Implement LWG 3096: path::lexically_relative is confused by trailing slashes

path("/dir/").lexically_relative("/dir"); now returns "." instead of ""

3 files changed, 9 insertions, 6 deletions

diff --git a/libcxx/src/filesystem/operations.cpp b/libcxx/src/filesystem/operations.cpp
index 0b79ef1cdac..e3bbc7b64b8 100644
--- a/libcxx/src/filesystem/operations.cpp
+++ b/libcxx/src/filesystem/operations.cpp
@@ -1478,7 +1478,7 @@ static int DetermineLexicalElementCount(PathParser PP) {
     auto Elem = *PP;
     if (Elem == "..")
       --Count;
-    else if (Elem != ".")
+    else if (Elem != "." && Elem != "")
       ++Count;
   }
   return Count;
@@ -1492,8 +1492,7 @@ path path::lexically_relative(const path& base) const {
       return PP.State != PPBase.State &&
              (PP.inRootPath() || PPBase.inRootPath());
     };
-    if (PP.State == PathParser::PS_InRootName &&
-        PPBase.State == PathParser::PS_InRootName) {
+    if (PP.inRootName() && PPBase.inRootName()) {
       if (*PP != *PPBase)
         return {};
     } else if (CheckIterMismatchAtBase())
@@ -1525,6 +1524,10 @@ path path::lexically_relative(const path& base) const {
   if (ElemCount < 0)
     return {};
 
+  // if n == 0 and (a == end() || a->empty()), returns path("."); otherwise
+  if (ElemCount == 0 && (PP.atEnd() || *PP == ""))
+    return ".";
+
   // return a path constructed with 'n' dot-dot elements, followed by the the
   // elements of '*this' after the mismatch.
   path Result;
diff --git a/libcxx/test/std/input.output/filesystems/class.path/path.member/path.gen/lexically_relative_and_proximate.pass.cpp b/libcxx/test/std/input.output/filesystems/class.path/path.member/path.gen/lexically_relative_and_proximate.pass.cpp
index 52c577bc8a7..f4e1d2f74df 100644
--- a/libcxx/test/std/input.output/filesystems/class.path/path.member/path.gen/lexically_relative_and_proximate.pass.cpp
+++ b/libcxx/test/std/input.output/filesystems/class.path/path.member/path.gen/lexically_relative_and_proximate.pass.cpp
@@ -40,8 +40,8 @@ int main() {
       {"a", "/", ""},
       {"//net", "a", ""},
       {"a", "//net", ""},
-      {"//net/", "//net", ""},
-      {"//net", "//net/", ".."},
+      {"//net/", "//net", "."},
+      {"//net", "//net/", "."},
       {"//base", "a", ""},
       {"a", "a", "."},
       {"a/b", "a/b", "."},
diff --git a/libcxx/www/cxx2a_status.html b/libcxx/www/cxx2a_status.html
index 1a072c9b054..63ae029ed4a 100644
--- a/libcxx/www/cxx2a_status.html
+++ b/libcxx/www/cxx2a_status.html
@@ -271,7 +271,7 @@
 	<tr><td><a href="https://wg21.link/LWG3038">3038</a></td><td><tt>polymorphic_allocator::allocate</tt> should not allow integer overflow to create vulnerabilities</td><td>San Diego</td><td></td></tr>
 	<tr><td><a href="https://wg21.link/LWG3054">3054</a></td><td><tt>uninitialized_copy</tt> appears to not be able to meet its exception-safety guarantee</td><td>San Diego</td><td></td></tr>
 	<tr><td><a href="https://wg21.link/LWG3065">3065</a></td><td>LWG 2989 missed that all <tt>path</tt>'s other operators should be hidden friends as well</td><td>San Diego</td><td>Complete</td></tr>
-	<tr><td><a href="https://wg21.link/LWG3096">3096</a></td><td><tt>path::lexically_relative</tt> is confused by trailing slashes</td><td>San Diego</td><td></td></tr>
+	<tr><td><a href="https://wg21.link/LWG3096">3096</a></td><td><tt>path::lexically_relative</tt> is confused by trailing slashes</td><td>San Diego</td><td>Complete</td></tr>
 	<tr><td><a href="https://wg21.link/LWG3116">3116</a></td><td><tt><i>OUTERMOST_ALLOC_TRAITS</i></tt> needs <tt>remove_reference_t</tt></td><td>San Diego</td><td></td></tr>
 	<tr><td><a href="https://wg21.link/LWG3122">3122</a></td><td><tt>__cpp_lib_chrono_udls</tt> was accidentally dropped</td><td>San Diego</td><td><i>We've already made the update; but we don't support all the test macros. When we do, this will be closed</i></td></tr>
 	<tr><td><a href="https://wg21.link/LWG3127">3127</a></td><td><tt>basic_osyncstream::rdbuf</tt> needs a <tt>const_cast</tt></td><td>San Diego</td><td></td></tr>