diagnostics, analyzer: add CFG edge visualization to path-printing

This patch adds some ability for links between labelled ranges when
quoting the user's source code, and uses this to add links between
events when printing diagnostic_paths, chopping them up further into
event ranges that can be printed together.
It adds links to the various "from..." - "...to" events in the
analyzer.

For example, previously we emitted this for
c-c++-common/analyzer/infinite-loop-linked-list.c's
while_loop_missing_next':

infinite-loop-linked-list.c:30:10: warning: infinite loop [CWE-835] [-Wanalyzer-infinite-loop]
   30 |   while (n)
      |          ^
  'while_loop_missing_next': events 1-5
   30 |   while (n)
      |          ^
      |          |
      |          (1) infinite loop here
      |          (2) when 'n' is non-NULL: always following 'true' branch...
      |          (5) ...to here
   31 |     {
   32 |       sum += n->val;
      |       ~~~~~~~~~~~~~
      |           |   |
      |           |   (3) ...to here
      |           (4) looping back...

whereas with the patch we now emit:

infinite-loop-linked-list.c:30:10: warning: infinite loop [CWE-835] [-Wanalyzer-infinite-loop]
   30 |   while (n)
      |          ^
  'while_loop_missing_next': events 1-3
   30 |   while (n)
      |          ^
      |          |
      |          (1) infinite loop here
      |          (2) when 'n' is non-NULL: always following 'true' branch... ->-+
      |                                                                         |
      |                                                                         |
      |+------------------------------------------------------------------------+
   31 ||    {
   32 ||      sum += n->val;
      ||             ~~~~~~
      ||              |
      |+------------->(3) ...to here
  'while_loop_missing_next': event 4
   32 |       sum += n->val;
      |       ~~~~^~~~~~~~~
      |           |
      |           (4) looping back... ->-+
      |                                  |
  'while_loop_missing_next': event 5
      |                                  |
      |+---------------------------------+
   30 ||  while (n)
      ||         ^
      ||         |
      |+-------->(5) ...to here

which I believe is easier to understand.

The patch also implements the use of unicode characters and colorization
for the lines (not shown in the above example).

There is a new option -fno-diagnostics-show-event-links for getting
back the old behavior (added to -fdiagnostics-plain-output).

gcc/analyzer/ChangeLog:
	* checker-event.h (checker_event::connect_to_next_event_p):
	Implement new diagnostic_event::connect_to_next_event_p vfunc.
	(start_cfg_edge_event::connect_to_next_event_p): Likewise.
	(start_consolidated_cfg_edges_event::connect_to_next_event_p):
	Likewise.
	* infinite-loop.cc (class looping_back_event): New subclass.
	(infinite_loop_diagnostic::add_final_event): Use it.

gcc/ChangeLog:
	* common.opt (fdiagnostics-show-event-links): New option.
	* diagnostic-label-effects.h: New file.
	* diagnostic-path.h (diagnostic_event::connect_to_next_event_p):
	New pure virtual function.
	(simple_diagnostic_event::connect_to_next_event_p): Implement it.
	(simple_diagnostic_event::connect_to_next_event): New.
	(simple_diagnostic_event::m_connected_to_next_event): New field.
	(simple_diagnostic_path::connect_to_next_event): New decl.
	* diagnostic-show-locus.cc: Include "text-art/theme.h" and
	"diagnostic-label-effects.h".
	(colorizer::set_cfg_edge): New.
	(layout::m_fallback_theme): New field.
	(layout::m_theme): New field.
	(layout::m_effect_info): New field.
	(layout::m_link_lhs_state): New enum and field.
	(layout::m_link_rhs_column): New field.
	(layout_range::has_in_edge): New.
	(layout_range::has_out_edge): New.
	(layout::layout): Add "effect_info" optional param.  Initialize
	m_theme, m_link_lhs_state, and m_link_rhs_column.
	(layout::maybe_add_location_range): Remove stray "FIXME" from
	leading comment.
	(layout::print_source_line): Replace space after margin with a
	call to print_leftmost_column.
	(layout::print_leftmost_column): New.
	(layout::start_annotation_line): Make non-const.  Gain
	responsibility for printing the leftmost column after the margin.
	(layout::print_annotation_line): Drop pp_space, as this is now
	added by start_annotation_line.
	(line_label::line_label): Add "has_in_edge" and "has_out_edge"
	params and initialize...
	(line_label::m_has_in_edge): New field.
	(line_label::m_has_out_edge): New field.
	(layout::print_any_labels): Pass edge information to line_label
	ctor.  Keep track of in-edges and out-edges, adding visualizations
	of these links between labels.
	(layout::print_leading_fixits):  Drop pp_character, as this is now
	added by start_annotation_line.
	(layout::print_trailing_fixits): Fix off-by-one errors in column
	calculation.
	(layout::move_to_column): Add comment about debugging.
	(layout::show_ruler): Make non-const.  Drop pp_space calls, as
	this is now added by start_annotation_line.
	(layout::print_line): Call print_any_right_to_left_edge_lines.
	(layout::print_any_right_to_left_edge_lines): New.
	(layout::update_any_effects): New.
	(gcc_rich_location::add_location_if_nearby): Initialize
	loc_range.m_label.
	(diagnostic_context::maybe_show_locus): Add "effects" param and
	pass it to diagnostic_context::show_locus.
	(diagnostic_context::show_locus): Add "effects" param, passing it
	to layout's ctor.  Call update_any_effects on the layout after
	printing the lines.
	(selftest::test_layout_x_offset_display_utf8): Update expected
	result for eliminated trailing newline.
	(selftest::test_layout_x_offset_display_utf8): Likewise.
	(selftest::test_layout_x_offset_display_tab): Likewise.
	* diagnostic.cc (diagnostic_context::initialize): Initialize
	m_source_printing.show_event_links_p.
	(simple_diagnostic_path::connect_to_next_event): New.
	(simple_diagnostic_event::simple_diagnostic_event): Initialize
	m_connected_to_next_event.
	* diagnostic.h (class diagnostic_source_effect_info): New forward
	decl.
	(diagnostic_source_printing_options::show_event_links_p): New
	field.
	(diagnostic_context::maybe_show_locus): Add optional "effect_info"
	param.
	(diagnostic_context::show_locus): Add "effect_info" param.
	(diagnostic_show_locus): Add optional "effect_info" param.
	* doc/invoke.texi: Add -fno-diagnostics-show-event-links.
	* lto-wrapper.cc (merge_and_complain): Add
	OPT_fdiagnostics_show_event_links to switch.
	(append_compiler_options): Likewise.
	(append_diag_options): Likewise.
	* opts-common.cc (decode_cmdline_options_to_array): Add
	"-fno-diagnostics-show-event-links" to -fdiagnostics-plain-output.
	* opts.cc (common_handle_option): Add case for
	OPT_fdiagnostics_show_event_links.
	* text-art/theme.cc (ascii_theme::get_cppchar): Handle
	cell_kind::CFG_*.
	(unicode_theme::get_cppchar): Likewise.
	* text-art/theme.h (theme::cell_kind): Add CFG_*.
	* toplev.cc (general_init): Initialize
	global_dc->m_source_printing.show_event_links_p.
	* tree-diagnostic-path.cc: Define INCLUDE_ALGORITHM,
	INCLUDE_MEMORY, and INCLUDE_STRING.  Include
	"diagnostic-label-effects.h".
	(path_label::path_label): Initialize m_effects.
	(path_label::get_effects): New.
	(class path_label::path_label_effects): New.
	(path_label::m_effects): New field.
	(class per_thread_summary): Add "friend struct event_range;".
	(per_thread_summary::per_thread_summary): Initialize m_last_event.
	(per_thread_summary::m_last_event): New field.
	(struct event_range::per_source_line_info): New.
	(event_range::event_range): Make "t" non-const.  Add
	"show_event_links" param and use it to initialize
	m_show_event_links.  Add info for initial event.
	(event_range::get_per_source_line_info): New.
	(event_range::maybe_add_event): Verify compatibility of the new
	label and existing labels with respect to the link-printing code.
	Update per-source-line info when an event is added.
	(event_range::print): Add"effect_info" param and pass to
	diagnostic_show_locus.
	(event_range::m_per_thread_summary): Make non-const.
	(event_range::m_source_line_info_map): New field.
	(event_range::m_show_event_links): New field.
	(path_summary::path_summary): Add "show_event_links" optional
	param, passing it to event_range ctor calls. Update
	pts.m_last_event.
	(thread_event_printer::print_swimlane_for_event_range): Add
	"effect_info" param and pass it to range->print.
	(print_path_summary_as_text): Keep track of the column for any
	out-edges at the end of printing each event_range and use as
	the leading in-edge for the next event_range.
	(default_tree_diagnostic_path_printer): Pass in show_event_links_p
	to path_summary ctor.
	(selftest::path_events_have_column_data_p): New.
	(class selftest::control_flow_test): New.
	(selftest::test_control_flow_1): New.
	(selftest::test_control_flow_2): New.
	(selftest::test_control_flow_3): New.
	(selftest::assert_cfg_edge_path_streq): New.
	(ASSERT_CFG_EDGE_PATH_STREQ): New macro.
	(selftest::test_control_flow_4): New.
	(selftest::test_control_flow_5): New.
	(selftest::test_control_flow_6): New.
	(selftest::control_flow_tests): New.
	(selftest::tree_diagnostic_path_cc_tests): Disable colorization on
	global_dc's printer.  Convert event_pp to a std::unique_ptr. Call
	control_flow_tests via for_each_line_table_case.
	(gen_command_line_string): Likewise.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/event-links-ascii.c: New test.
	* gcc.dg/analyzer/event-links-color.c: New test.
	* gcc.dg/analyzer/event-links-disabled.c: New test.
	* gcc.dg/analyzer/event-links-unicode.c: New test.

libcpp/ChangeLog:
	* include/rich-location.h (class label_effects): New forward decl.
	(range_label::get_effects): New vfunc.

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