AK: Properly implement steps for shortening a URLs path

Instead of implementing this inline, put it into a function. Use this
new function to correctly implement shortening paths for some places
where this logic was previously missing.

Before these changes, the pathname for the included test was incorrectly
being set to '/' as we were not considering the windows drive letter.

AK/URLParser.cpp

@@ -683,6 +683,24 @@ constexpr bool is_double_dot_path_segment(StringView input)
     return input == ".."sv || input.equals_ignoring_ascii_case(".%2e"sv) || input.equals_ignoring_ascii_case("%2e."sv) || input.equals_ignoring_ascii_case("%2e%2e"sv);
 }
 
+// https://url.spec.whatwg.org/#shorten-a-urls-path
+void URLParser::shorten_urls_path(URL& url)
+{
+    // 1. Assert: url does not have an opaque path.
+    VERIFY(!url.cannot_be_a_base_url());
+
+    // 2. Let path be url’s path.
+    auto& path = url.m_paths;
+
+    // 3. If url’s scheme is "file", path’s size is 1, and path[0] is a normalized Windows drive letter, then return.
+    if (url.scheme() == "file" && path.size() == 1 && is_normalized_windows_drive_letter(path[0]))
+        return;
+
+    // 4. Remove path’s last item, if any.
+    if (!path.is_empty())
+        path.take_last();
+}
+
 // https://url.spec.whatwg.org/#string-percent-encode-after-encoding
 ErrorOr<String> URLParser::percent_encode_after_encoding(StringView input, URL::PercentEncodeSet percent_encode_set, bool space_as_plus)
 {
@@ -1025,8 +1043,7 @@ URL URLParser::basic_parse(StringView raw_input, Optional<URL> const& base_url,
                     url->m_query = {};
 
                     // 2. Shorten url’s path.
-                    if (url->m_paths.size())
-                        url->m_paths.remove(url->m_paths.size() - 1);
+                    shorten_urls_path(*url);
 
                     // 3. Set state to path state and decrease pointer by 1.
                     state = State::Path;
@@ -1337,8 +1354,7 @@ URL URLParser::basic_parse(StringView raw_input, Optional<URL> const& base_url,
                     // 2. If the code point substring from pointer to the end of input does not start with a Windows drive letter, then shorten url’s path.
                     auto substring_from_pointer = input.substring_view(iterator - input.begin()).as_string();
                     if (!starts_with_windows_drive_letter(substring_from_pointer)) {
-                        if (!url->m_paths.is_empty() && !(url->scheme() == "file" && url->m_paths.size() == 1 && is_normalized_windows_drive_letter(url->m_paths[0])))
-                            url->m_paths.remove(url->m_paths.size() - 1);
+                        shorten_urls_path(*url);
                     }
                     // 3. Otherwise:
                     else {
@@ -1505,8 +1521,7 @@ URL URLParser::basic_parse(StringView raw_input, Optional<URL> const& base_url,
                 // 2. If buffer is a double-dot URL path segment, then:
                 if (is_double_dot_path_segment(buffer.string_view())) {
                     // 1. Shorten url’s path.
-                    if (!url->m_paths.is_empty())
-                        url->m_paths.remove(url->m_paths.size() - 1);
+                    shorten_urls_path(*url);
 
                     // 2. If neither c is U+002F (/), nor url is special and c is U+005C (\), append the empty string to url’s path.
                     if (code_point != '/' && !(url->is_special() && code_point == '\\'))

AK/URLParser.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, Max Wipfli <mail@maxwipfli.ch>
+ * Copyright (c) 2023, Shannon Booth <shannon@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -63,6 +64,9 @@ public:
 
     // https://url.spec.whatwg.org/#concept-host-serializer
     static ErrorOr<String> serialize_host(URL::Host const&);
+
+    // https://url.spec.whatwg.org/#shorten-a-urls-path
+    static void shorten_urls_path(URL&);
 };
 
 #undef ENUMERATE_STATES

Tests/LibWeb/Text/expected/URL/url.txt

@@ -68,3 +68,13 @@ port => ''
 pathname => '/hello'
 search => ''
 hash => ''
+new URL('//d:/..', 'file:///C:/a/b')
+protocol => 'file:'
+username => ''
+password => ''
+host => ''
+hostname => ''
+port => ''
+pathname => '/d:/'
+search => ''
+hash => ''

Tests/LibWeb/Text/input/URL/url.html

@@ -27,6 +27,7 @@
             { input: 'unknown://serenityos.org:0' },
             { input: 'http://serenityos.org/cat?dog#meow"woof' },
             { input: '/hello', base: 'file://friends/' },
+            { input: '//d:/..', base: 'file:///C:/a/b' },
         ]) {
             printURL(url.input, url.base);
         }