Fix tab completion of "SET variable TO|=" to not offer bogus completions.

Don't think that the context "UPDATE tab SET var =" is a GUC-setting
command.

If we have "SET var =" but the "var" is not a known GUC variable,
don't offer any completions.  The most likely explanation is that
we've misparsed the context and it's not really a GUC-setting command.

Per gripe from Ken Tanzer.  Back-patch to 9.6.  The issue exists
further back, but before 9.6 the code looks very different and it
doesn't actually know whether the "var" name matches anything,
so I desisted from trying to fix it.

Discussion: https://postgr.es/m/CAD3a31XpXzrZA9TT3BqLSHghdTK+=cXjNCE+oL2Zn4+oWoc=qA@mail.gmail.com

diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 83b2b9cee3c7c2cabf29ffaa848ecb4671d053a8..d47384295871a980dcaac7675883d53ca94e03c2 100644 (file)
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -3249,8 +3249,13 @@ psql_completion(const char *text, int start, int end)
    else if (HeadMatches2("ALTER", "DATABASE|FUNCTION|ROLE|USER") &&
             TailMatches2("SET", MatchAny))
        COMPLETE_WITH_LIST2("FROM CURRENT", "TO");
-   /* Suggest possible variable values */
-   else if (TailMatches3("SET", MatchAny, "TO|="))
+
+   /*
+    * Suggest possible variable values in SET variable TO|=, along with the
+    * preceding ALTER syntaxes.
+    */
+   else if (TailMatches3("SET", MatchAny, "TO|=") &&
+            !TailMatches5("UPDATE", MatchAny, "SET", MatchAny, "TO|="))
    {
        /* special cased code for individual GUCs */
        if (TailMatches2("DateStyle", "TO|="))
@@ -3273,21 +3278,29 @@ psql_completion(const char *text, int start, int end)
            /* generic, type based, GUC support */
            char       *guctype = get_guctype(prev2_wd);
 
-           if (guctype && strcmp(guctype, "enum") == 0)
+           /*
+            * Note: if we don't recognize the GUC name, it's important to not
+            * offer any completions, as most likely we've misinterpreted the
+            * context and this isn't a GUC-setting command at all.
+            */
+           if (guctype)
            {
-               char        querybuf[1024];
+               if (strcmp(guctype, "enum") == 0)
+               {
+                   char        querybuf[1024];
 
-               snprintf(querybuf, sizeof(querybuf), Query_for_enum, prev2_wd);
-               COMPLETE_WITH_QUERY(querybuf);
-           }
-           else if (guctype && strcmp(guctype, "bool") == 0)
-               COMPLETE_WITH_LIST9("on", "off", "true", "false", "yes", "no",
-                                   "1", "0", "DEFAULT");
-           else
-               COMPLETE_WITH_CONST("DEFAULT");
+                   snprintf(querybuf, sizeof(querybuf),
+                            Query_for_enum, prev2_wd);
+                   COMPLETE_WITH_QUERY(querybuf);
+               }
+               else if (strcmp(guctype, "bool") == 0)
+                   COMPLETE_WITH_LIST9("on", "off", "true", "false",
+                                       "yes", "no", "1", "0", "DEFAULT");
+               else
+                   COMPLETE_WITH_CONST("DEFAULT");
 
-           if (guctype)
                free(guctype);
+           }
        }
    }