c++: ICE with failed __is_constructible constraint [PR100474]

Here we're crashing when diagnosing an unsatisfied __is_constructible
constraint because diagnose_trait_expr doesn't recognize this trait
(along with a bunch of other traits).  Fix this by adding handling for
all remaining traits and removing the default case so that when adding a
new trait we'll get a warning that diagnose_trait_expr needs to handle it.

	PR c++/100474

gcc/cp/ChangeLog:

	* constraint.cc (diagnose_trait_expr): Handle all remaining
	traits appropriately.  Remove default case.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-traits3.C: New test.

1 files changed, 42 insertions, 1 deletions

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index c5a991b..94f6222 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3654,8 +3654,49 @@ diagnose_trait_expr (tree expr, tree args)
     case CPTK_IS_UNION:
       inform (loc, "  %qT is not a union", t1);
       break;
-    default:
+    case CPTK_IS_AGGREGATE:
+      inform (loc, "  %qT is not an aggregate", t1);
+      break;
+    case CPTK_IS_TRIVIALLY_COPYABLE:
+      inform (loc, "  %qT is not trivially copyable", t1);
+      break;
+    case CPTK_IS_ASSIGNABLE:
+      inform (loc, "  %qT is not assignable from %qT", t1, t2);
+      break;
+    case CPTK_IS_TRIVIALLY_ASSIGNABLE:
+      inform (loc, "  %qT is not trivially assignable from %qT", t1, t2);
+      break;
+    case CPTK_IS_NOTHROW_ASSIGNABLE:
+      inform (loc, "  %qT is not %<nothrow%> assignable from %qT", t1, t2);
+      break;
+    case CPTK_IS_CONSTRUCTIBLE:
+      if (!t2)
+	inform (loc, "  %qT is not default constructible", t1);
+      else
+	inform (loc, "  %qT is not constructible from %qE", t1, t2);
+      break;
+    case CPTK_IS_TRIVIALLY_CONSTRUCTIBLE:
+      if (!t2)
+	inform (loc, "  %qT is not trivially default constructible", t1);
+      else
+	inform (loc, "  %qT is not trivially constructible from %qE", t1, t2);
+      break;
+    case CPTK_IS_NOTHROW_CONSTRUCTIBLE:
+      if (!t2)
+	inform (loc, "  %qT is not %<nothrow%> default constructible", t1);
+      else
+	inform (loc, "  %qT is not %<nothrow%> constructible from %qE", t1, t2);
+      break;
+    case CPTK_HAS_UNIQUE_OBJ_REPRESENTATIONS:
+      inform (loc, "  %qT does not have unique object representations", t1);
+      break;
+    case CPTK_BASES:
+    case CPTK_DIRECT_BASES:
+    case CPTK_UNDERLYING_TYPE:
+      /* We shouldn't see these non-expression traits.  */
       gcc_unreachable ();
+    /* We deliberately omit the default case so that when adding a new
+       trait we'll get reminded (by way of a warning) to handle it here.  */
     }
 }