Do not format a file that contains an error in the LSP (#3447)

Co-authored-by: Doria Keung <[email protected]>

private/buf/buflsp/server.go

@@ -208,6 +208,18 @@ func (s *server) Formatting(
 		return nil, fmt.Errorf("received update for file that was not open: %q", params.TextDocument.URI)
 	}
 
+	// We check the diagnostics on the file, if there are any build errors, we do not want
+	// to format an invalid AST, so we skip formatting and return an error for logging.
+	errorCount := 0
+	for _, diagnostic := range file.diagnostics {
+		if diagnostic.Severity == protocol.DiagnosticSeverityError {
+			errorCount += 1
+		}
+	}
+	if errorCount > 0 {
+		return nil, fmt.Errorf("cannot format file %q, %v error(s) found.", file.uri.Filename(), errorCount)
+	}
+
 	// Currently we have no way to honor any of the parameters.
 	_ = params
 	if file.fileNode == nil {