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 ce4db03bc12eefc2d7910ffe2e0096032cd78d47..d9346f711db5dfea91a374c11b2314141526e3c4 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -9415,7 +9415,16 @@ 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);
@@ -9427,7 +9436,8 @@ 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);
@@ -9598,7 +9608,7 @@ 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;