[gcc r13-6633] c++: suppress -Wdangling-reference for std::span [PR107532]

[gcc r13-6633] c++: suppress -Wdangling-reference for std::span [PR107532]

[Marek Polacek]

https://gcc.gnu.org/g:ced122b849b8961b854053f0d1ac96983c5802e5

commit r13-6633-gced122b849b8961b854053f0d1ac96983c5802e5
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri Mar 10 12:23:13 2023 -0500

    c++: suppress -Wdangling-reference for std::span [PR107532]
    
    std::span is a view and therefore should be treated as a reference
    wrapper class for the purposes of -Wdangling-reference.  I'm not sure
    there's a pattern that we could check for.
    
            PR c++/107532
    
    gcc/cp/ChangeLog:
    
            * call.cc (reference_like_class_p): Check for std::span.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/Wdangling-reference10.C: New test.

Diff:
---
 gcc/cp/call.cc                                    |  1 +
 gcc/testsuite/g++.dg/warn/Wdangling-reference10.C | 12 ++++++++++++
 2 files changed, 13 insertions(+)

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 3dfa12a0733..c01e7b82457 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -13800,6 +13800,7 @@ reference_like_class_p (tree ctype)
       tree name = DECL_NAME (tdecl);
       return (name
 	      && (id_equal (name, "reference_wrapper")
+		  || id_equal (name, "span")
 		  || id_equal (name, "ref_view")));
     }
   for (tree fields = TYPE_FIELDS (ctype);
diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference10.C b/gcc/testsuite/g++.dg/warn/Wdangling-reference10.C
new file mode 100644
index 00000000000..733fb8cce63
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference10.C
@@ -0,0 +1,12 @@
+// PR c++/107532
+// { dg-do compile { target c++20 } }
+// { dg-options "-Wdangling-reference" }
+
+#include <span>
+#include <vector>
+
+void f(const std::vector<int>& v)
+{
+  const int& r = std::span<const int>(v)[0]; // { dg-bogus "dangling reference" }
+  (void) r;
+}