Adding a fix-it hint currently involves changing e.g.:

  error_at (token->location,
            "unknown type name %qE; did you mean %qs?",
            token->value, hint);
to:

  gcc_rich_location richloc (token->location);
  richloc.add_fixit_replace (hint);
  error_at_rich_loc (&richloc,
                     "unknown type name %qE; did you mean %qs?",
                     token->value, hint);

to make the change from taking a location_t to a rich_location *.

This patch renames the "*_at_rich_loc" diagnostic entrypoints to use
the same function names for rich_location * as for location_t,
via overloading, to simplify the above change to just changing from:

  error_at (token->location,
            "unknown type name %qE; did you mean %qs?",
            token->value, hint);
to:

  gcc_rich_location richloc (token->location);
  richloc.add_fixit_replace (hint);
  error_at (&richloc,
            "unknown type name %qE; did you mean %qs?",
            token->value, hint);

thus saving space (and typing) and usually avoiding the need to reindent
the "error_at" invocation.

With this change, 0 is no longer acceptable as a location_t to these
entrypoints, as e.g.:

../../src/gcc/auto-profile.c:855:37: error: call of overloaded
'inform(int, const char [18])' is ambiguous
       inform (0, "Not expected TAG.");
                                     ^
In file included from ../../src/gcc/auto-profile.c:35:0:
../../src/gcc/diagnostic-core.h:88:13: note: candidate:
'void inform(location_t, const char*, ...)'
 extern void inform (location_t, const char *, ...) ATTRIBUTE_GCC_DIAG(2,3);
             ^~~~~~
../../src/gcc/diagnostic-core.h:89:13: note: candidate:
'void inform(rich_location*, const char*, ...)'
 extern void inform (rich_location *, const char *, ...) ATTRIBUTE_GCC_DIAG(2,3);
             ^~~~~~

Such locations now need to be spelled out as UNKNOWN_LOCATION,
rather than 0.

I considered making the API take a rich_location & rather than a
rich_location *, but doing so would mean replacing
  diagnostic_set_info
and
  diagnostic_set_info_translated
with a constructor for diagnostic_info, which was a more invasive
change.  Maybe in the future.

gcc/ChangeLog:
	* auto-profile.c (autofdo_source_profile::read): Use
	UNKNOWN_LOCATION rather than 0.
	* diagnostic-core.h (warning_at_rich_loc): Rename to...
	(warning_at): ...this overload.
	(warning_at_rich_loc_n): Rename to...
	(warning_n): ...this overload.
	(error_at_rich_loc): Rename to...
	(error_at): ...this overload.
	(pedwarn_at_rich_loc): Rename to...
	(pedwarn): ...this overload.
	(permerror_at_rich_loc): Rename to...
	(permerror): ...this overload.
	(inform_at_rich_loc): Rename to...
	(inform): ...this overload.
	* diagnostic.c: (diagnostic_n_impl): Delete location_t-based decl.
	(diagnostic_n_impl_richloc): Rename to...
	(diagnostic_n_impl): ...this rich_location *-based decl.
	(inform_at_rich_loc): Rename to...
	(inform): ...this, and add an assertion.
	(inform_n): Update for removal of location_t-based diagnostic_n_impl.
	(warning_at_rich_loc): Rename to...
	(warning_at): ...this, and add an assertion.
	(warning_at_rich_loc_n): Rename to...
	(warning_n): ...this, and add an assertion.
	(warning_n): Update location_t-based implementation for removal of
	location_t-based diagnostic_n_impl.
	(pedwarn_at_rich_loc): Rename to...
	(pedwarn): ...this, and add an assertion.
	(permerror_at_rich_loc): Rename to...
	(permerror): ...this, and add an assertion.
	(error_n): Update for removal of location_t-based diagnostic_n_impl.
	(error_at_rich_loc): Rename to...
	(error_at): ...this, and add an assertion.
	* gcc.c (do_spec_1): Use UNKNOWN_LOCATION rather than 0.
	(driver::do_spec_on_infiles): Likewise.
	* substring-locations.c (format_warning_va): Update for renaming
	of inform_at_rich_loc.

gcc/c-family/ChangeLog:
	* c-common.c (binary_op_error): Update for renaming of
	error_at_rich_loc.
	(c_parse_error): Likewise.
	* c-warn.c (warn_logical_not_parentheses): Likewise for
	renaming of inform_at_rich_loc.
	(warn_for_restrict): Likewise for renaming of
	warning_at_rich_loc_n.

gcc/c/ChangeLog:
	* c-decl.c (implicit_decl_warning): Update for renaming of
	pedwarn_at_rich_loc and warning_at_rich_loc.
	(implicitly_declare): Likewise for renaming of inform_at_rich_loc.
	(undeclared_variable): Likewise for renaming of error_at_rich_loc.
	* c-parser.c (c_parser_declaration_or_fndef): Likewise.
	(c_parser_struct_or_union_specifier): Likewise for renaming of
	pedwarn_at_rich_loc.
	(c_parser_parameter_declaration): Likewise for renaming of
	error_at_rich_loc.
	* c-typeck.c (build_component_ref): Likewise.
	(build_unary_op): Likewise for renaming of inform_at_rich_loc.
	(pop_init_level): Likewise for renaming of warning_at_rich_loc.
	(set_init_label): Likewise for renaming of error_at_rich_loc.

gcc/cp/ChangeLog:
	* class.c (explain_non_literal_class): Use UNKNOWN_LOCATION rather
	than 0.
	* name-lookup.c (suggest_alternatives_for): Update for renaming of
	inform_at_rich_loc.
	(maybe_suggest_missing_header): Likewise.
	(suggest_alternative_in_explicit_scope): Likewise.
	* parser.c (cp_parser_diagnose_invalid_type_name): Likewise for
	renaming of error_at_rich_loc.
	(cp_parser_string_literal): Likewise.
	(cp_parser_nested_name_specifier_opt): Likewise.
	(cp_parser_cast_expression): Likewise for renaming of
	warning_at_rich_loc.
	(cp_parser_decl_specifier_seq): Likewise for renaming of
	error_at_rich_loc and warning_at_rich_loc.
	(cp_parser_elaborated_type_specifier): Likewise for renaming of
	pedwarn_at_rich_loc.
	(cp_parser_cv_qualifier_seq_opt): Likewise for renaming of
	error_at_rich_loc.
	(cp_parser_virt_specifier_seq_opt): Likewise.
	(cp_parser_class_specifier_1): Likewise.
	(cp_parser_class_head): Likewise.
	(cp_parser_member_declaration): Likewise for renaming of
	pedwarn_at_rich_loc, warning_at_rich_loc, and error_at_rich_loc.
	(cp_parser_enclosed_template_argument_list): Likewise for renaming
	of error_at_rich_loc.
	(set_and_check_decl_spec_loc): Likewise.
	* pt.c (listify): Likewise.
	* rtti.c (typeid_ok_p): Likewise.
	* semantics.c (process_outer_var_ref): Use UNKNOWN_LOCATION rather
	than 0.
	* typeck.c (access_failure_info::maybe_suggest_accessor): Update
	for renaming of inform_at_rich_loc.
	(finish_class_member_access_expr): Likewise for renaming of
	error_at_rich_loc.

gcc/objc/ChangeLog:
	* objc-gnu-runtime-abi-01.c (objc_gnu_runtime_abi_01_init): Use
	UNKNOWN_LOCATION rather than 0.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/diagnostic_plugin_show_trees.c (show_tree): Update
	for renaming of error_at_rich_loc and inform_at_rich_loc.
	* gcc.dg/plugin/diagnostic_plugin_test_show_locus.c
	(test_show_locus): Likewise for renaming of warning_at_rich_loc.

libcpp/ChangeLog:
	* directives.c (_cpp_handle_directive): Update for renaming of
	cpp_error_at_richloc to cpp_error_at.
	* errors.c (cpp_diagnostic_at_richloc): Rename to...
	(cpp_diagnostic_at): ...this, dropping the location_t-based
	implementation.
	(cpp_diagnostic): Update for removal of location_t-based
	cpp_diagnostic_at.
	(cpp_error_at): Likewise.
	(cpp_error_at_richloc): Rename to...
	(cpp_error_at): ...this, and update for renaming of
	cpp_diagnostic_at_richloc.
	* include/cpplib.h (cpp_error_at_richloc): Rename to...
	(cpp_error_at): ...this.

From-SVN: r254280