SQL Parser Derive Macro

Visit

This crate contains a procedural macro that can automatically derive implementations of the Visit trait in the sqlparser crate

```rust

[derive(Visit, VisitMut)]

struct Foo { boolean: bool, bar: Bar, }

[derive(Visit, VisitMut)]

enum Bar { A(), B(String, bool), C { named: i32 }, } ```

Will generate code akin to

```rust impl Visit for Foo { fn visit(&self, visitor: &mut V) -> ControlFlow { self.boolean.visit(visitor)?; self.bar.visit(visitor)?; ControlFlow::Continue(()) } }

impl Visit for Bar { fn visit(&self, visitor: &mut V) -> ControlFlow { match self { Self::A() => {} Self::B(_1, _2) => { _1.visit(visitor)?; _2.visit(visitor)?; } Self::C { named } => { named.visit(visitor)?; } } ControlFlow::Continue(()) } } ```

Additionally certain types may wish to call a corresponding method on visitor before recursing

```rust

[derive(Visit, VisitMut)]

[visit(with = "visit_expr")]

enum Expr { A(), B(String, #[cfgattr(feature = "visitor", visit(with = "visitrelation"))] ObjectName, bool), } ```

Will generate

rust impl Visit for Bar { fn visit<V: Visitor>(&self, visitor: &mut V) -> ControlFlow<V::Break> { visitor.visit_expr(self)?; match self { Self::A() => {} Self::B(_1, _2, _3) => { _1.visit(visitor)?; visitor.visit_relation(_3)?; _2.visit(visitor)?; _3.visit(visitor)?; } } ControlFlow::Continue(()) } }