuildGoToLocationFromSymbol( s ) for s in
+                sorted( symbols,
+                        key = lambda s: ( s[ 'kind' ], s[ 'name' ] ) ) ]
+
+  if not locations:
+    raise RuntimeError( "Symbol not found" )
+  elif len( locations ) == 1:
+    return locations[ 0 ]
+  else:
+    return locations
+
+
 def _LspLocationToLocationAndDescription( request_data,
                                           location,
                                           range_property = 'range' ):
diff --git a/ycmd/tests/language_server/language_server_completer_test.py b/ycmd/tests/language_server/language_server_completer_test.py
index 56f4f51c94..57c340969d 100644
--- a/ycmd/tests/language_server/language_server_completer_test.py
+++ b/ycmd/tests/language_server/language_server_completer_test.py
@@ -103,6 +103,71 @@ def _Check_Distance( point, start, end, expected ):
 
 
 class LanguageServerCompleterTest( TestCase ):
+  @IsolatedYcmd()
+  def test_LanguageServerCompleter_DocumentSymbol_Hierarchical( self, app ):
+    completer = MockCompleter()
+    completer._server_capabilities = { 'documentSymbolProvider': True }
+    request_data = RequestWrap( BuildRequest( filepath = '/foo' ) )
+    server_response = {
+      'result': [
+        {
+          "name": "testy",
+          "kind": 3,
+          "range": {
+            "start": { "line": 2, "character": 0 },
+            "end": { "line": 12, "character": 1 }
+          },
+          "children": [
+            {
+              "name": "MainClass",
+              "kind": 5,
+              "range": {
+                "start": { "line": 4, "character": 1 },
+                "end": { "line": 11, "character": 2 }
+              }
+            }
+          ]
+        },
+        {
+          "name": "other",
+          "kind": 3,
+          "range": {
+            "start": { "line": 14, "character": 0 },
+            "end": { "line": 15, "character": 1 }
+          },
+          "children": []
+        }
+      ]
+    }
+
+    with patch.object( completer, '_ServerIsInitialized', return_value = True ):
+      with patch.object( completer.GetConnection(),
+                         'GetResponse',
+                         return_value = server_response ):
+        document_outline = completer.GoToDocumentOutline( request_data )
+        print( f'result: { document_outline }' )
+        assert_that( document_outline, contains_exactly(
+          has_entries( {
+            'line_num': 15,
+            'column_num': 1,
+            'filepath': '/foo',
+            'description': 'Namespace: other',
+          } ),
+          has_entries( {
+            'line_num': 3,
+            'column_num': 1,
+            'filepath': '/foo',
+            'description': 'Namespace: testy',
+          } ),
+          has_entries( {
+            'line_num': 5,
+            'column_num': 2,
+            'filepath': '/foo',
+            'description': 'Class: MainClass',
+          } )
+        ) )
+
+
   @IsolatedYcmd( { 'global_ycm_extra_conf':
                    PathToTestFile( 'extra_confs', 'settings_extra_conf.py' ) } )
   def test_LanguageServerCompleter_ExtraConf_ServerReset( self, app ):