Handle empty object capabilities as truthy where applicable

Another one of those "be vscode plox" things.
Servers seem to expect things like
{
	"capabilities": {
		"whateverProvider": {}
	}
}
to mean that the server is really a provider of whatever.
Earliest offender is the swift server being a code action provider.

ycmd/completers/language_server/language_server_completer.py

@@ -1496,7 +1496,8 @@ def SignatureHelpAvailable( self ):
     if not self.ServerIsReady():
       return responses.SignatureHelpAvailalability.PENDING
 
-    if bool( self._server_capabilities.get( 'signatureHelpProvider' ) ):
+    if _IsCapabilityProvided( self._server_capabilities,
+                              'signatureHelpProvider' ):
       return responses.SignatureHelpAvailalability.AVAILABLE
     else:
       return responses.SignatureHelpAvailalability.NOT_AVAILABLE
@@ -1506,7 +1507,8 @@ def ComputeSignaturesInner( self, request_data ):
     if not self.ServerIsReady():
       return {}
 
-    if not self._server_capabilities.get( 'signatureHelpProvider' ):
+    if not _IsCapabilityProvided( self._server_capabilities,
+                                  'signatureHelpProvider' ):
       return {}
 
     self._UpdateServerWithCurrentFileContents( request_data )
@@ -1551,8 +1553,9 @@ def ComputeSemanticTokens( self, request_data ):
     if not self._semantic_token_atlas:
       return {}
 
-    range_supported = self._server_capabilities[ 'semanticTokensProvider' ].get(
-      'range', False )
+    range_supported = _IsCapabilityProvided(
+        self._server_capabilities[ 'semanticTokensProvider' ],
+        'range' )
 
     self._UpdateServerWithCurrentFileContents( request_data )
 
@@ -1588,7 +1591,8 @@ def ComputeInlayHints( self, request_data ):
     if not self._ServerIsInitialized():
       return []
 
-    if 'inlayHintProvider' not in self._server_capabilities:
+    if not _IsCapabilityProvided( self._server_capabilities,
+                                  'inlayHintProvider' ):
       return []
 
     self._UpdateServerWithCurrentFileContents( request_data )
@@ -1763,7 +1767,8 @@ def GetSubcommandsMap( self ):
       )
 
     if ( self._server_capabilities and
-         'callHierarchyProvider' in self._server_capabilities ):
+         _IsCapabilityProvided( self._server_capabilities,
+                                'callHierarchyProvider' ) ):
       commands[ 'GoToCallees' ] = (
         lambda self, request_data, args:
             self.CallHierarchy( request_data, [ 'outgoing' ] )
@@ -1787,9 +1792,10 @@ def _GetSubcommandProvider( self, provider_list ):
 
     for providers in provider_list:
       if isinstance( providers, tuple ):
-        if all( capabilities.get( provider ) for provider in providers ):
+        if all( _IsCapabilityProvided( capabilities, provider )
+                for provider in providers ):
           return providers
-      if capabilities.get( providers ):
+      if _IsCapabilityProvided( capabilities, providers ):
         return providers
     return None
 
@@ -2345,11 +2351,7 @@ def _SetUpSemanticTokenAtlas( self, capabilities: dict ):
     if server_config is None:
       return
 
-    server_full_support = server_config.get( 'full' )
-    if server_full_support == {}:
-      server_full_support = True
-
-    if not server_full_support:
+    if not _IsCapabilityProvided( server_config, 'full' ):
       return
 
     self._semantic_token_atlas = TokenAtlas( server_config[ 'legend' ] )
@@ -3539,6 +3541,11 @@ def DecodeModifiers( self, tokenModifiers ):
   return tokens
 
 
+def _IsCapabilityProvided( capabilities, query ):
+  capability = capabilities.get( query )
+  return bool( capability ) or capability == {}
+
+
 def RetryOnFailure( expected_error_codes, num_retries = 3 ):
   for i in range( num_retries ):
     try: