Support relation visitor to visit the Option field

derive/README.md

@@ -151,6 +151,55 @@ visitor.post_visit_expr(<is null operand>)
 visitor.post_visit_expr(<is null expr>)
 ```
 
+If the field is a `Option` and add `#[with = "visit_xxx"]` to the field, the generated code
+will try to access the field only if it is `Some`:
+
+```rust
+#[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
+pub struct ShowStatementIn {
+    pub clause: ShowStatementInClause,
+    pub parent_type: Option<ShowStatementInParentType>,
+    #[cfg_attr(feature = "visitor", visit(with = "visit_relation"))]
+    pub parent_name: Option<ObjectName>,
+}
+```
+
+This will generate
+
+```rust
+impl sqlparser::ast::Visit for ShowStatementIn {
+    fn visit<V: sqlparser::ast::Visitor>(
+        &self,
+        visitor: &mut V,
+    ) -> ::std::ops::ControlFlow<V::Break> {
+        sqlparser::ast::Visit::visit(&self.clause, visitor)?;
+        sqlparser::ast::Visit::visit(&self.parent_type, visitor)?;
+        if let Some(value) = &self.parent_name {
+            visitor.pre_visit_relation(value)?;
+            sqlparser::ast::Visit::visit(value, visitor)?;
+            visitor.post_visit_relation(value)?;
+        }
+        ::std::ops::ControlFlow::Continue(())
+    }
+}
+
+impl sqlparser::ast::VisitMut for ShowStatementIn {
+    fn visit<V: sqlparser::ast::VisitorMut>(
+        &mut self,
+        visitor: &mut V,
+    ) -> ::std::ops::ControlFlow<V::Break> {
+        sqlparser::ast::VisitMut::visit(&mut self.clause, visitor)?;
+        sqlparser::ast::VisitMut::visit(&mut self.parent_type, visitor)?;
+        if let Some(value) = &mut self.parent_name {
+            visitor.pre_visit_relation(value)?;
+            sqlparser::ast::VisitMut::visit(value, visitor)?;
+            visitor.post_visit_relation(value)?;
+        }
+        ::std::ops::ControlFlow::Continue(())
+    }
+}
+```
+
 ## Releasing
 
 This crate's release is not automated. Instead it is released manually as needed

derive/src/lib.rs

@@ -18,11 +18,8 @@
 use proc_macro2::TokenStream;
 use quote::{format_ident, quote, quote_spanned, ToTokens};
 use syn::spanned::Spanned;
-use syn::{
-    parse::{Parse, ParseStream},
-    parse_macro_input, parse_quote, Attribute, Data, DeriveInput, Fields, GenericParam, Generics,
-    Ident, Index, LitStr, Meta, Token,
-};
+use syn::{parse::{Parse, ParseStream}, parse_macro_input, parse_quote, Attribute, Data, DeriveInput, Fields, GenericParam, Generics, Ident, Index, LitStr, Meta, Token, Type, TypePath};
+use syn::{Path, PathArguments};
 
 /// Implementation of `[#derive(Visit)]`
 #[proc_macro_derive(VisitMut, attributes(visit))]
@@ -182,9 +179,21 @@ fn visit_children(
             Fields::Named(fields) => {
                 let recurse = fields.named.iter().map(|f| {
                     let name = &f.ident;
+                    let is_option = is_option(&f.ty);
                     let attributes = Attributes::parse(&f.attrs);
-                    let (pre_visit, post_visit) = attributes.visit(quote!(&#modifier self.#name));
-                    quote_spanned!(f.span() => #pre_visit sqlparser::ast::#visit_trait::visit(&#modifier self.#name, visitor)?; #post_visit)
+                    if is_option && attributes.with.is_some() {
+                        let (pre_visit, post_visit) = attributes.visit(quote!(value));
+                        quote_spanned!(f.span() =>
+                            if let Some(value) = &#modifier self.#name {
+                                #pre_visit sqlparser::ast::#visit_trait::visit(value, visitor)?; #post_visit
+                            }
+                        )
+                    } else {
+                        let (pre_visit, post_visit) = attributes.visit(quote!(&#modifier self.#name));
+                        quote_spanned!(f.span() =>
+                            #pre_visit sqlparser::ast::#visit_trait::visit(&#modifier self.#name, visitor)?; #post_visit
+                        )
+                    }
                 });
                 quote! {
                     #(#recurse)*
@@ -256,3 +265,16 @@ fn visit_children(
         Data::Union(_) => unimplemented!(),
     }
 }
+
+fn is_option(ty: &Type) -> bool {
+    if let Type::Path(TypePath { path: Path { segments, .. }, .. }) = ty {
+        if let Some(segment) = segments.last() {
+            if segment.ident == "Option" {
+                if let PathArguments::AngleBracketed(args) = &segment.arguments {
+                    return args.args.len() == 1;
+                }
+            }
+        }
+    }
+    false
+}

src/ast/mod.rs

@@ -7653,6 +7653,7 @@ impl fmt::Display for ShowStatementInParentType {
 pub struct ShowStatementIn {
     pub clause: ShowStatementInClause,
     pub parent_type: Option<ShowStatementInParentType>,
+    #[cfg_attr(feature = "visitor", visit(with = "visit_relation"))]
     pub parent_name: Option<ObjectName>,
 }
 

src/ast/visitor.rs

@@ -876,7 +876,16 @@ mod tests {
                     "POST: QUERY: SELECT * FROM monthly_sales PIVOT(SUM(a.amount) FOR a.MONTH IN ('JAN', 'FEB', 'MAR', 'APR')) AS p (c, d) ORDER BY EMPID",
                     "POST: STATEMENT: SELECT * FROM monthly_sales PIVOT(SUM(a.amount) FOR a.MONTH IN ('JAN', 'FEB', 'MAR', 'APR')) AS p (c, d) ORDER BY EMPID",
                 ]
-            )
+            ),
+            (
+                "SHOW COLUMNS FROM t1",
+                vec![
+                    "PRE: STATEMENT: SHOW COLUMNS FROM t1",
+                    "PRE: RELATION: t1",
+                    "POST: RELATION: t1",
+                    "POST: STATEMENT: SHOW COLUMNS FROM t1",
+                ],
+            ),
         ];
         for (sql, expected) in tests {
             let actual = do_visit(sql);