Add Docker init opt-out

crates/prek-consts/src/env_vars.rs

@@ -30,6 +30,7 @@ impl EnvVars {
     pub const SSL_CERT_FILE: &'static str = "SSL_CERT_FILE";
     pub const SSL_CERT_DIR: &'static str = "SSL_CERT_DIR";
     pub const PREK_CONTAINER_RUNTIME: &'static str = "PREK_CONTAINER_RUNTIME";
+    pub const PREK_DOCKER_NO_INIT: &'static str = "PREK_DOCKER_NO_INIT";
     pub const PREK_QUIET: &'static str = "PREK_QUIET";
     pub const PREK_LOG_TRUNCATE_LIMIT: &'static str = "PREK_LOG_TRUNCATE_LIMIT";
 

crates/prek/src/languages/docker.rs

@@ -417,7 +417,9 @@ impl Docker {
         };
         let volume = format!("{}:/src:rw{z}", work_dir.display());
 
-        if !CONTAINER_RUNTIME.is_apple_container() {
+        if !CONTAINER_RUNTIME.is_apple_container()
+            && !EnvVars::var_as_bool(EnvVars::PREK_DOCKER_NO_INIT).unwrap_or(false)
+        {
             // Run an init inside the container that forwards signals and reaps processes
             command.arg("--init");
         }

docs/languages.md

@@ -193,12 +193,14 @@ Runtime behavior:
 - The container is run with `--entrypoint` set to the hook `entry`, so the image’s default command is not used when filenames are passed.
 - Environment variables configured via `env` are passed using `-e`.
 - On Linux, prek tries to run as a non-root user and handles rootless Podman with `--userns=keep-id`.
+- For Docker and Podman, prek passes `--init` so signals are forwarded and child processes are reaped inside the container.
 
 Use `docker` when you need a language runtime that isn’t otherwise supported; the container provides the execution environment.
 
 !!! note "prek-only"
 
     prek auto-detects the container runtime (Docker, Podman, or [Container](https://github.com/apple/container)) and can be overridden with `PREK_CONTAINER_RUNTIME`.
+    Set `PREK_DOCKER_NO_INIT=1` to skip Docker's `--init` flag in container environments that cannot run the init helper. This is a compatibility escape hatch; disabling `--init` can leave containers running after Ctrl-C if the container's PID 1 does not handle forwarded signals.
     See [Environment Variable Reference](reference/environment-variables.md) for details.
 
 ### docker_image
@@ -209,6 +211,7 @@ Runtime behavior:
 
 - Uses the same bind-mount and `/src` working directory as `docker` hooks.
 - Environment variables configured via `env` are passed using `-e`.
+- Uses the same `--init` behavior as `docker` hooks.
 
 If the image already defines an `ENTRYPOINT`, you can omit `--entrypoint` in `entry`. Otherwise, specify it explicitly in `entry`.
 

docs/reference/environment-variables.md

@@ -74,6 +74,12 @@ Options:
 - `podman`
 - `container` (Apple's Container runtime on macOS, see [container](https://github.com/apple/container))
 
+### `PREK_DOCKER_NO_INIT`
+
+Disable passing `--init` to Docker and Podman when running `docker` and `docker_image` hooks.
+This is a compatibility escape hatch for container environments that cannot run Docker's init helper.
+Disabling `--init` can leave containers running after Ctrl-C if the container's PID 1 does not handle forwarded signals.
+
 ### `PREK_LOG_TRUNCATE_LIMIT`
 
 Control the truncation limit for command lines shown in trace logs (`Executing ...`).