On 3/19/20 12:50 PM, Patrick Palka wrote:
On Thu, 19 Mar 2020, Jason Merrill wrote:

On 3/18/20 3:26 PM, Patrick Palka wrote:
+  if (map)
+    {
+      pp_cxx_whitespace (pp);
+      pp_cxx_left_bracket (pp);
+      pp->translate_string ("with");
+      pp_cxx_whitespace (pp);
+      pp_cxx_parameter_mapping (pp, map);
+      pp_cxx_right_bracket (pp);
+    }

Perhaps we should move the [with ] bits into pp_cxx_parameter_mapping rather
than duplicate them here.

Like this?

-- >8 --

gcc/cp/ChangeLog:

        * cxx-pretty-print.c (pp_cxx_parameter_mapping): Make extern.  Move
        the "[with ]" bits to here from ...
        (pp_cxx_atomic_constraint): ... here.
        * cxx-pretty-print.h (pp_cxx_parameter_mapping): Declare.
        * error.c (rebuild_concept_check): Delete.
        (print_concept_check_info): Print the dependent form of the constraint 
and the
        preferably substituted parameter mapping alongside it.

gcc/testsuite/ChangeLog:

        * g++.dg/concepts/diagnostic6.C: New test.
---
  gcc/cp/cxx-pretty-print.c                   | 12 ++++---
  gcc/cp/cxx-pretty-print.h                   |  1 +
  gcc/cp/error.c                              | 36 +++++++--------------
  gcc/testsuite/g++.dg/concepts/diagnostic6.C | 14 ++++++++
  4 files changed, 33 insertions(+), 30 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/concepts/diagnostic6.C

diff --git a/gcc/cp/cxx-pretty-print.c b/gcc/cp/cxx-pretty-print.c
index 100154e400f..15d8b7eb609 100644
--- a/gcc/cp/cxx-pretty-print.c
+++ b/gcc/cp/cxx-pretty-print.c
@@ -2878,9 +2878,13 @@ pp_cxx_check_constraint (cxx_pretty_printer *pp, tree t)
  /* Output the "[with ...]" clause for a parameter mapping of an atomic
     constraint.   */
-static void
+void
  pp_cxx_parameter_mapping (cxx_pretty_printer *pp, tree map)
  {
+  pp_cxx_left_bracket (pp);
+  pp->translate_string ("with");
+  pp_cxx_whitespace (pp);
+
    for (tree p = map; p; p = TREE_CHAIN (p))
      {
        tree parm = TREE_VALUE (p);
@@ -2903,6 +2907,8 @@ pp_cxx_parameter_mapping (cxx_pretty_printer *pp, tree 
map)
        if (TREE_CHAIN (p) != NULL_TREE)
        pp_cxx_separate_with (pp, ';');
      }
+
+  pp_cxx_right_bracket (pp);
  }
void
@@ -2915,12 +2921,8 @@ pp_cxx_atomic_constraint (cxx_pretty_printer *pp, tree t)
    tree map = ATOMIC_CONSTR_MAP (t);
    if (map && map != error_mark_node)
      {
-      pp_cxx_whitespace (pp);
-      pp_cxx_left_bracket (pp);
-      pp->translate_string ("with");
        pp_cxx_whitespace (pp);

Is there a reason not to move the initial whitespace as well, like in dump_substitution? OK with that change.

        pp_cxx_parameter_mapping (pp, map);
-      pp_cxx_right_bracket (pp);
     }
  }
diff --git a/gcc/cp/cxx-pretty-print.h b/gcc/cp/cxx-pretty-print.h
index 7c7347f57ba..494f3fdde59 100644
--- a/gcc/cp/cxx-pretty-print.h
+++ b/gcc/cp/cxx-pretty-print.h
@@ -112,5 +112,6 @@ void pp_cxx_conjunction (cxx_pretty_printer *, tree);
  void pp_cxx_disjunction (cxx_pretty_printer *, tree);
  void pp_cxx_constraint (cxx_pretty_printer *, tree);
  void pp_cxx_constrained_type_spec (cxx_pretty_printer *, tree);
+void pp_cxx_parameter_mapping (cxx_pretty_printer *, tree);
#endif /* GCC_CXX_PRETTY_PRINT_H */
diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index cc51b6ffe13..9f19e9bbaa4 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -3680,27 +3680,6 @@ print_location (diagnostic_context *context, location_t 
loc)
                   "locus", xloc.file, xloc.line);
  }
-/* Instantiate the concept check for the purpose of diagnosing an error. */
-
-static tree
-rebuild_concept_check (tree expr, tree map, tree args)
-{
-  /* Instantiate the parameter mapping for the template-id.  */
-  map = tsubst_parameter_mapping (map, args, tf_none, NULL_TREE);
-  if (map == error_mark_node)
-    return error_mark_node;
-  args = get_mapped_args (map);
-
-  /* Rebuild the template id using substituted arguments. Substituting
-     directly through the expression will trigger recursive satisfaction,
-     so don't do that.  */
-  tree id = unpack_concept_check (expr);
-  args = tsubst_template_args (TREE_OPERAND (id, 1), args, tf_none, NULL_TREE);
-  if (args == error_mark_node)
-    return error_mark_node;
-  return build_nt (TEMPLATE_ID_EXPR, TREE_OPERAND (id, 0), args);
-}
-
  static void
  print_constrained_decl_info (diagnostic_context *context, tree decl)
  {
@@ -3717,12 +3696,19 @@ print_concept_check_info (diagnostic_context *context, 
tree expr, tree map, tree
    tree tmpl = TREE_OPERAND (id, 0);
    if (OVL_P (tmpl))
      tmpl = OVL_FIRST (tmpl);
-  tree check = rebuild_concept_check (expr, map, args);
-  if (check == error_mark_node)
-    check = expr;
print_location (context, DECL_SOURCE_LOCATION (tmpl));
-  pp_verbatim (context->printer, "required for the satisfaction of %qE\n", 
check);
+
+  cxx_pretty_printer *pp = (cxx_pretty_printer *)context->printer;
+  pp_verbatim (pp, "required for the satisfaction of %qE", expr);
+  if (map)
+    {
+      tree subst_map = tsubst_parameter_mapping (map, args, tf_none, 
NULL_TREE);
+      pp_cxx_whitespace (pp);
+      pp_cxx_parameter_mapping (pp, (subst_map != error_mark_node
+                                    ? subst_map : map));
+    }
+  pp_newline (pp);
  }
/* Diagnose the entry point into the satisfaction error. Returns the next
diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic6.C 
b/gcc/testsuite/g++.dg/concepts/diagnostic6.C
new file mode 100644
index 00000000000..06b17caccbe
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic6.C
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++2a } }
+
+template<typename T>
+  concept C = requires (T t) { t + 0; };
+// { dg-message "satisfaction of .C<T>. .with T = typename T::type." "" { 
target *-*-* } .-1 }
+
+template<typename T>
+  concept D = C<T>;
+// { dg-message "satisfaction of .D<typename T::type>. .with T = int." "" { 
target *-*-* } .-1 }
+
+template<typename T>
+  concept E = D<typename T::type>;
+
+static_assert(E<int>); // { dg-error "static assertion failed|not a class" }


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