cp: Copy sources into destination if it is already a directory

Previously, copying a file to a directory, like this:
```cp README.md Desktop```
correctly copied it to Desktop/README.md, but would fail if the
source was also a directory, for example:
```cp -R Documents Desktop```
Now, that correctly copies it to Desktop/Documents, as you would
expect. :^)

1 files changed, 13 insertions, 6 deletions

diff --git a/Userland/Utilities/cp.cpp b/Userland/Utilities/cp.cpp
index c0ca9a96fc..86a08e6877 100644
--- a/Userland/Utilities/cp.cpp
+++ b/Userland/Utilities/cp.cpp
@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/LexicalPath.h>
 #include <LibCore/ArgsParser.h>
 #include <LibCore/File.h>
 #include <stdio.h>
@@ -19,21 +20,27 @@ int main(int argc, char** argv)
     bool link = false;
     bool recursion_allowed = false;
     bool verbose = false;
-    Vector<const char*> sources;
-    const char* destination = nullptr;
+    Vector<String> sources;
+    String destination;
 
     Core::ArgsParser args_parser;
     args_parser.add_option(link, "Link files instead of copying", "link", 'l');
     args_parser.add_option(recursion_allowed, "Copy directories recursively", "recursive", 'R');
     args_parser.add_option(recursion_allowed, "Same as -R", nullptr, 'r');
     args_parser.add_option(verbose, "Verbose", "verbose", 'v');
-    args_parser.add_positional_argument(sources, "Source file path", "source");
+    args_parser.add_positional_argument(sources, "Source file paths", "source");
     args_parser.add_positional_argument(destination, "Destination file path", "destination");
     args_parser.parse(argc, argv);
 
+    bool destination_is_existing_dir = Core::File::is_directory(destination);
+
     for (auto& source : sources) {
+        auto destination_path = destination_is_existing_dir
+            ? String::formatted("{}/{}", destination, LexicalPath(source).basename())
+            : destination;
+
         auto result = Core::File::copy_file_or_directory(
-            destination, source,
+            destination_path, source,
             recursion_allowed ? Core::File::RecursionMode::Allowed : Core::File::RecursionMode::Disallowed,
             link ? Core::File::LinkMode::Allowed : Core::File::LinkMode::Disallowed,
             Core::File::AddDuplicateFileMarker::No);
@@ -42,12 +49,12 @@ int main(int argc, char** argv)
             if (result.error().tried_recursing)
                 warnln("cp: -R not specified; omitting directory '{}'", source);
             else
-                warnln("cp: unable to copy '{}': {}", source, result.error().error_code);
+                warnln("cp: unable to copy '{}' to '{}': {}", source, destination_path, result.error().error_code);
             return 1;
         }
 
         if (verbose)
-            outln("'{}' -> '{}'", source, destination);
+            outln("'{}' -> '{}'", source, destination_path);
     }
     return 0;
 }