c++: Some improvements to concept diagnostics

This patch improves our concept diagnostics in two ways.  First, it sets a more
precise location for the constraint expressions built in
finish_constraint_binary_op.  As a result, when a disjunction is unsatisfied we
now print e.g.

.../include/bits/range_access.h:467:2: note: neither operand of the disjunction is satisfied
  466 |  requires is_bounded_array_v<remove_reference_t<_Tp>> || __member_end<_Tp>
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  467 |  || __adl_end<_Tp>
      |  ^~~~~~~~~~~~~~~~~

instead of

.../include/bits/range_access.h:467:2: note: neither operand of the disjunction is satisfied
  467 |  || __adl_end<_Tp>
      |  ^~

Second, this patch changes diagnose_atomic_constraint to print unsatisfied
atomic constraint expressions with their template arguments.  So e.g. we now
print

cpp2a/concepts-pr67719.C:9:8: note: the expression ‘(... &&(C<Tx>)()) [with Tx = {int, long int, void}]’ evaluated to ‘false’

instead of

cpp2a/concepts-pr67719.C:9:8: note: the expression ‘(... &&(C<Tx>)())’ evaluated to ‘false’

Tested on x86_64-pc-linux-gnu, and verified that all the diagnostics emitted in
our concept tests are no worse with this patch.

gcc/cp/ChangeLog:

	* constraint.cc (finish_constraint_binary_op): Set expr's location range
	to the range of its operands.
	(satisfy_atom): Pass MAP instead of ARGS to diagnose_atomic_constraint.
	(diagnose_trait_expr): Take the instantiated parameter mapping MAP
	instead of the corresponding template arguments ARGS and adjust body
	accordingly.
	(diagnose_requires_expr): Likewise.
	(diagnose_atomic_constraint): Likewise.  When printing an atomic
	constraint expression, print the instantiated parameter mapping
	alongside it.
	* cxx-pretty-print.cc (cxx_pretty_printer::expression)
	[NONTYPE_ARGUMENT_PACK]: Print braces around a NONTYPE_ARGUMENT_PACK.
	(cxx_pretty_printer::type_id): Handle TYPE_ARGUMENT_PACK.

gcc/testsuite/ChangeLog:

	* g++.dg/concepts/diagnostic2.C: New test.
	* g++.dg/concepts/diagnostic3.C: New test.

2 files changed, 59 insertions, 0 deletions

diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic2.C b/gcc/testsuite/g++.dg/concepts/diagnostic2.C
new file mode 100644
index 0000000..ce51b71
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic2.C
@@ -0,0 +1,30 @@
+// { dg-do compile { target c++2a } }
+// { dg-options "-fdiagnostics-show-caret" }
+
+template<typename T>
+  inline constexpr bool foo_v = false;
+
+template<typename T>
+  concept foo = foo_v<T> || foo_v<T&>; // { dg-message "neither operand" }
+/* { dg-begin-multiline-output "" }
+   concept foo = foo_v<T> || foo_v<T&>;
+                 ~~~~~~~~~^~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+
+template<typename T>
+  requires foo<T>
+  void bar();
+/* { dg-begin-multiline-output "" }
+   void bar();
+   { dg-end-multiline-output "" } */
+/* { dg-prune-output "~" } */
+
+void
+baz()
+{
+  bar<int>(); // { dg-error "unsatisfied constraints" }
+/* { dg-begin-multiline-output "" }
+   bar<int>();
+            ^
+   { dg-end-multiline-output "" } */
+}
diff --git a/gcc/testsuite/g++.dg/concepts/diagnostic3.C b/gcc/testsuite/g++.dg/concepts/diagnostic3.C
new file mode 100644
index 0000000..b4c7540
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic3.C
@@ -0,0 +1,29 @@
+// { dg-do compile { target c++2a } }
+
+template<typename T>
+  inline constexpr bool foo_v = false;
+
+template<typename T>
+  concept foo = (bool)(foo_v<T> | foo_v<T&>);
+
+template<typename... Ts>
+requires (foo<Ts> && ...)
+void
+bar() // { dg-message "with Ts = .int, char... evaluated to .false." }
+{ }
+
+template<int>
+struct S { };
+
+template<int... Is>
+requires (foo<S<Is>> && ...)
+void
+baz() // { dg-message "with Is = .2, 3, 4... evaluated to .false." }
+{ }
+
+void
+baz()
+{
+  bar<int, char>(); // { dg-error "unsatisfied constraints" }
+  baz<2,3,4>(); // { dg-error "unsatisfied constraints" }
+}