refactor: introduce RestMr interface

Credit: [@Musisimaru](https://gitlab.com/Musisimaru) (originally
introduced in
[!229](https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/merge_requests/229))

src/gitlab/gitlab_new_service.ts

@@ -38,6 +38,7 @@ import {
 import { createDiffNoteMutation, GqlDiffPositionInput } from './graphql/create_diff_comment';
 import { removeLeadingSlash } from '../utils/remove_leading_slash';
 import { log, logError } from '../log';
+import { isMr } from '../utils/is_mr';
 
 interface CreateNoteResult {
   createNote: {
@@ -109,7 +110,6 @@ const updateNoteBodyMutation = gql`
 `;
 
 const getProjectPath = (issuable: RestIssuable) => issuable.references.full.split(/[#!]/)[0];
-const isMr = (issuable: RestIssuable) => Boolean(issuable.sha);
 const getIssuableGqlId = (issuable: RestIssuable) =>
   `gid://gitlab/${isMr(issuable) ? 'MergeRequest' : 'Issue'}/${issuable.id}`;
 const getMrGqlId = (id: number) => `gid://gitlab/MergeRequest/${id}`;

src/types.d.ts

@@ -14,7 +14,6 @@ interface RestIssuable {
   project_id: number;
   web_url: string;
   author: { name: string; avatar_url: string | null };
-  sha?: string; // only present in MR, legacy logic uses the presence to decide issuable type
   references: {
     full: string; // e.g. "gitlab-org/gitlab#219925"
   };
@@ -22,6 +21,10 @@ interface RestIssuable {
   name: string;
 }
 
+interface RestMr extends RestIssuable {
+  sha: string;
+}
+
 interface RestMrVersion {
   head_commit_sha: string;
   base_commit_sha: string;

src/utils/is_mr.ts

+export const isMr = (issuable: RestIssuable): issuable is RestMr =>
+  Boolean((issuable as RestMr).sha);

src/webview_controller.ts

@@ -7,6 +7,7 @@ import * as gitLabService from './gitlab_service';
 import { createGitLabNewService } from './service_factory';
 import { logError } from './log';
 import { getInstanceUrl } from './utils/get_instance_url';
+import { isMr } from './utils/is_mr';
 
 const webviewResourcePaths = {
   appScriptUri: 'src/webview/dist/js/app.js',
@@ -140,8 +141,7 @@ class WebviewController {
     const lightMrIcon = getIconUri('light', 'merge_requests.svg');
     const darkIssueIcon = getIconUri('dark', 'issues.svg');
     const darkMrIcon = getIconUri('dark', 'merge_requests.svg');
-    const isMr = issuable.sha !== undefined;
-    return isMr
+    return isMr(issuable)
       ? { light: lightMrIcon, dark: darkMrIcon }
       : { light: lightIssueIcon, dark: darkIssueIcon };
   }