Report formatting fixes on pull requests

Summary:
Add a GitHub Actions formatting check that runs the repository-wide formatter check and posts line-level suggested fixes through the GitHub API for files that need reformatting.

Changelog: [Internal]

Differential Revision: D119487616

Author: cortinico

.github/workflow-scripts/__tests__/reportFormattingErrors-test.js

@@ -0,0 +1,110 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+'use strict';
+
+const {
+  changedFilesFromPatch,
+  commentableRightLines,
+  parsePatch,
+} = require('../reportFormattingErrors');
+
+describe('reportFormattingErrors', () => {
+  test('converts formatter hunks into minimal suggestions', () => {
+    const patch = `diff --git a/example.js b/example.js
+--- a/example.js
++++ b/example.js
+@@ -10,3 +10,3 @@
+ unchanged
+-const value={answer:42};
++const value = {answer: 42};
+ unchanged
+`;
+
+    expect(parsePatch(patch)).toEqual([
+      {
+        path: 'example.js',
+        startLine: 11,
+        endLine: 11,
+        replacement: 'const value = {answer: 42};',
+      },
+    ]);
+  });
+
+  test('tracks lines that can receive right-side review comments', () => {
+    const lines = commentableRightLines(`@@ -4,2 +4,3 @@
+ context
+-old
++new
++added
+`);
+
+    expect([...lines]).toEqual([4, 5, 6]);
+  });
+
+  test.each(['../../../etc/passwd', '/absolute/path', `\0evil`])(
+    'rejects unsafe patch path %p',
+    unsafePath => {
+      const patch = `diff --git a/file b/file
+--- a/file
++++ b/${unsafePath}
+@@ -1 +1 @@
+-old
++new
+`;
+
+      expect(parsePatch(patch)).toEqual([]);
+      expect(changedFilesFromPatch(patch)).toEqual([]);
+    },
+  );
+
+  test('parses multiple files without carrying hunk state across headers', () => {
+    const patch = `diff --git a/one.js b/one.js
+--- a/one.js
++++ b/one.js
+@@ -1 +1 @@
+-one
++first
+diff --git a/two.js b/two.js
+--- a/two.js
++++ b/two.js
+@@ -2 +2 @@
+-two
++second
+`;
+
+    expect(parsePatch(patch)).toEqual([
+      {path: 'one.js', startLine: 1, endLine: 1, replacement: 'first'},
+      {path: 'two.js', startLine: 2, endLine: 2, replacement: 'second'},
+    ]);
+    expect(changedFilesFromPatch(patch)).toEqual(['one.js', 'two.js']);
+  });
+
+  test('reports files even when a hunk cannot become a suggestion', () => {
+    const patch = `diff --git a/example.js b/example.js
+--- a/example.js
++++ b/example.js
+@@ -1 +1 @@
+-old
++\`\`\`unsafe suggestion fence
+`;
+
+    expect(parsePatch(patch)).toEqual([]);
+    expect(changedFilesFromPatch(patch)).toEqual(['example.js']);
+  });
+
+  test('ignores non-hunk lines when collecting commentable lines', () => {
+    const lines = commentableRightLines(`@@ -4 +4 @@
++new
+index 123..456 100644
+`);
+
+    expect([...lines]).toEqual([4]);
+  });
+});