api-macro: add json_schema!() macro

This allows using the json schema notation to generate `Schema`
expressions.

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

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

@@ -761,3 +761,13 @@ pub(crate) fn api(attr: TokenStream, item: TokenStream) -> Result<TokenStream, E
         _ => bail!(item => "api macro only works on functions"),
     }
 }
+
+/// Directly convert a json schema into a `Schema` expression.
+pub(crate) fn json_schema(item: TokenStream) -> Result<TokenStream, Error> {
+    let attribs = JSONObject::parse_inner.parse2(item)?;
+    let schema: Schema = attribs.try_into()?;
+
+    let mut ts = TokenStream::new();
+    schema.to_schema(&mut ts)?;
+    Ok(ts)
+}

proxmox-api-macro/src/lib.rs

@@ -295,6 +295,24 @@ pub fn api(attr: TokenStream_1, item: TokenStream_1) -> TokenStream_1 {
     handle_error(item.clone(), api::api(attr.into(), item)).into()
 }
 
+/// *Experimental:* Transform a json-like schema definition into an expression yielding a `Schema`.
+///
+/// This is currently considered experimental as it should not be required for normal code.
+#[proc_macro]
+pub fn json_schema(item: TokenStream_1) -> TokenStream_1 {
+    let _error_guard = init_local_error();
+    let item: TokenStream = item.into();
+    let mut output = take_non_fatal_errors();
+    match api::json_schema(item) {
+        Ok(ts) => output.extend(ts),
+        Err(err) => match err.downcast::<syn::Error>() {
+            Ok(err) => output.extend(err.to_compile_error()),
+            Err(err) => panic!("error in json_schema!() macro: {err}"),
+        },
+    }
+    quote::quote!({ #output }).into()
+}
+
 /// This is a dummy derive macro actually handled by `#[api]`!
 #[doc(hidden)]
 #[proc_macro_derive(Updater, attributes(updater, serde))]

proxmox-api-macro/tests/types.rs

@@ -5,7 +5,7 @@
 
 use std::collections::HashMap;
 
-use proxmox_api_macro::api;
+use proxmox_api_macro::{api, json_schema};
 use proxmox_schema as schema;
 use proxmox_schema::{ApiType, EnumEntry};
 
@@ -68,6 +68,24 @@ fn test_struct() {
     .schema();
 
     assert_eq!(TEST_SCHEMA, TestStruct::API_SCHEMA);
+
+    const TEST_JSON_SCHEMA: ::proxmox_schema::Schema = json_schema! {
+        description: "An example of a simple struct type.",
+        properties: {
+            another: {
+                type: String,
+                description: "An optional auto-derived value for testing:",
+                optional: true,
+            },
+            test_string: {
+                type: String,
+                description: "A test string.",
+                optional: false,
+            },
+        },
+    };
+
+    assert_eq!(TEST_SCHEMA, TEST_JSON_SCHEMA);
 }
 
 #[api]