api-macro: support empty api macro on structs

The description comes from the doc comment, the field types
and description from field doc comments and types.
Previously we needed to add at least the hint that the
schema is an object schema. Now we support an empty #[api]
attribute as well.

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

proxmox-api-macro/src/api.rs

@@ -109,6 +109,15 @@ impl Schema {
         }
     }
 
+    fn empty_object(span: Span) -> Self {
+        Self {
+            span,
+            description: None,
+            item: SchemaItem::Object(SchemaObject::new()),
+            properties: Vec::new(),
+        }
+    }
+
     fn to_typed_schema(&self, ts: &mut TokenStream) -> Result<(), Error> {
         self.item.to_schema(
             ts,
@@ -331,6 +340,12 @@ pub struct SchemaObject {
 }
 
 impl SchemaObject {
+    pub fn new() -> Self {
+        Self {
+            properties: Vec::new(),
+        }
+    }
+
     fn try_extract_from(obj: &mut JSONObject) -> Result<Self, syn::Error> {
         Ok(Self {
             properties: obj

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

@@ -3,7 +3,7 @@ use std::convert::{TryFrom, TryInto};
 
 use failure::Error;
 
-use proc_macro2::{Ident, TokenStream};
+use proc_macro2::{Ident, Span, TokenStream};
 use quote::quote_spanned;
 
 use super::Schema;
@@ -12,7 +12,11 @@ use crate::serde;
 use crate::util::{self, FieldName, JSONObject};
 
 pub fn handle_struct(attribs: JSONObject, mut stru: syn::ItemStruct) -> Result<TokenStream, Error> {
-    let mut schema: Schema = attribs.try_into()?;
+    let mut schema: Schema = if attribs.is_empty() {
+        Schema::empty_object(Span::call_site())
+    } else {
+        attribs.try_into()?
+    };
 
     if schema.description.is_none() {
         let (doc_comment, doc_span) = util::get_doc_comments(&stru.attrs)?;

proxmox-api-macro/src/util.rs

@@ -298,6 +298,10 @@ pub struct JSONObject {
 }
 
 impl JSONObject {
+    pub fn is_empty(&self) -> bool {
+        self.elements.is_empty()
+    }
+
     fn parse_elements(input: ParseStream) -> syn::Result<HashMap<FieldName, JSONValue>> {
         let map_elems: Punctuated<JSONMapEntry, Token![,]> =
             input.parse_terminated(JSONMapEntry::parse)?;

proxmox-api-macro/tests/types.rs

@@ -16,9 +16,7 @@ use serde_json::Value;
 //#[derive(Clone, Debug, Deserialize, Serialize)]
 pub struct OkString(String);
 
-#[api(
+#[api]
-    properties: {}
-)]
 /// A Foo.
 pub struct Foo {
     /// A test string.