libcpp: Improve encapsulation of label_text

  I'm not sure if label_text::get () is the best name for the new
accessor. Other options include buffer () and c_str () but I don't see a
compelling reason to prefer either of those.

As a follow-up patch we could change label_text::m_buffer (and
pod_label_text::m_buffer) to be const char*, since those labels are
never modified once a label_text takes ownership of it. That would
make it clear to callers that they are not supposed to modify the
contents, and would remove the const_cast currently used by
label_text::borrow (), which is a code smell (returning a non-const
char* makes it look like it's OK to write into it, which is definitely
not true for a borrowed string that was originally a string literal).
That would require using const_cast when passing the buffer to free for
deallocation, but that's fine, and avoids the impression that the object
holds a modifiable string buffer.

Tested x86_64-linux, OK for trunk?


-- >8 --

This adjusts the API of label_text so that the data members are private
and cannot be modified by callers.  Add accessors for them instead.
Also rename moved_from () to the more idiomatic release ().  Also remove
the unused take_or_copy () member function which has confusing ownership
semantics.

gcc/analyzer/ChangeLog:

	* call-info.cc (call_info::print): Adjust to new label_text API.
	* checker-path.cc (checker_event::dump): Likewise.
	(region_creation_event::get_desc): Likewise.
	(state_change_event::get_desc): Likewise.
	(superedge_event::should_filter_p): Likewise.
	(start_cfg_edge_event::get_desc): Likewise.
	(call_event::get_desc): Likewise.
	(return_event::get_desc): Likewise.
	(warning_event::get_desc): Likewise.
	(checker_path::dump): Likewise.
	(checker_path::debug): Likewise.
	* diagnostic-manager.cc (diagnostic_manager::prune_for_sm_diagnostic):
	Likewise.
	(diagnostic_manager::prune_interproc_events): Likewise.
	* engine.cc (feasibility_state::maybe_update_for_edge):
	Likewise.
	* program-state.cc (sm_state_map::to_json): Likewise.
	* region-model-impl-calls.cc (region_model::impl_call_analyzer_describe): Likewise.
	(region_model::impl_call_analyzer_dump_capacity): Likewise.
	* region.cc (region::to_json): Likewise.
	* sm-malloc.cc (inform_nonnull_attribute): Likewise.
	* store.cc (binding_map::to_json): Likewise.
	(store::to_json): Likewise.
	* supergraph.cc (superedge::dump): Likewise.
	* svalue.cc (svalue::to_json): Likewise.

gcc/c-family/ChangeLog:

	* c-format.cc (class range_label_for_format_type_mismatch):
	Adjust to new label_text API.

gcc/ChangeLog:

	* diagnostic-format-json.cc (json_from_location_range): Adjust
	to new label_text API.
	* diagnostic-format-sarif.cc (sarif_builder::make_location_object):
	Likewise.
	* diagnostic-show-locus.cc (struct pod_label_text): Likewise.
	(layout::print_any_labels): Likewise.
	* tree-diagnostic-path.cc (class path_label): Likewise.
	(struct event_range): Likewise.
	(default_tree_diagnostic_path_printer): Likewise.
	(default_tree_make_json_for_path): Likewise.

libcpp/ChangeLog:

	* include/line-map.h (label_text::take_or_copy): Remove.
	(label_text::moved_from): Rename to release.
	(label_text::m_buffer, label_text::m_owned): Make private.
	(label_text::get, label_text::is_owned): New accessors.
---
 gcc/analyzer/call-info.cc               |  2 +-
 gcc/analyzer/checker-path.cc            | 46 ++++++++++++-------------
 gcc/analyzer/diagnostic-manager.cc      | 20 +++++------
 gcc/analyzer/engine.cc                  |  2 +-
 gcc/analyzer/program-state.cc           |  2 +-
 gcc/analyzer/region-model-impl-calls.cc |  4 +--
 gcc/analyzer/region.cc                  |  2 +-
 gcc/analyzer/sm-malloc.cc               | 10 +++---
 gcc/analyzer/store.cc                   |  6 ++--
 gcc/analyzer/supergraph.cc              |  4 +--
 gcc/analyzer/svalue.cc                  |  2 +-
 gcc/c-family/c-format.cc                |  4 +--
 gcc/diagnostic-format-json.cc           |  4 +--
 gcc/diagnostic-format-sarif.cc          |  2 +-
 gcc/diagnostic-show-locus.cc            |  6 ++--
 gcc/tree-diagnostic-path.cc             | 16 ++++-----
 libcpp/include/line-map.h               | 27 ++++++++-------
 17 files changed, 80 insertions(+), 79 deletions(-)
  

On Thu, 2022-07-14 at 22:10 +0100, Jonathan Wakely wrote:

Thanks for the patch.

> I'm not sure if label_text::get () is the best name for the new
> accessor. Other options include buffer () and c_str () but I don't
> see a
> compelling reason to prefer either of those.

label_text::get should return a const char *, rather than a char *.

I don't think anything uses label_text::is_owner; do we need that?

> 
> As a follow-up patch we could change label_text::m_buffer (and
> pod_label_text::m_buffer) to be const char*, since those labels are
> never modified once a label_text takes ownership of it. That would
> make it clear to callers that they are not supposed to modify the
> contents, and would remove the const_cast currently used by
> label_text::borrow (), which is a code smell (returning a non-const
> char* makes it look like it's OK to write into it, which is
> definitely
> not true for a borrowed string that was originally a string literal).
> That would require using const_cast when passing the buffer to free
> for
> deallocation, but that's fine, and avoids the impression that the
> object
> holds a modifiable string buffer.

I'm not sure I agree with your reasoning about the proposed follow-up,
but the patch below is OK for trunk, with the above nits fixed.

Thanks
Dave

> 
> Tested x86_64-linux, OK for trunk?
> 
> 
> -- >8 --
> 
> This adjusts the API of label_text so that the data members are
> private
> and cannot be modified by callers.  Add accessors for them instead.
> Also rename moved_from () to the more idiomatic release ().  Also
> remove
> the unused take_or_copy () member function which has confusing
> ownership
> semantics.
> 
> gcc/analyzer/ChangeLog:
> 
>         * call-info.cc (call_info::print): Adjust to new label_text
> API.
>         * checker-path.cc (checker_event::dump): Likewise.
>         (region_creation_event::get_desc): Likewise.
>         (state_change_event::get_desc): Likewise.
>         (superedge_event::should_filter_p): Likewise.
>         (start_cfg_edge_event::get_desc): Likewise.
>         (call_event::get_desc): Likewise.
>         (return_event::get_desc): Likewise.
>         (warning_event::get_desc): Likewise.
>         (checker_path::dump): Likewise.
>         (checker_path::debug): Likewise.
>         * diagnostic-manager.cc
> (diagnostic_manager::prune_for_sm_diagnostic):
>         Likewise.
>         (diagnostic_manager::prune_interproc_events): Likewise.
>         * engine.cc (feasibility_state::maybe_update_for_edge):
>         Likewise.
>         * program-state.cc (sm_state_map::to_json): Likewise.
>         * region-model-impl-calls.cc
> (region_model::impl_call_analyzer_describe): Likewise.
>         (region_model::impl_call_analyzer_dump_capacity): Likewise.
>         * region.cc (region::to_json): Likewise.
>         * sm-malloc.cc (inform_nonnull_attribute): Likewise.
>         * store.cc (binding_map::to_json): Likewise.
>         (store::to_json): Likewise.
>         * supergraph.cc (superedge::dump): Likewise.
>         * svalue.cc (svalue::to_json): Likewise.
> 
> gcc/c-family/ChangeLog:
> 
>         * c-format.cc (class range_label_for_format_type_mismatch):
>         Adjust to new label_text API.
> 
> gcc/ChangeLog:
> 
>         * diagnostic-format-json.cc (json_from_location_range):
> Adjust
>         to new label_text API.
>         * diagnostic-format-sarif.cc
> (sarif_builder::make_location_object):
>         Likewise.
>         * diagnostic-show-locus.cc (struct pod_label_text): Likewise.
>         (layout::print_any_labels): Likewise.
>         * tree-diagnostic-path.cc (class path_label): Likewise.
>         (struct event_range): Likewise.
>         (default_tree_diagnostic_path_printer): Likewise.
>         (default_tree_make_json_for_path): Likewise.
> 
> libcpp/ChangeLog:
> 
>         * include/line-map.h (label_text::take_or_copy): Remove.
>         (label_text::moved_from): Rename to release.
>         (label_text::m_buffer, label_text::m_owned): Make private.
>         (label_text::get, label_text::is_owned): New accessors.
> ---
>  gcc/analyzer/call-info.cc               |  2 +-
>  gcc/analyzer/checker-path.cc            | 46 ++++++++++++-----------
> --
>  gcc/analyzer/diagnostic-manager.cc      | 20 +++++------
>  gcc/analyzer/engine.cc                  |  2 +-
>  gcc/analyzer/program-state.cc           |  2 +-
>  gcc/analyzer/region-model-impl-calls.cc |  4 +--
>  gcc/analyzer/region.cc                  |  2 +-
>  gcc/analyzer/sm-malloc.cc               | 10 +++---
>  gcc/analyzer/store.cc                   |  6 ++--
>  gcc/analyzer/supergraph.cc              |  4 +--
>  gcc/analyzer/svalue.cc                  |  2 +-
>  gcc/c-family/c-format.cc                |  4 +--
>  gcc/diagnostic-format-json.cc           |  4 +--
>  gcc/diagnostic-format-sarif.cc          |  2 +-
>  gcc/diagnostic-show-locus.cc            |  6 ++--
>  gcc/tree-diagnostic-path.cc             | 16 ++++-----
>  libcpp/include/line-map.h               | 27 ++++++++-------
>  17 files changed, 80 insertions(+), 79 deletions(-)
> 
> diff --git a/gcc/analyzer/call-info.cc b/gcc/analyzer/call-info.cc
> index e1142d743a3..efc070b8bed 100644
> --- a/gcc/analyzer/call-info.cc
> +++ b/gcc/analyzer/call-info.cc
> @@ -75,7 +75,7 @@ void
>  call_info::print (pretty_printer *pp) const
>  {
>    label_text desc (get_desc (pp_show_color (pp)));
> -  pp_string (pp, desc.m_buffer);
> +  pp_string (pp, desc.get ());
>  }
>  
>  /* Implementation of custom_edge_info::add_events_to_path vfunc for
> diff --git a/gcc/analyzer/checker-path.cc b/gcc/analyzer/checker-
> path.cc
> index 211cf3e0333..273f40d3a57 100644
> --- a/gcc/analyzer/checker-path.cc
> +++ b/gcc/analyzer/checker-path.cc
> @@ -195,7 +195,7 @@ checker_event::dump (pretty_printer *pp) const
>  {
>    label_text event_desc (get_desc (false));
>    pp_printf (pp, "\"%s\" (depth %i",
> -            event_desc.m_buffer, m_effective_depth);
> +            event_desc.get (), m_effective_depth);
>  
>    if (m_effective_depth != m_original_depth)
>      pp_printf (pp, " corrected from %i",
> @@ -307,7 +307,7 @@ region_creation_event::get_desc (bool
> can_colorize) const
>        label_text custom_desc
>             = m_pending_diagnostic->describe_region_creation_event
>                 (evdesc::region_creation (can_colorize, m_reg));
> -      if (custom_desc.m_buffer)
> +      if (custom_desc.get ())
>         return custom_desc;
>      }
>  
> @@ -390,7 +390,7 @@ state_change_event::get_desc (bool can_colorize)
> const
>         = m_pending_diagnostic->describe_state_change
>             (evdesc::state_change (can_colorize, var, origin,
>                                    m_from, m_to, m_emission_id,
> *this));
> -      if (custom_desc.m_buffer)
> +      if (custom_desc.get ())
>         {
>           if (flag_analyzer_verbose_state_changes)
>             {
> @@ -404,7 +404,7 @@ state_change_event::get_desc (bool can_colorize)
> const
>                 return make_label_text
>                   (can_colorize,
>                    "%s (state of %qE: %qs -> %qs, origin: %qE,
> meaning: %s)",
> -                  custom_desc.m_buffer,
> +                  custom_desc.get (),
>                    var,
>                    m_from->get_name (),
>                    m_to->get_name (),
> @@ -414,7 +414,7 @@ state_change_event::get_desc (bool can_colorize)
> const
>                 return make_label_text
>                   (can_colorize,
>                    "%s (state of %qE: %qs -> %qs, NULL origin,
> meaning: %s)",
> -                  custom_desc.m_buffer,
> +                  custom_desc.get (),
>                    var,
>                    m_from->get_name (),
>                    m_to->get_name (),
> @@ -435,16 +435,16 @@ state_change_event::get_desc (bool
> can_colorize) const
>           return make_label_text
>             (can_colorize,
>              "state of %qs: %qs -> %qs (origin: %qs)",
> -            sval_desc.m_buffer,
> +            sval_desc.get (),
>              m_from->get_name (),
>              m_to->get_name (),
> -            origin_desc.m_buffer);
> +            origin_desc.get ());
>         }
>        else
>         return make_label_text
>           (can_colorize,
>            "state of %qs: %qs -> %qs (NULL origin)",
> -          sval_desc.m_buffer,
> +          sval_desc.get (),
>            m_from->get_name (),
>            m_to->get_name ());
>      }
> @@ -509,8 +509,8 @@ superedge_event::should_filter_p (int verbosity)
> const
>             /* Filter events with empty descriptions.  This ought to
> filter
>                FALLTHRU, but retain true/false/switch edges.  */
>             label_text desc = get_desc (false);
> -           gcc_assert (desc.m_buffer);
> -           if (desc.m_buffer[0] == '\0')
> +           gcc_assert (desc.get ());
> +           if (desc.get ()[0] == '\0')
>               return true;
>           }
>        }
> @@ -597,28 +597,28 @@ start_cfg_edge_event::get_desc (bool
> can_colorize) const
>    label_text edge_desc (m_sedge->get_description (user_facing));
>    if (user_facing)
>      {
> -      if (edge_desc.m_buffer && strlen (edge_desc.m_buffer) > 0)
> +      if (edge_desc.get () && strlen (edge_desc.get ()) > 0)
>         {
>           label_text cond_desc = maybe_describe_condition
> (can_colorize);
>           label_text result;
> -         if (cond_desc.m_buffer)
> +         if (cond_desc.get ())
>             return make_label_text (can_colorize,
>                                     "following %qs branch (%s)...",
> -                                   edge_desc.m_buffer,
> cond_desc.m_buffer);
> +                                   edge_desc.get (), cond_desc.get
> ());
>           else
>             return make_label_text (can_colorize,
>                                     "following %qs branch...",
> -                                   edge_desc.m_buffer);
> +                                   edge_desc.get ());
>         }
>        else
>         return label_text::borrow ("");
>      }
>    else
>      {
> -      if (strlen (edge_desc.m_buffer) > 0)
> +      if (strlen (edge_desc.get ()) > 0)
>         return make_label_text (can_colorize,
>                                 "taking %qs edge SN:%i -> SN:%i",
> -                               edge_desc.m_buffer,
> +                               edge_desc.get (),
>                                 m_sedge->m_src->m_index,
>                                 m_sedge->m_dest->m_index);
>        else
> @@ -798,7 +798,7 @@ call_event::get_desc (bool can_colorize) const
>                                       m_dest_snode->m_fun->decl,
>                                       var,
>                                       m_critical_state));
> -      if (custom_desc.m_buffer)
> +      if (custom_desc.get ())
>         return custom_desc;
>      }
>  
> @@ -878,7 +878,7 @@ return_event::get_desc (bool can_colorize) const
>                                       m_dest_snode->m_fun->decl,
>                                       m_src_snode->m_fun->decl,
>                                       m_critical_state));
> -      if (custom_desc.m_buffer)
> +      if (custom_desc.get ())
>         return custom_desc;
>      }
>    return make_label_text (can_colorize,
> @@ -1105,19 +1105,19 @@ warning_event::get_desc (bool can_colorize)
> const
>        label_text ev_desc
>         = m_pending_diagnostic->describe_final_event
>             (evdesc::final_event (can_colorize, var, m_state));
> -      if (ev_desc.m_buffer)
> +      if (ev_desc.get ())
>         {
>           if (m_sm && flag_analyzer_verbose_state_changes)
>             {
>               if (var)
>                 return make_label_text (can_colorize,
>                                         "%s (%qE is in state %qs)",
> -                                       ev_desc.m_buffer,
> +                                       ev_desc.get (),
>                                         var, m_state->get_name ());
>               else
>                 return make_label_text (can_colorize,
>                                         "%s (in global state %qs)",
> -                                       ev_desc.m_buffer,
> +                                       ev_desc.get (),
>                                         m_state->get_name ());
>             }
>           else
> @@ -1163,7 +1163,7 @@ checker_path::dump (pretty_printer *pp) const
>        if (i > 0)
>         pp_string (pp, ", ");
>        label_text event_desc (e->get_desc (false));
> -      pp_printf (pp, "\"%s\"", event_desc.m_buffer);
> +      pp_printf (pp, "\"%s\"", event_desc.get ());
>      }
>    pp_character (pp, ']');
>  }
> @@ -1203,7 +1203,7 @@ checker_path::debug () const
>                "[%i]: %s \"%s\"\n",
>                i,
>                event_kind_to_string (m_events[i]->m_kind),
> -              event_desc.m_buffer);
> +              event_desc.get ());
>      }
>  }
>  
> diff --git a/gcc/analyzer/diagnostic-manager.cc
> b/gcc/analyzer/diagnostic-manager.cc
> index 083f66bd739..fded8281e57 100644
> --- a/gcc/analyzer/diagnostic-manager.cc
> +++ b/gcc/analyzer/diagnostic-manager.cc
> @@ -2297,7 +2297,7 @@ diagnostic_manager::prune_for_sm_diagnostic
> (checker_path *path,
>                   label_text sval_desc = sval->get_desc ();
>                   log ("considering event %i (%s), with sval: %qs,
> state: %qs",
>                        idx, event_kind_to_string (base_event-
> >m_kind),
> -                      sval_desc.m_buffer, state->get_name ());
> +                      sval_desc.get (), state->get_name ());
>                 }
>               else
>                 log ("considering event %i (%s), with global state:
> %qs",
> @@ -2363,8 +2363,8 @@ diagnostic_manager::prune_for_sm_diagnostic
> (checker_path *path,
>                           = state_change->m_origin->get_desc ();
>                         log ("event %i:"
>                              " switching var of interest from %qs to
> %qs",
> -                            idx, sval_desc.m_buffer,
> -                            origin_sval_desc.m_buffer);
> +                            idx, sval_desc.get (),
> +                            origin_sval_desc.get ());
>                       }
>                     sval = state_change->m_origin;
>                   }
> @@ -2386,12 +2386,12 @@ diagnostic_manager::prune_for_sm_diagnostic
> (checker_path *path,
>                             label_text sval_desc = sval->get_desc ();
>                             log ("filtering event %i:"
>                                  " state change to %qs unrelated to
> %qs",
> -                                idx, change_sval_desc.m_buffer,
> -                                sval_desc.m_buffer);
> +                                idx, change_sval_desc.get (),
> +                                sval_desc.get ());
>                           }
>                         else
>                           log ("filtering event %i: state change to
> %qs",
> -                              idx, change_sval_desc.m_buffer);
> +                              idx, change_sval_desc.get ());
>                       }
>                     else
>                       log ("filtering event %i: global state change",
> idx);
> @@ -2460,7 +2460,7 @@ diagnostic_manager::prune_for_sm_diagnostic
> (checker_path *path,
>                     log ("event %i:"
>                          " recording critical state for %qs at call"
>                          " from %qE in callee to %qE in caller",
> -                        idx, sval_desc.m_buffer, callee_var,
> caller_var);
> +                        idx, sval_desc.get (), callee_var,
> caller_var);
>                   }
>                 if (expr.param_p ())
>                   event->record_critical_state (caller_var, state);
> @@ -2503,7 +2503,7 @@ diagnostic_manager::prune_for_sm_diagnostic
> (checker_path *path,
>                         log ("event %i:"
>                              " recording critical state for %qs at
> return"
>                              " from %qE in caller to %qE in callee",
> -                            idx, sval_desc.m_buffer, callee_var,
> callee_var);
> +                            idx, sval_desc.get (), callee_var,
> callee_var);
>                       }
>                     if (expr.return_value_p ())
>                       event->record_critical_state (callee_var,
> state);
> @@ -2586,7 +2586,7 @@ diagnostic_manager::prune_interproc_events
> (checker_path *path) const
>                     (path->get_checker_event (idx)->get_desc
> (false));
>                   log ("filtering events %i-%i:"
>                        " irrelevant call/entry/return: %s",
> -                      idx, idx + 2, desc.m_buffer);
> +                      idx, idx + 2, desc.get ());
>                 }
>               path->delete_event (idx + 2);
>               path->delete_event (idx + 1);
> @@ -2608,7 +2608,7 @@ diagnostic_manager::prune_interproc_events
> (checker_path *path) const
>                     (path->get_checker_event (idx)->get_desc
> (false));
>                   log ("filtering events %i-%i:"
>                        " irrelevant call/return: %s",
> -                      idx, idx + 1, desc.m_buffer);
> +                      idx, idx + 1, desc.get ());
>                 }
>               path->delete_event (idx + 1);
>               path->delete_event (idx);
> diff --git a/gcc/analyzer/engine.cc b/gcc/analyzer/engine.cc
> index 888123f2b95..9ffcc410839 100644
> --- a/gcc/analyzer/engine.cc
> +++ b/gcc/analyzer/engine.cc
> @@ -4590,7 +4590,7 @@ feasibility_state::maybe_update_for_edge
> (logger *logger,
>           logger->log ("  sedge: SN:%i -> SN:%i %s",
>                        sedge->m_src->m_index,
>                        sedge->m_dest->m_index,
> -                      desc.m_buffer);
> +                      desc.get ());
>         }
>  
>        const gimple *last_stmt = src_point.get_supernode ()-
> >get_last_stmt ();
> diff --git a/gcc/analyzer/program-state.cc b/gcc/analyzer/program-
> state.cc
> index 90a56e3fba4..f0f40465aad 100644
> --- a/gcc/analyzer/program-state.cc
> +++ b/gcc/analyzer/program-state.cc
> @@ -300,7 +300,7 @@ sm_state_map::to_json () const
>        entry_t e = (*iter).second;
>  
>        label_text sval_desc = sval->get_desc ();
> -      map_obj->set (sval_desc.m_buffer, e.m_state->to_json ());
> +      map_obj->set (sval_desc.get (), e.m_state->to_json ());
>  
>        /* This doesn't yet JSONify e.m_origin.  */
>      }
> diff --git a/gcc/analyzer/region-model-impl-calls.cc
> b/gcc/analyzer/region-model-impl-calls.cc
> index 55d6fa7f76b..8c38e9206fa 100644
> --- a/gcc/analyzer/region-model-impl-calls.cc
> +++ b/gcc/analyzer/region-model-impl-calls.cc
> @@ -255,7 +255,7 @@ region_model::impl_call_analyzer_describe (const
> gcall *call,
>    const svalue *sval = get_rvalue (t_val, ctxt);
>    bool simple = zerop (t_verbosity);
>    label_text desc = sval->get_desc (simple);
> -  warning_at (call->location, 0, "svalue: %qs", desc.m_buffer);
> +  warning_at (call->location, 0, "svalue: %qs", desc.get ());
>  }
>  
>  /* Handle a call to "__analyzer_dump_capacity".
> @@ -274,7 +274,7 @@ region_model::impl_call_analyzer_dump_capacity
> (const gcall *call,
>    const region *base_reg = reg->get_base_region ();
>    const svalue *capacity = get_capacity (base_reg);
>    label_text desc = capacity->get_desc (true);
> -  warning_at (call->location, 0, "capacity: %qs", desc.m_buffer);
> +  warning_at (call->location, 0, "capacity: %qs", desc.get ());
>  }
>  
>  /* Compare D1 and D2 using their names, and then IDs to order them. 
> */
> diff --git a/gcc/analyzer/region.cc b/gcc/analyzer/region.cc
> index 5b00e6a5f46..a8d1ae92deb 100644
> --- a/gcc/analyzer/region.cc
> +++ b/gcc/analyzer/region.cc
> @@ -589,7 +589,7 @@ json::value *
>  region::to_json () const
>  {
>    label_text desc = get_desc (true);
> -  json::value *reg_js = new json::string (desc.m_buffer);
> +  json::value *reg_js = new json::string (desc.get ());
>    return reg_js;
>  }
>  
> diff --git a/gcc/analyzer/sm-malloc.cc b/gcc/analyzer/sm-malloc.cc
> index 553fcd80085..608aceb1abe 100644
> --- a/gcc/analyzer/sm-malloc.cc
> +++ b/gcc/analyzer/sm-malloc.cc
> @@ -1007,7 +1007,7 @@ inform_nonnull_attribute (tree fndecl, int
> arg_idx)
>    label_text arg_desc = describe_argument_index (fndecl, arg_idx);
>    inform (DECL_SOURCE_LOCATION (fndecl),
>           "argument %s of %qD must be non-null",
> -         arg_desc.m_buffer, fndecl);
> +         arg_desc.get (), fndecl);
>    /* Ideally we would use the location of the parm and underline the
>       attribute also - but we don't have the location_t values at
> this point
>       in the middle-end.
> @@ -1065,12 +1065,12 @@ public:
>      if (m_origin_of_unchecked_event.known_p ())
>        result = ev.formatted_print ("argument %s (%qE) from %@ could
> be NULL"
>                                    " where non-null expected",
> -                                  arg_desc.m_buffer, ev.m_expr,
> +                                  arg_desc.get (), ev.m_expr,
>                                    &m_origin_of_unchecked_event);
>      else
>        result = ev.formatted_print ("argument %s (%qE) could be NULL"
>                                    " where non-null expected",
> -                                  arg_desc.m_buffer, ev.m_expr);
> +                                  arg_desc.get (), ev.m_expr);
>      return result;
>    }
>  
> @@ -1173,11 +1173,11 @@ public:
>      label_text result;
>      if (zerop (ev.m_expr))
>        result = ev.formatted_print ("argument %s NULL where non-null
> expected",
> -                                  arg_desc.m_buffer);
> +                                  arg_desc.get ());
>      else
>        result = ev.formatted_print ("argument %s (%qE) NULL"
>                                    " where non-null expected",
> -                                  arg_desc.m_buffer, ev.m_expr);
> +                                  arg_desc.get (), ev.m_expr);
>      return result;
>    }
>  
> diff --git a/gcc/analyzer/store.cc b/gcc/analyzer/store.cc
> index d558d477115..06151d8c041 100644
> --- a/gcc/analyzer/store.cc
> +++ b/gcc/analyzer/store.cc
> @@ -675,7 +675,7 @@ binding_map::to_json () const
>      {
>        const svalue *value = *const_cast <map_t &> (m_map).get (key);
>        label_text key_desc = key->get_desc ();
> -      map_obj->set (key_desc.m_buffer, value->to_json ());
> +      map_obj->set (key_desc.get (), value->to_json ());
>      }
>  
>    return map_obj;
> @@ -2402,11 +2402,11 @@ store::to_json () const
>           binding_cluster *cluster
>             = *const_cast<cluster_map_t &> (m_cluster_map).get
> (base_reg);
>           label_text base_reg_desc = base_reg->get_desc ();
> -         clusters_in_parent_reg_obj->set (base_reg_desc.m_buffer,
> +         clusters_in_parent_reg_obj->set (base_reg_desc.get (),
>                                            cluster->to_json ());
>         }
>        label_text parent_reg_desc = parent_reg->get_desc ();
> -      store_obj->set (parent_reg_desc.m_buffer,
> clusters_in_parent_reg_obj);
> +      store_obj->set (parent_reg_desc.get (),
> clusters_in_parent_reg_obj);
>      }
>  
>    store_obj->set ("called_unknown_fn", new json::literal
> (m_called_unknown_fn));
> diff --git a/gcc/analyzer/supergraph.cc b/gcc/analyzer/supergraph.cc
> index 52b4852404d..01e30f7f6d0 100644
> --- a/gcc/analyzer/supergraph.cc
> +++ b/gcc/analyzer/supergraph.cc
> @@ -855,10 +855,10 @@ superedge::dump (pretty_printer *pp) const
>  {
>    pp_printf (pp, "edge: SN: %i -> SN: %i", m_src->m_index, m_dest-
> >m_index);
>    label_text desc (get_description (false));
> -  if (strlen (desc.m_buffer) > 0)
> +  if (strlen (desc.get ()) > 0)
>      {
>        pp_space (pp);
> -      pp_string (pp, desc.m_buffer);
> +      pp_string (pp, desc.get ());
>      }
>  }
>  
> diff --git a/gcc/analyzer/svalue.cc b/gcc/analyzer/svalue.cc
> index 78a6eeff05f..f5a5f1c9697 100644
> --- a/gcc/analyzer/svalue.cc
> +++ b/gcc/analyzer/svalue.cc
> @@ -96,7 +96,7 @@ json::value *
>  svalue::to_json () const
>  {
>    label_text desc = get_desc (true);
> -  json::value *sval_js = new json::string (desc.m_buffer);
> +  json::value *sval_js = new json::string (desc.get ());
>    return sval_js;
>  }
>  
> diff --git a/gcc/c-family/c-format.cc b/gcc/c-family/c-format.cc
> index 2faed0c1607..68b94da40cc 100644
> --- a/gcc/c-family/c-format.cc
> +++ b/gcc/c-family/c-format.cc
> @@ -4617,14 +4617,14 @@ class range_label_for_format_type_mismatch
>    label_text get_text (unsigned range_idx) const final override
>    {
>      label_text text = range_label_for_type_mismatch::get_text
> (range_idx);
> -    if (text.m_buffer == NULL)
> +    if (text.get () == NULL)
>        return text;
>  
>      indirection_suffix suffix (m_pointer_count);
>      char *p = (char *) alloca (suffix.get_buffer_size ());
>      suffix.fill_buffer (p);
>  
> -    char *result = concat (text.m_buffer, p, NULL);
> +    char *result = concat (text.get (), p, NULL);
>      return label_text::take (result);
>    }
>  
> diff --git a/gcc/diagnostic-format-json.cc b/gcc/diagnostic-format-
> json.cc
> index 872c67e53ed..baadc4b27c9 100644
> --- a/gcc/diagnostic-format-json.cc
> +++ b/gcc/diagnostic-format-json.cc
> @@ -102,8 +102,8 @@ json_from_location_range (diagnostic_context
> *context,
>    if (loc_range->m_label)
>      {
>        label_text text (loc_range->m_label->get_text (range_idx));
> -      if (text.m_buffer)
> -       result->set ("label", new json::string (text.m_buffer));
> +      if (text.get ())
> +       result->set ("label", new json::string (text.get ()));
>      }
>  
>    return result;
> diff --git a/gcc/diagnostic-format-sarif.cc b/gcc/diagnostic-format-
> sarif.cc
> index 1e4ebc8ad38..fc28d160c38 100644
> --- a/gcc/diagnostic-format-sarif.cc
> +++ b/gcc/diagnostic-format-sarif.cc
> @@ -582,7 +582,7 @@ sarif_builder::make_location_object (const
> diagnostic_event &event)
>  
>    /* "message" property (SARIF v2.1.0 section 3.28.5).  */
>    label_text ev_desc = event.get_desc (false);
> -  json::object *message_obj = make_message_object
> (ev_desc.m_buffer);
> +  json::object *message_obj = make_message_object (ev_desc.get ());
>    location_obj->set ("message", message_obj);
>  
>    return location_obj;
> diff --git a/gcc/diagnostic-show-locus.cc b/gcc/diagnostic-show-
> locus.cc
> index 08dab20e6cd..bcaa52ec779 100644
> --- a/gcc/diagnostic-show-locus.cc
> +++ b/gcc/diagnostic-show-locus.cc
> @@ -1877,9 +1877,9 @@ struct pod_label_text
>    {}
>  
>    pod_label_text (label_text &&other)
> -  : m_buffer (other.m_buffer), m_caller_owned (other.m_owned)
> +  : m_buffer (other.get ()), m_caller_owned (other.is_owner ())
>    {
> -    other.moved_from ();
> +    other.release ();
>    }
>  
>    void maybe_free ()
> @@ -1963,7 +1963,7 @@ layout::print_any_labels (linenum_type row)
>         /* Allow for labels that return NULL from their get_text
>            implementation (so e.g. such labels can control their own
>            visibility).  */
> -       if (text.m_buffer == NULL)
> +       if (text.get () == NULL)
>           continue;
>  
>         labels.safe_push (line_label (m_policy, i, disp_col,
> std::move (text)));
> diff --git a/gcc/tree-diagnostic-path.cc b/gcc/tree-diagnostic-
> path.cc
> index 2f297faed34..6612b617471 100644
> --- a/gcc/tree-diagnostic-path.cc
> +++ b/gcc/tree-diagnostic-path.cc
> @@ -61,11 +61,11 @@ class path_label : public range_label
>         is special-cased for diagnostic paths.  */
>      bool colorize = pp_show_color (global_dc->printer);
>      label_text event_text (event.get_desc (colorize));
> -    gcc_assert (event_text.m_buffer);
> +    gcc_assert (event_text.get ());
>      pretty_printer pp;
>      pp_show_color (&pp) = pp_show_color (global_dc->printer);
>      diagnostic_event_id_t event_id (event_idx);
> -    pp_printf (&pp, "%@ %s", &event_id, event_text.m_buffer);
> +    pp_printf (&pp, "%@ %s", &event_id, event_text.get ());
>      label_text result = label_text::take (xstrdup (pp_formatted_text
> (&pp)));
>      return result;
>    }
> @@ -173,7 +173,7 @@ struct event_range
>             diagnostic_event_id_t event_id (i);
>             label_text event_text (iter_event.get_desc (true));
>             pretty_printer *pp = dc->printer;
> -           pp_printf (pp, " %@: %s", &event_id,
> event_text.m_buffer);
> +           pp_printf (pp, " %@: %s", &event_id, event_text.get ());
>             pp_newline (pp);
>           }
>         return;
> @@ -459,7 +459,7 @@ default_tree_diagnostic_path_printer
> (diagnostic_context *context,
>           {
>             const diagnostic_event &event = path->get_event (i);
>             label_text event_text (event.get_desc (false));
> -           gcc_assert (event_text.m_buffer);
> +           gcc_assert (event_text.get ());
>             diagnostic_event_id_t event_id (i);
>             if (context->show_path_depths)
>               {
> @@ -471,17 +471,17 @@ default_tree_diagnostic_path_printer
> (diagnostic_context *context,
>                 if (fndecl)
>                   inform (event.get_location (),
>                           "%@ %s (fndecl %qD, depth %i)",
> -                         &event_id, event_text.m_buffer,
> +                         &event_id, event_text.get (),
>                           fndecl, stack_depth);
>                 else
>                   inform (event.get_location (),
>                           "%@ %s (depth %i)",
> -                         &event_id, event_text.m_buffer,
> +                         &event_id, event_text.get (),
>                           stack_depth);
>               }
>             else
>               inform (event.get_location (),
> -                     "%@ %s", &event_id, event_text.m_buffer);
> +                     "%@ %s", &event_id, event_text.get ());
>           }
>        }
>        break;
> @@ -519,7 +519,7 @@ default_tree_make_json_for_path
> (diagnostic_context *context,
>                         json_from_expanded_location (context,
>                                                     
> event.get_location ()));
>        label_text event_text (event.get_desc (false));
> -      event_obj->set ("description", new json::string
> (event_text.m_buffer));
> +      event_obj->set ("description", new json::string
> (event_text.get ()));
>        if (tree fndecl = event.get_fndecl ())
>         {
>           const char *function
> diff --git a/libcpp/include/line-map.h b/libcpp/include/line-map.h
> index c434a246b13..193fec0a45f 100644
> --- a/libcpp/include/line-map.h
> +++ b/libcpp/include/line-map.h
> @@ -1851,7 +1851,7 @@ public:
>    label_text (label_text &&other)
>    : m_buffer (other.m_buffer), m_owned (other.m_owned)
>    {
> -    other.moved_from ();
> +    other.release ();
>    }
>  
>    /* Move assignment.  */
> @@ -1861,7 +1861,7 @@ public:
>        free (m_buffer);
>      m_buffer = other.m_buffer;
>      m_owned = other.m_owned;
> -    other.moved_from ();
> +    other.release ();
>      return *this;
>    }
>  
> @@ -1882,25 +1882,26 @@ public:
>      return label_text (buffer, true);
>    }
>  
> -  /* Take ownership of the buffer, copying if necessary.  */
> -  char *take_or_copy ()
> -  {
> -    if (m_owned)
> -      return m_buffer;
> -    else
> -      return xstrdup (m_buffer);
> -  }
> -
> -  void moved_from ()
> +  void release ()
>    {
>      m_buffer = NULL;
>      m_owned = false;
>    }
>  
> +  char *get () const
> +  {
> +    return m_buffer;
> +  }
> +
> +  bool is_owner () const
> +  {
> +    return m_owned;
> +  }
> +
> +private:
>    char *m_buffer;
>    bool m_owned;
>  
> -private:
>    label_text (char *buffer, bool owned)
>    : m_buffer (buffer), m_owned (owned)
>    {}
  

On Thu, 14 Jul 2022 at 22:31, David Malcolm wrote:
>
> On Thu, 2022-07-14 at 22:10 +0100, Jonathan Wakely wrote:
>
> Thanks for the patch.
>
> > I'm not sure if label_text::get () is the best name for the new
> > accessor. Other options include buffer () and c_str () but I don't
> > see a
> > compelling reason to prefer either of those.
>
> label_text::get should return a const char *, rather than a char *.

OK. That requires a tweak to pod_label_text, as it wants to store the
result of get() as a char*.

> I don't think anything uses label_text::is_owner; do we need that?

The pod_label_text constructor that transfers ownership from a
label_text uses it.

An alternative to adding the is_owner accessor is to make
pod_label_text a friend of label_text. Alternatively, move
pod_label_text into libcpp and make it label_text know how to convert
itself to a pod_label_text (setting the bool correctly). That might be
overkill given that pod_label_text is used exactly once in one place,
but then arguably so is the is_owner() accessor that's needed exactly
once.


>
> >
> > As a follow-up patch we could change label_text::m_buffer (and
> > pod_label_text::m_buffer) to be const char*, since those labels are
> > never modified once a label_text takes ownership of it. That would
> > make it clear to callers that they are not supposed to modify the
> > contents, and would remove the const_cast currently used by
> > label_text::borrow (), which is a code smell (returning a non-const
> > char* makes it look like it's OK to write into it, which is
> > definitely
> > not true for a borrowed string that was originally a string literal).
> > That would require using const_cast when passing the buffer to free
> > for
> > deallocation, but that's fine, and avoids the impression that the
> > object
> > holds a modifiable string buffer.
>
> I'm not sure I agree with your reasoning about the proposed follow-up,

You mean you don't want the member to be a const char*? Works for me.
My goal is to stop users of label_text modifying it, and now that they
can only get to it via the get() accessor, that's enforced by making
the accessor return const. Changing the member isn't necessary.

> but the patch below is OK for trunk, with the above nits fixed.

Thanks, pushed to trunk.

Here's the incremental diff between the reviewed patch and what I pushed:

diff --git a/gcc/diagnostic-show-locus.cc b/gcc/diagnostic-show-locus.cc
index bcaa52ec779..9d430b5189c 100644
--- a/gcc/diagnostic-show-locus.cc
+++ b/gcc/diagnostic-show-locus.cc
@@ -1877,7 +1877,8 @@ struct pod_label_text
  {}

  pod_label_text (label_text &&other)
-  : m_buffer (other.get ()), m_caller_owned (other.is_owner ())
+  : m_buffer (const_cast<char*> (other.get ())),
+    m_caller_owned (other.is_owner ())
  {
    other.release ();
  }
diff --git a/libcpp/include/line-map.h b/libcpp/include/line-map.h
index 193fec0a45f..9bdd5b9d30c 100644
--- a/libcpp/include/line-map.h
+++ b/libcpp/include/line-map.h
@@ -1888,7 +1888,7 @@ public:
    m_owned = false;
  }

-  char *get () const
+  const char *get () const
  {
    return m_buffer;
  }