Clean up psql's behavior for a few more control variables.

Modify FETCH_COUNT to always have a defined value, like other control
variables, mainly so it will always appear in "\set" output.

Add hooks to force HISTSIZE to be defined and require it to have an
integer value.  (I don't see any point in allowing it to be set to
non-integral values.)

Add hooks to force IGNOREEOF to be defined and require it to have an
integer value.  Unlike the other cases, here we're trying to be
bug-compatible with a rather bogus externally-defined behavior, so I think
we need to continue to allow "\set IGNOREEOF whatever".  Fix it so that
the substitution hook silently replace non-numeric values with "10",
so that the stored value always reflects what we're really doing.

Add a dummy assign hook for HISTFILE, just so it's always in
variables.c's list.  We can't require it to be defined always, because
that would break the interaction with the PSQL_HISTORY environment
variable, so there isn't any change in visible behavior here.

Remove tab-complete.c's private list of known variable names, since that's
really a maintenance nuisance.  Given the preceding changes, there are no
control variables it won't show anyway.  This does mean that if for some
reason you've unset one of the status variables (DBNAME, HOST, etc), that
variable would not appear in tab completion for \set.  But I think that's
fine, for at least two reasons: we shouldn't be encouraging people to use
those variables as regular variables, and if someone does do so anyway,
why shouldn't it act just like a regular variable?

Remove ugly and no-longer-used-anywhere GetVariableNum().  In general,
future additions of integer-valued control variables should follow the
paradigm of adding an assign hook using ParseVariableNum(), so there's
no reason to expect we'd need this again later.

Discussion: https://postgr.es/m/17516.1485973973@sss.pgh.pa.us

doc/src/sgml/ref/psql-ref.sgml

@@ -3247,12 +3247,6 @@ bar
         fail after having already displayed some rows.
         </para>
 
-        <para>
-        <varname>FETCH_COUNT</varname> is ignored if it is unset or does not
-        have a positive value.  It cannot be set to a value that is not
-        syntactically an integer.
-        </para>
-
         <tip>
         <para>
         Although you can use any output format with this feature,
@@ -3316,10 +3310,8 @@ bar
         <term><varname>HISTSIZE</varname></term>
         <listitem>
         <para>
-        The maximum number of commands to store in the command history.
-        If unset, at most 500 commands are stored by default.
-        If set to a value that is negative or not an integer, no limit is
-        applied.
+        The maximum number of commands to store in the command history
+        (default 500).  If set to a negative value, no limit is applied.
         </para>
         <note>
         <para>
@@ -3345,13 +3337,13 @@ bar
         <term><varname>IGNOREEOF</varname></term>
         <listitem>
         <para>
-         If unset, sending an <acronym>EOF</> character (usually
+         If set to 1 or less, sending an <acronym>EOF</> character (usually
          <keycombo action="simul"><keycap>Control</><keycap>D</></>)
          to an interactive session of <application>psql</application>
-         will terminate the application. If set to a numeric value,
-         that many <acronym>EOF</> characters are ignored before the
-         application terminates.  If the variable is set but not to a
-         numeric value, the default is 10.
+         will terminate the application.  If set to a larger numeric value,
+         that many consecutive <acronym>EOF</> characters must be typed to
+         make an interactive session terminate.  If the variable is set to a
+         non-numeric value, it is interpreted as 10.
         </para>
         <note>
         <para>

src/bin/psql/help.c

@@ -348,9 +348,9 @@ helpVariables(unsigned short int pager)
 					  "                     (default: 0=unlimited)\n"));
 	fprintf(output, _("  HISTCONTROL        controls command history [ignorespace, ignoredups, ignoreboth]\n"));
 	fprintf(output, _("  HISTFILE           file name used to store the command history\n"));
-	fprintf(output, _("  HISTSIZE           the number of commands to store in the command history\n"));
+	fprintf(output, _("  HISTSIZE           max number of commands to store in the command history\n"));
 	fprintf(output, _("  HOST               the currently connected database server host\n"));
-	fprintf(output, _("  IGNOREEOF          if unset, sending an EOF to interactive session terminates application\n"));
+	fprintf(output, _("  IGNOREEOF          number of EOFs needed to terminate an interactive session\n"));
 	fprintf(output, _("  LASTOID            value of the last affected OID\n"));
 	fprintf(output, _("  ON_ERROR_ROLLBACK  if set, an error doesn't stop a transaction (uses implicit savepoints)\n"));
 	fprintf(output, _("  ON_ERROR_STOP      stop batch execution after error\n"));

src/bin/psql/input.c

@@ -539,10 +539,7 @@ finishInput(void)
 #ifdef USE_READLINE
 	if (useHistory && psql_history)
 	{
-		int			hist_size;
-
-		hist_size = GetVariableNum(pset.vars, "HISTSIZE", 500, -1);
-		(void) saveHistory(psql_history, hist_size);
+		(void) saveHistory(psql_history, pset.histsize);
 		free(psql_history);
 		psql_history = NULL;
 	}

src/bin/psql/mainloop.c

@@ -162,7 +162,7 @@ MainLoop(FILE *source)
 				/* This tries to mimic bash's IGNOREEOF feature. */
 				count_eof++;
 
-				if (count_eof < GetVariableNum(pset.vars, "IGNOREEOF", 0, 10))
+				if (count_eof < pset.ignoreeof)
 				{
 					if (!pset.quiet)
 						printf(_("Use \"\\q\" to leave %s.\n"), pset.progname);

src/bin/psql/settings.h

@@ -125,6 +125,8 @@ typedef struct _psqlSettings
 	bool		singleline;
 	bool		singlestep;
 	int			fetch_count;
+	int			histsize;
+	int			ignoreeof;
 	PSQL_ECHO	echo;
 	PSQL_ECHO_HIDDEN echo_hidden;
 	PSQL_ERROR_ROLLBACK on_error_rollback;

src/bin/psql/startup.c

@@ -774,6 +774,11 @@ showVersion(void)
  * Substitute hooks and assign hooks for psql variables.
  *
  * This isn't an amazingly good place for them, but neither is anywhere else.
+ *
+ * By policy, every special variable that controls any psql behavior should
+ * have one or both hooks, even if they're just no-ops.  This ensures that
+ * the variable will remain present in variables.c's list even when unset,
+ * which ensures that it's known to tab completion.
  */
 
 static char *
@@ -823,16 +828,71 @@ singlestep_hook(const char *newval)
 	return ParseVariableBool(newval, "SINGLESTEP", &pset.singlestep);
 }
 
+static char *
+fetch_count_substitute_hook(char *newval)
+{
+	if (newval == NULL)
+		newval = pg_strdup("0");
+	return newval;
+}
+
 static bool
 fetch_count_hook(const char *newval)
 {
-	if (newval == NULL)
-		pset.fetch_count = -1;	/* default value */
-	else if (!ParseVariableNum(newval, "FETCH_COUNT", &pset.fetch_count))
-		return false;
+	return ParseVariableNum(newval, "FETCH_COUNT", &pset.fetch_count);
+}
+
+static bool
+histfile_hook(const char *newval)
+{
+	/*
+	 * Someday we might try to validate the filename, but for now, this is
+	 * just a placeholder to ensure HISTFILE is known to tab completion.
+	 */
 	return true;
 }
 
+static char *
+histsize_substitute_hook(char *newval)
+{
+	if (newval == NULL)
+		newval = pg_strdup("500");
+	return newval;
+}
+
+static bool
+histsize_hook(const char *newval)
+{
+	return ParseVariableNum(newval, "HISTSIZE", &pset.histsize);
+}
+
+static char *
+ignoreeof_substitute_hook(char *newval)
+{
+	int			dummy;
+
+	/*
+	 * This tries to mimic the behavior of bash, to wit "If set, the value is
+	 * the number of consecutive EOF characters which must be typed as the
+	 * first characters on an input line before bash exits.  If the variable
+	 * exists but does not have a numeric value, or has no value, the default
+	 * value is 10.  If it does not exist, EOF signifies the end of input to
+	 * the shell."  Unlike bash, however, we insist on the stored value
+	 * actually being a valid integer.
+	 */
+	if (newval == NULL)
+		newval = pg_strdup("0");
+	else if (!ParseVariableNum(newval, NULL, &dummy))
+		newval = pg_strdup("10");
+	return newval;
+}
+
+static bool
+ignoreeof_hook(const char *newval)
+{
+	return ParseVariableNum(newval, "IGNOREEOF", &pset.ignoreeof);
+}
+
 static char *
 echo_substitute_hook(char *newval)
 {
@@ -1062,8 +1122,17 @@ EstablishVariableSpace(void)
 					 bool_substitute_hook,
 					 singlestep_hook);
 	SetVariableHooks(pset.vars, "FETCH_COUNT",
-					 NULL,
+					 fetch_count_substitute_hook,
 					 fetch_count_hook);
+	SetVariableHooks(pset.vars, "HISTFILE",
+					 NULL,
+					 histfile_hook);
+	SetVariableHooks(pset.vars, "HISTSIZE",
+					 histsize_substitute_hook,
+					 histsize_hook);
+	SetVariableHooks(pset.vars, "IGNOREEOF",
+					 ignoreeof_substitute_hook,
+					 ignoreeof_hook);
 	SetVariableHooks(pset.vars, "ECHO",
 					 echo_substitute_hook,
 					 echo_hook);

src/bin/psql/tab-complete.c

@@ -3775,8 +3775,9 @@ append_variable_names(char ***varnames, int *nvars,
 /*
  * This function supports completion with the name of a psql variable.
  * The variable names can be prefixed and suffixed with additional text
- * to support quoting usages. If need_value is true, only the variables
- * that have the set values are picked up.
+ * to support quoting usages. If need_value is true, only variables
+ * that are currently set are included; otherwise, special variables
+ * (those that have hooks) are included even if currently unset.
  */
 static char **
 complete_from_variables(const char *text, const char *prefix, const char *suffix,
@@ -3789,33 +3790,12 @@ complete_from_variables(const char *text, const char *prefix, const char *suffix
 	int			i;
 	struct _variable *ptr;
 
-	static const char *const known_varnames[] = {
-		"AUTOCOMMIT", "COMP_KEYWORD_CASE", "DBNAME", "ECHO", "ECHO_HIDDEN",
-		"ENCODING", "FETCH_COUNT", "HISTCONTROL", "HISTFILE", "HISTSIZE",
-		"HOST", "IGNOREEOF", "LASTOID", "ON_ERROR_ROLLBACK", "ON_ERROR_STOP",
-		"PORT", "PROMPT1", "PROMPT2", "PROMPT3", "QUIET",
-		"SHOW_CONTEXT", "SINGLELINE", "SINGLESTEP",
-		"USER", "VERBOSITY", NULL
-	};
-
 	varnames = (char **) pg_malloc((maxvars + 1) * sizeof(char *));
 
-	if (!need_value)
-	{
-		for (i = 0; known_varnames[i] && nvars < maxvars; i++)
-			append_variable_names(&varnames, &nvars, &maxvars,
-								  known_varnames[i], prefix, suffix);
-	}
-
 	for (ptr = pset.vars->next; ptr; ptr = ptr->next)
 	{
 		if (need_value && !(ptr->value))
 			continue;
-		for (i = 0; known_varnames[i]; i++)		/* remove duplicate entry */
-		{
-			if (strcmp(ptr->name, known_varnames[i]) == 0)
-				continue;
-		}
 		append_variable_names(&varnames, &nvars, &maxvars, ptr->name,
 							  prefix, suffix);
 	}

src/bin/psql/variables.c

@@ -179,31 +179,6 @@ ParseVariableNum(const char *value, const char *name, int *result)
 	}
 }
 
-/*
- * Read integer value of the numeric variable named "name".
- *
- * Return defaultval if it is not set, or faultval if its value is not a
- * valid integer.  (No error message is issued.)
- */
-int
-GetVariableNum(VariableSpace space,
-			   const char *name,
-			   int defaultval,
-			   int faultval)
-{
-	const char *val;
-	int			result;
-
-	val = GetVariable(space, name);
-	if (!val)
-		return defaultval;
-
-	if (ParseVariableNum(val, NULL, &result))
-		return result;
-	else
-		return faultval;
-}
-
 /*
  * Print values of all variables.
  */

src/bin/psql/variables.h

@@ -81,11 +81,6 @@ bool ParseVariableBool(const char *value, const char *name,
 bool ParseVariableNum(const char *value, const char *name,
 				 int *result);
 
-int GetVariableNum(VariableSpace space,
-			   const char *name,
-			   int defaultval,
-			   int faultval);
-
 void		PrintVariables(VariableSpace space);
 
 bool		SetVariable(VariableSpace space, const char *name, const char *value);