coprocessor: move 'is_unsigned' to 'FieldTypeAccessor' (tikv#5095)

Signed-off-by: Lonng <heng@lonng.org>

Author: lonng

components/cop_datatype/src/def/field_type.rs

@@ -193,6 +193,11 @@ pub trait FieldTypeAccessor {
     fn is_non_binary_string_like(&self) -> bool {
         self.collation() != Collation::Binary && self.is_string_like()
     }
+
+    /// Whether the flag contains `FieldTypeFlag::UNSIGNED`
+    fn is_unsigned(&self) -> bool {
+        self.flag().contains(FieldTypeFlag::UNSIGNED)
+    }
 }
 
 impl FieldTypeAccessor for FieldType {

src/coprocessor/dag/rpn_expr/impl_cast.rs

@@ -3,7 +3,7 @@
 use std::convert::TryFrom;
 
 use cop_codegen::rpn_fn;
-use cop_datatype::{EvalType, FieldTypeAccessor, FieldTypeFlag};
+use cop_datatype::{EvalType, FieldTypeAccessor};
 use tipb::expression::FieldType;
 
 use crate::coprocessor::codec::data_type::*;
@@ -23,7 +23,7 @@ pub fn get_cast_fn_rpn_node(
     let to = box_try!(EvalType::try_from(to_field_type.tp()));
     let func_meta = match (from, to) {
         (EvalType::Int, EvalType::Decimal) => {
-            if !is_unsigned(from_field_type) && !is_unsigned(&to_field_type) {
+            if !from_field_type.is_unsigned() && !to_field_type.is_unsigned() {
                 cast_int_as_decimal_fn_meta()
             } else {
                 cast_uint_as_decimal_fn_meta()
@@ -47,11 +47,6 @@ pub fn get_cast_fn_rpn_node(
     })
 }
 
-#[inline]
-fn is_unsigned(ft: &FieldType) -> bool {
-    ft.as_accessor().flag().contains(FieldTypeFlag::UNSIGNED)
-}
-
 fn produce_dec_with_specified_tp(
     ctx: &mut EvalContext,
     dec: Decimal,