error message when promised line could not select region should identify the region that can not be selected

bundle agent __main__
{
  vars:
      '_config[section 1][color]'string => "red";
      '_config[section_2][something]'     string => "else";
      "sections" slist => getindices( _config );

  files:
    "/tmp/config"
      create => 'true',
      edit_line => set_variable_values_ini( "$(this.namespace):$(this.bundle)._config", $(sections) );

  reports:
      "/tmp/config" printfile => cat( $(this.promiser) );
}

#+begin_src from_stdlib
body select_region INI_section(x)
# @brief Restrict the `edit_line` promise to the lines in section `[x]`
# @param x The name of the section in an INI-like configuration file
{
        select_start => "\[$(x)\]\s*";
        select_end => "\[.*\]\s*";

@if minimum_version(3.10)
        select_end_match_eof => "true";
@endif
}
bundle edit_line set_variable_values_ini(tab, sectionName)
# @brief Sets the RHS of configuration items in the file of the form
# `LHS=RHS`
#
# If the line is commented out with `#`, it gets uncommented first.
# Adds a new line if none exists.
#
# @param tab An associative array containing `tab[sectionName][LHS]="RHS"`.
# The value is not changed when the `RHS` is "dontchange"
# @param sectionName The section in the file within which values should be
# modified
#
# **See also:** `manage_variable_values_ini()`
{
  vars:
      "index" slist => getindices("$(tab)[$(sectionName)]");

      # Be careful if the index string contains funny chars
      "cindex[$(index)]" string => canonify("$(index)");

  classes:
      "edit_$(cindex[$(index)])"
        not => strcmp("$($(tab)[$(sectionName)][$(index)])","dontchange"),

        comment => "Create conditions to make changes";

  field_edits:

      # If the line is there, but commented out, first uncomment it
      "#+\s*$(index)\s*=.*"
      select_region => INI_section(escape("$(sectionName)")),
      edit_field => col("\s*=\s*","1","$(index)","set"),
        if => and("_section_$(section_name)_present_reached",
                  "edit_$(cindex[$(index)])");


      # match a line starting like the key something
      "\s*$(index)\s*=.*"
      edit_field => col("\s*=\s*","2","$($(tab)[$(sectionName)][$(index)])","set"),
      select_region => INI_section(escape("$(sectionName)")),
      classes => results("bundle", "set_variable_values_ini_not_$(cindex[$(index)])"),
        if => and("_section_$(section_name)_present_reached",
                   "edit_$(cindex[$(index)])");

  insert_lines:
      "[$(sectionName)]"
      location => start,
      comment => "Insert lines",
      classes => results( "bundle", "_section_$(section_name)_present" );

      "$(index)=$($(tab)[$(sectionName)][$(index)])"
      select_region => INI_section(escape("$(sectionName)")),
        if => "!(set_variable_values_ini_not_$(cindex[$(index)])_kept|set_variable_values_ini_not_$(cindex[$(index)])_repaired).edit_$(cindex[$(index)])";

}
body edit_field col(split,col,newval,method)
# @brief Edit tabluar data with comma-separated sub-values
# @param split The separator that defines columns
# @param col The (1-based) index of the value to change
# @param newval The new value
# @param method The method by which to edit the field
{
        field_separator    => "$(split)";
        select_field       => "$(col)";
        value_separator    => ",";
        field_value        => "$(newval)";
        field_operation    => "$(method)";
        extend_fields      => "true";
        allow_blank_fields => "true";
}

body location start
# @brief Editing occurs before the matched line
{
        before_after => "before";
}
body classes results(scope, class_prefix)
# @brief Define classes prefixed with `class_prefix` and suffixed with
# appropriate outcomes: _kept, _repaired, _not_kept, _error, _failed,
# _denied, _timeout, _reached
#
# @param scope The scope in which the class should be defined (`bundle` or `namespace`)
# @param class_prefix The prefix for the classes defined
#
# This body can be applied to any promise and sets global
# (`namespace`) or local (`bundle`) classes based on its outcome. For
# instance, with `class_prefix` set to `abc`:
#
# * if the promise is to change a file's owner to `nick` and the file
# was already owned by `nick`, the classes `abc_reached` and
# `abc_kept` will be set.
#
# * if the promise is to change a file's owner to `nick` and the file
# was owned by `adam` and the change succeeded, the classes
# `abc_reached` and `abc_repaired` will be set.
#
# This body is a simpler, more consistent version of the body
# `scoped_classes_generic`, which see. The key difference is that
# fewer classes are defined, and only for outcomes that we can know.
# For example this body does not define "OK/not OK" outcome classes,
# since a promise can be both kept and failed at the same time.
#
# It's important to understand that promises may do multiple things,
# so a promise is not simply "OK" or "not OK." The best way to
# understand what will happen when your specific promises get this
# body is to test it in all the possible combinations.
#
# **Suffix Notes:**
#
# * `_reached` indicates the promise was tried. Any outcome will result
#   in a class with this suffix being defined.
#
# * `_kept` indicates some aspect of the promise was kept
#
# * `_repaired` indicates some aspect of the promise was repaired
#
# * `_not_kept` indicates some aspect of the promise was not kept.
#   error, failed, denied and timeout outcomes will result in a class
#   with this suffix being defined
#
# * `_error` indicates the promise repair encountered an error
#
# * `_failed` indicates the promise failed
#
# * `_denied` indicates the promise repair was denied
#
# * `_timeout` indicates the promise timed out
#
# **Example:**
#
# ```cf3
# bundle agent example
# {
#   commands:
#     "/bin/true"
#       classes => results("bundle", "my_class_prefix");
#
#   reports:
#     my_class_prefix_kept::
#       "My promise was kept";
#
#     my_class_prefix_repaired::
#       "My promise was repaired";
# }
# ```
#
# **See also:** `scope`, `scoped_classes_generic`, `classes_generic`
{
  scope => "$(scope)";

  promise_kept => { "$(class_prefix)_reached",
                    "$(class_prefix)_kept" };

  promise_repaired => { "$(class_prefix)_reached",
                        "$(class_prefix)_repaired" };

  repair_failed => { "$(class_prefix)_reached",
                     "$(class_prefix)_error",
                     "$(class_prefix)_not_kept",
                     "$(class_prefix)_failed" };

  repair_denied => { "$(class_prefix)_reached",
                     "$(class_prefix)_error",
                     "$(class_prefix)_not_kept",
                     "$(class_prefix)_denied" };

  repair_timeout => { "$(class_prefix)_reached",
                      "$(class_prefix)_error",
                      "$(class_prefix)_not_kept",
                      "$(class_prefix)_timeout" };
}
body printfile cat(file)
# @brief Report the contents of a file
# @param file The full path of the file to report
{
        file_to_print => "$(file)";
        number_of_lines => "inf";
}
#+end_src