[PATCH] libstdc++: Fix flat_map::operator[] for const lvalue keys [PR120432]

[Patrick Palka]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk/15?

The 'volatile' issue from that PR Will be fixed in a separate patch as
operator[] isn't the only operation that's affected.

-- >8 --

The const lvalue operator[] overload wasn't properly forwarding the key
type to the generic overload.

        PR libstdc++/120432

libstdc++-v3/ChangeLog:

        * include/std/flat_map (_Flat_map_base::operator[]): Correct
        forwarding from the const lvalue key overload.
        * testsuite/23_containers/flat_map/1.cc (test08): New test.
        * testsuite/23_containers/flat_multimap/1.cc (test08): New test.
---
 libstdc++-v3/include/std/flat_map                      |  2 +-
 libstdc++-v3/testsuite/23_containers/flat_map/1.cc     | 10 ++++++++++
 .../testsuite/23_containers/flat_multimap/1.cc         | 10 ++++++++++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/flat_map 
b/libstdc++-v3/include/std/flat_map
index 6593988d213c..4d9ced1e8191 100644
--- a/libstdc++-v3/include/std/flat_map
+++ b/libstdc++-v3/include/std/flat_map
@@ -1142,7 +1142,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       // element access
       mapped_type&
       operator[](const key_type& __x)
-      { return operator[]<const key_type>(__x); }
+      { return operator[]<const key_type&>(__x); }
 
       mapped_type&
       operator[](key_type&& __x)
diff --git a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc 
b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
index a9690208b09f..2af516410279 100644
--- a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
@@ -253,6 +253,15 @@ test07()
   VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4}}) );
 }
 
+void
+test08()
+{
+  // PR libstdc++/120432 - flat_map operator[] is broken for const lvalue keys
+  std::flat_map<int, int> m;
+  const int k = 42;
+  m[k] = 0;
+}
+
 int
 main()
 {
@@ -266,4 +275,5 @@ main()
   test05();
   test06();
   test07();
+  test08();
 }
diff --git a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc 
b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
index 1c5c9a88ab6b..638b269011d4 100644
--- a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
@@ -231,6 +231,15 @@ test07()
   VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4},{3,3}}) );
 }
 
+void
+test08()
+{
+  // PR libstdc++/120432 - flat_map operator[] is broken for const lvalue keys
+  std::flat_multimap<int, int> m;
+  const int k = 42;
+  m[k] = 0;
+}
+
 int
 main()
 {
@@ -244,4 +253,5 @@ main()
   test05();
   test06();
   test07();
+  test08();
 }
-- 
2.49.0.654.g845c48a16a