Support doubled-quote escaping in Cypher string literals (issue #2222)

SQL drivers (psycopg2, JDBC, etc.) escape single quotes by doubling
them ('isn''t') when substituting parameters into queries. When these
substitutions land inside Cypher's $$ block, the Cypher scanner rejects
them because it only recognizes backslash escaping (\'). This makes it
difficult to pass strings containing apostrophes through SQL drivers.

Add '' and "" as escape sequences in the Cypher scanner, following the
same pattern already used for backtick-quoted identifiers (``). Flex
picks the longer two-character match over the one-character closing
quote, so the change is backwards-compatible -- '' was previously a
syntax error.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: gregfelice

regress/expected/scan.out

@@ -294,6 +294,47 @@ $$) AS t(a agtype, b agtype, c agtype);
  " \" \" ' ' " | " ' ' \" \" " | " / / \\ \b \f \n \r \t "
 (1 row)
 
+-- doubled-quote escape sequences for SQL driver compatibility (issue #2222)
+SELECT * FROM cypher('scan', $$
+RETURN 'isn''t'
+$$) AS t(a agtype);
+    a    
+---------
+ "isn't"
+(1 row)
+
+SELECT * FROM cypher('scan', $$
+RETURN '''hello'
+$$) AS t(a agtype);
+    a     
+----------
+ "'hello"
+(1 row)
+
+SELECT * FROM cypher('scan', $$
+RETURN 'hello'''
+$$) AS t(a agtype);
+    a     
+----------
+ "hello'"
+(1 row)
+
+SELECT * FROM cypher('scan', $$
+RETURN 'it''s a ''test'''
+$$) AS t(a agtype);
+        a        
+-----------------
+ "it's a 'test'"
+(1 row)
+
+SELECT * FROM cypher('scan', $$
+RETURN "she said ""hello"""
+$$) AS t(a agtype);
+          a           
+----------------------
+ "she said \"hello\""
+(1 row)
+
 -- invalid escape sequence
 SELECT * FROM cypher('scan', $$
 RETURN "\a"

regress/sql/scan.sql

@@ -202,6 +202,27 @@ SELECT * FROM cypher('scan', $$
 RETURN " \" \" ' \' ", ' \' \' " \" ', " / \/ \\ \b \f \n \r \t "
 $$) AS t(a agtype, b agtype, c agtype);
 
+-- doubled-quote escape sequences for SQL driver compatibility (issue #2222)
+SELECT * FROM cypher('scan', $$
+RETURN 'isn''t'
+$$) AS t(a agtype);
+
+SELECT * FROM cypher('scan', $$
+RETURN '''hello'
+$$) AS t(a agtype);
+
+SELECT * FROM cypher('scan', $$
+RETURN 'hello'''
+$$) AS t(a agtype);
+
+SELECT * FROM cypher('scan', $$
+RETURN 'it''s a ''test'''
+$$) AS t(a agtype);
+
+SELECT * FROM cypher('scan', $$
+RETURN "she said ""hello"""
+$$) AS t(a agtype);
+
 -- invalid escape sequence
 SELECT * FROM cypher('scan', $$
 RETURN "\a"

src/backend/parser/ag_scanner.l

@@ -195,6 +195,8 @@ dquote        \"
 dqchars       [^"\\]+
 squote        '
 sqchars       [^'\\]+
+esdquote      {dquote}{dquote}
+essquote      {squote}{squote}
 esascii       \\["'/\\bfnrt]
 esasciifail   \\[^Uu]?
 esunicode     \\(U{hexdigit}{8}|u{hexdigit}{4})
@@ -420,6 +422,14 @@ ag_token token;
     strbuf_append_buf(&yyextra.literal_buf, yytext, yyleng);
 }
 
+<dqstr>{esdquote} {
+    strbuf_append_char(&yyextra.literal_buf, '"');
+}
+
+<sqstr>{essquote} {
+    strbuf_append_char(&yyextra.literal_buf, '\'');
+}
+
 <dqstr,sqstr>{esascii} {
     char c;