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 2bd789256bcfd3bb4e063ebde560886a53e793d7..d4734cf133e349c5ebcd12c2717fc85d4195d003 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -8079,7 +8079,16 @@ 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);
@@ -8091,7 +8100,8 @@ 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);