cli: add `--watch`

PR-URL: https://github.com/nodejs/node/pull/44366
Backport-PR-URL: https://github.com/nodejs/node/pull/44815
Fixes: https://github.com/nodejs/node/issues/40429
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

5 files changed, 50 insertions, 2 deletions

diff --git a/src/env-inl.h b/src/env-inl.h
index cbe4b734b1c..e38531800e7 100644
--- a/src/env-inl.h
+++ b/src/env-inl.h
@@ -655,7 +655,8 @@ inline bool Environment::owns_inspector() const {
 }
 
 inline bool Environment::should_create_inspector() const {
-  return (flags_ & EnvironmentFlags::kNoCreateInspector) == 0;
+  return (flags_ & EnvironmentFlags::kNoCreateInspector) == 0 &&
+         !options_->test_runner && !options_->watch_mode;
 }
 
 inline bool Environment::tracks_unmanaged_fds() const {
diff --git a/src/inspector_agent.cc b/src/inspector_agent.cc
index 34bb11e7d71..9ee779fb597 100644
--- a/src/inspector_agent.cc
+++ b/src/inspector_agent.cc
@@ -676,6 +676,9 @@ bool Agent::Start(const std::string& path,
                   const DebugOptions& options,
                   std::shared_ptr<ExclusiveAccess<HostPort>> host_port,
                   bool is_main) {
+  if (!options.allow_attaching_debugger) {
+    return false;
+  }
   path_ = path;
   debug_options_ = options;
   CHECK_NOT_NULL(host_port);
diff --git a/src/node.cc b/src/node.cc
index 38ecd530148..c722ae31235 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -497,6 +497,10 @@ MaybeLocal<Value> StartExecution(Environment* env, StartExecutionCallback cb) {
     return StartExecution(env, "internal/main/test_runner");
   }
 
+  if (env->options()->watch_mode && !first_argv.empty()) {
+    return StartExecution(env, "internal/main/watch_mode");
+  }
+
   if (!first_argv.empty() && first_argv != "-") {
     return StartExecution(env, "internal/main/run_main_module");
   }
diff --git a/src/node_options.cc b/src/node_options.cc
index bd4ad2f6408..d08184f3da5 100644
--- a/src/node_options.cc
+++ b/src/node_options.cc
@@ -156,9 +156,36 @@ void EnvironmentOptions::CheckOptions(std::vector<std::string>* errors) {
       errors->push_back("either --test or --interactive can be used, not both");
     }
 
+    if (watch_mode) {
+      // TODO(MoLow): Support (incremental?) watch mode within test runner
+      errors->push_back("either --test or --watch can be used, not both");
+    }
+
     if (debug_options_.inspector_enabled) {
       errors->push_back("the inspector cannot be used with --test");
     }
+#ifndef ALLOW_ATTACHING_DEBUGGER_IN_TEST_RUNNER
+    debug_options_.allow_attaching_debugger = false;
+#endif
+  }
+
+  if (watch_mode) {
+    if (syntax_check_only) {
+      errors->push_back("either --watch or --check can be used, not both");
+    }
+
+    if (has_eval_string) {
+      errors->push_back("either --watch or --eval can be used, not both");
+    }
+
+    if (force_repl) {
+      errors->push_back("either --watch or --interactive "
+                        "can be used, not both");
+    }
+
+#ifndef ALLOW_ATTACHING_DEBUGGER_IN_WATCH_MODE
+    debug_options_.allow_attaching_debugger = false;
+#endif
   }
 
 #if HAVE_INSPECTOR
@@ -586,7 +613,15 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "", /* undocumented, only for debugging */
             &EnvironmentOptions::verify_base_objects,
             kAllowedInEnvironment);
-
+  AddOption("--watch",
+            "run in watch mode",
+            &EnvironmentOptions::watch_mode,
+            kAllowedInEnvironment);
+  AddOption("--watch-path",
+            "path to watch",
+            &EnvironmentOptions::watch_mode_paths,
+            kAllowedInEnvironment);
+  Implies("--watch-path", "--watch");
   AddOption("--check",
             "syntax check script without executing",
             &EnvironmentOptions::syntax_check_only);
diff --git a/src/node_options.h b/src/node_options.h
index b20cfae1419..2f114242978 100644
--- a/src/node_options.h
+++ b/src/node_options.h
@@ -71,6 +71,7 @@ class DebugOptions : public Options {
   DebugOptions(DebugOptions&&) = default;
   DebugOptions& operator=(DebugOptions&&) = default;
 
+  bool allow_attaching_debugger = true;
   // --inspect
   bool inspector_enabled = false;
   // --debug
@@ -172,6 +173,10 @@ class EnvironmentOptions : public Options {
       false;
 #endif  // DEBUG
 
+  bool watch_mode = false;
+  bool watch_mode_report_to_parent = false;
+  std::vector<std::string> watch_mode_paths;
+
   bool syntax_check_only = false;
   bool has_eval_string = false;
   bool experimental_wasi = false;