Support empty double-quoted string in SQL object body

contrib/babelfishpg_tsql/src/tsqlIface.cpp

@@ -3347,6 +3347,24 @@ class tsqlMutator : public TSqlParserBaseListener
 		}
 	}
 
+	void enterChar_string(TSqlParser::Char_stringContext *ctx) override
+	{
+		std::string str = getFullText(ctx);
+		if ((str.front() == '"') && (str.back() == '"') && (str.length() == 2))
+		{
+			// This means we have a double-quoted empty, zero-length string. The PG equivalent is a zero-length 
+			// single-quoted string.
+			// Whenever we reference a double-quoted empty string inside the body of a T-SQL procedure, function or trigger,
+			// this is passed onto the PG backend where PG interprets double-quoted items as delimited identifiers. 
+			// However those cannot be zero-length, so an error is then raised.
+			// By changing any double-quoted empty string to a single-quoted empty string we address this use case here.
+			// This also addresses any references outside those objects; those would otherwise have been rewritten as a
+			// single-quoted string by rewriteDoubleQuotedString() in the exitChar_string() functions, but doing it 
+			// here preempts that and removes potential complexity from the rewriting in the mutator. 
+			stream.setText(ctx->start->getStartIndex(), "''");	
+		}		
+	}
+
 	// NB: similar code is in tsqlBuilder
 	void exitChar_string(TSqlParser::Char_stringContext *ctx) override
 	{

test/JDBC/expected/empty_dq_string_in_object-vu-cleanup.out

@@ -0,0 +1,58 @@
+drop table t1_empty_dq_string
+go
+drop table t2_empty_dq_string
+go
+drop table t3_empty_dq_string
+go
+drop table t4_empty_dq_string
+go
+drop table t5_empty_dq_string
+go
+drop table t6_empty_dq_string
+go
+drop table t7_empty_dq_string
+go
+drop procedure p1_empty_dq_string
+go
+drop function f1_empty_dq_string
+go
+drop procedure p2_empty_dq_string
+go
+drop function f2_empty_dq_string
+go
+drop procedure p2a_empty_dq_string
+go
+drop function f2a_empty_dq_string
+go
+drop procedure p2b_empty_dq_string
+go
+drop procedure p3_empty_dq_string
+go
+drop procedure p4_empty_dq_string
+go
+drop function f4_empty_dq_string
+go
+drop procedure p5_empty_dq_string
+go
+drop function f5_empty_dq_string
+go
+drop procedure p6_empty_dq_string
+go
+drop procedure p7_empty_dq_string
+go
+drop procedure p7a_empty_dq_string
+go
+drop procedure p7b_empty_dq_string
+go
+drop function f7b_empty_dq_string
+go
+drop procedure p7c_empty_dq_string
+go
+set quoted_identifier on
+go
+drop table "t8_empty_dq_string"
+go
+drop procedure "p8_empty_dq_string"
+go
+drop function "f8_empty_dq_string"
+go

test/JDBC/expected/empty_dq_string_in_object-vu-prepare.out

@@ -0,0 +1,31 @@
+create table t1_empty_dq_string(a int)
+go
+create table t2_empty_dq_string(a int)
+go
+create table t3_empty_dq_string(a int)
+go
+create table t4_empty_dq_string(a int)
+go
+create table t5_empty_dq_string(a int, b varchar(10))
+insert t5_empty_dq_string values(1, 'test 1')
+go
+~~ROW COUNT: 1~~
+
+create table t6_empty_dq_string(a int, b varchar(10))
+insert t6_empty_dq_string values(1, 'test 1')
+go
+~~ROW COUNT: 1~~
+
+create table t7_empty_dq_string(a int, b varchar(10))
+insert t7_empty_dq_string values(1, 'test 1')
+go
+~~ROW COUNT: 1~~
+
+
+set quoted_identifier on
+go
+create table "t8_empty_dq_string"("a" int, "b" varchar(10))
+insert "t8_empty_dq_string" values(1, 'test 1')
+go
+~~ROW COUNT: 1~~
+