Passing `--protocol-traffic-log=` causes `dart language-server` to start the legacy server protocol

[5hirish]

This tracker is for issues related to:

• Analyser
• Dart SDK Version: Dart SDK version: 3.0.0 (stable) (Thu May 4 01:11:00 2023 -0700) on "macos_arm64"

Passing --protocol-traffic-log seems to cause it to start the legacy server protocol. If I remove that argument, it starts the LSP protocol.

dart language-server --client-id my-editor.my-plugin --client-version 1.2 --protocol-traffic-log log.txt

Workaround: As a workaround, use --instrumentation-log-file instead of --protocol-traffic-log. They are aliases and do the same thing, but only the second one triggers this bug.

cc: @DanTup

[DanTup]

The problem seems to be here:

https://github.com/dart-lang/sdk/blob/fa5e8e2e0dcfb8646baa43b25629f5597a8ec1e6/pkg/dartdev/lib/src/commands/language_server.dart#L47

It's only passing --protocol=lsp is there is no argument that starts with --protocol, and --protocol-traffic-log starts with it.

My guess is that it's to handle --protocol=, but I think it should probably be == '--$protocol' || startsWith('--$protocol=') (and if there is any other valid syntax besides =).

[srawlins]

Thanks for digging, Danny!