c++: Fix diagnostic for binding lvalue reference to volatile rvalue [PR 100635]

The current diagnostic assumes the reference binding fails because the
reference is non-const, but it can also fail if the rvalue is volatile.

Use the current diagnostic for non-const cases, and a modified
diagnostic otherwise.

gcc/cp/ChangeLog:

	PR c++/100635
	* call.c (convert_like_internal): Print different diagnostic if
	the lvalue reference is const.

gcc/testsuite/ChangeLog:

	* g++.dg/conversion/pr100635.C: New test.

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index f07e09a..1e2d1d4 100644 (file)
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -7900,9 +7900,13 @@ convert_like_internal (conversion *convs, tree expr, tree fn, int argnum,
                              "type %qH to a value of type %qI",
                              totype, next->type);
                  }
-               else
+               else if (!CP_TYPE_CONST_P (TREE_TYPE (ref_type)))
                  error_at (loc, "cannot bind non-const lvalue reference of "
                            "type %qH to an rvalue of type %qI", totype, extype);
+               else // extype is volatile
+                 error_at (loc, "cannot bind lvalue reference of type "
+                           "%qH to an rvalue of type %qI", totype,
+                           extype);
              }
            else if (!reference_compatible_p (TREE_TYPE (totype), extype))
              {

diff --git a/gcc/testsuite/g++.dg/conversion/pr100635.C b/gcc/testsuite/g++.dg/conversion/pr100635.C
new file mode 100644 (file)
index 0000000..5841215
--- /dev/null
+++ b/gcc/testsuite/g++.dg/conversion/pr100635.C
@@ -0,0 +1,12 @@
+// PR c++/100635
+// { dg-do compile }
+// { dg-additional-options "-Wno-volatile" { target c++2a } }
+
+struct S { };
+volatile S v();
+const volatile S& svol = v(); // { dg-error "cannot bind lvalue reference of type 'const volatile S&' to an rvalue of type 'volatile S'" }
+
+#if __cplusplus >= 201103L
+volatile int&& declvol();
+const volatile int& voli = declvol(); // { dg-error "cannot bind lvalue reference of type 'const volatile int&' to an rvalue of type 'volatile int'" "" { target c++11} }
+#endif