Type-check daemon

tsc-rs --check-pipe is a long-running type checker. It loads a project once, then answers "check this file" requests over JSON lines. It is built for editors and coding agents, where the question is asked many times against the same project.

The cost model:

Start-up parses and binds the whole project once. That is a few seconds on a monorepo of 5,000 files.
Each request re-checks a single file against the cached project state, typically in tens of milliseconds.

Start#

Any of these forms works. With no argument, ./tsconfig.json is used.

tsc-rs --check-pipe -p tsconfig.json
tsc-rs --check-pipe tsconfig.json
tsc-rs --check-pipe

After initialization the daemon prints one banner line:

{"event":"ready","files":5732,"elapsed_ms":4321}

If any project file could not be read, one more line follows:

{"event":"init_diagnostics","diagnostics":[]}

Requests#

One JSON object per line.

Check a file as it is on disk:

{"id":"1","cmd":"check","file":"src/foo.ts"}

Check a file with unsaved content:

{"id":"1","cmd":"check","file":"src/foo.ts","source":"export const x: number = 1;"}

Check several files in one request:

{"id":"2","cmd":"check_files","files":[{"file":"a.ts"},{"file":"b.ts","source":"..."}]}

Stop the daemon:

{"id":"3","cmd":"shutdown"}

Response#

{
  "id": "1",
  "ok": true,
  "elapsed_ms": 48,
  "file": "src/foo.ts",
  "diagnostics": [
    {
      "file": "src/foo.ts",
      "line": 117,
      "col": 38,
      "code": 2345,
      "severity": "error",
      "message": "Argument of type 'number' is not assignable to parameter of type 'number[]'."
    }
  ]
}

line and col are 1-based, matching the command line output.

Staleness#

The project state is built once at start-up. While the daemon runs, edits to files other than the one being checked are not visible to it.

To answer "did I break this file?", send a check for that file. This is the common case and it is always current for that file.
To answer "did changing A break B?", send both files in one check_files request.
To pick up other cross-file changes, restart the daemon.

Lifetime caps#

Variable	Default	Effect
`TSC_RS_CHECK_PIPE_MAX_REQUESTS`	10000	Exit cleanly after this many requests
`TSC_RS_CHECK_PIPE_MAX_MEMORY_MB`	2048	Exit cleanly when resident memory passes this value

When a cap is reached the daemon answers the current request and exits, so a supervisor can respawn it. Set TSC_RS_INIT_TIMING to log a timing breakdown of start-up.

Accuracy#

The daemon uses the same checker as tsc-rs --noEmit, with the same gaps. See Limitations.

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