Remove operator_precedence_warning.

This GUC was always intended as a temporary solution to help with
finding 9.4-to-9.5 migration issues.  Now that all pre-9.5 branches
are out of support, and 9.5 will be too before v14 is released,
it seems like it's okay to drop it.  Doing so allows removal of
several hundred lines of poorly-tested code in parse_expr.c,
which have been a fertile source of bugs when people did use this.

Discussion: https://postgr.es/m/2234320.1607117945@sss.pgh.pa.us

doc/src/sgml/config.sgml

@@ -9389,29 +9389,6 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
-     <varlistentry id="guc-operator-precedence-warning" xreflabel="operator_precedence_warning">
-      <term><varname>operator_precedence_warning</varname> (<type>boolean</type>)
-      <indexterm>
-       <primary><varname>operator_precedence_warning</varname> configuration parameter</primary>
-      </indexterm>
-      </term>
-      <listitem>
-       <para>
-        When on, the parser will emit a warning for any construct that might
-        have changed meanings since <productname>PostgreSQL</productname> 9.4 as a result
-        of changes in operator precedence.  This is useful for auditing
-        applications to see if precedence changes have broken anything; but it
-        is not meant to be kept turned on in production, since it will warn
-        about some perfectly valid, standard-compliant SQL code.
-        The default is <literal>off</literal>.
-       </para>
-
-       <para>
-        See <xref linkend="sql-precedence"/> for more information.
-       </para>
-      </listitem>
-     </varlistentry>
-
     <varlistentry id="guc-quote-all-identifiers" xreflabel="quote-all-identifiers">
       <term><varname>quote_all_identifiers</varname> (<type>boolean</type>)
       <indexterm>

doc/src/sgml/syntax.sgml

@@ -1121,11 +1121,7 @@ SELECT 3 OPERATOR(pg_catalog.+) 4;
      cases, these changes will result in no behavioral change, or perhaps
      in <quote>no such operator</quote> failures which can be resolved by adding
      parentheses.  However there are corner cases in which a query might
-     change behavior without any parsing error being reported.  If you are
-     concerned about whether these changes have silently broken something,
-     you can test your application with the configuration
-     parameter <xref linkend="guc-operator-precedence-warning"/> turned on
-     to see if any warnings are logged.
+     change behavior without any parsing error being reported.
     </para>
    </note>
   </sect2>

src/backend/nodes/outfuncs.c

@@ -3264,9 +3264,6 @@ _outAExpr(StringInfo str, const A_Expr *node)
 			appendStringInfoString(str, " NOT_BETWEEN_SYM ");
 			WRITE_NODE_FIELD(name);
 			break;
-		case AEXPR_PAREN:
-			appendStringInfoString(str, " PAREN");
-			break;
 		default:
 			appendStringInfoString(str, " ??");
 			break;

src/backend/parser/gram.y

@@ -59,7 +59,6 @@
 #include "nodes/nodeFuncs.h"
 #include "parser/gramparse.h"
 #include "parser/parser.h"
-#include "parser/parse_expr.h"
 #include "storage/lmgr.h"
 #include "utils/date.h"
 #include "utils/datetime.h"
@@ -13461,28 +13460,6 @@ c_expr:		columnref								{ $$ = $1; }
 						n->indirection = check_indirection($4, yyscanner);
 						$$ = (Node *)n;
 					}
-					else if (operator_precedence_warning)
-					{
-						/*
-						 * If precedence warnings are enabled, insert
-						 * AEXPR_PAREN nodes wrapping all explicitly
-						 * parenthesized subexpressions; this prevents bogus
-						 * warnings from being issued when the ordering has
-						 * been forced by parentheses.  Take care that an
-						 * AEXPR_PAREN node has the same exprLocation as its
-						 * child, so as not to cause surprising changes in
-						 * error cursor positioning.
-						 *
-						 * In principle we should not be relying on a GUC to
-						 * decide whether to insert AEXPR_PAREN nodes.
-						 * However, since they have no effect except to
-						 * suppress warnings, it's probably safe enough; and
-						 * we'd just as soon not waste cycles on dummy parse
-						 * nodes if we don't have to.
-						 */
-						$$ = (Node *) makeA_Expr(AEXPR_PAREN, NIL, $2, NULL,
-												 exprLocation($2));
-					}
 					else
 						$$ = $2;
 				}
@@ -16516,16 +16493,10 @@ doNegateFloat(Value *v)
 static Node *
 makeAndExpr(Node *lexpr, Node *rexpr, int location)
 {
-	Node	   *lexp = lexpr;
-
-	/* Look through AEXPR_PAREN nodes so they don't affect flattening */
-	while (IsA(lexp, A_Expr) &&
-		   ((A_Expr *) lexp)->kind == AEXPR_PAREN)
-		lexp = ((A_Expr *) lexp)->lexpr;
 	/* Flatten "a AND b AND c ..." to a single BoolExpr on sight */
-	if (IsA(lexp, BoolExpr))
+	if (IsA(lexpr, BoolExpr))
 	{
-		BoolExpr *blexpr = (BoolExpr *) lexp;
+		BoolExpr *blexpr = (BoolExpr *) lexpr;
 
 		if (blexpr->boolop == AND_EXPR)
 		{
@@ -16539,16 +16510,10 @@ makeAndExpr(Node *lexpr, Node *rexpr, int location)
 static Node *
 makeOrExpr(Node *lexpr, Node *rexpr, int location)
 {
-	Node	   *lexp = lexpr;
-
-	/* Look through AEXPR_PAREN nodes so they don't affect flattening */
-	while (IsA(lexp, A_Expr) &&
-		   ((A_Expr *) lexp)->kind == AEXPR_PAREN)
-		lexp = ((A_Expr *) lexp)->lexpr;
 	/* Flatten "a OR b OR c ..." to a single BoolExpr on sight */
-	if (IsA(lexp, BoolExpr))
+	if (IsA(lexpr, BoolExpr))
 	{
-		BoolExpr *blexpr = (BoolExpr *) lexp;
+		BoolExpr *blexpr = (BoolExpr *) lexpr;
 
 		if (blexpr->boolop == OR_EXPR)
 		{

src/backend/parser/parse_target.c

@@ -1755,11 +1755,6 @@ FigureColnameInternal(Node *node, char **name)
 				*name = "nullif";
 				return 2;
 			}
-			if (((A_Expr *) node)->kind == AEXPR_PAREN)
-			{
-				/* look through dummy parenthesis node */
-				return FigureColnameInternal(((A_Expr *) node)->lexpr, name);
-			}
 			break;
 		case T_TypeCast:
 			strength = FigureColnameInternal(((TypeCast *) node)->arg,

src/backend/utils/misc/guc.c

@@ -1878,16 +1878,6 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
-	{
-		{"operator_precedence_warning", PGC_USERSET, COMPAT_OPTIONS_PREVIOUS,
-			gettext_noop("Emit a warning for constructs that changed meaning since PostgreSQL 9.4."),
-			NULL,
-		},
-		&operator_precedence_warning,
-		false,
-		NULL, NULL, NULL
-	},
-
 	{
 		{"quote_all_identifiers", PGC_USERSET, COMPAT_OPTIONS_PREVIOUS,
 			gettext_noop("When generating SQL fragments, quote all identifiers."),

src/backend/utils/misc/postgresql.conf.sample

@@ -740,7 +740,6 @@
 #backslash_quote = safe_encoding	# on, off, or safe_encoding
 #escape_string_warning = on
 #lo_compat_privileges = off
-#operator_precedence_warning = off
 #quote_all_identifiers = off
 #standard_conforming_strings = on
 #synchronize_seqscans = on

src/include/nodes/parsenodes.h

@@ -265,8 +265,7 @@ typedef enum A_Expr_Kind
 	AEXPR_BETWEEN,				/* name must be "BETWEEN" */
 	AEXPR_NOT_BETWEEN,			/* name must be "NOT BETWEEN" */
 	AEXPR_BETWEEN_SYM,			/* name must be "BETWEEN SYMMETRIC" */
-	AEXPR_NOT_BETWEEN_SYM,		/* name must be "NOT BETWEEN SYMMETRIC" */
-	AEXPR_PAREN					/* nameless dummy node for parentheses */
+	AEXPR_NOT_BETWEEN_SYM		/* name must be "NOT BETWEEN SYMMETRIC" */
 } A_Expr_Kind;
 
 typedef struct A_Expr

src/include/parser/parse_expr.h

@@ -16,7 +16,6 @@
 #include "parser/parse_node.h"
 
 /* GUC parameters */
-extern bool operator_precedence_warning;
 extern bool Transform_null_equals;
 
 extern Node *transformExpr(ParseState *pstate, Node *expr, ParseExprKind exprKind);