Eliminate fixit_hint class hierarchy

Eliminate fixit_hint class hierarchy

The original implementation of fix-it hints (r230674) had an abstract
base class "fixit_hint" and three subclasses, representing
each of insertions, replacements, and deletions.

Having multiple classes for fix-it hints was a nuisance, as it required
per-class logic everywhere that the hints were handled.

In r239632 I eliminated the deletion subclass in favor of replacement
with the empty string (two subclasses are easier than three).

This patch eliminates the class hierarchy altogether by implementing
insertion in terms of replacement, by representing replacements via
a half-open interval (so that for an insertion, start == next location,
and we're effectively replacing an empty range at the insertion point
with the new string).

This greatly simplifies the code for handling fix-it hints; for example
it allows removal of a parallel class hierarchy of line_event within
edit-context.c.

It also improves consolidation of hints: we can now consolidate
insertions at the same location, affecting a couple of tests
(selftest::test_one_liner_many_fixits and
gcc.dg/Wmissing-braces-fixits.c).

gcc/ChangeLog:
	* diagnostic-show-locus.c (layout::get_expanded_location): Rewrite
	to use new fixit_hint representation, using the "replace" logic.
	(get_line_span_for_fixit_hint): Likewise.
	(layout::print_any_fixits): Likewise.
	(selftest::test_one_liner_many_fixits): Rename to...
	(selftest::test_one_liner_many_fixits_1): ...this, and update
	comment and expected output to reflect that the multiple fix-it
	hints are now consolidated into one insertion.
	(selftest::test_one_liner_many_fixits_2): New test.
	(selftest::test_diagnostic_show_locus_one_liner): Update for
	above.
	(selftest::test_fixit_consolidation): Update for fix-it API
	change.
	* diagnostic.c (print_parseable_fixits): Likewise.
	* edit-context.c (edited_line::m_line_events): Convert from
	auto_vec <line_event *> to auto_vec <line_event>.
	(class line_event): Convert from abstract base class to a concrete
	class, taking over the role of replace_event.
	(class insert_event): Delete.
	(class replace_event): Rename to class line_event.  Convert to
	half-open range.
	(edit_context::add_fixits): Reimplement.
	(edit_context::apply_insert): Delete.
	(edit_context::apply_replace): Rename to...
	(edit_context::apply_fixit): ...this.  Convert to half-open range.
	(edited_file::apply_insert): Delete.
	(edited_file::apply_replace): Rename to...
	(edited_file::apply_fixit): ...this.
	(edited_line::~edited_line): Drop deletion of events.
	(edited_line::apply_insert): Delete.
	(edited_line::apply_replace): Rename to...
	(edited_line::apply_fixit): ...this.  Convert to half-open range.
	Update for change to type of m_line_events.
	* edit-context.h (edit_context::apply_insert): Delete.
	(edit_context::apply_replace): Rename to...
	(edit_context::apply_fixit): ...this.

gcc/testsuite/ChangeLog:
	* gcc.dg/Wmissing-braces-fixits.c: Update expected output to
	reflect insertion fix-it hints at the same location now being
	consolidated.

libcpp/ChangeLog:
	* include/line-map.h (source_range::intersects_line_p): Delete.
	(rich_location::add_fixit): Delete.
	(rich_location::maybe_add_fixit): New method.
	(class fixit_hint): Reimplement in terms of...
	(class fixit_replace): ...this.
	(class fixit_insert): Delete.
	* line-map.c (linemap_position_for_loc_and_offset): Drop overzealous
	linemap_assert_fails.
	(source_range::intersects_line_p): Rename to...
	(fixit_hint::affects_line_p): New function.
	(rich_location::add_fixit_insert_before): Reimplement in terms of
	maybe_add_fixit, moving validation there.
	(rich_location::add_fixit_insert_after): Likewise.
	(column_before_p): Delete.
	(rich_location::add_fixit_replace): Reimplement in terms of
	maybe_add_fixit, moving validation there.  Convert closed input range
	to half-open range.
	(rich_location::add_fixit): Delete.
	(rich_location::maybe_add_fixit): New function.
	(fixit_insert::fixit_insert): Delete.
	(fixit_insert::~fixit_insert): Delete.
	(fixit_insert::affects_line_p): Delete.
	(fixit_insert::maybe_append_replace): Delete.
	(fixit_replace::fixit_replace): Rename to...
	(fixit_hint::fixit_hint): ...this, rewriting as necessary.
	(fixit_replace::~fixit_replace): Delete.
	(fixit_replace::affects_line_p): Delete.
	(fixit_replace::maybe_append_replace): Rename to...
	(fixit_hint::maybe_append): ...this, rewriting as necessary.

From-SVN: r247445