Cleanup parsing of use and hide commands (#705)

crates/nu-protocol/src/ast/expression.rs

@@ -1,4 +1,5 @@
 use super::{Expr, Operator, Statement};
+use crate::ast::ImportPattern;
 use crate::{engine::StateWorkingSet, BlockId, Signature, Span, Type, VarId, IN_VARIABLE_ID};
 
 #[derive(Debug, Clone)]
@@ -96,6 +97,13 @@ impl Expression {
         }
     }
 
+    pub fn as_import_pattern(&self) -> Option<ImportPattern> {
+        match &self.expr {
+            Expr::ImportPattern(pattern) => Some(pattern.clone()),
+            _ => None,
+        }
+    }
+
     pub fn has_in_variable(&self, working_set: &StateWorkingSet) -> bool {
         match &self.expr {
             Expr::BinaryOp(left, _, right) => {