c++: use diagnostic nesting [PR116253]

c++: use diagnostic nesting [PR116253]

This patch uses the nested diagnostics capabilities added in the earlier
patch in the C++ frontend.

With this, and enabling the non-standard text formatting via:
  -fdiagnostics-set-output=text:experimental-nesting=yes
and using:
  -std=c++20 -fconcepts-diagnostics-depth=2
then the output for the example in SG15's P3358R0 ("SARIF for Structured
Diagnostics") is:

P3358R0.C: In function ‘int main()’:
P3358R0.C:26:6: error: no matching function for call to ‘pet(lizard)’
   26 |   pet(lizard{});
      |   ~~~^~~~~~~~~~
  • note: candidate: ‘template<class auto:1>  requires  pettable<auto:1> void pet(auto:1)’
    P3358R0.C:21:6:
       21 | void pet(pettable auto t);
          |      ^~~
    • note: template argument deduction/substitution failed:
      • note: constraints not satisfied
        • P3358R0.C: In substitution of ‘template<class auto:1>  requires  pettable<auto:1> void pet(auto:1) [with auto:1 = lizard]’:
        • required from here
          P3358R0.C:26:6:
             26 |   pet(lizard{});
                |   ~~~^~~~~~~~~~
        • required for the satisfaction of ‘pettable<auto:1>’ [with auto:1 = lizard]
          P3358R0.C:19:9:
             19 | concept pettable = has_member_pet<T> or has_default_pet<T>;
                |         ^~~~~~~~
        • note: no operand of the disjunction is satisfied
          P3358R0.C:19:38:
             19 | concept pettable = has_member_pet<T> or has_default_pet<T>;
                |                    ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
          • note: the operand ‘has_member_pet<T>’ is unsatisfied because
            P3358R0.C:19:20:
               19 | concept pettable = has_member_pet<T> or has_default_pet<T>;
                  |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            • required for the satisfaction of ‘has_member_pet<T>’ [with T = lizard]
              P3358R0.C:13:9:
                 13 | concept has_member_pet = requires(T t) { t.pet(); };
                    |         ^~~~~~~~~~~~~~
            • required for the satisfaction of ‘pettable<auto:1>’ [with auto:1 = lizard]
              P3358R0.C:19:9:
                 19 | concept pettable = has_member_pet<T> or has_default_pet<T>;
                    |         ^~~~~~~~
            • in requirements with ‘T t’ [with T = lizard]
              P3358R0.C:13:26:
                 13 | concept has_member_pet = requires(T t) { t.pet(); };
                    |                          ^~~~~~~~~~~~~~~~~~~~~~~~~~
            • note: the required expression ‘t.pet()’ is invalid, because
              P3358R0.C:13:47:
                 13 | concept has_member_pet = requires(T t) { t.pet(); };
                    |                                          ~~~~~^~
              • error: ‘struct lizard’ has no member named ‘pet’
                P3358R0.C:13:44:
                   13 | concept has_member_pet = requires(T t) { t.pet(); };
                      |                                          ~~^~~
          • note: the operand ‘has_default_pet<T>’ is unsatisfied because
            P3358R0.C:19:41:
               19 | concept pettable = has_member_pet<T> or has_default_pet<T>;
                  |                    ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
            • required for the satisfaction of ‘has_default_pet<T>’ [with T = lizard]
              P3358R0.C:16:9:
                 16 | concept has_default_pet = T::is_pettable;
                    |         ^~~~~~~~~~~~~~~
            • required for the satisfaction of ‘pettable<auto:1>’ [with auto:1 = lizard]
              P3358R0.C:19:9:
                 19 | concept pettable = has_member_pet<T> or has_default_pet<T>;
                    |         ^~~~~~~~
            • error: ‘is_pettable’ is not a member of ‘lizard’
              P3358R0.C:16:30:
                 16 | concept has_default_pet = T::is_pettable;
                    |                              ^~~~~~~~~~~
  • note: candidate: ‘void pet(dog)’
    P3358R0.C:9:6:
        9 | void pet(dog);
          |      ^~~
    • note: no known conversion for argument 1 from ‘lizard’ to ‘dog’
      P3358R0.C:9:10:
          9 | void pet(dog);
            |          ^~~
  • note: candidate: ‘void pet(cat)’
    P3358R0.C:10:6:
       10 | void pet(cat);
          |      ^~~
    • note: no known conversion for argument 1 from ‘lizard’ to ‘cat’
      P3358R0.C:10:10:
         10 | void pet(cat);
            |          ^~~

showing the hierarchical structure of the messages; ideally there
would be a UI here allowing the user to expand/collapse the messages
to drill out into the detail they are interested in.

The structure is also captured in SARIF output (via the "nestingLevel"
property).

gcc/cp/ChangeLog:
	PR other/116253
	* call.cc (print_conversion_rejection): Remove leading space from
	diagnostic messages.
	(print_conversion_rejection): Likewise.
	(print_arity_information): Likewise.
	(print_z_candidate): Likewise.  Add auto_diagnostic_nesting_level
	before calls to fn_type_unification and diagnose_constraints.
	(print_z_candidates): Add auto_diagnostic_nesting_level before
	looping over candidates.
	(conversion_null_warnings): Remove leading space from
	diagnostic messages.
	(maybe_inform_about_fndecl_for_bogus_argument_init): Likewise.
	* constraint.cc (tsubst_valid_expression_requirement): Add
	auto_diagnostic_nesting_level when showing why the expression is
	invalid.
	(satisfy_disjunction): Likewise when showing operans, and again
	when replaying each branch of the disjunction.
	(diagnose_constraints): Likewise when replaying satisfaction.
	* error.cc (cp_diagnostic_text_starter): Set prefix.
	(print_instantiation_full_context): Only show the file
	if we're not showing nesting or the user has opted in to
	showing location information in nested diagnostics.
	(class auto_context_line): New.
	(print_instantiation_partial_context_line): Replace calls to
	print_location and to diagnostic_show_locus with an
	auto_context_line.
	(print_instantiation_partial_context): Replace calls to
	print_location with an auto_context_line.
	(maybe_print_constexpr_context): Likewise.
	(print_constrained_decl_info): Likewise.
	(print_concept_check_info): Likewise.
	(print_constraint_context_head): Likewise.
	(print_requires_expression_info): Likewise.

gcc/testsuite/ChangeLog:
	PR other/116253
	* g++.dg/concepts/nested-diagnostics-1-truncated.C: New test.
	* g++.dg/concepts/nested-diagnostics-1.C: New test.
	* g++.dg/concepts/nested-diagnostics-2.C: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>