From 04abbe1adfaeb2d3c257d2ad4fd8e052d7925c46 Mon Sep 17 00:00:00 2001
From: Henson Choi <assam258@gmail.com>
Date: Tue, 8 Sep 2026 11:22:42 +0900
Subject: [PATCH] Return "|" as a single-character token

Row pattern recognition spells pattern alternation with "|", and
row_pattern_alt matches it as the character token '|'.  The lexer,
however, lists "|" in op_chars but not in self, so a "|" standing on
its own arrives as an Op and that production never fires.  PATTERN
(A | B) then fails with "unsupported quantifier".

Add "|" to the self character class, and to the one-character fallback
in the rule for "operator", so that a lone "|" is returned as a
character token.  That stops it from being lexed as an operator, so
restore its use as one: prefix and infix productions in a_expr and
b_expr, an entry in MathOp, and "|" in the precedence declaration for
Op.

This lexer behavior was in the tree as part of SQL/PGQ, which used "|"
for label disjunction, and row pattern alternation has been relying on
it.  SQL/PGQ was reverted in b1f106c80cb, so the change has to be
carried here.
---
 src/backend/parser/gram.y | 11 ++++++++++-
 src/backend/parser/scan.l |  4 ++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 41f46d242fa..3a5fcfc9c81 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -924,7 +924,7 @@ static bool rpr_is_quantifier_token(const char *tok);
 %nonassoc	IDENT PARTITION RANGE ROWS GROUPS PRECEDING FOLLOWING CUBE ROLLUP
 			SET KEYS OBJECT_P SCALAR TO USING VALUE_P WITH WITHOUT PATH
 			AFTER INITIAL_P SEEK PATTERN_P PERMUTE
-%left		Op OPERATOR		/* multi-character ops and user-defined operators */
+%left		Op OPERATOR '|'	/* multi-character ops and user-defined operators */
 %left		'+' '-'
 %left		'*' '/' '%'
 %left		'^'
@@ -15482,6 +15482,10 @@ a_expr:		c_expr									{ $$ = $1; }
 				{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, ">=", $1, $3, @2); }
 			| a_expr NOT_EQUALS a_expr
 				{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "<>", $1, $3, @2); }
+			| '|' a_expr
+				{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "|", NULL, $2, @1); }
+			| a_expr '|' a_expr
+				{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "|", $1, $3, @2); }
 
 			| a_expr qual_Op a_expr				%prec Op
 				{ $$ = (Node *) makeA_Expr(AEXPR_OP, $2, $1, $3, @2); }
@@ -15962,6 +15966,10 @@ b_expr:		c_expr
 				{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, ">=", $1, $3, @2); }
 			| b_expr NOT_EQUALS b_expr
 				{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "<>", $1, $3, @2); }
+			| '|' b_expr
+				{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "|", NULL, $2, @1); }
+			| b_expr '|' b_expr
+				{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "|", $1, $3, @2); }
 			| b_expr qual_Op b_expr				%prec Op
 				{ $$ = (Node *) makeA_Expr(AEXPR_OP, $2, $1, $3, @2); }
 			| qual_Op b_expr					%prec Op
@@ -17627,6 +17635,7 @@ MathOp:		 '+'									{ $$ = "+"; }
 			| LESS_EQUALS							{ $$ = "<="; }
 			| GREATER_EQUALS						{ $$ = ">="; }
 			| NOT_EQUALS							{ $$ = "<>"; }
+			| '|'									{ $$ = "|"; }
 		;
 
 qual_Op:	Op
diff --git a/src/backend/parser/scan.l b/src/backend/parser/scan.l
index 6c162f48342..78654b45ad0 100644
--- a/src/backend/parser/scan.l
+++ b/src/backend/parser/scan.l
@@ -359,7 +359,7 @@ not_equals		"!="
  * If you change either set, adjust the character lists appearing in the
  * rule for "operator"!
  */
-self			[,()\[\].;\:\+\-\*\/\%\^\<\>\=]
+self			[,()\[\].;\:\|\+\-\*\/\%\^\<\>\=]
 op_chars		[\~\!\@\#\^\&\|\`\?\+\-\*\/\%\<\>\=]
 operator		{op_chars}+
 
@@ -930,7 +930,7 @@ other			.
 						 * that the "self" rule would have.
 						 */
 						if (nchars == 1 &&
-							strchr(",()[].;:+-*/%^<>=", yytext[0]))
+							strchr(",()[].;:|+-*/%^<>=", yytext[0]))
 							return yytext[0];
 						/*
 						 * Likewise, if what we have left is two chars, and