Allow application/json uploads when fileinfo detects them as text/plain

src/wp-includes/functions.php

@@ -3247,6 +3247,7 @@ function wp_check_filetype_and_ext( $file, $filename, $mimes = null ) {
 					'text/richtext',
 					'text/tsv',
 					'text/vtt',
+					'application/json',
 				),
 				true
 			)

tests/phpunit/data/uploads/test.json

@@ -0,0 +1 @@
+"just a string"

tests/phpunit/tests/functions.php

@@ -1839,6 +1839,32 @@ public function data_wp_check_filetype_and_ext() {
 		return $data;
 	}
 
+	/**
+	 * @ticket 54193
+	 * @group ms-excluded
+	 * @requires extension fileinfo
+	 */
+	public function test_wp_check_filetype_and_ext_with_filtered_json() {
+		$file     = DIR_TESTDATA . '/uploads/test.json';
+		$filename = 'test.json';
+
+		$expected = array(
+			'ext'             => 'json',
+			'type'            => 'application/json',
+			'proper_filename' => false,
+		);
+
+		add_filter(
+			'upload_mimes',
+			static function ( $mimes ) {
+				$mimes['json'] = 'application/json';
+				return $mimes;
+			}
+		);
+
+		$this->assertSame( $expected, wp_check_filetype_and_ext( $file, $filename ) );
+	}
+
 	/**
 	 * @ticket 39550
 	 * @group ms-excluded