Add support for tuple structs (#2)

* Add support for tuple structs * Document tuple struct support --------- Co-authored-by: tlaferriere <[email protected]>
valsteen · Jun 17, 2023 · 8e59c1f · 8e59c1f
1 parent 31bd69a
commit 8e59c1f
Show file tree

Hide file tree

Showing 2 changed files with 62 additions and 16 deletions.
diff --git a/README.md b/README.md
@@ -28,7 +28,7 @@ Fields that should be used for sorting are marked with the attribute `#[sort_by]
 Alternatively, or in combination with, a struct-level or enum-level `#[sort_by(method1(),method2(),attr1,nested.attr)]` can be declared. This top-level declaration takes precedence,
 fields comparison will be considered if top-level comparisons are all `eq`. The top-level `sort_by` attribute takes a list of attributes or method calls; items will be prepended with `self.`.
 
-#### Example
+#### Examples
 
 ```rust
 #[derive(SortBy)]
@@ -75,6 +75,21 @@ impl core::cmp::Ord for Something {
 }
 ```
 
+You can use it the same way with tuple structs:
+
+```rust
+#[derive(SortBy)]
+#[sort_by(somemethod())]
+struct Something (
+  #[sort_by]
+  u16,
+  #[sort_by]
+  u32,
+  f32
+)
+```
+This will expand the same way as a normal struct, with the proper numerical fields.
+
 ### EnumAccessor
 
 This derive macro is similar to [enum_dispatch](https://crates.io/crates/enum_dispatch). `enum_dispatch` requires structs to implement a common trait, which can be useful if a common set of functions applies to all variants . `EnumAccessor` takes the opposite approach: common fields and methods are declared at enum level, and you can have variants that don't have a given field or method. This may be more practical if there is a large amount of variants and your only concern is accessing fields, because individual structs just hold data. This is typical for events - they represent a state change and are generally consumed as a whole, individual structs have no code of their own.

diff --git a/src/sort_by.rs b/src/sort_by.rs
@@ -1,9 +1,9 @@
-use proc_macro2::{Span, TokenStream};
+use proc_macro2::{Literal, Span, TokenStream};
 use quote::{quote_spanned, ToTokens};
 
 use syn::{
     self, spanned::Spanned, Attribute, Data, DataStruct, DeriveInput, Error, Expr, ExprLit, Fields,
-    FieldsNamed, GenericParam, Lit, Meta, NestedMeta,
+    FieldsNamed, FieldsUnnamed, GenericParam, Lit, Meta, NestedMeta,
 };
 
 const HELP_SORTBY: &str = r#"SortBy: invalid sort_by attribute, expected list form i.e #[sort_by(attr1, attr2, methodcall())]"#;
@@ -34,34 +34,38 @@ pub fn impl_sort_by_derive(input: DeriveInput) -> TokenStream {
         Data::Struct(DataStruct {
             fields: Fields::Named(fields),
             ..
-        }) => match parse_fields(fields) {
+        }) => match parse_named_fields(fields) {
+            Ok(mut result) => sortable_expressions.append(&mut result),
+            Err(e) => return e.into_compile_error(),
+        },
+        Data::Struct(DataStruct {
+            fields: Fields::Unnamed(fields),
+            ..
+        }) => match parse_unnamed_fields(fields) {
             Ok(mut result) => sortable_expressions.append(&mut result),
             Err(e) => return e.into_compile_error(),
         },
         Data::Enum(_) => (),
         _ => {
-            return Error::new(
-                input_span,
-                r#"SortBy: expected an enum or a struct with named fields"#,
-            )
-            .into_compile_error();
+            return Error::new(input_span, r#"SortBy: expected an enum or a struct"#)
+                .into_compile_error();
         }
     };
 
     let mut iter_sort_expressions = sortable_expressions.iter();
-    let ord_statement = if let Some(sort_expression) = iter_sort_expressions.next() {
-        quote_spanned! { sort_expression.span() =>
-            core::cmp::Ord::cmp(&self.#sort_expression, &other.#sort_expression)
+    let ord_statement = if let Some(field) = iter_sort_expressions.next() {
+        quote_spanned! { field.span() =>
+            core::cmp::Ord::cmp(&self.#field, &other.#field)
         }
     } else {
         return quote::quote! {
             compile_error!(r#"SortBy: no field to sort on. Mark fields to sort on with #[sort_by]"#);
         };
     };
 
-    let ord_statement = iter_sort_expressions.fold(ord_statement, |ord_statement, field_name| {
-        syn::parse_quote_spanned! {field_name.span() =>
-            #ord_statement.then_with(|| self.#field_name.cmp(&other.#field_name))
+    let ord_statement = iter_sort_expressions.fold(ord_statement, |ord_statement, field| {
+        syn::parse_quote_spanned! {field.span() =>
+            #ord_statement.then_with(|| self.#field.cmp(&other.#field))
         }
     });
 
@@ -112,7 +116,34 @@ pub fn impl_sort_by_derive(input: DeriveInput) -> TokenStream {
     }
 }
 
-fn parse_fields(fields: FieldsNamed) -> Result<Vec<Expr>, Error> {
+fn parse_unnamed_fields(fields: FieldsUnnamed) -> Result<Vec<Expr>, Error> {
+    let mut sortable_expressions = vec![];
+
+    for (index, field) in fields.unnamed.iter().enumerate() {
+        let span = field.span();
+        let mut attrs = field
+            .attrs
+            .iter()
+            .filter(|i| i.path.get_ident().map_or(false, |i| i == "sort_by"));
+
+        if attrs.next().is_none() {
+            continue;
+        }
+
+        let expr: Expr = syn::parse2(Literal::usize_unsuffixed(index).to_token_stream())?;
+        sortable_expressions.push(expr);
+
+        if attrs.next().is_some() {
+            return Err(Error::new(
+                span,
+                r#"SortBy: expected at most one `sort_by` attribute"#,
+            ));
+        }
+    }
+    Ok(sortable_expressions)
+}
+
+fn parse_named_fields(fields: FieldsNamed) -> Result<Vec<Expr>, Error> {
     let mut sortable_expressions = vec![];
 
     for field in fields.named {