Make psql ignore trailing semicolons in \sf, \ef, etc

We had a complaint (see [1], but it's not the first IIRC) about how
psql doesn't behave very nicely if one ends \sf or allied commands
with a semicolon:

regression=# \sf sin(float8);
ERROR:  expected a right parenthesis

This is a bit of a usability gotcha, since many other backslash
commands are forgiving about trailing semicolons.  I looked at
the code and found that it's actually trying to ignore semicolons,
by passing semicolon = true to psql_scan_slash_option.  But that
fails to work because it's also passing type = OT_WHOLE_LINE,
and the whole-line code path ignores the semicolon flag.  Probably
that's just because nobody needed to use that combination back in
the day.  There's another user of OT_WHOLE_LINE, exec_command_help,
which also wants this behavior and has written its own stripping
code to get it.  That seems pretty silly, so here's a quick finger
exercise to move that logic into psql_scan_slash_option.

Is this enough of a bug to deserve back-patching?  I'm not sure.

            regards, tom lane

[1] https://www.postgresql.org/message-id/CAEs%3D6D%3DnwX2wm0hjkaw6C_LnqR%2BNFtnnzbSzeZq-xcfi_ooKSw%40mail.gmail.com

diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 9103bc3465..2f74bfdc96 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -1640,18 +1640,7 @@ exec_command_help(PsqlScanState scan_state, bool active_branch)
     if (active_branch)
     {
         char       *opt = psql_scan_slash_option(scan_state,
-                                                 OT_WHOLE_LINE, NULL, false);
-        size_t        len;
-
-        /* strip any trailing spaces and semicolons */
-        if (opt)
-        {
-            len = strlen(opt);
-            while (len > 0 &&
-                   (isspace((unsigned char) opt[len - 1])
-                    || opt[len - 1] == ';'))
-                opt[--len] = '\0';
-        }
+                                                 OT_WHOLE_LINE, NULL, true);

         helpSQL(opt, pset.popt.topt.pager);
         free(opt);
@@ -3165,6 +3154,10 @@ ignore_slash_filepipe(PsqlScanState scan_state)
  * This *MUST* be used for inactive-branch processing of any slash command
  * that takes an OT_WHOLE_LINE option.  Otherwise we might consume a different
  * amount of option text in active and inactive cases.
+ *
+ * Note: although callers might pass "semicolon" as either true or false,
+ * we need not duplicate that here, since it doesn't affect the amount of
+ * input text consumed.
  */
 static void
 ignore_slash_whole_line(PsqlScanState scan_state)
diff --git a/src/bin/psql/psqlscanslash.l b/src/bin/psql/psqlscanslash.l
index 514977e59d..10a35dffc4 100644
--- a/src/bin/psql/psqlscanslash.l
+++ b/src/bin/psql/psqlscanslash.l
@@ -18,6 +18,8 @@
  */
 #include "postgres_fe.h"

+#include <ctype.h>
+
 #include "common.h"
 #include "psqlscanslash.h"

@@ -640,7 +642,22 @@ psql_scan_slash_option(PsqlScanState state,
             termPQExpBuffer(&mybuf);
             return NULL;
         case xslashwholeline:
-            /* always okay */
+            /*
+             * In whole-line mode, we interpret semicolon = true as stripping
+             * trailing whitespace as well as semi-colons; this gives the
+             * nearest equivalent to what semicolon = true does in normal
+             * mode.  Note there's no concept of quoting in this mode.
+             */
+            if (semicolon)
+            {
+                while (mybuf.len > 0 &&
+                       (mybuf.data[mybuf.len - 1] == ';' ||
+                        (isascii((unsigned char) mybuf.data[mybuf.len - 1]) &&
+                         isspace((unsigned char) mybuf.data[mybuf.len - 1]))))
+                {
+                    mybuf.data[--mybuf.len] = '\0';
+                }
+            }
             break;
         default:
             /* can't get here */
diff --git a/src/test/regress/expected/psql.out b/src/test/regress/expected/psql.out
index 5d61e4c7bb..4f3fd46420 100644
--- a/src/test/regress/expected/psql.out
+++ b/src/test/regress/expected/psql.out
@@ -5323,7 +5323,7 @@ END
          LANGUAGE sql
          IMMUTABLE PARALLEL SAFE STRICT COST 1
 1       RETURN ($2 + $1)
-\sf ts_debug(text)
+\sf ts_debug(text);
 CREATE OR REPLACE FUNCTION pg_catalog.ts_debug(document text, OUT alias text, OUT description text, OUT token text,
OUTdictionaries regdictionary[], OUT dictionary regdictionary, OUT lexemes text[]) 
  RETURNS SETOF record
  LANGUAGE sql
diff --git a/src/test/regress/sql/psql.sql b/src/test/regress/sql/psql.sql
index f199d624d3..c997106b9f 100644
--- a/src/test/regress/sql/psql.sql
+++ b/src/test/regress/sql/psql.sql
@@ -1315,7 +1315,7 @@ drop role regress_psql_user;
 \sf information_schema._pg_index_position
 \sf+ information_schema._pg_index_position
 \sf+ interval_pl_time
-\sf ts_debug(text)
+\sf ts_debug(text);
 \sf+ ts_debug(text)

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