[gcc(refs/vendors/ARM/heads/arm-struct-reorg-wip)] c++: explicit(bool) malfunction with dependent expression [PR95066]

[Tamar Christina]

https://gcc.gnu.org/g:ae275b986b8cc747a5b4f389cb05a71fdee1f886

commit ae275b986b8cc747a5b4f389cb05a71fdee1f886
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Jun 11 16:33:13 2020 -0400

    c++: explicit(bool) malfunction with dependent expression [PR95066]
    
    I forgot to set DECL_HAS_DEPENDENT_EXPLICIT_SPEC_P when merging two
    function declarations and as a sad consequence, we never tsubsted
    the dependent explicit-specifier in tsubst_function_decl, leading to
    disregarding the explicit-specifier altogether, and wrongly accepting
    this test.
    
            PR c++/95066
            * decl.c (duplicate_decls): Set DECL_HAS_DEPENDENT_EXPLICIT_SPEC_P.
    
            * g++.dg/cpp2a/explicit16.C: New test.

Diff:
---
 gcc/cp/decl.c                           |  2 ++
 gcc/testsuite/g++.dg/cpp2a/explicit16.C | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index ae8fd32d83b..4199778fe4e 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -2035,6 +2035,8 @@ duplicate_decls (tree newdecl, tree olddecl, bool newdecl_is_friend)
       DECL_FINAL_P (newdecl) |= DECL_FINAL_P (olddecl);
       DECL_OVERRIDE_P (newdecl) |= DECL_OVERRIDE_P (olddecl);
       DECL_THIS_STATIC (newdecl) |= DECL_THIS_STATIC (olddecl);
+      DECL_HAS_DEPENDENT_EXPLICIT_SPEC_P (newdecl)
+	|= DECL_HAS_DEPENDENT_EXPLICIT_SPEC_P (olddecl);
       if (DECL_OVERLOADED_OPERATOR_P (olddecl))
 	DECL_OVERLOADED_OPERATOR_CODE_RAW (newdecl)
 	  = DECL_OVERLOADED_OPERATOR_CODE_RAW (olddecl);
diff --git a/gcc/testsuite/g++.dg/cpp2a/explicit16.C b/gcc/testsuite/g++.dg/cpp2a/explicit16.C
new file mode 100644
index 00000000000..9d95b0d669e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/explicit16.C
@@ -0,0 +1,21 @@
+// PR c++/95066 - explicit malfunction with dependent expression.
+// { dg-do compile { target c++2a } }
+
+template <typename T>
+struct Foo {
+  template <typename U>
+  explicit(static_cast<U>(true)) operator Foo<U>();
+};
+
+template <typename T>
+template <typename U>
+Foo<T>::operator Foo<U>() {
+  return {};
+}
+
+int
+main ()
+{
+  Foo<float> a;
+  Foo<int> b = a; // { dg-error "conversion" }
+}