feat: add lsp completion and hover handlers (#1724)

See #1533 

Still needs some work to link to console, but these are nice DevX
improvements for FTL/VSCode users.



https://github.com/TBD54566975/ftl/assets/51647/949201f9-6ea6-40d2-abd9-6cfb6395f106

lsp/completion.go

@@ -0,0 +1,144 @@
+package lsp
+
+import (
+	_ "embed"
+	"os"
+	"strings"
+
+	"github.com/tliron/glsp"
+	protocol "github.com/tliron/glsp/protocol_3_16"
+)
+
+//go:embed markdown/completion/verb.md
+var verbCompletionDocs string
+
+//go:embed markdown/completion/enumType.md
+var enumTypeCompletionDocs string
+
+//go:embed markdown/completion/enumValue.md
+var enumValueCompletionDocs string
+
+var (
+	snippetKind      = protocol.CompletionItemKindSnippet
+	insertTextFormat = protocol.InsertTextFormatSnippet
+
+	verbCompletionItem = protocol.CompletionItem{
+		Label:  "ftl:verb",
+		Kind:   &snippetKind,
+		Detail: stringPtr("FTL Verb"),
+		InsertText: stringPtr(`type ${1:Request} struct {}
+type ${2:Response} struct{}
+
+//ftl:verb
+func ${3:Name}(ctx context.Context, req ${1:Request}) (${2:Response}, error) {
+	return ${2:Response}{}, nil
+}`),
+		Documentation: &protocol.MarkupContent{
+			Kind:  protocol.MarkupKindMarkdown,
+			Value: verbCompletionDocs,
+		},
+		InsertTextFormat: &insertTextFormat,
+	}
+
+	enumTypeCompletionItem = protocol.CompletionItem{
+		Label:  "ftl:enum (sum type)",
+		Kind:   &snippetKind,
+		Detail: stringPtr("FTL Enum (sum type)"),
+		InsertText: stringPtr(`//ftl:enum
+type ${1:Enum} string
+
+const (
+	${2:Value1} ${1:Enum} = "${2:Value1}"
+	${3:Value2} ${1:Enum} = "${3:Value2}"
+)`),
+		Documentation: &protocol.MarkupContent{
+			Kind:  protocol.MarkupKindMarkdown,
+			Value: enumTypeCompletionDocs,
+		},
+		InsertTextFormat: &insertTextFormat,
+	}
+
+	enumValueCompletionItem = protocol.CompletionItem{
+		Label:  "ftl:enum (value)",
+		Kind:   &snippetKind,
+		Detail: stringPtr("FTL enum (value type)"),
+		InsertText: stringPtr(`//ftl:enum
+type ${1:Type} interface { ${2:interface}() }
+
+type ${3:Value} struct {}
+func (${3:Value}) ${2:interface}() {}
+`),
+		Documentation: &protocol.MarkupContent{
+			Kind:  protocol.MarkupKindMarkdown,
+			Value: enumValueCompletionDocs,
+		},
+		InsertTextFormat: &insertTextFormat,
+	}
+)
+
+var completionItems = []protocol.CompletionItem{
+	verbCompletionItem,
+	enumTypeCompletionItem,
+	enumValueCompletionItem,
+}
+
+func (s *Server) textDocumentCompletion() protocol.TextDocumentCompletionFunc {
+	return func(context *glsp.Context, params *protocol.CompletionParams) (interface{}, error) {
+		uri := params.TextDocument.URI
+		position := params.Position
+
+		doc, ok := s.documents.get(uri)
+		if !ok {
+			return nil, nil
+		}
+
+		line := int(position.Line - 1)
+		if line >= len(doc.lines) {
+			return nil, nil
+		}
+
+		lineContent := doc.lines[line]
+		character := int(position.Character - 1)
+		if character > len(lineContent) {
+			character = len(lineContent)
+		}
+
+		prefix := lineContent[:character]
+
+		// Filter completion items based on the prefix
+		var filteredItems []protocol.CompletionItem
+		for _, item := range completionItems {
+			if strings.HasPrefix(item.Label, prefix) || strings.Contains(item.Label, prefix) {
+				filteredItems = append(filteredItems, item)
+			}
+		}
+
+		return &protocol.CompletionList{
+			IsIncomplete: false,
+			Items:        filteredItems,
+		}, nil
+	}
+}
+
+func (s *Server) completionItemResolve() protocol.CompletionItemResolveFunc {
+	return func(context *glsp.Context, params *protocol.CompletionItem) (*protocol.CompletionItem, error) {
+		if path, ok := params.Data.(string); ok {
+			content, err := os.ReadFile(path)
+			if err != nil {
+				return nil, err
+			}
+
+			params.Documentation = &protocol.MarkupContent{
+				Kind:  protocol.MarkupKindMarkdown,
+				Value: string(content),
+			}
+		}
+
+		return params, nil
+	}
+}
+
+func stringPtr(v string) *string {
+	s := v
+	return &s
+}

lsp/document.go

@@ -0,0 +1,60 @@
+package lsp
+
+import (
+	"strings"
+
+	protocol "github.com/tliron/glsp/protocol_3_16"
+)
+
+// document represents a document that is open in the editor.
+// The Content and lines are parsed when the document is opened or changed to avoid having to perform
+// the same operation multiple times and to keep the interaction snappy for hover operations.
+type document struct {
+	uri     protocol.DocumentUri
+	Content string
+	lines   []string
+}
+
+// documentStore is a simple in-memory store for documents that are open in the editor.
+// Its primary purpose it to provide quick access to open files for operations like hover.
+// Rather than reading the file from disk, we can get the document from the store.
+type documentStore struct {
+	documents map[protocol.DocumentUri]*document
+}
+
+func newDocumentStore() *documentStore {
+	return &documentStore{
+		documents: make(map[protocol.DocumentUri]*document),
+	}
+}
+
+func (ds *documentStore) get(uri protocol.DocumentUri) (*document, bool) {
+	doc, ok := ds.documents[uri]
+	return doc, ok
+}
+
+func (ds *documentStore) set(uri protocol.DocumentUri, content string) {
+	ds.documents[uri] = &document{
+		uri:     uri,
+		Content: content,
+		lines:   strings.Split(content, "\n"),
+	}
+}
+
+func (ds *documentStore) delete(uri protocol.DocumentUri) {
+	delete(ds.documents, uri)
+}
+
+func (d *document) update(changes []interface{}) {
+	for _, change := range changes {
+		switch c := change.(type) {
+		case protocol.TextDocumentContentChangeEvent:
+			startIndex, endIndex := c.Range.IndexesIn(d.Content)
+			d.Content = d.Content[:startIndex] + c.Text + d.Content[endIndex:]
+		case protocol.TextDocumentContentChangeEventWhole:
+			d.Content = c.Text
+		}
+	}
+
+	d.lines = strings.Split(d.Content, "\n")
+}

lsp/hover.go

@@ -0,0 +1,57 @@
+package lsp
+
+import (
+	_ "embed"
+	"strings"
+
+	"github.com/tliron/glsp"
+	protocol "github.com/tliron/glsp/protocol_3_16"
+)
+
+//go:embed markdown/hover/verb.md
+var verbHoverContent string
+
+//go:embed markdown/hover/enum.md
+var enumHoverContent string
+
+var hoverMap = map[string]string{
+	"//ftl:verb": verbHoverContent,
+	"//ftl:enum": enumHoverContent,
+}
+
+func (s *Server) textDocumentHover() protocol.TextDocumentHoverFunc {
+	return func(context *glsp.Context, params *protocol.HoverParams) (*protocol.Hover, error) {
+		uri := params.TextDocument.URI
+		position := params.Position
+
+		doc, ok := s.documents.get(uri)
+		if !ok {
+			return nil, nil
+		}
+
+		line := int(position.Line)
+		if line >= len(doc.lines) {
+			return nil, nil
+		}
+
+		lineContent := doc.lines[line]
+		character := int(position.Character)
+		if character > len(lineContent) {
+			character = len(lineContent)
+		}
+
+		for hoverString, hoverContent := range hoverMap {
+			startIndex := strings.Index(lineContent, hoverString)
+			if startIndex != -1 && startIndex <= character && character <= startIndex+len(hoverString) {
+				return &protocol.Hover{
+					Contents: &protocol.MarkupContent{
+						Kind:  protocol.MarkupKindMarkdown,
+						Value: hoverContent,
+					},
+				}, nil
+			}
+		}
+
+		return nil, nil
+	}
+}

lsp/lsp.go

@@ -29,6 +29,7 @@ type Server struct {
 	handler     protocol.Handler
 	logger      log.Logger
 	diagnostics *xsync.MapOf[protocol.DocumentUri, []protocol.Diagnostic]
+	documents   *documentStore
 }
 
 // NewServer creates a new language server.
@@ -39,13 +40,24 @@ func NewServer(ctx context.Context) *Server {
 		SetTrace:    setTrace,
 		LogTrace:    logTrace,
 	}
+
 	s := glspServer.NewServer(&handler, lsName, false)
 	server := &Server{
 		server:      s,
 		logger:      *log.FromContext(ctx).Scope("lsp"),
 		diagnostics: xsync.NewMapOf[protocol.DocumentUri, []protocol.Diagnostic](),
+		documents:   newDocumentStore(),
 	}
+
+	handler.TextDocumentDidOpen = server.textDocumentDidOpen()
+	handler.TextDocumentDidChange = server.textDocumentDidChange()
+	handler.TextDocumentDidClose = server.textDocumentDidClose()
+	handler.TextDocumentDidSave = server.textDocumentDidSave()
+	handler.TextDocumentCompletion = server.textDocumentCompletion()
+	handler.CompletionItemResolve = server.completionItemResolve()
+	handler.TextDocumentHover = server.textDocumentHover()
 	handler.Initialize = server.initialize()
+
 	return server
 }
 
@@ -179,6 +191,15 @@ func (s *Server) initialize() protocol.InitializeFunc {
 		}
 
 		serverCapabilities := s.handler.CreateServerCapabilities()
+		serverCapabilities.TextDocumentSync = protocol.TextDocumentSyncKindIncremental
+		serverCapabilities.HoverProvider = true
+
+		trueValue := true
+		serverCapabilities.CompletionProvider = &protocol.CompletionOptions{
+			ResolveProvider:   &trueValue,
+			TriggerCharacters: []string{"/", "f"},
+		}
+
 		return protocol.InitializeResult{
 			Capabilities: serverCapabilities,
 			ServerInfo: &protocol.InitializeResultServerInfo{
@@ -207,6 +228,41 @@ func setTrace(context *glsp.Context, params *protocol.SetTraceParams) error {
 	return nil
 }
 
+func (s *Server) textDocumentDidOpen() protocol.TextDocumentDidOpenFunc {
+	return func(context *glsp.Context, params *protocol.DidOpenTextDocumentParams) error {
+		uri := params.TextDocument.URI
+		content := params.TextDocument.Text
+		s.documents.set(uri, content)
+		return nil
+	}
+}
+
+func (s *Server) textDocumentDidChange() protocol.TextDocumentDidChangeFunc {
+	return func(context *glsp.Context, params *protocol.DidChangeTextDocumentParams) error {
+		doc, ok := s.documents.get(params.TextDocument.URI)
+		if !ok {
+			return nil
+		}
+
+		doc.update(params.ContentChanges)
+		return nil
+	}
+}
+
+func (s *Server) textDocumentDidClose() protocol.TextDocumentDidCloseFunc {
+	return func(context *glsp.Context, params *protocol.DidCloseTextDocumentParams) error {
+		uri := params.TextDocument.URI
+		s.documents.delete(uri)
+		return nil
+	}
+}
+
+func (s *Server) textDocumentDidSave() protocol.TextDocumentDidSaveFunc {
+	return func(context *glsp.Context, params *protocol.DidSaveTextDocumentParams) error {
+		return nil
+	}
+}
+
 // getLineOrWordLength returns the length of the line or the length of the word starting at the given column.
 // If wholeLine is true, it returns the length of the entire line.
 // If wholeLine is false, it returns the length of the word starting at the column.

lsp/markdown/completion/enumType.md

@@ -0,0 +1,11 @@
+Snippet for defining a type enum (sum types).
+
+```go
+//ftl:enum
+type MyEnum string
+
+const (
+	Value1 MyEnum = "Value1"
+	Value2 MyEnum = "Value2"
+)
+```

lsp/markdown/completion/enumValue.md

@@ -0,0 +1,9 @@
+Snippet for defining a value enum.
+
+```go
+//ftl:enum
+type Animal interface { animal() }
+
+type Cat struct {}
+func (Cat) animal() {}
+```

lsp/markdown/completion/verb.md

@@ -0,0 +1,6 @@
+Snippet for defining a verb function.
+
+```go
+//ftl:verb
+func Name(ctx context.Context, req Request) (Response, error) {}
+```