Use a proc macro for being able to derive schemas for our action structs

Cargo.toml

@@ -1,6 +1,7 @@
 [workspace]
 members = [
     "acceptance",
+    "derive-macros",
     "ffi",
     "kernel",
     "kernel/examples/*",

derive-macros/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "derive-macros"
+authors.workspace = true
+edition.workspace = true
+homepage.workspace = true
+keywords.workspace = true
+license.workspace = true
+repository.workspace = true
+readme.workspace = true
+version.workspace = true
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1"
+syn = { version = "2.0", features = ["extra-traits"] }
+quote = "1.0"
+
+

derive-macros/src/lib.rs

@@ -0,0 +1,87 @@
+use proc_macro2::{Ident, TokenStream};
+use quote::{quote, quote_spanned};
+use syn::spanned::Spanned;
+use syn::{parse_macro_input, Data, DataStruct, DeriveInput, Fields, PathArguments, Type};
+
+#[proc_macro_derive(Schema, attributes(schema))]
+pub fn derive_schema(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    let struct_ident = input.ident;
+
+    let schema_fields = gen_schema_fields(&input.data);
+    let output = quote! {
+        impl crate::actions::schemas::GetField for #struct_ident {
+            fn get_field(name: impl Into<String>) -> crate::schema::StructField {
+                use crate::actions::schemas::GetField;
+                crate::schema::StructField::new(
+                    name,
+                    crate::schema::StructType::new(vec![
+                        #schema_fields
+                    ]),
+                    // By default not nullable. To make something nullable wrap it in an Option
+                    false,
+                )
+            }
+        }
+    };
+    proc_macro::TokenStream::from(output)
+}
+
+// turn our struct name into the schema name, goes from snake_case to camelCase
+fn get_schema_name(name: &Ident) -> Ident {
+    let snake_name = name.to_string();
+    let mut next_caps = false;
+    let ret: String = snake_name
+        .chars()
+        .filter_map(|c| {
+            if c == '_' {
+                next_caps = true;
+                None
+            } else if next_caps {
+                next_caps = false;
+                // This assumes we're using ascii, should be okay
+                Some(c.to_ascii_uppercase())
+            } else {
+                Some(c)
+            }
+        })
+        .collect();
+    Ident::new(&ret, name.span())
+}
+
+fn gen_schema_fields(data: &Data) -> TokenStream {
+    let fields = match data {
+        Data::Struct(DataStruct {
+            fields: Fields::Named(fields),
+            ..
+        }) => &fields.named,
+        _ => panic!("this derive macro only works on structs with named fields"),
+    };
+
+    let schema_fields = fields.iter().map(|field| {
+        let name = field.ident.as_ref().unwrap(); // we know these are named fields
+        let name = get_schema_name(name);
+        match field.ty {
+            Type::Path(ref type_path) => {
+                if let Some(fin) = type_path.path.segments.iter().last() {
+                    let type_ident = &fin.ident;
+                    if let PathArguments::AngleBracketed(angle_args) = &fin.arguments {
+                        quote_spanned! {field.span()=>
+                                        #type_ident::#angle_args::get_field(stringify!(#name))
+                        }
+                    } else {
+                        quote_spanned! {field.span()=>
+                                        #type_ident::get_field(stringify!(#name))
+                        }
+                    }
+                } else {
+                    panic!("Couldn't get type");
+                }
+            }
+            _ => {
+                panic!("Can't handle type: {:?}", field.ty);
+            }
+        }
+    });
+    quote! { #(#schema_fields),* }
+}

kernel/Cargo.toml

@@ -29,6 +29,9 @@ url = "2"
 uuid = "1.3.0"
 z85 = "3.0.5"
 
+# bring in our derive macros
+derive-macros = { path = "../derive-macros" }
+
 # used for developer-visibility
 visibility = "0.1.0"
 

kernel/src/actions/deletion_vector.rs

@@ -4,12 +4,13 @@ use std::io::{Cursor, Read};
 use std::sync::Arc;
 
 use bytes::Bytes;
+use derive_macros::Schema;
 use roaring::RoaringTreemap;
 use url::Url;
 
 use crate::{DeltaResult, Error, FileSystemClient};
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Schema)]
 pub struct DeletionVectorDescriptor {
     /// A single character to indicate how to access the DV. Legal options are: ['u', 'i', 'p'].
     pub storage_type: String,