Fixed file templates not clearing in Web IDE

This fixes a bug where the file templates would not be cleared
after changing the template type.
Previously the templates would get pushed into the array
creating a list of templates for the different types.
This changes that by clearing the templates array
when the template type gets changed.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/52487

Author: iamphill

app/assets/javascripts/ide/stores/modules/file_templates/mutations.js

@@ -13,6 +13,7 @@ export default {
   },
   [types.SET_SELECTED_TEMPLATE_TYPE](state, type) {
     state.selectedTemplateType = type;
+    state.templates = [];
   },
   [types.SET_UPDATE_SUCCESS](state, success) {
     state.updateSuccess = success;

changelogs/unreleased/ide-file-templates-clear.yml

@@ -0,0 +1,5 @@
+---
+title: Clear fetched file templates when changing template type in Web IDE
+merge_request:
+author:
+type: fixed

spec/javascripts/ide/stores/modules/file_templates/mutations_spec.js

@@ -49,6 +49,14 @@ describe('IDE file templates mutations', () => {
 
       expect(state.selectedTemplateType).toBe('type');
     });
+
+    it('clears templates', () => {
+      state.templates = ['test'];
+
+      mutations[types.SET_SELECTED_TEMPLATE_TYPE](state, 'type');
+
+      expect(state.templates).toEqual([]);
+    });
   });
 
   describe(types.SET_UPDATE_SUCCESS, () => {