freyja_main! usability improvements (#116)

- re-export the `freyja_common` crate so that users don't need to manually reference it (I tried to do this with `tokio` too but couldn't get it to work)
- add some validation to the macro to ensure you don't write something functionally useless

freyja/src/lib.rs

@@ -2,7 +2,8 @@
 // Licensed under the MIT license.
 // SPDX-License-Identifier: MIT
 
-// Re-export this macro for convenience so users don't need to manually import the proc_macros crate
+// Re-export these items for convenience so users don't need to manually import them
+pub use freyja_common;
 pub use proc_macros::freyja_main;
 
 mod cartographer;

proc_macros/src/freyja_main/generate.rs

@@ -27,7 +27,7 @@ pub(crate) fn generate(ir: FreyjaMainOutput) -> TokenStream {
     quote! {
         #[tokio::main]
         async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
-            use freyja_common::data_adapter::DataAdapterFactory;
+            use freyja::freyja_common::data_adapter::DataAdapterFactory;
             let factories: Vec<Box<dyn DataAdapterFactory + Send + Sync>> = vec![
                 #(Box::new(
                     #data_adapter_factory_types::create_new()

proc_macros/src/freyja_main/parse.rs

@@ -45,7 +45,11 @@ impl Parse for FreyjaMainArgs {
             Punctuated::<Ident, Token![,]>::parse_terminated(&data_adapter_content)
                 .unwrap()
                 .into_iter()
-                .collect();
+                .collect::<Vec<_>>();
+
+        if data_adapter_factory_types.is_empty() {
+            panic!("At least one DataAdapterFactory is required");
+        }
 
         let trailing_comma_result = if !input.is_empty() {
             Some(input.parse::<Token![,]>())
@@ -144,4 +148,15 @@ mod freyja_main_parse_tests {
         let result = catch_unwind(|| parse(input));
         assert!(result.is_err());
     }
+
+    #[test]
+    fn parse_panics_with_empty_factory_list() {
+        let foo_ident = format_ident!("Foo");
+        let bar_ident = format_ident!("Bar");
+        let baz_ident = format_ident!("Baz");
+
+        let input = quote! { #foo_ident, #bar_ident, #baz_ident, [], };
+        let result = catch_unwind(|| parse(input));
+        assert!(result.is_err());
+    }
 }