3 files changed, 65 insertions, 0 deletions
diff --git a/source/content.ts b/source/content.ts
index ac1d0d62..02df64d8 100644
--- a/source/content.ts
+++ b/source/content.ts
@@ -165,6 +165,7 @@ import './features/cross-deleted-pr-branches';
 import './features/repo-wide-file-finder';
 import './features/preserve-file-finder-term';
 import './features/file-finder-buffer';
+import './features/pr-commit-lines-changed';
 
 // Add global for easier debugging
 (window as any).select = select;
diff --git a/source/features/pr-commit-lines-changed.tsx b/source/features/pr-commit-lines-changed.tsx
new file mode 100644
index 00000000..fd38072f
--- /dev/null
+++ b/source/features/pr-commit-lines-changed.tsx
@@ -0,0 +1,52 @@
+import React from 'dom-chef';
+import cache from 'webext-storage-cache';
+import select from 'select-dom';
+import elementReady from 'element-ready';
+import * as api from '../libs/api';
+import features from '../libs/features';
+import {getRepoGQL, pluralize} from '../libs/utils';
+
+const getCommitChanges = cache.function(async (commit: string): Promise<[number, number]> => {
+	const {repository} = await api.v4(`
+		repository(${getRepoGQL()}) {
+			object(expression: "${commit}") {
+				... on Commit {
+					additions
+					deletions
+				}
+			}
+		}
+	`);
+
+	return [repository.object.additions, repository.object.deletions];
+}, {
+	cacheKey: ([commit]) => 'commit-changes:' + commit
+});
+
+async function init(): Promise<void> {
+	const commitSha = (await elementReady('.sha.user-select-contain'))!.textContent!;
+	const [additions, deletions] = await getCommitChanges(commitSha);
+	const tooltip = pluralize(additions + deletions, '1 line changed', '$$ lines changed');
+	select('.diffstat')!.replaceWith(
+		<span className="ml-2 diffstat tooltipped tooltipped-s" aria-label={tooltip}>
+			<span className="text-green">+{additions}</span>{' '}
+			<span className="text-red">−{deletions}</span>{' '}
+			<span className="diffstat-block-neutral"/>
+			<span className="diffstat-block-neutral"/>
+			<span className="diffstat-block-neutral"/>
+			<span className="diffstat-block-neutral"/>
+			<span className="diffstat-block-neutral"/>
+		</span>
+	);
+}
+
+features.add({
+	id: __featureName__,
+	description: 'Adds diff stats on PR commits.',
+	screenshot: 'https://user-images.githubusercontent.com/16872793/76107253-48deeb00-5fa6-11ea-9931-721cde553bdf.png',
+	include: [
+		features.isPRCommit
+	],
+	load: features.nowAndOnAjaxedPages,
+	init
+});
diff --git a/source/libs/utils.ts b/source/libs/utils.ts
index 73b5fb09..8f0729e0 100644
--- a/source/libs/utils.ts
+++ b/source/libs/utils.ts
@@ -27,6 +27,18 @@ export const getDiscussionNumber = (): string | undefined => {
 	return undefined;
 };
 
+export const pluralize = (count: number, single: string, plural: string, zero?: string): string => {
+	if (count === 0 && zero) {
+		return zero.replace('$$', '0');
+	}
+
+	if (count === 1) {
+		return single.replace('$$', '1');
+	}
+
+	return plural.replace('$$', String(count));
+};
+
 // Drops leading and trailing slash to avoid /\/?/ everywhere
 export const getCleanPathname = (): string => location.pathname.replace(/^[/]|[/]$/g, '');