1 files changed, 140 insertions, 0 deletions
diff --git a/gopls/internal/lsp/completion.go b/gopls/internal/lsp/completion.go
new file mode 100644
index 000000000..3052a5cbf
--- /dev/null
+++ b/gopls/internal/lsp/completion.go
@@ -0,0 +1,140 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package lsp
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"golang.org/x/tools/gopls/internal/lsp/protocol"
+	"golang.org/x/tools/gopls/internal/lsp/source"
+	"golang.org/x/tools/gopls/internal/lsp/source/completion"
+	"golang.org/x/tools/gopls/internal/lsp/template"
+	"golang.org/x/tools/gopls/internal/lsp/work"
+	"golang.org/x/tools/internal/event"
+	"golang.org/x/tools/internal/event/tag"
+)
+
+func (s *Server) completion(ctx context.Context, params *protocol.CompletionParams) (*protocol.CompletionList, error) {
+	snapshot, fh, ok, release, err := s.beginFileRequest(ctx, params.TextDocument.URI, source.UnknownKind)
+	defer release()
+	if !ok {
+		return nil, err
+	}
+	var candidates []completion.CompletionItem
+	var surrounding *completion.Selection
+	switch snapshot.View().FileKind(fh) {
+	case source.Go:
+		candidates, surrounding, err = completion.Completion(ctx, snapshot, fh, params.Position, params.Context)
+	case source.Mod:
+		candidates, surrounding = nil, nil
+	case source.Work:
+		cl, err := work.Completion(ctx, snapshot, fh, params.Position)
+		if err != nil {
+			break
+		}
+		return cl, nil
+	case source.Tmpl:
+		var cl *protocol.CompletionList
+		cl, err = template.Completion(ctx, snapshot, fh, params.Position, params.Context)
+		if err != nil {
+			break // use common error handling, candidates==nil
+		}
+		return cl, nil
+	}
+	if err != nil {
+		event.Error(ctx, "no completions found", err, tag.Position.Of(params.Position))
+	}
+	if candidates == nil {
+		return &protocol.CompletionList{
+			IsIncomplete: true,
+			Items:        []protocol.CompletionItem{},
+		}, nil
+	}
+
+	rng, err := surrounding.Range()
+	if err != nil {
+		return nil, err
+	}
+
+	// When using deep completions/fuzzy matching, report results as incomplete so
+	// client fetches updated completions after every key stroke.
+	options := snapshot.View().Options()
+	incompleteResults := options.DeepCompletion || options.Matcher == source.Fuzzy
+
+	items := toProtocolCompletionItems(candidates, rng, options)
+
+	return &protocol.CompletionList{
+		IsIncomplete: incompleteResults,
+		Items:        items,
+	}, nil
+}
+
+func toProtocolCompletionItems(candidates []completion.CompletionItem, rng protocol.Range, options *source.Options) []protocol.CompletionItem {
+	var (
+		items                  = make([]protocol.CompletionItem, 0, len(candidates))
+		numDeepCompletionsSeen int
+	)
+	for i, candidate := range candidates {
+		// Limit the number of deep completions to not overwhelm the user in cases
+		// with dozens of deep completion matches.
+		if candidate.Depth > 0 {
+			if !options.DeepCompletion {
+				continue
+			}
+			if numDeepCompletionsSeen >= completion.MaxDeepCompletions {
+				continue
+			}
+			numDeepCompletionsSeen++
+		}
+		insertText := candidate.InsertText
+		if options.InsertTextFormat == protocol.SnippetTextFormat {
+			insertText = candidate.Snippet()
+		}
+
+		// This can happen if the client has snippets disabled but the
+		// candidate only supports snippet insertion.
+		if insertText == "" {
+			continue
+		}
+
+		doc := &protocol.Or_CompletionItem_documentation{
+			Value: protocol.MarkupContent{
+				Kind:  protocol.Markdown,
+				Value: source.CommentToMarkdown(candidate.Documentation, options),
+			},
+		}
+		if options.PreferredContentFormat != protocol.Markdown {
+			doc.Value = candidate.Documentation
+		}
+		item := protocol.CompletionItem{
+			Label:  candidate.Label,
+			Detail: candidate.Detail,
+			Kind:   candidate.Kind,
+			TextEdit: &protocol.TextEdit{
+				NewText: insertText,
+				Range:   rng,
+			},
+			InsertTextFormat:    &options.InsertTextFormat,
+			AdditionalTextEdits: candidate.AdditionalTextEdits,
+			// This is a hack so that the client sorts completion results in the order
+			// according to their score. This can be removed upon the resolution of
+			// https://github.com/Microsoft/language-server-protocol/issues/348.
+			SortText: fmt.Sprintf("%05d", i),
+
+			// Trim operators (VSCode doesn't like weird characters in
+			// filterText).
+			FilterText: strings.TrimLeft(candidate.InsertText, "&*"),
+
+			Preselect:     i == 0,
+			Documentation: doc,
+			Tags:          candidate.Tags,
+			Deprecated:    candidate.Deprecated,
+		}
+		items = append(items, item)
+	}
+	return items
+}