AK: Make LexicalPath immutable

This replaces the current LexicalPath::append() API with a new method
that returns a new LexicalPath object and doesn't touch the this-object.
With this, LexicalPath is now immutable. It also adds a
LexicalPath::parent() method and the relevant test cases.

Author: MaxWipfli

AK/LexicalPath.cpp

@@ -137,15 +137,14 @@ String LexicalPath::relative_path(String absolute_path, String const& prefix)
     return absolute_path.substring(prefix_length);
 }
 
-void LexicalPath::append(String const& component)
+LexicalPath LexicalPath::append(StringView const& value) const
 {
-    StringBuilder builder;
-    builder.append(m_string);
-    builder.append('/');
-    builder.append(component);
+    return LexicalPath::join(m_string, value);
+}
 
-    m_string = builder.to_string();
-    canonicalize();
+LexicalPath LexicalPath::parent() const
+{
+    return append("..");
 }
 
 }

AK/LexicalPath.h

@@ -30,7 +30,8 @@ class LexicalPath {
 
     bool has_extension(StringView const&) const;
 
-    void append(String const& component);
+    [[nodiscard]] LexicalPath append(StringView const&) const;
+    [[nodiscard]] LexicalPath parent() const;
 
     static String canonicalized_path(String);
     static String relative_path(String absolute_path, String const& prefix);

Tests/AK/TestLexicalPath.cpp

@@ -165,11 +165,38 @@ TEST_CASE(join)
     EXPECT_EQ(LexicalPath::join("anon", "foo.txt").string(), "anon/foo.txt");
     EXPECT_EQ(LexicalPath::join("/home", "anon/foo.txt").string(), "/home/anon/foo.txt");
     EXPECT_EQ(LexicalPath::join("/", "foo.txt").string(), "/foo.txt");
+    EXPECT_EQ(LexicalPath::join("/home", "anon", "foo.txt").string(), "/home/anon/foo.txt");
 }
 
 TEST_CASE(append)
 {
-    LexicalPath path("/home/anon");
-    path.append("foo.txt");
-    EXPECT_EQ(path.string(), "/home/anon/foo.txt");
+    LexicalPath path("/home/anon/");
+    auto new_path = path.append("foo.txt");
+    EXPECT_EQ(new_path.string(), "/home/anon/foo.txt");
+}
+
+TEST_CASE(parent)
+{
+    {
+        LexicalPath path("/home/anon/foo.txt");
+        auto parent = path.parent();
+        EXPECT_EQ(parent.string(), "/home/anon");
+    }
+    {
+        LexicalPath path("anon/foo.txt");
+        auto parent = path.parent();
+        EXPECT_EQ(parent.string(), "anon");
+    }
+    {
+        LexicalPath path("foo.txt");
+        auto parent = path.parent();
+        EXPECT_EQ(parent.string(), ".");
+        auto parent_of_parent = parent.parent();
+        EXPECT_EQ(parent_of_parent.string(), "..");
+    }
+    {
+        LexicalPath path("/");
+        auto parent = path.parent();
+        EXPECT_EQ(parent.string(), "/");
+    }
 }