Derive macro getting works

terustform-macros/src/lib.rs

@@ -1,6 +1,104 @@
+use quote::quote;
+use syn::spanned::Spanned;
+
+// This macro should only reference items in `terustform::__derive_private`.
+
 #[proc_macro_derive(DataSourceModel)]
-pub fn data_source_model(
-    _input: proc_macro::TokenStream,
-) -> proc_macro::TokenStream {
-    Default::default()
+pub fn data_source_model(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let input = syn::parse_macro_input!(input as syn::DeriveInput);
+    match data_source_model_inner(input) {
+        Ok(ts) => ts.into(),
+        Err(err) => err.into_compile_error().into(),
+    }
+}
+
+fn data_source_model_inner(
+    input: syn::DeriveInput,
+) -> Result<proc_macro2::TokenStream, syn::Error> {
+    let struct_name = input.ident;
+
+    let syn::Data::Struct(data) = input.data else {
+        return Err(syn::Error::new(
+            struct_name.span(),
+            "models must be structs",
+        ));
+    };
+    let syn::Fields::Named(fields) = data.fields else {
+        return Err(syn::Error::new(
+            struct_name.span(),
+            "models must have named fields",
+        ));
+    };
+
+    let terustform = quote!(::terustform::__derive_private);
+
+    let fields = fields
+        .named
+        .into_iter()
+        .map(|field| {
+            let Some(name) = field.ident else {
+                return Err(syn::Error::new(field.span(), "field must be named"));
+            };
+
+            Ok((name, field.ty))
+        })
+        .collect::<Result<Vec<_>, _>>()?;
+
+
+    let field_extractions = fields.iter().map(|(name, ty)| {
+        let name_str = proc_macro2::Literal::string(&name.to_string());
+        quote! {
+            let #terustform::Some(#name) = obj.remove(#name_str) else {
+                return #terustform::Err(
+                    #terustform::Diagnostics::error_string(
+                        format!("Expected property '{}', which was not present", #name_str),
+                    ).with_path(path.clone())
+                );
+            };
+            let #name = <#ty as #terustform::ValueModel>::from_value(
+                #name,
+                &path.append_attribute_name(#terustform::ToOwned::to_owned(#name_str))
+            )?;
+        }
+    });
+    let constructor_fields = fields.iter().map(|(name, _)| quote! { #name, });
+
+    let (impl_generics, type_generics, where_clause) = input.generics.split_for_impl();
+
+    Ok(quote! {
+        #[automatically_derived]
+        impl #impl_generics #terustform::ValueModel
+            for #struct_name #type_generics #where_clause
+        {
+            fn from_value(v: #terustform::Value, path: &#terustform::AttrPath) -> #terustform::DResult<Self> {
+                match v {
+                    #terustform::BaseValue::Unknown => {
+                        return #terustform::Err(#terustform::Diagnostics::with_path(
+                            #terustform::Diagnostics::error_string(#terustform::ToOwned::to_owned("Expected object, found unknown value")),
+                            #terustform::Clone::clone(&path),
+                        ));
+                    },
+                    #terustform::BaseValue::Null => {
+                        return #terustform::Err(#terustform::Diagnostics::with_path(
+                            #terustform::Diagnostics::error_string(#terustform::ToOwned::to_owned("Expected object, found null value")),
+                            #terustform::Clone::clone(&path),
+                        ));
+                    },
+                    #terustform::BaseValue::Known(#terustform::ValueKind::Object(mut obj)) => {
+                        #(#field_extractions)*
+
+                        Ok(#struct_name {
+                            #(#constructor_fields)*
+                        })
+                    },
+                    #terustform::BaseValue::Known(v) => {
+                        return #terustform::Err(#terustform::Diagnostics::with_path(
+                            #terustform::Diagnostics::error_string(format!("Expected object, found {} value", v.diagnostic_type_str())),
+                            #terustform::Clone::clone(&path),
+                        ));
+                    },
+                }
+            }
+        }
+    })
 }