feat(baml_language): add ProcessOptions.detached for session-detached child processes - #4550
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feat(baml_language): add ProcessOptions.detached for session-detached child processes#4550schneiderlin wants to merge 3 commits into
ProcessOptions.detached for session-detached child processes#4550schneiderlin wants to merge 3 commits into
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Repository UI Review profile: CHILL Plan: Pro Plus Run ID: ⛔ Files ignored due to path filters (5)
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🚧 Files skipped from review as they are similar to previous changes (6)
Included review availability: Your plan provides up to 8 included reviews per hour; 7 remain after this review. 📝 WalkthroughWalkthroughThe PR adds detached child-process support to ChangesDetached process support
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: ⚪ Minimal · up to The PR adds detached child-process support with explicit validation for incompatible options and platform-specific behavior. No actionable merge-blocking risk remains beyond normal checks and review. Sequence Diagram(s)sequenceDiagram
participant BAML as BAML process API
participant Native as sys_native
participant OS as Unix or Windows
participant Child as Detached child process
BAML->>Native: start_process(detached=true)
Native->>OS: apply detached spawn configuration
OS->>Child: create separate session or process group
Native->>Child: disable kill_on_drop
Child-->>BAML: return process handle
Poem
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 62.96% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 27 functions across 3 files. (3 skipped: 3 unsupported.)
✨ Finishing Touches 💡 1🛠️ Fix failing CI checks 💡
🧪 Generate unit tests (beta)
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Inline comments:
In `@baml_language/crates/bridge_wasm/src/wasm_sys.rs`:
- Around line 100-102: Validate unsupported detached options before dispatch:
reject detached: true for exec and shell, and reject detached: true when
timeout_ms is set for start_process, returning VmBamlError::InvalidArgument in
each case. Update the relevant dispatch methods while preserving existing
supported behavior and avoid relying on callback failures or the current
Unsupported result.
In `@baml_language/crates/sys_native/src/io_impls.rs`:
- Around line 1573-1624: Update the start_process throws contract to include
root.errors.Unsupported alongside Io and InvalidArgument, and document that
detached process startup returns Unsupported on platforms without detached-spawn
support. Keep apply_detached_spawn_options and the existing error behavior
unchanged.
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baml_language/Cargo.lockis excluded by!**/*.lockbaml_language/crates/baml_cli/src/snapshots/baml_cli__describe_command_tests__render_builtin_package_listing.snapis excluded by!**/*.snapbaml_language/crates/baml_tests/snapshots/baml_src/stdlib/ai/bytecode.snapis excluded by!**/*.snapbaml_language/crates/baml_tests/snapshots/baml_src/stdlib/ai/mir.snapis excluded by!**/*.snapbaml_language/crates/baml_tests/snapshots/baml_src/stdlib/baml/ppir.snapis excluded by!**/*.snap
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baml_language/Cargo.tomlbaml_language/crates/baml_builtins2/baml_std/baml/ns_sys/sys.bamlbaml_language/crates/baml_tests/tests/shell.rsbaml_language/crates/bridge_wasm/src/wasm_sys.rsbaml_language/crates/sys_native/Cargo.tomlbaml_language/crates/sys_native/src/io_impls.rs
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…ed child processes Adds an optional `detached: bool?` to `baml.sys.ProcessOptions`, honored by `start_process`: the child is spawned in its own session/process group so it survives parent exit and terminal close (daemon/supervisor use case). Unix calls `setsid()` in the child before exec (tokio `pre_exec`); Windows spawns with `DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP` (`CREATE_BREAKAWAY_FROM_JOB` was considered and deliberately left out: escaping a Job object requires the job to permit breakaway and is too situational for a general-purpose flag). Detached handles spawn with `kill_on_drop(false)` so dropping the handle at runtime shutdown does not kill the child. Semantics chosen for the contradictions detaching creates: - `exec`/`shell` reject `detached: true` with `baml.errors.InvalidArgument`: they buffer output until process exit, which contradicts detaching a child that may outlive its parent. - `detached: true` combined with `timeout_ms` throws `baml.errors.InvalidArgument` at spawn: timeout enforcement lives in the parent runtime and is meaningless for a detached child. The doc comment notes that a detached child's piped stdio still dies with the parent. Wasm passes the flag through to the JS host bridge; other platforms without setsid/creation-flags support get `baml.errors.Unsupported`. Tests cover detached spawn with a Linux /proc session-separation check, a Windows handle-usability variant, the detached+timeout rejection, and the exec/shell rejection.
Amp-Thread-ID: https://ampcode.com/threads/T-01a03cfd-803e-735b-a374-086766bbadbf Co-authored-by: Amp <amp@ampcode.com>
Amp-Thread-ID: https://ampcode.com/threads/T-01a03cfd-803e-735b-a374-086766bbadbf Co-authored-by: Amp <amp@ampcode.com>
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Issue Reference
No tracking issue — this follows from the same Discord discussion with @2kai2kai2 about process-control primitives for supervisor use cases as #4540. This is the second slice: daemon-style spawn.
Changes
Adds
detached: bool?tobaml.sys.ProcessOptions:Semantics: the child is detached from the parent's session and process group, so it keeps running when the parent exits, the launching terminal closes (no SIGHUP), or Ctrl+C hits the parent's process group. This is the spawn half of a cross-invocation process supervisor: one CLI invocation starts a long-lived service detached and records its
Process.pid()(#4540); later invocations manage it by pid.setsid()in the child between fork and exec (pre_exec).DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUPviacreation_flags.CREATE_BREAKAWAY_FROM_JOBwas considered and deliberately left out — it requires the job to permit breakaway and fails otherwise; documented in a comment.detached: true+timeout_ms→baml.errors.InvalidArgumentat spawn. Timeout enforcement lives entirely in the parent runtime (a deadline stored in the process handle), so it is meaningless — and misleading — for a child designed to outlive its parent.detached: trueonexec/shell→baml.errors.InvalidArgument. Those buffer stdout/stderr until exit, which contradicts detaching;start_processis the only sane carrier.kill_on_drop(false)— dropping the handle must not kill a process whose whole point is to outlive it.ReadPipe/WritePipe+io.Read/io.Write, pumping output into a log file is expressible in pure BAML — no native stdio-to-file option is included here on purpose).Testing
baml_tests/tests/shell.rs:detached + timeout_msthrowsInvalidArgument;detachedonexecthrowsInvalidArgument;/proc/<pid>/stat: sid == pid, sid != parent sid), gated to Linux.cargo test -p baml_tests --test shell— 19/19 pass on Linux. Windows variants compile-checked via--target x86_64-pc-windows-msvc --no-default-features; execution needs a Windows CI lane.baml describebuiltin listing) and re-run clean.cargo checkclean forsys_ops,sys_native,bridge_wasm(wasm32);cargo fmt --check+ clippy show no new warnings.PR Checklist
sys.baml)Additional Notes
Independent of #4540 and #4476; will rebase whichever lands second. Graceful/pid-based signaling (SIGTERM, liveness, process groups) is a separate follow-up PR.
Summary by CodeRabbit
New Features
Bug Fixes
exec, orshell.