[gcc(refs/users/marxin/heads/marxin-gcc-benchmark-branch)] c++: Include the constraint parameter mapping in diagnostic constraint contexts

[gcc(refs/users/marxin/heads/marxin-gcc-benchmark-branch)] c++: Include the constraint parameter mapping in diagnostic constraint contexts

[Martin Liska]

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https://gcc.gnu.org/g:828878c35c8585978e3ac22deddbf10f33c0a576

commit 828878c35c8585978e3ac22deddbf10f33c0a576
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Mar 18 13:57:24 2020 -0400

    c++: Include the constraint parameter mapping in diagnostic constraint contexts
    
    When diagnosing a constraint error, we currently try to print the constraint
    inside a diagnostic constraint context with its template arguments substituted
    in.  If substitution fails, then we instead just print the dependent form, as in
    the test case below:
    
      .../diagnostic6.C:14:15: error: static assertion failed
         14 | static_assert(E<int>); // { dg-error "static assertion failed|not a class" }
            |               ^~~~~~
      .../diagnostic6.C:14:15: note: constraints not satisfied
      .../diagnostic6.C:4:11:   required for the satisfaction of ‘C<T>’
      .../diagnostic6.C:8:11:   required for the satisfaction of ‘D<typename T::type>’
      .../diagnostic6.C:14:15: error: ‘int’ is not a class, struct, or union type
    
    But printing just the dependent form sometimes makes it difficult to understand
    the underlying failure.  In the above example, for instance, there's no
    indication of how the template argument 'int' relates to either of the 'T's.
    
    This patch improves the situation by changing these diagnostics to always print
    the dependent form of the constraint, and alongside it the (preferably
    substituted) constraint parameter mapping.  So with the same test case below we
    now get:
    
      .../diagnostic6.C:14:15: error: static assertion failed
         14 | static_assert(E<int>); // { dg-error "static assertion failed|not a class" }
            |               ^~~~~~
      .../diagnostic6.C:14:15: note: constraints not satisfied
      .../diagnostic6.C:4:11:   required for the satisfaction of ‘C<T>’ [with T = typename T::type]
      .../diagnostic6.C:8:11:   required for the satisfaction of ‘D<typename T::type>’ [with T = int]
      .../diagnostic6.C:14:15: error: ‘int’ is not a class, struct, or union type
    
    This change arguably makes it easier to figure out what's going on whenever a
    constraint fails due to substitution creating an invalid type rather than
    failing due to the constraint evaluating to false.
    
    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.

Diff:
---
 gcc/cp/ChangeLog                            | 10 +++++++++
 gcc/cp/cxx-pretty-print.c                   | 18 +++++++--------
 gcc/cp/cxx-pretty-print.h                   |  1 +
 gcc/cp/error.c                              | 35 +++++++++--------------------
 gcc/testsuite/ChangeLog                     |  4 ++++
 gcc/testsuite/g++.dg/concepts/diagnostic6.C | 14 ++++++++++++
 6 files changed, 48 insertions(+), 34 deletions(-)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 929e709fadf..0e01056aaee 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,13 @@
+2020-03-20  Patrick Palka  <ppalka@redhat.com>
+
+	* 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.
+
 2020-03-19  Jason Merrill  <jason@redhat.com>
 
 	PR c++/94175
diff --git a/gcc/cp/cxx-pretty-print.c b/gcc/cp/cxx-pretty-print.c
index 100154e400f..840b5a8db8b 100644
--- a/gcc/cp/cxx-pretty-print.c
+++ b/gcc/cp/cxx-pretty-print.c
@@ -2878,9 +2878,14 @@ 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_whitespace (pp);
+  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 +2908,8 @@ 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
@@ -2914,14 +2921,7 @@ pp_cxx_atomic_constraint (cxx_pretty_printer *pp, tree t)
   /* Emit the parameter mapping.  */
   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);
-      pp_cxx_parameter_mapping (pp, map);
-      pp_cxx_right_bracket (pp);
-   }
+    pp_cxx_parameter_mapping (pp, map);
 }
 
 void
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..61d1218dc90 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 +3696,18 @@ 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 && map != error_mark_node)
+    {
+      tree subst_map = tsubst_parameter_mapping (map, args, tf_none, NULL_TREE);
+      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/ChangeLog b/gcc/testsuite/ChangeLog
index adf53b3e245..12076d56e14 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2020-03-20  Patrick Palka  <ppalka@redhat.com>
+
+	* g++.dg/concepts/diagnostic6.C: New test.
+
 2020-03-20  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>
 
 	* gcc.target/arm/mve/intrinsics/vabdq_x_f16.c: New test.
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" }