[Debug] Add a '-log' flag.

INSTALL.md

@@ -28,7 +28,7 @@ You can also use [Meson](https://mesonbuild.com/) as an alternative.
 *   libpangocairo
 *   libcairo
 *   libcairo-xcb
-*   libglib2.0 >= 2.40
+*   libglib2.0 >= 2.68
     *   gmodule-2.0
     *   gio-unix-2.0
 *   libgdk-pixbuf-2.0

doc/rofi-debugging.5

@@ -175,6 +175,22 @@ For full list see \fB\fCman rofi\fR\&.
 .PP
 Example: \fB\fCG_MESSAGES_DEBUG=Dialogs.DRun rofi -show drun\fR To get specific output from the Desktop file run dialog.
 
+.PP
+To redirect the debug output to a file (\fB\fC~/rofi.log\fR) add:
+
+.PP
+.RS
+
+.nf
+rofi -show drun -log ~/rofi.log
+
+.fi
+.RE
+
+.PP
+Specifying the logfile automatically enabled all log domains.
+This can be useful when rofi is launched from a window manager.
+
 .SH Creating a backtrace.
 .PP
 First make sure you compile \fBrofi\fP with debug symbols:

doc/rofi-debugging.5.markdown

@@ -128,7 +128,16 @@ environment variable. At the time of creation of this page, the following debug
 
 For full list see `man rofi`.
 
-Example: ```G_MESSAGES_DEBUG=Dialogs.DRun rofi -show drun``` To get specific output from the Desktop file run dialog.
+Example: `G_MESSAGES_DEBUG=Dialogs.DRun rofi -show drun` To get specific output from the Desktop file run dialog.
+
+To redirect the debug output to a file (`~/rofi.log`) add:
+
+```
+rofi -show drun -log ~/rofi.log
+```
+
+Specifying the logfile automatically enabled all log domains.
+This can be useful when rofi is launched from a window manager.
 
 
 ## Creating a backtrace.

source/rofi.c

@@ -771,6 +771,13 @@ static gboolean record(G_GNUC_UNUSED void *data) {
   rofi_capture_screenshot();
   return G_SOURCE_CONTINUE;
 }
+static void rofi_custom_log_function(const char *log_domain,
+                                     GLogLevelFlags log_level,
+                                     const gchar *message, gpointer user_data) {
+  int fp = GPOINTER_TO_INT(user_data);
+  dprintf(fp, "[%s]: %s\n", log_domain == NULL ? "default" : log_domain,
+          message);
+}
 /**
  * @param argc number of input arguments.
  * @param argv array of the input arguments.
@@ -780,9 +787,26 @@ static gboolean record(G_GNUC_UNUSED void *data) {
  * @returns return code of rofi.
  */
 int main(int argc, char *argv[]) {
-  TIMINGS_START();
-
   cmd_set_arguments(argc, argv);
+  if (find_arg("-log") >= 0) {
+    char *logfile = NULL;
+    find_arg_str("-log", &logfile);
+    if (logfile != NULL) {
+      int fp = open(logfile, O_CLOEXEC | O_APPEND | O_CREAT | O_WRONLY,
+                    S_IRUSR | S_IWUSR);
+      if (fp != -1) {
+        g_log_set_default_handler(rofi_custom_log_function,
+                                  GINT_TO_POINTER(fp));
+
+      } else {
+        g_error("Failed to open logfile '%s': %s.", logfile, strerror(errno));
+      }
+
+    } else {
+      g_warning("Option '-log' should pass in a filename.");
+    }
+  }
+  TIMINGS_START();
 
   // Version
   if (find_arg("-v") >= 0 || find_arg("-version") >= 0) {