[gcc/devel/gccgo] c++: Parameter pack in requires parameter list [PR94808]

[Ian Lance Taylor]

https://gcc.gnu.org/g:43439d5e8424f3a746003ef8953e1cdc120fbbd7

commit 43439d5e8424f3a746003ef8953e1cdc120fbbd7
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Apr 28 21:45:54 2020 -0400

    c++: Parameter pack in requires parameter list [PR94808]
    
    When printing the substituted parameter list of a requires-expression as
    part of the "in requirements with ..." context line during concepts
    diagnostics, we weren't considering that substitution into a parameter
    pack can yield zero or multiple parameters.
    
    This patch changes the way we print the parameter list of a
    requires-expression in print_requires_expression_info.  We now print the
    dependent form of the parameter list (along with its template parameter
    mapping) instead of printing its substituted form.  Besides being an
    improvement in its own, this also sidesteps the substitution issue in the
    PR altogether.
    
    gcc/cp/ChangeLog:
    
            PR c++/94808
            * error.c (print_requires_expression_info): Print the dependent
            form of the parameter list with its template parameter mapping,
            rather than printing the substituted form.
    
    gcc/testsuite/ChangeLog:
    
            PR c++/94808
            * g++.dg/concepts/diagnostic12.C: New test.
            * g++.dg/concepts/diagnostic5.C: Adjust dg-message.

Diff:
---
 gcc/cp/ChangeLog                             |  7 +++++++
 gcc/cp/error.c                               | 16 ++++------------
 gcc/testsuite/ChangeLog                      |  6 ++++++
 gcc/testsuite/g++.dg/concepts/diagnostic12.C | 16 ++++++++++++++++
 gcc/testsuite/g++.dg/concepts/diagnostic5.C  |  4 ++--
 5 files changed, 35 insertions(+), 14 deletions(-)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 8728389be83..c0558015eb8 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,10 @@
+2020-04-29  Patrick Palka  <ppalka@redhat.com>
+
+	PR c++/94808
+	* error.c (print_requires_expression_info): Print the dependent
+	form of the parameter list with its template parameter mapping,
+	rather than printing the substituted form.
+
 2020-04-28  Jason Merrill  <jason@redhat.com>
 
 	PR c++/94583
diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index 98c163db572..46970f9b699 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -3746,7 +3746,6 @@ print_requires_expression_info (diagnostic_context *context, tree constr, tree a
   map = tsubst_parameter_mapping (map, args, tf_none, NULL_TREE);
   if (map == error_mark_node)
     return;
-  args = get_mapped_args (map);
 
   print_location (context, cp_expr_loc_or_input_loc (expr));
   pp_verbatim (context->printer, "in requirements ");
@@ -3756,19 +3755,12 @@ print_requires_expression_info (diagnostic_context *context, tree constr, tree a
     pp_verbatim (context->printer, "with ");
   while (parms)
     {
-      tree next = TREE_CHAIN (parms);
-
-      TREE_CHAIN (parms) = NULL_TREE;
-      cp_unevaluated u;
-      tree p = tsubst (parms, args, tf_none, NULL_TREE);
-      pp_verbatim (context->printer, "%q#D", p);
-      TREE_CHAIN (parms) = next;
-
-      if (next)
+      pp_verbatim (context->printer, "%q#D", parms);
+      if (TREE_CHAIN (parms))
         pp_separate_with_comma ((cxx_pretty_printer *)context->printer);
-
-      parms = next;
+      parms = TREE_CHAIN (parms);
     }
+  pp_cxx_parameter_mapping ((cxx_pretty_printer *)context->printer, map);
 
   pp_verbatim (context->printer, "\n");
 }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index d20308b376c..a824ba8424e 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-29  Patrick Palka  <ppalka@redhat.com>
+
+	PR c++/94808
+	* g++.dg/concepts/diagnostic12.C: New test.
+	* g++.dg/concepts/diagnostic5.C: Adjust dg-message.
+
 2020-04-28  Alexandre Oliva <oliva@adacore.com>
 
 	PR target/94812
diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic12.C b/gcc/testsuite/g++.dg/concepts/diagnostic12.C
new file mode 100644
index 00000000000..a757342f754
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic12.C
@@ -0,0 +1,16 @@
+// PR c++/94808
+// { dg-do compile { target concepts } }
+
+template<typename T, typename... Args>
+  concept c1 = requires (T t, Args... args) { *t; };
+// { dg-message "in requirements with .T t., .Args ... args. .with.* Args = \{\}" "" { target *-*-* } .-1 }
+
+static_assert(c1<int>); // { dg-error "failed" }
+
+void f(...);
+
+template<typename... Args>
+  concept c2 = requires (Args... args) { f(*args...); };
+// { dg-message "in requirements with .Args ... args. .with Args = \{int, char\}" "" { target *-*-* } .-1 }
+
+static_assert(c2<int, char>); // { dg-error "failed" }
diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic5.C b/gcc/testsuite/g++.dg/concepts/diagnostic5.C
index 0d890d6f548..81705f6a0c6 100644
--- a/gcc/testsuite/g++.dg/concepts/diagnostic5.C
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic5.C
@@ -9,7 +9,7 @@ template<typename T>
 template<typename T>
   concept c2 = requires (T x) { *x; };
 // { dg-message "satisfaction of .c2<T>. .with T = char." "" { target *-*-* } .-1 }
-// { dg-message "in requirements with .char x." "" { target *-*-* } .-2 }
+// { dg-message "in requirements with .T x. .with T = char." "" { target *-*-* } .-2 }
 // { dg-message "required expression .* is invalid" "" { target *-*-* } .-3 }
 
 template<typename T>
@@ -25,7 +25,7 @@ template<typename T>
 template<typename T>
   concept c5 = requires (T x) { { &x } -> c1; };
 // { dg-message "satisfaction of .c5<T>. .with T = char." "" { target *-*-* } .-1 }
-// { dg-message "in requirements with .char x." "" { target *-*-* } .-2 }
+// { dg-message "in requirements with .T x. .with T = char." "" { target *-*-* } .-2 }
 
 template<typename T>
   requires (c1<T> || c2<T>) || (c3<T> || c4<T>) || c5<T> // { dg-message "49: no operand" }