Place fish --interactive in its own process group

Fixes fish-shell#5909

src/fish.cpp

@@ -396,7 +396,7 @@ static int fish_parse_opt(int argc, char **argv, fish_cmd_opts_t *opts) {
     // command or file to execute and stdin is a tty. Note that the -i or
     // --interactive options also force interactive mode.
     if (opts->batch_cmds.empty() && optind == argc && isatty(STDIN_FILENO)) {
-        set_interactive_session(true);
+        set_interactive_session(SESSION_INTERACTIVE);
     }
 
     return optind;
@@ -446,7 +446,7 @@ int main(int argc, char **argv) {
     // Apply our options.
     if (opts.is_login) mark_login();
     if (opts.no_exec) mark_no_exec();
-    if (opts.is_interactive_session) set_interactive_session(true);
+    if (opts.is_interactive_session) set_interactive_session(SESSION_INTERACTIVE_EXPLICIT);
 
     // Only save (and therefore restore) the fg process group if we are interactive. See issues
     // #197 and #1002.

src/fish_key_reader.cpp

@@ -287,7 +287,7 @@ static void install_our_signal_handlers() {
 
 /// Setup our environment (e.g., tty modes), process key strokes, then reset the environment.
 static void setup_and_process_keys(bool continuous_mode) {
-    set_interactive_session(true);  // by definition this program is interactive
+    set_interactive_session(SESSION_INTERACTIVE);  // by definition this program is interactive
     set_main_thread();
     setup_fork_guards();
     env_init();

src/fish_tests.cpp

@@ -1071,8 +1071,8 @@ static void test_cancellation() {
     // Test for #3780
     // Ugly hack - temporarily set is_interactive_session
     // else we will SIGINT ourselves in response to our child death
-    bool iis = is_interactive_session();
-    set_interactive_session(true);
+    session_interactivity_t iis = is_interactive_session();
+    set_interactive_session(SESSION_INTERACTIVE);
     const wchar_t *child_self_destructor = L"while true ; sh -c 'sleep .25; kill -s INT $$' ; end";
     parser_t::principal_parser().eval(child_self_destructor, io_chain_t(), TOP);
     set_interactive_session(iis);

src/proc.cpp

@@ -54,9 +54,9 @@
 /// The signals that signify crashes to us.
 static const int crashsignals[] = {SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGSYS};
 
-static relaxed_atomic_bool_t s_is_interactive_session{false};
-bool is_interactive_session() { return s_is_interactive_session; }
-void set_interactive_session(bool flag) { s_is_interactive_session = flag; }
+static relaxed_atomic_t<session_interactivity_t> s_is_interactive_session{SESSION_NON_INTERACTIVE};
+session_interactivity_t is_interactive_session() { return s_is_interactive_session; }
+void set_interactive_session(session_interactivity_t flag) { s_is_interactive_session = flag; }
 
 static relaxed_atomic_bool_t s_is_login{false};
 bool get_login() { return s_is_login; }

src/proc.h

@@ -475,8 +475,13 @@ class job_t {
 };
 
 /// Whether this shell is attached to the keyboard at all.
-bool is_interactive_session();
-void set_interactive_session(bool flag);
+enum session_interactivity_t {
+    SESSION_NON_INTERACTIVE,
+    SESSION_INTERACTIVE,
+    SESSION_INTERACTIVE_EXPLICIT
+};
+session_interactivity_t is_interactive_session();
+void set_interactive_session(session_interactivity_t flag);
 
 /// Whether we are a login shell.
 bool get_login();

src/reader.cpp

@@ -1772,7 +1772,8 @@ static void reader_interactive_init(parser_t &parser) {
     // It shouldn't be necessary to place fish in its own process group and force control
     // of the terminal, but that works around fish being started with an invalid pgroup,
     // such as when launched via firejail (#5295)
-    if (shell_pgid == 0) {
+    // Also become the process group leader if flag -i/--interactive was given (#5909).
+    if (shell_pgid == 0 || is_interactive_session() == SESSION_INTERACTIVE_EXPLICIT) {
         shell_pgid = getpid();
         if (setpgid(shell_pgid, shell_pgid) < 0) {
             FLOG(error, _(L"Failed to assign shell to its own process group"));