api: support #[default] attribute

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

proxmox-api-macro/src/api/enums.rs

@@ -25,6 +25,8 @@ pub fn handle_enum(
         error!(fmt.span(), "illegal key 'format', will be autogenerated");
     }
 
+    let has_default_attrib = attribs.get("default").map(|def| def.span());
+
     let schema = {
         let mut schema: Schema = attribs.try_into()?;
 
@@ -39,6 +41,8 @@ pub fn handle_enum(
     };
 
     let container_attrs = serde::ContainerAttrib::try_from(&enum_ty.attrs[..])?;
+    let derives_default = util::derives_trait(&enum_ty.attrs, "Default");
+    let mut default_value = None;
 
     let mut variants = TokenStream::new();
     for variant in &mut enum_ty.variants {
@@ -64,6 +68,21 @@ pub fn handle_enum(
             syn::LitStr::new(&name.to_string(), name.span())
         };
 
+        if derives_default {
+            if let Some(attr) = variant.attrs.iter().find(|a| a.path.is_ident("default")) {
+                if let Some(default_value) = &default_value {
+                    error!(attr => "multiple default values defined");
+                    error!(default_value => "default previously defined here");
+                } else {
+                    default_value = Some(variant_string.clone());
+                    if let Some(span) = has_default_attrib {
+                        error!(attr => "#[default] attribute in use with 'default' #[api] key");
+                        error!(span, "'default' also defined here");
+                    }
+                }
+            }
+        }
+
         variants.extend(quote_spanned! { variant.ident.span() =>
             ::proxmox_schema::EnumEntry {
                 value: #variant_string,
@@ -74,6 +93,11 @@ pub fn handle_enum(
 
     let name = &enum_ty.ident;
 
+    let default_value = match default_value {
+        Some(value) => quote_spanned!(value.span() => .default(#value)),
+        None => TokenStream::new(),
+    };
+
     Ok(quote_spanned! { name.span() =>
         #enum_ty
 
@@ -81,6 +105,7 @@ pub fn handle_enum(
             const API_SCHEMA: ::proxmox_schema::Schema =
                 #schema
                 .format(&::proxmox_schema::ApiStringFormat::Enum(&[#variants]))
+                #default_value
                 .schema();
         }
 

proxmox-api-macro/src/api/structs.rs

@@ -404,7 +404,7 @@ fn derive_updater(
     let original_name = &original_struct.ident;
     stru.ident = Ident::new(&format!("{}Updater", stru.ident), stru.ident.span());
 
-    if !util::derived_items(&original_struct.attrs).any(|p| p.is_ident("Default")) {
+    if !util::derives_trait(&original_struct.attrs, "Default") {
         stru.attrs.push(util::make_derive_attribute(
             Span::call_site(),
             quote::quote! { Default },

proxmox-api-macro/src/util.rs

@@ -699,6 +699,11 @@ pub fn derived_items(attributes: &[syn::Attribute]) -> DerivedItems {
     }
 }
 
+/// Helper to check if a certain trait is being derived.
+pub fn derives_trait(attributes: &[syn::Attribute], ident: &str) -> bool {
+    derived_items(&attributes).any(|p| p.is_ident(ident))
+}
+
 /// Iterator over the types found in `#[derive(...)]` attributes.
 pub struct DerivedItems<'a> {
     current: Option<<Punctuated<syn::NestedMeta, Token![,]> as IntoIterator>::IntoIter>,

proxmox-api-macro/tests/types.rs

@@ -103,7 +103,7 @@ fn renamed_struct() {
 }
 
 #[api]
-#[derive(Deserialize)]
+#[derive(Default, Deserialize)]
 #[serde(rename_all = "kebab-case")]
 /// A selection of either 'onekind', 'another-kind' or 'selection-number-three'.
 pub enum Selection {
@@ -111,6 +111,7 @@ pub enum Selection {
     #[serde(rename = "onekind")]
     OneKind,
     /// Some other kind.
+    #[default]
     AnotherKind,
     /// And yet another.
     SelectionNumberThree,
@@ -126,6 +127,7 @@ fn selection_test() {
         EnumEntry::new("another-kind", "Some other kind."),
         EnumEntry::new("selection-number-three", "And yet another."),
     ]))
+    .default("another-kind")
     .schema();
 
     assert_eq!(TEST_SCHEMA, Selection::API_SCHEMA);