[gcc/devel/c++-coroutines] c++: Fix CTAD with multiple-arg ctor template [93248].

[Iain D Sandoe]

https://gcc.gnu.org/g:c393c99d3dc8329dc1a36011e70faa9700185051

commit c393c99d3dc8329dc1a36011e70faa9700185051
Author: Jason Merrill <jason@redhat.com>
Date:   Sat Mar 14 17:10:39 2020 -0400

    c++: Fix CTAD with multiple-arg ctor template [93248].
    
    When cp_unevaluated_operand is set, tsubst_decl thinks that if it sees a
    PARM_DECL that isn't already in local_specializations, we're in a decltype
    in a trailing return type or some such, and so we only want a substitution
    for a single PARM_DECL.  In this case, we want the whole chain, so make sure
    cp_unevaluated_operand is cleared.
    
    gcc/cp/ChangeLog
    2020-03-14  Jason Merrill  <jason@redhat.com>
    
            PR c++/93248
            * pt.c (build_deduction_guide): Clear cp_unevaluated_operand for
            substituting DECL_ARGUMENTS.

Diff:
---
 gcc/cp/ChangeLog                               | 6 ++++++
 gcc/cp/pt.c                                    | 5 ++++-
 gcc/testsuite/g++.dg/cpp1z/class-deduction71.C | 6 ++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 79434c9d45e..b4fa15047b5 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-03-14  Jason Merrill  <jason@redhat.com>
+
+	PR c++/93248
+	* pt.c (build_deduction_guide): Clear cp_unevaluated_operand for
+	substituting DECL_ARGUMENTS.
+
 2020-03-14  Jakub Jelinek  <jakub@redhat.com>
 
 	* logic.cc (formula::formula): Change "a an" to "an" in a comment.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 789ccdbbbd1..0f3c2ad8fec 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -28071,10 +28071,13 @@ build_deduction_guide (tree type, tree ctor, tree outer_args, tsubst_flags_t com
 				     complain, ctor);
 	  if (fparms == error_mark_node)
 	    ok = false;
-	  fargs = tsubst (fargs, tsubst_args, complain, ctor);
 	  if (ci)
 	    ci = tsubst_constraint_info (ci, tsubst_args, complain, ctor);
 
+	  /* Parms are to have DECL_CHAIN tsubsted, which would be skipped if
+	     cp_unevaluated_operand.  */
+	  cp_evaluated ev;
+	  fargs = tsubst (fargs, tsubst_args, complain, ctor);
 	  current_template_parms = save_parms;
 	}
 
diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction71.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction71.C
new file mode 100644
index 00000000000..2fc71de8d95
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction71.C
@@ -0,0 +1,6 @@
+// PR c++/93248
+// { dg-do compile { target c++17 } }
+
+template <typename T> struct S
+{ template <typename V> S (T, V, long = 0); };
+using U = decltype(S{0, 4u});