internal/lsp: trigger signature help after completing a function

Change-Id: Ib0ee79a11dd828c77bdf22a19a24ed9d883d8393
Reviewed-on: https://go-review.googlesource.com/c/tools/+/172600
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>

internal/lsp/completion.go

@@ -33,20 +33,16 @@ func (s *Server) completion(ctx context.Context, params *protocol.CompletionPara
 	}
 	items, prefix, err := source.Completion(ctx, f, rng.Start)
 	if err != nil {
-		s.log.Infof(ctx, "no completions found for %s:%v:%v", uri, int(params.Position.Line), int(params.Position.Character))
+		s.log.Infof(ctx, "no completions found for %s:%v:%v: %v", uri, int(params.Position.Line), int(params.Position.Character), err)
 		items = []source.CompletionItem{}
 	}
 	return &protocol.CompletionList{
 		IsIncomplete: false,
-		Items:        toProtocolCompletionItems(items, prefix, params.Position, s.snippetsSupported, s.usePlaceholders),
+		Items:        toProtocolCompletionItems(items, prefix, params.Position, s.insertTextFormat, s.usePlaceholders),
 	}, nil
 }
 
-func toProtocolCompletionItems(candidates []source.CompletionItem, prefix string, pos protocol.Position, snippetsSupported, usePlaceholders bool) []protocol.CompletionItem {
+func toProtocolCompletionItems(candidates []source.CompletionItem, prefix string, pos protocol.Position, insertTextFormat protocol.InsertTextFormat, usePlaceholders bool) []protocol.CompletionItem {
-	insertTextFormat := protocol.PlainTextTextFormat
-	if snippetsSupported {
-		insertTextFormat = protocol.SnippetTextFormat
-	}
 	sort.SliceStable(candidates, func(i, j int) bool {
 		return candidates[i].Score > candidates[j].Score
 	})
@@ -79,6 +75,15 @@ func toProtocolCompletionItems(candidates []source.CompletionItem, prefix string
 			FilterText: insertText,
 			Preselect:  i == 0,
 		}
+		// Trigger signature help for any function or method completion.
+		// This is helpful even if a function does not have parameters,
+		// since we show return types as well.
+		switch item.Kind {
+		case protocol.FunctionCompletion, protocol.MethodCompletion:
+			item.Command = &protocol.Command{
+				Command: "editor.action.triggerParameterHints",
+			}
+		}
 		items = append(items, item)
 	}
 	return items

internal/lsp/general.go

@@ -98,7 +98,10 @@ func (s *Server) initialize(ctx context.Context, params *protocol.InitializePara
 
 func (s *Server) setClientCapabilities(caps protocol.ClientCapabilities) {
 	// Check if the client supports snippets in completion items.
-	s.snippetsSupported = caps.TextDocument.Completion.CompletionItem.SnippetSupport
+	s.insertTextFormat = protocol.PlainTextTextFormat
+	if caps.TextDocument.Completion.CompletionItem.SnippetSupport {
+		s.insertTextFormat = protocol.SnippetTextFormat
+	}
 	// Check if the client supports configuration messages.
 	s.configurationSupported = caps.Workspace.Configuration
 	s.dynamicConfigurationSupported = caps.Workspace.DidChangeConfiguration.DynamicRegistration

internal/lsp/server.go

@@ -74,7 +74,7 @@ type Server struct {
 	// Configurations.
 	// TODO(rstambler): Separate these into their own struct?
 	usePlaceholders               bool
-	snippetsSupported             bool
+	insertTextFormat              protocol.InsertTextFormat
 	configurationSupported        bool
 	dynamicConfigurationSupported bool