feat(lsp): add go-to-definition for labels

lsp/handlers.go

@@ -90,6 +90,41 @@ func (s *Server) hover(p hoverParams) *Hover {
 	}
 }
 
+// definition returns the location of the label definition for a label reference.
+func (s *Server) definition(p definitionParams) []Location {
+	text := s.docs[p.TextDocument.URI]
+	word, _ := wordAt(text, p.Position)
+	if word == "" {
+		return nil
+	}
+
+	// Parse the document to find label definitions.
+	f, errs := parser.Parse(uriPath(p.TextDocument.URI), text)
+	if f == nil || len(errs) > 0 {
+		return nil
+	}
+
+	// Find the label definition.
+	for _, d := range f.Decls {
+		if t, ok := d.(*ast.Text); ok {
+			for _, stmt := range t.Body {
+				if lbl, ok := stmt.(*ast.Label); ok {
+					if lbl.Name.Text == word {
+						return []Location{{
+							URI: p.TextDocument.URI,
+							Range: Range{
+								Start: Position{Line: lbl.Name.Pos.Line - 1, Character: lbl.Name.Pos.Column - 1},
+								End:   Position{Line: lbl.Name.Pos.Line - 1, Character: lbl.Name.Pos.Column - 1 + len(word)},
+							},
+						}}
+					}
+				}
+			}
+		}
+	}
+	return nil
+}
+
 // documentSymbols returns functions and their labels, plus global symbols.
 func (s *Server) documentSymbols(p documentSymbolParams) []DocumentSymbol {
 	text := s.docs[p.TextDocument.URI]

lsp/protocol.go

@@ -152,6 +152,11 @@ type hoverParams struct {
 	Position     Position               `json:"position"`
 }
 
+type definitionParams struct {
+	TextDocument textDocumentIdentifier `json:"textDocument"`
+	Position     Position               `json:"position"`
+}
+
 // Hover is the hover response.
 type Hover struct {
 	Contents markupContent `json:"contents"`

lsp/server.go

@@ -170,6 +170,11 @@ func (s *Server) dispatch(msg *rpcMessage) (exit bool) {
 		json.Unmarshal(msg.Params, &p)
 		s.respond(msg.ID, s.hover(p))
 
+	case "textDocument/definition":
+		var p definitionParams
+		json.Unmarshal(msg.Params, &p)
+		s.respond(msg.ID, s.definition(p))
+
 	case "textDocument/documentSymbol":
 		var p documentSymbolParams
 		json.Unmarshal(msg.Params, &p)