Allow multiple outputs for workspace output

`i3 4.16` allows users to list multiple outputs for a workspace and the
first available will be used. The syntax is as follows:
`workspace <workspace> output <outputs...>`

Additionally when the workspace is created, the outputs get added to the
output priority list in the order specified. This ensures that if a higher
output gets connected, the workspace will move to the higher output. This
works the same way as if the user had a workspace on an output, disconnected
the output, and then later reconnected the output.

4 files changed, 65 insertions, 24 deletions

diff --git a/sway/commands/workspace.c b/sway/commands/workspace.c
index 168494d2..92118ecf 100644
--- a/sway/commands/workspace.c
+++ b/sway/commands/workspace.c
@@ -21,6 +21,7 @@ static struct workspace_config *workspace_config_find_or_create(char *ws_name) {
                 return NULL;
         }
         wsc->workspace = strdup(ws_name);
+        wsc->outputs = create_list();
         wsc->gaps_inner = INT_MIN;
         wsc->gaps_outer.top = INT_MIN;
         wsc->gaps_outer.right = INT_MIN;
@@ -32,7 +33,7 @@ static struct workspace_config *workspace_config_find_or_create(char *ws_name) {
 
 void free_workspace_config(struct workspace_config *wsc) {
         free(wsc->workspace);
-        free(wsc->output);
+        free_flat_list(wsc->outputs);
         free(wsc);
 }
 
@@ -141,18 +142,20 @@ struct cmd_results *cmd_workspace(int argc, char **argv) {
                 }
         }
         if (output_location >= 0) {
-                if ((error = checkarg(argc, "workspace", EXPECTED_EQUAL_TO, output_location + 2))) {
+                if ((error = checkarg(argc, "workspace", EXPECTED_AT_LEAST,
+                                                output_location + 2))) {
                         return error;
                 }
-                char *ws_name = join_args(argv, argc - 2);
+                char *ws_name = join_args(argv, output_location);
                 struct workspace_config *wsc = workspace_config_find_or_create(ws_name);
                 free(ws_name);
                 if (!wsc) {
                         return cmd_results_new(CMD_FAILURE, "workspace output",
                                         "Unable to allocate workspace output");
                 }
-                free(wsc->output);
-                wsc->output = strdup(argv[output_location + 1]);
+                for (int i = output_location + 1; i < argc; ++i) {
+                        list_add(wsc->outputs, strdup(argv[i]));
+                }
         } else if (gaps_location >= 0) {
                 if ((error = cmd_workspace_gaps(argc, argv, gaps_location))) {
                         return error;
diff --git a/sway/sway.5.scd b/sway/sway.5.scd
index 8f6b35f1..1a11015f 100644
--- a/sway/sway.5.scd
+++ b/sway/sway.5.scd
@@ -573,8 +573,12 @@ The default colors are:
         Specifies that workspace _name_ should have the given gaps settings when it
         is created.
 
-*workspace* <name> output <output>
-        Specifies that workspace _name_ should be shown on the specified _output_.
+*workspace* <name> output <outputs...>
+        Specifies that workspace _name_ should be shown on the specified _outputs_.
+        Multiple outputs can be listed and the first available will be used. If the
+        workspace gets placed on an output further down the list and an output that
+        is higher on the list becomes available, the workspace will be move to the
+        higher priority output.
 
 *workspace\_auto\_back\_and\_forth* yes|no
         When _yes_, repeating a workspace switch command will switch back to the
diff --git a/sway/tree/output.c b/sway/tree/output.c
index 2704920d..3c4614a8 100644
--- a/sway/tree/output.c
+++ b/sway/tree/output.c
@@ -31,6 +31,13 @@ static void restore_workspaces(struct sway_output *output) {
                                 j--;
                         }
                 }
+
+                if (other->workspaces->length == 0) {
+                        char *next = workspace_next_name(other->wlr_output->name);
+                        struct sway_workspace *ws = workspace_create(other, next);
+                        free(next);
+                        ipc_event_workspace(NULL, ws, "init");
+                }
         }
 
         // Saved workspaces
diff --git a/sway/tree/workspace.c b/sway/tree/workspace.c
index 93ce50de..4be63311 100644
--- a/sway/tree/workspace.c
+++ b/sway/tree/workspace.c
@@ -33,14 +33,15 @@ struct workspace_config *workspace_find_config(const char *ws_name) {
 struct sway_output *workspace_get_initial_output(const char *name) {
         // Check workspace configs for a workspace<->output pair
         struct workspace_config *wsc = workspace_find_config(name);
-        if (wsc && wsc->output) {
-                struct sway_output *output = output_by_name(wsc->output);
-                if (!output) {
-                        output = output_by_identifier(wsc->output);
-                }
-                
-                if (output) {
-                        return output;
+        if (wsc) {
+                for (int i = 0; i < wsc->outputs->length; i++) {
+                        struct sway_output *output = output_by_name(wsc->outputs->items[i]);
+                        if (!output) {
+                                output = output_by_identifier(wsc->outputs->items[i]);
+                        }
+                        if (output) {
+                                return output;
+                        }
                 }
         }
         // Otherwise put it on the focused output
@@ -85,7 +86,6 @@ struct sway_workspace *workspace_create(struct sway_output *output,
         ws->floating = create_list();
         ws->tiling = create_list();
         ws->output_priority = create_list();
-        workspace_output_add_priority(ws, output);
 
         ws->gaps_outer = config->gaps_outer;
         ws->gaps_inner = config->gaps_inner;
@@ -110,9 +110,17 @@ struct sway_workspace *workspace_create(struct sway_output *output,
                         // Since default outer gaps can be smaller than the negation of
                         // workspace specific inner gaps, check outer gaps again
                         prevent_invalid_outer_gaps(ws);
+
+                        // Add output priorities
+                        for (int i = 0; i < wsc->outputs->length; ++i) {
+                                list_add(ws->output_priority, strdup(wsc->outputs->items[i]));
+                        }
                 }
         }
 
+        // If not already added, add the output to the lowest priority
+        workspace_output_add_priority(ws, output);
+
         output_add_workspace(output, ws);
         output_sort_workspaces(output);
 
@@ -134,8 +142,7 @@ void workspace_destroy(struct sway_workspace *workspace) {
 
         free(workspace->name);
         free(workspace->representation);
-        list_foreach(workspace->output_priority, free);
-        list_free(workspace->output_priority);
+        free_flat_list(workspace->output_priority);
         list_free(workspace->floating);
         list_free(workspace->tiling);
         list_free(workspace->current.floating);
@@ -177,8 +184,19 @@ static bool workspace_valid_on_output(const char *output_name,
         char identifier[128];
         struct sway_output *output = output_by_name(output_name);
         output_get_identifier(identifier, sizeof(identifier), output);
-                
-        return !wsc || !wsc->output || strcmp(wsc->output, output_name) == 0 || strcasecmp(identifier, output_name) == 0;
+
+        if (!wsc) {
+                return true;
+        }
+
+        for (int i = 0; i < wsc->outputs->length; i++) {
+                if (strcmp(wsc->outputs->items[i], output_name) == 0 ||
+                                strcmp(wsc->outputs->items[i], identifier) == 0) {
+                        return true;
+                }
+        }
+
+        return false;
 }
 
 static void workspace_name_from_binding(const struct sway_binding * binding,
@@ -281,10 +299,19 @@ char *workspace_next_name(const char *output_name) {
         for (int i = 0; i < config->workspace_configs->length; ++i) {
                 // Unlike with bindings, this does not guarantee order
                 const struct workspace_config *wsc = config->workspace_configs->items[i];
-                if (wsc->output && strcmp(wsc->output, output_name) == 0
-                                && workspace_by_name(wsc->workspace) == NULL) {
-                        free(target);
-                        target = strdup(wsc->workspace);
+                if (workspace_by_name(wsc->workspace)) {
+                        continue;
+                }
+                bool found = false;
+                for (int j = 0; j < wsc->outputs->length; ++j) {
+                        if (strcmp(wsc->outputs->items[j], output_name) == 0) {
+                                found = true;
+                                free(target);
+                                target = strdup(wsc->workspace);
+                                break;
+                        }
+                }
+                if (found) {
                         break;
                 }
         }