[gcc r13-7830] c++: improve class NTTP object pretty printing [PR111471]

[Patrick Palka]

https://gcc.gnu.org/g:b7d2bb488efbdeab42cf047d92cf0f9acdc1c5ec

commit r13-7830-gb7d2bb488efbdeab42cf047d92cf0f9acdc1c5ec
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Sep 20 12:09:36 2023 -0400

    c++: improve class NTTP object pretty printing [PR111471]
    
    1. Move class NTTP object pretty printing to a more general spot in
       the pretty printer, so that we always print its value instead of
       its (mangled) name even when it appears outside of a template
       argument list.
    2. Print the type of an class NTTP object alongside its CONSTRUCTOR
       value, like dump_expr would have done.
    3. Don't print const VIEW_CONVERT_EXPR wrappers for class NTTPs.
    
            PR c++/111471
    
    gcc/cp/ChangeLog:
    
            * cxx-pretty-print.cc (cxx_pretty_printer::expression)
            <case VAR_DECL>: Handle class NTTP objects by printing
            their type and value.
            <case VIEW_CONVERT_EXPR>: Strip const VIEW_CONVERT_EXPR
            wrappers for class NTTPs.
            (pp_cxx_template_argument_list): Don't handle class NTTP
            objects here.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/concepts/diagnostic19.C: New test.
    
    (cherry picked from commit 75c4b0cde4835b45350da0a5cd82f1d1a0a7a2f1)

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

diff --git a/gcc/cp/cxx-pretty-print.cc b/gcc/cp/cxx-pretty-print.cc
index 7f4556d0da2..33820aa96b2 100644
--- a/gcc/cp/cxx-pretty-print.cc
+++ b/gcc/cp/cxx-pretty-print.cc
@@ -1116,6 +1116,15 @@ 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 the
+	     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:
@@ -1256,6 +1265,14 @@ 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;
@@ -1960,8 +1977,6 @@ 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 (TREE_CODE (arg) == VAR_DECL && 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..70af30b8d4f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic19.C
@@ -0,0 +1,20 @@
+// Verify 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" } 
+}