Implement Group derive proc macro

cove-macro/Cargo.toml

@@ -4,6 +4,7 @@ version = { workspace = true }
 edition = { workspace = true }
 
 [dependencies]
+case = "1.0.0"
 proc-macro2 = "1.0.56"
 quote = "1.0.26"
 syn = "2.0.15"

cove-macro/src/document.rs

@@ -2,39 +2,9 @@ use proc_macro2::TokenStream;
 use quote::quote;
 use syn::punctuated::Punctuated;
 use syn::spanned::Spanned;
-use syn::{Data, DeriveInput, Expr, ExprLit, Field, Lit, LitStr, MetaNameValue, Token};
+use syn::{Data, DeriveInput, Field, MetaNameValue, Token};
 
-fn strlit(expr: &Expr) -> Option<&LitStr> {
-    match expr {
-        Expr::Lit(ExprLit {
-            lit: Lit::Str(lit), ..
-        }) => Some(lit),
-        _ => None,
-    }
-}
-
-/// Given a struct field, this finds all attributes like `#[doc = "bla"]`,
-/// unindents, concatenates and returns them.
-fn docstring(field: &Field) -> syn::Result<String> {
-    let mut lines = vec![];
-
-    for attr in field
-        .attrs
-        .iter()
-        .filter(|attr| attr.path().is_ident("doc"))
-    {
-        if let Some(lit) = strlit(&attr.meta.require_name_value()?.value) {
-            let value = lit.value();
-            let value = value
-                .strip_prefix(' ')
-                .map(|value| value.to_string())
-                .unwrap_or(value);
-            lines.push(value);
-        }
-    }
-
-    Ok(lines.join("\n"))
-}
+use crate::util::docstring;
 
 /// Given a struct field, this finds all key-value pairs of the form
 /// `#[document(key = value, ...)]`.

cove-macro/src/group.rs

@@ -0,0 +1,63 @@
+use case::CaseExt;
+use proc_macro2::TokenStream;
+use quote::{format_ident, quote};
+use syn::spanned::Spanned;
+use syn::{Data, DeriveInput};
+
+use crate::util;
+
+fn decapitalize(s: &str) -> String {
+    let mut chars = s.chars();
+    if let Some(char) = chars.next() {
+        char.to_lowercase().chain(chars).collect()
+    } else {
+        String::new()
+    }
+}
+
+pub fn derive_impl(input: DeriveInput) -> syn::Result<TokenStream> {
+    let Data::Struct(data) = input.data else {
+        return Err(syn::Error::new(input.span(), "Must be a struct"));
+    };
+
+    let struct_ident = input.ident;
+    let enum_ident = format_ident!("{}Action", struct_ident);
+
+    let mut enum_variants = vec![];
+    let mut match_cases = vec![];
+    for field in &data.fields {
+        if let Some(field_ident) = &field.ident {
+            let docstring = util::docstring(field)?;
+            let variant_ident = format_ident!("{}", field_ident.to_string().to_camel());
+
+            enum_variants.push(quote! {
+                #[doc = #docstring]
+                #variant_ident,
+            });
+
+            let description = decapitalize(&docstring);
+            let description = description.strip_suffix('.').unwrap_or(&description);
+            match_cases.push(quote!{
+                () if input.matches(&self.#field_ident, #description) => Some(Self::Action::#variant_ident),
+            });
+        }
+    }
+
+    Ok(quote! {
+        #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+        pub enum #enum_ident {
+            #( #enum_variants )*
+        }
+
+        impl crate::Group for #struct_ident {
+            type Action = #enum_ident;
+
+            fn action(&self, input: &mut crate::Input) -> Option<Self::Action> {
+                match () {
+                    #( #match_cases )*
+                    () => None,
+                }
+            }
+        }
+    })
+}

cove-macro/src/lib.rs

@@ -12,6 +12,8 @@
 use syn::{parse_macro_input, DeriveInput};
 
 mod document;
+mod group;
+mod util;
 
 #[proc_macro_derive(Document, attributes(document))]
 pub fn derive_document(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
@@ -21,3 +23,12 @@ pub fn derive_document(input: proc_macro::TokenStream) -> proc_macro::TokenStrea
         Err(err) => err.into_compile_error().into(),
     }
 }
+
+#[proc_macro_derive(Group)]
+pub fn derive_group(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    match group::derive_impl(input) {
+        Ok(tokens) => tokens.into(),
+        Err(err) => err.into_compile_error().into(),
+    }
+}

cove-macro/src/util.rs

@@ -0,0 +1,33 @@
+use syn::{Expr, ExprLit, Field, Lit, LitStr};
+
+pub fn strlit(expr: &Expr) -> Option<&LitStr> {
+    match expr {
+        Expr::Lit(ExprLit {
+            lit: Lit::Str(lit), ..
+        }) => Some(lit),
+        _ => None,
+    }
+}
+
+/// Given a struct field, this finds all attributes like `#[doc = "bla"]`,
+/// unindents, concatenates and returns them.
+pub fn docstring(field: &Field) -> syn::Result<String> {
+    let mut lines = vec![];
+
+    for attr in field
+        .attrs
+        .iter()
+        .filter(|attr| attr.path().is_ident("doc"))
+    {
+        if let Some(lit) = strlit(&attr.meta.require_name_value()?.value) {
+            let value = lit.value();
+            let value = value
+                .strip_prefix(' ')
+                .map(|value| value.to_string())
+                .unwrap_or(value);
+            lines.push(value);
+        }
+    }
+
+    Ok(lines.join("\n"))
+}