feat: bun dev target support

internal/BUILD.bazel

@@ -3,6 +3,7 @@ package(default_visibility = ["//visibility:public"])
 exports_files([
 	"bun_binary.bzl",
 	"bun_bundle.bzl",
+	"bun_dev.bzl",
 	"bun_install.bzl",
 	"bun_test.bzl",
 	"js_library.bzl",

internal/bun_dev.bzl

@@ -0,0 +1,142 @@
+"""Rule for running JS/TS scripts with Bun in watch mode for development."""
+
+
+def _bun_dev_impl(ctx):
+    toolchain = ctx.toolchains["//bun:toolchain_type"]
+    bun_bin = toolchain.bun.bun_bin
+    entry_point = ctx.file.entry_point
+
+    restart_watch_paths = "\n".join([path.short_path for path in ctx.files.restart_on])
+
+    launcher = ctx.actions.declare_file(ctx.label.name)
+    ctx.actions.write(
+        output = launcher,
+        is_executable = True,
+        content = """#!/usr/bin/env bash
+set -euo pipefail
+
+runfiles_dir="${{RUNFILES_DIR:-$0.runfiles}}"
+bun_bin="${{runfiles_dir}}/_main/{bun_short_path}"
+entry_point="${{runfiles_dir}}/_main/{entry_short_path}"
+cd "${{runfiles_dir}}/_main"
+
+watch_mode="{watch_mode}"
+if [[ "${{watch_mode}}" == "hot" ]]; then
+    dev_flag="--hot"
+else
+    dev_flag="--watch"
+fi
+
+run_dev() {{
+    exec "${{bun_bin}}" "${{dev_flag}}" run "${{entry_point}}" "$@"
+}}
+
+if [[ {restart_count} -eq 0 ]]; then
+    run_dev "$@"
+fi
+
+readarray -t restart_paths <<'EOF_RESTART_PATHS'
+{restart_watch_paths}
+EOF_RESTART_PATHS
+
+file_mtime() {{
+    local p="$1"
+    if stat -f '%m' "${{p}}" >/dev/null 2>&1; then
+        stat -f '%m' "${{p}}"
+        return 0
+    fi
+    stat -c '%Y' "${{p}}"
+}}
+
+declare -A mtimes
+for rel in "${{restart_paths[@]}}"; do
+    if [[ -e "${{rel}}" ]]; then
+        mtimes["${{rel}}"]="$(file_mtime "${{rel}}")"
+    else
+        mtimes["${{rel}}"]="missing"
+    fi
+done
+
+child_pid=""
+restart_child() {{
+    if [[ -n "${{child_pid}}" ]] && kill -0 "${{child_pid}}" 2>/dev/null; then
+        kill "${{child_pid}}"
+        wait "${{child_pid}}" || true
+    fi
+    "${{bun_bin}}" "${{dev_flag}}" run "${{entry_point}}" "$@" &
+    child_pid=$!
+}}
+
+cleanup() {{
+    if [[ -n "${{child_pid}}" ]] && kill -0 "${{child_pid}}" 2>/dev/null; then
+        kill "${{child_pid}}"
+        wait "${{child_pid}}" || true
+    fi
+}}
+
+trap cleanup EXIT INT TERM
+
+restart_child "$@"
+
+while true; do
+    sleep 1
+    changed=0
+    for rel in "${{restart_paths[@]}}"; do
+        if [[ -e "${{rel}}" ]]; then
+            current="$(file_mtime "${{rel}}")"
+        else
+            current="missing"
+        fi
+        if [[ "${{current}}" != "${{mtimes[${{rel}}]}}" ]]; then
+            mtimes["${{rel}}"]="${{current}}"
+            changed=1
+        fi
+    done
+    if [[ "${{changed}}" -eq 1 ]]; then
+        restart_child "$@"
+    fi
+done
+""".format(
+            bun_short_path = bun_bin.short_path,
+            entry_short_path = entry_point.short_path,
+            watch_mode = ctx.attr.watch_mode,
+            restart_count = len(ctx.files.restart_on),
+            restart_watch_paths = restart_watch_paths,
+        ),
+    )
+
+    transitive_files = []
+    if ctx.attr.node_modules:
+        transitive_files.append(ctx.attr.node_modules[DefaultInfo].files)
+
+    runfiles = ctx.runfiles(
+        files = [bun_bin, entry_point] + ctx.files.data + ctx.files.restart_on,
+        transitive_files = depset(transitive = transitive_files),
+    )
+
+    return [
+        DefaultInfo(
+            executable = launcher,
+            runfiles = runfiles,
+        ),
+    ]
+
+
+bun_dev = rule(
+    implementation = _bun_dev_impl,
+    attrs = {
+        "entry_point": attr.label(
+            mandatory = True,
+            allow_single_file = [".js", ".ts", ".jsx", ".tsx", ".mjs", ".cjs"],
+        ),
+        "watch_mode": attr.string(
+            default = "watch",
+            values = ["watch", "hot"],
+        ),
+        "restart_on": attr.label_list(allow_files = True),
+        "node_modules": attr.label(),
+        "data": attr.label_list(allow_files = True),
+    },
+    executable = True,
+    toolchains = ["//bun:toolchain_type"],
+)