Feat: allow explicit aliasing in if(...) expressions (#4963)

Author: georgesittas

sqlglot/parser.py

@@ -6164,7 +6164,9 @@ def _parse_case(self) -> t.Optional[exp.Expression]:
 
     def _parse_if(self) -> t.Optional[exp.Expression]:
         if self._match(TokenType.L_PAREN):
-            args = self._parse_csv(self._parse_assignment)
+            args = self._parse_csv(
+                lambda: self._parse_alias(self._parse_assignment(), explicit=True)
+            )
             this = self.validate_expression(exp.If.from_arg_list(args), args)
             self._match_r_paren()
         else:

tests/dialects/test_spark.py

@@ -245,6 +245,7 @@ def test_spark(self):
             "REFRESH TABLE t",
         )
 
+        self.validate_identity("IF(cond, foo AS bar, bla AS baz)")
         self.validate_identity("any_value(col, true)", "ANY_VALUE(col) IGNORE NULLS")
         self.validate_identity("first(col, true)", "FIRST(col) IGNORE NULLS")
         self.validate_identity("first_value(col, true)", "FIRST_VALUE(col) IGNORE NULLS")