Add export_keys optional param to native_db macro

This adds an optional `export_keys` bool param to the `native_db` proc macro that controls the visibility of the model's secondary key enum.

Default value is `false`, which matches the existing behaviour of setting the visibility of the secondary key enum to `pub(crate)`. Using `#[native_db(export_keys = true)]` changes this to `pub`.

See vincent-herlemont#220 for discussion.

native_db_macro/src/model_attributes.rs

@@ -1,16 +1,16 @@
 use crate::keys::{KeyDefinition, KeyOptions};
 use crate::struct_name::StructName;
-use proc_macro::Ident;
 use std::collections::HashSet;
 use syn::meta::ParseNestedMeta;
 use syn::parse::Result;
-use syn::Field;
+use syn::{Field, LitBool};
 
 #[derive(Clone)]
 pub(crate) struct ModelAttributes {
     pub(crate) struct_name: StructName,
     pub(crate) primary_key: Option<KeyDefinition<()>>,
     pub(crate) secondary_keys: HashSet<KeyDefinition<KeyOptions>>,
+    pub(crate) do_export_keys: Option<LitBool>,
 }
 
 impl ModelAttributes {
@@ -60,6 +60,8 @@ impl ModelAttributes {
                 Ok(())
             })?;
             self.secondary_keys.insert(key);
+        } else if meta.path.is_ident("export_keys") {
+            self.do_export_keys = Some(meta.value()?.parse()?);
         } else {
             panic!(
                 "Unknown attribute: {}",

native_db_macro/src/model_native_db.rs

@@ -3,7 +3,7 @@ use crate::struct_name::StructName;
 use crate::ToTokenStream;
 use proc_macro::Span;
 use quote::quote;
-use syn::Ident;
+use syn::{Ident};
 
 pub(crate) struct ModelNativeDB {
     struct_name: StructName,
@@ -116,6 +116,21 @@ impl ModelNativeDB {
         Ident::new(&format!("{}Key", struct_name), Span::call_site().into())
     }
 
+    pub(crate) fn keys_enum_visibility(&self) -> proc_macro2::TokenStream {
+        let do_export = match &self.attrs.do_export_keys {
+            Some(do_export_keys) => do_export_keys.value,
+            None => false,
+        };
+
+        let visibility = if do_export {
+            ""
+        } else {
+            "(crate)"
+        };
+
+        format!("pub{}", visibility).parse().unwrap()
+    }
+
     pub(crate) fn secondary_keys_enum(&self) -> Vec<proc_macro2::TokenStream> {
         self.attrs
             .secondary_keys

native_db_macro/src/native_db.rs

@@ -13,6 +13,7 @@ pub fn native_db(args: TokenStream, input: TokenStream) -> TokenStream {
         struct_name: struct_name.clone(),
         primary_key: None,
         secondary_keys: Default::default(),
+        do_export_keys: None,
     };
     let model_attributes_parser = syn::meta::parser(|meta| attrs.parse(meta));
     parse_macro_input!(args with model_attributes_parser);
@@ -33,6 +34,7 @@ pub fn native_db(args: TokenStream, input: TokenStream) -> TokenStream {
     let native_db_gks = model_native_db.native_db_secondary_key();
     let native_db_model = model_native_db.native_db_model();
 
+    let keys_enum_visibility = model_native_db.keys_enum_visibility();
     let keys_enum_name = model_native_db.keys_enum_name();
     let keys_enum = model_native_db.secondary_keys_enum();
     let keys_enum_database_key = model_native_db.keys_enum_database_key();
@@ -56,7 +58,7 @@ pub fn native_db(args: TokenStream, input: TokenStream) -> TokenStream {
             #native_db_gks
         }
 
-        pub(crate) enum #keys_enum_name {
+        #keys_enum_visibility enum #keys_enum_name {
             #(#keys_enum),*
         }
 

src/lib.rs

@@ -386,6 +386,11 @@ doc_comment! {
     include_str!("../README.md")
 }
 
-/// Macro which link [`native_model`](https://crates.io/crates/native_model) to the Native DB. See [`Builder.define`](struct.Builder.html#method.define) for more information.
+/// Macro which link [`native_model`](https://crates.io/crates/native_model) to the Native DB. See
+/// [`Builder.define`](struct.Builder.html#method.define) for more information.
+///
+/// Optional parameter `export_keys` controls whether the model keys enum is visible outside of the
+/// crate, default value is false with visibility limited to `pub(crate)`. Use
+/// `#[native_db(export_keys = true)]` to make enum visible outside of crate (ie. `pub`).
 pub use native_db_macro::*;
 pub use serialization::*;