Handle NULL for short descriptions of custom GUC variables

If a short description is specified as NULL in one of the various
DefineCustomXXXVariable() functions available to external modules to
define a custom parameter, SHOW ALL would crash.  This change teaches
SHOW ALL to properly handle NULL short descriptions, as well as any code
paths that manipulate it, to gain in flexibility.  Note that
help_config.c was already able to do that, when describing a set of GUCs
for postgres --describe-config.

Author: Steve Chavez
Reviewed by: Nathan Bossart, Andres Freund, Michael Paquier, Tom Lane
Discussion: https://postgr.es/m/CAGRrpzY6hO-Kmykna_XvsTv8P2DshGiU6G3j8yGao4mk0CqjHA%40mail.gmail.com
Backpatch-through: 10

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 086b666cc1326deb6fe4c797c1a791205d1a3726..608794bbda7728d7aa8bd77ad9adb7d74afc3553 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -8858,7 +8858,16 @@ ShowAllGUCConfig(DestReceiver *dest)
                        isnull[1] = true;
                }
 
-               values[2] = PointerGetDatum(cstring_to_text(conf->short_desc));
+               if (conf->short_desc)
+               {
+                       values[2] = PointerGetDatum(cstring_to_text(conf->short_desc));
+                       isnull[2] = false;
+               }
+               else
+               {
+                       values[2] = PointerGetDatum(NULL);
+                       isnull[2] = true;
+               }
 
                /* send it to dest */
                do_tup_output(tstate, values, isnull);
@@ -8870,7 +8879,8 @@ ShowAllGUCConfig(DestReceiver *dest)
                        pfree(setting);
                        pfree(DatumGetPointer(values[1]));
                }
-               pfree(DatumGetPointer(values[2]));
+               if (conf->short_desc)
+                       pfree(DatumGetPointer(values[2]));
        }
 
        end_tup_output(tstate);
@@ -9048,7 +9058,7 @@ GetConfigOptionByNum(int varnum, const char **values, bool *noshow)
        values[3] = _(config_group_names[conf->group]);
 
        /* short_desc */
-       values[4] = _(conf->short_desc);
+       values[4] = conf->short_desc != NULL ? _(conf->short_desc) : NULL;
 
        /* extra_desc */
        values[5] = conf->long_desc != NULL ? _(conf->long_desc) : NULL;