Support remaining functions in protobuf serialization, add expr_fn for StructFunction (#8100)

* working fix for #8098

* Added enum match for StringToArray

* Added enum match for StructFun as well as mapping to a supporting scalar function

* cargo fmt

---------

Co-authored-by: Jacob Ogle <jacob@ghst.local>

Author: JacobOgle

datafusion/expr/src/expr_fn.rs

@@ -871,6 +871,13 @@ scalar_expr!(
 
 scalar_expr!(ArrowTypeof, arrow_typeof, val, "data type");
 
+scalar_expr!(
+    Struct,
+    struct_fun,
+    val,
+    "returns a vector of fields from the struct"
+);
+
 /// Create a CASE WHEN statement with literal WHEN expressions for comparison to the base expression.
 pub fn case(expr: Expr) -> CaseBuilder {
     CaseBuilder::new(Some(Box::new(expr)), vec![], vec![], None)

datafusion/proto/src/logical_plan/from_proto.rs

@@ -43,19 +43,20 @@ use datafusion_expr::{
     array_has, array_has_all, array_has_any, array_length, array_ndims, array_position,
     array_positions, array_prepend, array_remove, array_remove_all, array_remove_n,
     array_repeat, array_replace, array_replace_all, array_replace_n, array_slice,
-    array_to_string, ascii, asin, asinh, atan, atan2, atanh, bit_length, btrim,
-    cardinality, cbrt, ceil, character_length, chr, coalesce, concat_expr,
+    array_to_string, arrow_typeof, ascii, asin, asinh, atan, atan2, atanh, bit_length,
+    btrim, cardinality, cbrt, ceil, character_length, chr, coalesce, concat_expr,
     concat_ws_expr, cos, cosh, cot, current_date, current_time, date_bin, date_part,
     date_trunc, decode, degrees, digest, encode, exp,
     expr::{self, InList, Sort, WindowFunction},
-    factorial, floor, from_unixtime, gcd, isnan, iszero, lcm, left, ln, log, log10, log2,
+    factorial, flatten, floor, from_unixtime, gcd, isnan, iszero, lcm, left, ln, log,
+    log10, log2,
     logical_plan::{PlanType, StringifiedPlan},
     lower, lpad, ltrim, md5, nanvl, now, nullif, octet_length, pi, power, radians,
     random, regexp_match, regexp_replace, repeat, replace, reverse, right, round, rpad,
     rtrim, sha224, sha256, sha384, sha512, signum, sin, sinh, split_part, sqrt,
-    starts_with, strpos, substr, substring, tan, tanh, to_hex, to_timestamp_micros,
-    to_timestamp_millis, to_timestamp_nanos, to_timestamp_seconds, translate, trim,
-    trunc, upper, uuid,
+    starts_with, string_to_array, strpos, struct_fun, substr, substring, tan, tanh,
+    to_hex, to_timestamp_micros, to_timestamp_millis, to_timestamp_nanos,
+    to_timestamp_seconds, translate, trim, trunc, upper, uuid,
     window_frame::regularize,
     AggregateFunction, Between, BinaryExpr, BuiltInWindowFunction, BuiltinScalarFunction,
     Case, Cast, Expr, GetFieldAccess, GetIndexedField, GroupingSet,
@@ -1645,9 +1646,21 @@ pub fn parse_expr(
                 )),
                 ScalarFunction::Isnan => Ok(isnan(parse_expr(&args[0], registry)?)),
                 ScalarFunction::Iszero => Ok(iszero(parse_expr(&args[0], registry)?)),
-                _ => Err(proto_error(
-                    "Protobuf deserialization error: Unsupported scalar function",
+                ScalarFunction::ArrowTypeof => {
+                    Ok(arrow_typeof(parse_expr(&args[0], registry)?))
+                }
+                ScalarFunction::ToTimestamp => {
+                    Ok(to_timestamp_seconds(parse_expr(&args[0], registry)?))
+                }
+                ScalarFunction::Flatten => Ok(flatten(parse_expr(&args[0], registry)?)),
+                ScalarFunction::StringToArray => Ok(string_to_array(
+                    parse_expr(&args[0], registry)?,
+                    parse_expr(&args[1], registry)?,
+                    parse_expr(&args[2], registry)?,
                 )),
+                ScalarFunction::StructFun => {
+                    Ok(struct_fun(parse_expr(&args[0], registry)?))
+                }
             }
         }
         ExprType::ScalarUdfExpr(protobuf::ScalarUdfExprNode { fun_name, args }) => {