provide I3_WINDOW_ID to processes called with exec when possible (#6160)

fixes #1729

include/startup.h

@@ -30,7 +30,7 @@
  * (and ID) should be created, which is the default and encouraged behavior.
  *
  */
-void start_application(const char *command, bool no_startup_id);
+void start_application(const char *command, bool no_startup_id, xcb_window_t window_id);
 
 /**
  * Deletes a startup sequence, ignoring whether its timeout has elapsed.

src/commands.c

@@ -1262,7 +1262,9 @@ void cmd_exec(I3_CMD, const char *nosn, const char *command) {
 
     TAILQ_FOREACH (current, &OWINDOWS, owindows) {
         DLOG("should execute %s, no_startup_id = %d\n", command, no_startup_id);
-        start_application(command, no_startup_id);
+        start_application(
+            command, no_startup_id,
+            current->con->window == NULL ? XCB_NONE : current->con->window->id);
     }
 
     ysuccess(true);

src/main.c

@@ -1175,7 +1175,7 @@ int main(int argc, char *argv[]) {
             struct Autostart *exec = TAILQ_FIRST(&autostarts);
 
             LOG("auto-starting %s\n", exec->command);
-            start_application(exec->command, exec->no_startup_id);
+            start_application(exec->command, exec->no_startup_id, XCB_NONE);
 
             FREE(exec->command);
             TAILQ_REMOVE(&autostarts, exec, autostarts);
@@ -1188,7 +1188,7 @@ int main(int argc, char *argv[]) {
         struct Autostart *exec_always = TAILQ_FIRST(&autostarts_always);
 
         LOG("auto-starting (always!) %s\n", exec_always->command);
-        start_application(exec_always->command, exec_always->no_startup_id);
+        start_application(exec_always->command, exec_always->no_startup_id, XCB_NONE);
 
         FREE(exec_always->command);
         TAILQ_REMOVE(&autostarts_always, exec_always, autostarts_always);
@@ -1204,7 +1204,7 @@ int main(int argc, char *argv[]) {
                   barconfig->verbose ? "-V" : "",
                   barconfig->id, current_socketpath);
         LOG("Starting bar process: %s\n", command);
-        start_application(command, true);
+        start_application(command, true, XCB_NONE);
         free(command);
     }
 

src/startup.c

@@ -129,8 +129,11 @@ void startup_sequence_delete(struct Startup_Sequence *sequence) {
  * The no_startup_id flag determines whether a startup notification context
  * (and ID) should be created, which is the default and encouraged behavior.
  *
+ * The window_id, if given, will be provided to the child process via the
+ * I3_WINDOW_ID environment variable.
+ *
  */
-void start_application(const char *command, bool no_startup_id) {
+void start_application(const char *command, bool no_startup_id, xcb_window_t window_id) {
     SnLauncherContext *context = NULL;
 
     if (!no_startup_id) {
@@ -194,6 +197,13 @@ void start_application(const char *command, bool no_startup_id) {
         }
         setenv("I3SOCK", current_socketpath, 1);
 
+        if (window_id != XCB_NONE) {
+            char *window_id_str;
+            sasprintf(&window_id_str, "%d", window_id);
+            setenv("I3_WINDOW_ID", window_id_str, 1);
+            free(window_id_str);
+        }
+
         execl(_PATH_BSHELL, _PATH_BSHELL, "-c", command, NULL);
         err(EXIT_FAILURE, "execl return"); /* only reached on error */
     }

testcases/t/165-for_window.t

@@ -15,10 +15,15 @@
 #   (unless you are already familiar with Perl)
 #
 use i3test i3_autostart => 0;
+use POSIX qw(mkfifo);
+use File::Temp qw(:POSIX);
 use X11::XCB qw(PROP_MODE_REPLACE);
 
 my (@nodes);
 
+my $exec_tmp = tmpnam();
+mkfifo($exec_tmp, 0600) or BAIL_OUT "Could not create FIFO in $exec_tmp: $!";
+
 my $config = <<'EOT';
 font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
 
@@ -51,6 +56,11 @@ for_window [window_role="i3test"] border none
 for_window [workspace="trigger"] floating enable, mark triggered
 EOT
 
+$config .= <<EOT;
+# test 13
+for_window [class="exec"] exec echo "\$I3_WINDOW_ID" > "$exec_tmp"
+EOT
+
 # test all window types
 my %window_types = (
     'normal'        => '_NET_WM_WINDOW_TYPE_NORMAL',
@@ -390,6 +400,21 @@ is_deeply($nodes[0]->{nodes}[0]->{marks}, [ 'triggered' ], "mark set for workspa
 
 kill_all_windows;
 
+##############################################################
+# 13: check that we pass $I3_WINDOW_ID to exec'ed subprocesses
+##############################################################
+
+$window = open_window(wm_class => 'exec');
+
+open my $fh, '<', $exec_tmp
+    or die "couldn't open FIFO $exec_tmp for reading: $!";
+chomp(my $window_id = do { local $/; <$fh> });
+is($window_id, $window->id, "got the expected window id from \$I3_WINDOW_ID");
+
+kill_all_windows;
+
+unlink($exec_tmp);
+
 ##############################################################
 
 exit_gracefully($pid);