FEATURE: land on specified category page when creating topic via URL

app/assets/javascripts/discourse/controllers/composer.js.es6

@@ -814,32 +814,6 @@ export default Ember.Controller.extend({
 
     if (opts.topicCategoryId) {
       this.set("model.categoryId", opts.topicCategoryId);
-    } else if (opts.topicCategory) {
-      const splitCategory = opts.topicCategory.split("/");
-      let category;
-
-      if (!splitCategory[1]) {
-        category = this.site
-          .get("categories")
-          .findBy("nameLower", splitCategory[0].toLowerCase());
-      } else {
-        const categories = this.site.get("categories");
-        const mainCategory = categories.findBy(
-          "nameLower",
-          splitCategory[0].toLowerCase()
-        );
-        category = categories.find(function(item) {
-          return (
-            item &&
-            item.get("nameLower") === splitCategory[1].toLowerCase() &&
-            item.get("parent_category_id") === mainCategory.id
-          );
-        });
-      }
-
-      if (category) {
-        this.set("model.categoryId", category.get("id"));
-      }
     }
 
     if (

app/assets/javascripts/discourse/mixins/open-composer.js.es6

@@ -16,7 +16,6 @@ export default Ember.Mixin.create({
     topicTitle,
     topicBody,
     topicCategoryId,
-    topicCategory,
     topicTags
   ) {
     this.controllerFor("composer").open({
@@ -24,7 +23,6 @@ export default Ember.Mixin.create({
       topicTitle,
       topicBody,
       topicCategoryId,
-      topicCategory,
       topicTags,
       draftKey: controller.get("model.draft_key"),
       draftSequence: controller.get("model.draft_sequence")

app/assets/javascripts/discourse/routes/application.js.es6

@@ -183,13 +183,12 @@ const ApplicationRoute = Discourse.Route.extend(OpenComposer, {
       });
     },
 
-    createNewTopicViaParams(title, body, category_id, category, tags) {
+    createNewTopicViaParams(title, body, category_id, tags) {
       this.openComposerWithTopicParams(
         this.controllerFor("discovery/topics"),
         title,
         body,
         category_id,
-        category,
         tags
       );
     },

app/assets/javascripts/discourse/routes/new-topic.js.es6

@@ -1,23 +1,81 @@
+import Category from "discourse/models/category";
+
 export default Discourse.Route.extend({
   beforeModel: function(transition) {
     const self = this;
     if (Discourse.User.current()) {
-      // User is logged in
-      self.replaceWith("discovery.latest").then(function(e) {
-        if (self.controllerFor("navigation/default").get("canCreateTopic")) {
-          // User can create topic
+      let category, category_id;
+
+      if (transition.queryParams.category_id) {
+        category_id = transition.queryParams.category_id;
+        category = Category.findById(category_id);
+      } else if (transition.queryParams.category) {
+        const splitCategory = transition.queryParams.category.split("/");
+
+        if (!splitCategory[1]) {
+          category = this.site
+            .get("categories")
+            .findBy("nameLower", splitCategory[0].toLowerCase());
+        } else {
+          const categories = this.site.get("categories");
+          const mainCategory = categories.findBy(
+            "nameLower",
+            splitCategory[0].toLowerCase()
+          );
+          category = categories.find(function(item) {
+            return (
+              item &&
+              item.get("nameLower") === splitCategory[1].toLowerCase() &&
+              item.get("parent_category_id") === mainCategory.id
+            );
+          });
+        }
+
+        if (category) {
+          category_id = category.get("id");
+        }
+      }
+
+      if (Boolean(category)) {
+        let route = "discovery.parentCategory";
+        let params = { category, slug: category.get("slug") };
+        if (category.get("parentCategory")) {
+          route = "discovery.category";
+          params = {
+            category,
+            parentSlug: category.get("parentCategory.slug"),
+            slug: category.get("slug")
+          };
+        }
+
+        self.replaceWith(route, params).then(function(e) {
+          if (self.controllerFor("navigation/category").get("canCreateTopic")) {
             Ember.run.next(function() {
               e.send(
                 "createNewTopicViaParams",
                 transition.queryParams.title,
                 transition.queryParams.body,
-              transition.queryParams.category_id,
-              transition.queryParams.category,
+                category_id,
                 transition.queryParams.tags
               );
             });
           }
         });
+      } else {
+        self.replaceWith("discovery.latest").then(function(e) {
+          if (self.controllerFor("navigation/default").get("canCreateTopic")) {
+            Ember.run.next(function() {
+              e.send(
+                "createNewTopicViaParams",
+                transition.queryParams.title,
+                transition.queryParams.body,
+                null,
+                transition.queryParams.tags
+              );
+            });
+          }
+        });
+      }
     } else {
       // User is not logged in
       $.cookie("destination_url", window.location.href);