Make visitor feature no_std-compatible

.github/workflows/rust.yml

@@ -82,6 +82,7 @@ jobs:
         with:
           targets: 'thumbv6m-none-eabi'
       - run: cargo check --no-default-features --target thumbv6m-none-eabi
+      - run: cargo check --no-default-features --features visitor --target thumbv6m-none-eabi
 
   test:
     strategy:

derive/src/visit.rs

@@ -62,11 +62,11 @@ pub(crate) fn derive_visit(
             fn visit<V: sqlparser::ast::#visitor_trait>(
                 &#modifier self,
                 visitor: &mut V
-            ) -> ::std::ops::ControlFlow<V::Break> {
+            ) -> ::core::ops::ControlFlow<V::Break> {
                 #pre_visit
                 #children
                 #post_visit
-                ::std::ops::ControlFlow::Continue(())
+                ::core::ops::ControlFlow::Continue(())
             }
         }
     };

src/ast/visitor.rs

@@ -17,9 +17,12 @@
 
 //! Recursive visitors for ast Nodes. See [`Visitor`] for more details.
 
-use crate::ast::{Expr, ObjectName, Query, Select, Statement, TableFactor, ValueWithSpan};
+#[cfg(not(feature = "std"))]
+use alloc::{boxed::Box, string::String, vec::Vec};
 use core::ops::ControlFlow;
 
+use crate::ast::{Expr, ObjectName, Query, Select, Statement, TableFactor, ValueWithSpan};
+
 /// A type that can be visited by a [`Visitor`]. See [`Visitor`] for
 /// recursively visiting parsed SQL statements.
 ///