Add upgrade tests for database level collation (#439)

This commit adds upgrade tests for database level collation. For any collatable default constraint, PG adds EXPLICIT
collate clause for the default string (const node) iff the collation of the attribute is different from the collation of the
datatype stored in pg_type catalog. This is the result of invocation of pg_get_constraintdef() function which finally calls
get_const_expr(). To set the collation of the Const node, it calls get_const_collation() function where explicit COLLATE
clause is added based on the aforementioned condition.

Hence, when we create a database with non-default collation then the collatable columns get collated with the
database level collation (if not mentioned explicitly). But we store the collation of the collatable datatypes as server
level collation which fulfils the condition mentioned above. To solve this issue, we simply enclose the decompiled
DEFAULT expression by PARENTHESIS to avoid invalid syntax.

Extension PR: babelfish-for-postgresql/babelfish_extensions#2919

Task: BABEL-5141
Signed-off-by: Shameem Ahmed <[email protected]>

src/bin/pg_dump/dump_babel_utils.c

@@ -504,8 +504,28 @@ fixTsqlDefaultExpr(Archive *fout, AttrDefInfo *attrDefInfo)
 	char *runtimeErrStr = "'An empty or space-only string cannot be converted into numeric/decimal data type'";
 	char *atttypname;
 
-	if (!isBabelfishDatabase(fout) ||
-		!strstr(source, runtimeErrStr) ||
+	/* 
+	 * We need to re-write the decompiled DEFAULT expression for non-default
+	 * database level collation. Else, pg_dump adds explicit COLLATE clause
+	 * after the DEFAULT expression as well. This creates two explicit
+	 * COLLATE clause during dump -
+	 * 	1. For the column itself
+	 * 	2. For the default expression
+	 * Eg: CREATE TABLE t1(a nvarchar(11) DEFAULT 'default') --> 
+	 * CREATE TABLE t1("a" "sys"."nvarchar" DEFAULT 'default'::"sys"."varchar" COLLATE <non_default_collation> COLLATE <non_default_collation>)
+	 * This is an invalid syntax, hence it will fail during restore.
+	 * Hence we re-write it to:
+	 * CREATE TABLE t1("a" "sys"."nvarchar" DEFAULT ('default'::"sys"."varchar" COLLATE <non_default_collation>) COLLATE <non_default_collation>)
+	 * by adding parenthesis. As adding parenthesis is optional in PG, 
+	 * we update all such default expressions for babelfish
+	 */
+	if (!isBabelfishDatabase(fout))
+		return;
+	attrDefInfo->adef_expr = psprintf("(%s)", source);
+	free(source);
+	source = attrDefInfo->adef_expr;
+
+	if (!strstr(source, runtimeErrStr) ||
 		strstr(source, runtimeErrFunc) ||
 		attrDefInfo->adnum < 1)
 		return;