Enable synchronous API connections to existing servers

[Jake Bailey (jakebailey)]

This is some work I had back on the old repo that I've now brought back up to date.

Right now, you can only open an async connection with an existing server process. But, we can provide the sync API if we use FIFOs/named pipes; such a thing is not possible from Node as it irritatingly does not have mkfifo or anything, but we can just do that on the Go side and then the API can talk to that instead, which to that process just looks like stdio.

[Copilot]

🟡 Changes recommended

The Unix client retains nonblocking FIFO descriptors, adding polling latency to synchronous requests.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds synchronous API connections to existing standalone and LSP servers using FIFOs on Unix and named pipes on Windows.

Changes:

• Adds selectable stdio, socket, and synchronous transports.
• Extends clients and VS Code integration with synchronous sessions.
• Adds cross-platform connection and cleanup tests.

File summaries

File	Description
tsc/internal/lsp/server.go	Creates async or synchronous API sessions.
tsc/internal/lsp/lsproto/lsp_generated.go	Adds the synchronous request option.
tsc/internal/lsp/lsproto/_generate/generate.mts	Generates the new protocol field.
tsc/internal/ipc/transport.go	Adds cancellable transport acceptance.
tsc/internal/ipc/transport_windows.go	Uses named pipes for sync transport.
tsc/internal/ipc/transport_unix.go	Implements FIFO transport and cleanup.
tsc/internal/api/server.go	Generalizes server transport selection.
tsc/cmd/tsc/api.go	Adds the --transport option.
packages/vscode-typescript/src/session.ts	Forwards synchronous session requests.
packages/vscode-typescript/src/extension.ts	Exposes synchronous connection selection.
packages/vscode-typescript/src/client.ts	Sends the synchronous protocol field.
packages/typescript/test/sync/connection.test.ts	Tests standalone and LSP sync connections.
packages/typescript/src/api/syncChannel.ts	Connects sync channels to existing servers.
packages/typescript/src/api/sync/client.ts	Enables socket-style sync clients.
packages/typescript/src/api/sync/api.ts	Updates generated sync API documentation.
packages/typescript/src/api/options.ts	Documents transport-specific pipe behavior.
packages/typescript/src/api/async/api.ts	Updates connection documentation.

Review details

Files not reviewed (1)

• tsc/internal/lsp/lsproto/lsp_generated.go: Generated file

• Files reviewed: 16/17 changed files
• Comments generated: 2
• Review effort level: Balanced

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[Copilot]

🟡 Changes recommended

The Unix readiness marker can let the LSP server unlink FIFO paths before the client opens its final descriptors.

1 open finding

• Create readiness marker after opening both final descriptors · New

2 resolved since last review

• The descriptors returned here are the nonblocking probe descriptors opened with O_NONBLOCK above.…
• Close the parenthetical phrase so this protocol requirement reads correctly.

Files not reviewed (1)

• tsc/internal/lsp/lsproto/lsp_generated.go: Generated file

🧠 Review effort: Balanced

[Copilot]

🔵 Needs a closer look

Cross-platform FIFO and named-pipe lifecycle behavior warrants final human validation.

0 open findings

1 resolved since last review

• Create readiness marker after opening both final descriptors

Files not reviewed (1)

• tsc/internal/lsp/lsproto/lsp_generated.go: Generated file

🧠 Review effort: Balanced