From 76fd9207e5a2c16de1b15f35e53f87118b9bcfb6 Mon Sep 17 00:00:00 2001
From: Ashley Wulber <ashley@system76.com>
Date: Fri, 19 May 2023 15:36:15 -0400
Subject: [PATCH] feat: derive macro for loading a cosmic-config

---
 Cargo.toml                      |  1 +
 cosmic-config-derive/Cargo.toml | 12 ++++++
 cosmic-config-derive/src/lib.rs | 68 +++++++++++++++++++++++++++++++++
 cosmic-config/Cargo.toml        | 10 ++++-
 cosmic-config/src/lib.rs        |  9 +++++
 5 files changed, 98 insertions(+), 2 deletions(-)
 create mode 100644 cosmic-config-derive/Cargo.toml
 create mode 100644 cosmic-config-derive/src/lib.rs

diff --git a/Cargo.toml b/Cargo.toml
index dbbb4611..0879d0f9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -76,6 +76,7 @@ optional = true
 [workspace]
 members = [
   "cosmic-config",
+  "cosmic-config-derive",
   "examples/*",
 ]
 exclude = [
diff --git a/cosmic-config-derive/Cargo.toml b/cosmic-config-derive/Cargo.toml
new file mode 100644
index 00000000..44f960ec
--- /dev/null
+++ b/cosmic-config-derive/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "cosmic-config-derive"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = "1.0"
+quote = "1.0"
diff --git a/cosmic-config-derive/src/lib.rs b/cosmic-config-derive/src/lib.rs
new file mode 100644
index 00000000..9f6fe37e
--- /dev/null
+++ b/cosmic-config-derive/src/lib.rs
@@ -0,0 +1,68 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn;
+
+#[proc_macro_derive(CosmicConfigEntry)]
+pub fn cosmic_config_entry_derive(input: TokenStream) -> TokenStream {
+    // Construct a representation of Rust code as a syntax tree
+    // that we can manipulate
+    let ast = syn::parse(input).unwrap();
+
+    // Build the trait implementation
+    impl_cosmic_config_entry_macro(&ast)
+}
+
+fn impl_cosmic_config_entry_macro(ast: &syn::DeriveInput) -> TokenStream {
+    let name = &ast.ident;
+
+        // Get the fields of the struct
+    let fields = match ast.data {
+        syn::Data::Struct(ref data_struct) => match data_struct.fields {
+            syn::Fields::Named(ref fields) => &fields.named,
+            _ => unimplemented!("Only named fields are supported"),
+        },
+        _ => unimplemented!("Only structs are supported"),
+    };
+
+    let write_each_config_field = fields.iter().map(|field| {
+        let field_name = &field.ident;
+        quote! {
+            config.set(stringify!(#field_name), &self.#field_name)?;
+        }
+    });
+
+    let get_each_config_field = fields.iter().map(|field| {
+        let field_name = &field.ident;
+        let field_type = &field.ty;
+        quote! {
+            match config.get::<#field_type>(stringify!(#field_name)) {
+                Ok(#field_name) => default.#field_name = #field_name,
+                Err(e) => errors.push(e),
+            }
+        }
+    });
+
+    let gen = quote! {
+        impl CosmicConfigEntry for #name {
+            fn write_entry(&self, config: &Config) -> Result<(), cosmic_config::Error> {
+                #(#write_each_config_field)*
+                Ok(())
+            }
+
+            fn get_entry(config: &Config) -> Result<Self, (Vec<cosmic_config::Error>, Self)> {
+                let mut default = Self::default();
+                let mut errors = Vec::new();
+
+                #(#get_each_config_field)*
+                
+                if errors.is_empty() {
+                    Ok(default)
+                } else {
+                    Err((errors, default))
+                }
+            }
+        }
+    };
+
+    gen.into()
+}
diff --git a/cosmic-config/Cargo.toml b/cosmic-config/Cargo.toml
index 38cf3e41..d7af68ed 100644
--- a/cosmic-config/Cargo.toml
+++ b/cosmic-config/Cargo.toml
@@ -3,10 +3,16 @@ name = "cosmic-config"
 version = "0.1.0"
 edition = "2021"
 
+[features]
+default = ["macro"]
+macro = ["cosmic-config-derive"]
+
 [dependencies]
 atomicwrites = "0.4.0"
 calloop = { version = "0.10.5", optional = true }
-dirs = "4.0.0"
-notify = "5.1.0"
+dirs = "5.0.1"
+notify = "6.0.0"
 ron = "0.8.0"
 serde = "1.0.152"
+cosmic-config-derive = { path = "../cosmic-config-derive/", optional = true }
+
diff --git a/cosmic-config/src/lib.rs b/cosmic-config/src/lib.rs
index e4b237a1..b4964028 100644
--- a/cosmic-config/src/lib.rs
+++ b/cosmic-config/src/lib.rs
@@ -7,6 +7,9 @@ use std::{
     sync::Mutex,
 };
 
+#[cfg(feature = "macro")]
+pub use cosmic_config_derive;
+
 #[cfg(feature = "calloop")]
 pub mod calloop;
 
@@ -251,3 +254,9 @@ impl<'a> ConfigSet for ConfigTransaction<'a> {
         Ok(())
     }
 }
+
+pub trait CosmicConfigEntry where Self: Sized + Default {
+    fn write_entry(&self, config: &Config) -> Result<(), crate::Error>;
+    fn get_entry(config: &Config) -> Result<Self, (Vec<crate::Error>, Self)>;
+}
+