[PATCH] c++: improve class NTTP object pretty printing [PR111471]

[Patrick Palka]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk/13?

-- >8 --

1. Move class NTTP object pretty printing to a more general spot in
   the pretty printer.
2. Print the type of an class NTTP object alongside its CONSTRUCTOR
   value, like dump_expr would have done.
3. Don't pretty print const VIEW_CONVERT_EXPR wrapping class NTTPs.

        PR c++/111471

gcc/cp/ChangeLog:

        * cxx-pretty-print.cc (cxx_pretty_printer::expression)
        <case VAR_DECL>: Print the value of a class NTTP object.
        <case VIEW_CONVERT_EXPR>: Strip cosnt VIEW_CONVERT_EXPR
        wrappers for class NTTPs.
        (pp_cxx_template_argument_list): Don't handle the class
        NTTP objects here.

gcc/testsuite/ChangeLog:

        * g++.dg/concepts/diagnostic19.C: New test.
---
 gcc/cp/cxx-pretty-print.cc                   | 19 +++++++++++++++++--
 gcc/testsuite/g++.dg/concepts/diagnostic19.C | 20 ++++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/concepts/diagnostic19.C

diff --git a/gcc/cp/cxx-pretty-print.cc b/gcc/cp/cxx-pretty-print.cc
index 909a9dc917f..7cd43151592 100644
--- a/gcc/cp/cxx-pretty-print.cc
+++ b/gcc/cp/cxx-pretty-print.cc
@@ -1121,6 +1121,15 @@ cxx_pretty_printer::expression (tree t)
       t = OVL_FIRST (t);
       /* FALLTHRU */
     case VAR_DECL:
+      if (DECL_NTTP_OBJECT_P (t))
+       {
+         /* Print the type followed by the CONSTRUCTOR value of an
+            NTTP object.  */
+         simple_type_specifier (cv_unqualified (TREE_TYPE (t)));
+         expression (DECL_INITIAL (t));
+         break;
+       }
+      /* FALLTHRU */
     case PARM_DECL:
     case FIELD_DECL:
     case CONST_DECL:
@@ -1261,6 +1270,14 @@ cxx_pretty_printer::expression (tree t)
       pp_cxx_right_paren (this);
       break;
 
+    case VIEW_CONVERT_EXPR:
+      if (TREE_CODE (TREE_OPERAND (t, 0)) == TEMPLATE_PARM_INDEX)
+       {
+         /* Strip const VIEW_CONVERT_EXPR wrappers for class NTTPs.  */
+         expression (TREE_OPERAND (t, 0));
+         break;
+       }
+      /* FALLTHRU */
     default:
       c_pretty_printer::expression (t);
       break;
@@ -1966,8 +1983,6 @@ pp_cxx_template_argument_list (cxx_pretty_printer *pp, 
tree t)
          if (TYPE_P (arg) || (TREE_CODE (arg) == TEMPLATE_DECL
                               && TYPE_P (DECL_TEMPLATE_RESULT (arg))))
            pp->type_id (arg);
-         else if (VAR_P (arg) && DECL_NTTP_OBJECT_P (arg))
-           pp->expression (DECL_INITIAL (arg));
          else
            pp->expression (arg);
        }
diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic19.C 
b/gcc/testsuite/g++.dg/concepts/diagnostic19.C
new file mode 100644
index 00000000000..20cdb63380b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic19.C
@@ -0,0 +1,20 @@
+// Verify our pretty printing of class NTTP objects.
+// PR c++/111471
+// { dg-do compile { target c++20 } }
+
+struct A { bool value; };
+
+template<A V>
+  requires (V.value) // { dg-message {'\(V\).value \[with V = A\{false\}\]'} }
+void f();
+
+template<A V> struct B { static constexpr auto value = V.value; };
+
+template<class T>
+  requires T::value // { dg-message {'T::value \[with T = B<A\{false\}>\]'} }
+void g();
+
+int main() {
+  f<A{false}>(); // { dg-error "no match" }
+  g<B<A{false}>>(); // { dg-error "no match" } 
+}
-- 
2.42.0.216.gbda494f404