The API for adding "insert text" fix-it hints was unclear
about exactly where the text should be inserted relative
to the given insertion point.

This patch clarifies things by renaming the pertinent methods from
  richloc.add_fixit_insert
to
  richloc.add_fixit_insert_before
and adding:
  richloc.add_fixit_insert_after

The latter allows us to consolidate some failure-handling into
class rich_location, rather than having to have every such diagnostic
check for it.

The patch also adds a description of how fix-it hints work to the
comment for class rich_location within libcpp/include/line-map.h.

gcc/c-family/ChangeLog:
	* c-common.c (warn_logical_not_parentheses): Replace
	rich_location::add_fixit_insert calls with add_fixit_insert_before
	and add_fixit_insert_after, eliminating the "next_loc" calculation.

gcc/c/ChangeLog:
	* c-parser.c (c_parser_declaration_or_fndef): Update for renaming
	of add_fixit_insert to add_fixit_insert_before.

gcc/cp/ChangeLog:
	* parser.c (cp_parser_class_specifier_1): Update for renaming of
	add_fixit_insert to add_fixit_insert_before.
	(cp_parser_class_head): Likewise.

gcc/ChangeLog:
	* diagnostic-show-locus.c (selftest::test_one_liner_fixit_insert):
	Rename to...
	(selftest::test_one_liner_fixit_insert_before): ...this, and update
	for renaming of add_fixit_insert to add_fixit_insert_before.
	(selftest::test_one_liner_fixit_insert_after): New function.
	(selftest::test_one_liner_fixit_validation_adhoc_locations):
	Update for renaming of add_fixit_insert to
	add_fixit_insert_before.
	(selftest::test_one_liner_many_fixits): Likewise.
	(selftest::test_diagnostic_show_locus_one_liner): Update for
	renaming, call new test function.
	(selftest::test_diagnostic_show_locus_fixit_lines): Update for
	renaming of add_fixit_insert to add_fixit_insert_before.
	(selftest::test_fixit_consolidation): Likewise.
	* diagnostic.c (selftest::test_print_parseable_fixits_insert):
	Likewise.
	* edit-context.c (selftest::test_applying_fixits_insert): Rename
	to...
	(selftest::test_applying_fixits_insert_before): ...this.
	(selftest::test_applying_fixits_insert): Update for renaming of
	add_fixit_insert to add_fixit_insert_before.
	(selftest::test_applying_fixits_insert_after): New function.
	(selftest::test_applying_fixits_insert_after_at_line_end): New
	function.
	(selftest::test_applying_fixits_insert_after_failure): New
	function.
	(selftest::test_applying_fixits_multiple): Update for renaming of
	add_fixit_insert to add_fixit_insert_before.
	(selftest::change_line): Likewise.
	(selftest::test_applying_fixits_unreadable_file): Likewise.
	(selftest::test_applying_fixits_line_out_of_range): Likewise.
	(selftest::test_applying_fixits_column_validation): Likewise.
	(selftest::test_applying_fixits_column_validation): Likewise.
	(selftest::edit_context_c_tests): Update for renamed test
	function; call new test functions.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/diagnostic_plugin_test_show_locus.c
	(test_show_locus): Replace rich_location::add_fixit_insert calls
	with add_fixit_insert_before and add_fixit_insert_after.

libcpp/ChangeLog:
	* include/line-map.h (class rich_location): Add description of
	fix-it hints to leading comment.
	(rich_location::add_fixit_insert): Rename both overloaded methods
	to..
	(rich_location::add_fixit_insert_before): ...this, updating their
	comments.
	(rich_location::add_fixit_insert_after): Two new overloaded
	methods.
	(rich_location::stop_supporting_fixits): New method.
	* line-map.c (rich_location::add_fixit_insert): Rename both
	overloaded methods to..
	(rich_location::add_fixit_insert_before): ...this, updating their
	comments.
	(rich_location::add_fixit_insert_after): Two new methods.
	(rich_location::reject_impossible_fixit): Split out
	failure-handling into...
	(rich_location::stop_supporting_fixits): New method.

From-SVN: r240115