cmd_output: support current output alias

Similar to seat command, this provides an alias for the current output.
Instead of the output name or identifier, `-` can be used to operate on
the focused output by name and `--` can be used to operate on the
focused output by its identifier. This will prevent operating on the
no-op output when using either alias.

2 files changed, 29 insertions, 2 deletions

diff --git a/sway/commands/output.c b/sway/commands/output.c
index 3903f10d..59bc598c 100644
--- a/sway/commands/output.c
+++ b/sway/commands/output.c
@@ -36,7 +36,32 @@ struct cmd_results *cmd_output(int argc, char **argv) {
                                 "Refusing to configure the no op output");
         }
 
-        struct output_config *output = new_output_config(argv[0]);
+        struct output_config *output = NULL;
+        if (strcmp(argv[0], "-") == 0 || strcmp(argv[0], "--") == 0) {
+                if (config->reading) {
+                        return cmd_results_new(CMD_FAILURE,
+                                        "Current output alias (%s) cannot be used in the config",
+                                        argv[0]);
+                }
+                struct sway_output *sway_output = config->handler_context.node ?
+                        node_get_output(config->handler_context.node) : NULL;
+                if (!sway_output) {
+                        return cmd_results_new(CMD_FAILURE, "Unknown output");
+                }
+                if (sway_output == root->noop_output) {
+                        return cmd_results_new(CMD_FAILURE,
+                                        "Refusing to configure the no op output");
+                }
+                if (strcmp(argv[0], "-") == 0) {
+                        output = new_output_config(sway_output->wlr_output->name);
+                } else {
+                        char identifier[128];
+                        output_get_identifier(identifier, 128, sway_output);
+                        output = new_output_config(identifier);
+                }
+        } else {
+                output = new_output_config(argv[0]);
+        }
         if (!output) {
                 sway_log(SWAY_ERROR, "Failed to allocate output config");
                 return NULL;
diff --git a/sway/sway-output.5.scd b/sway/sway-output.5.scd
index e20d0aba..806054fc 100644
--- a/sway/sway-output.5.scd
+++ b/sway/sway-output.5.scd
@@ -11,7 +11,9 @@ You may combine output commands into one, like so:
         output HDMI-A-1 mode 1920x1080 pos 1920,0 bg ~/wallpaper.png stretch
 
 You can get a list of output names with *swaymsg -t get_outputs*. You may also
-match any output by using the output name "\*".
+match any output by using the output name "\*". Additionally, "-" can be used
+to match the focused output by name and "--" can be used to match the focused
+output by its identifier.
 
 Some outputs may have different names when disconnecting and reconnecting. To
 identify these, the name can be substituted for a string consisting of the make,