Merge pull request #25 from kas-gui/work

0.5.2: add singleton! macro

CHANGELOG.md

@@ -2,6 +2,10 @@
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.5.2] — 2022-10-06
+
+-   Add `singleton!` macro (#25)
+
 ## [0.5.1] — 2022-09-23
 
 -   Fix: do not copy attributes on trait items (#24)

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "impl-tools"
-version = "0.5.1"
+version = "0.5.2"
 authors = ["Diggory Hardy <git@dhardy.name>"]
 edition = "2021"
 license = "MIT/Apache-2.0"
@@ -21,7 +21,7 @@ proc-macro-error = "1.0"
 version = "1.0.14"
 
 [dependencies.impl-tools-lib]
-version = "0.5.1"
+version = "0.5.2"
 path = "lib"
 
 [dev-dependencies]

README.md

@@ -71,12 +71,10 @@ fn main() {
 `#[impl_default]` implements `std::default::Default`:
 
 ```rust
-use impl_tools::{impl_default, impl_scope};
-
-#[impl_default(Tree::Ash)]
+#[impl_tools::impl_default(Tree::Ash)]
 enum Tree { Ash, Beech, Birch, Willow }
 
-impl_scope! {
+impl_tools::impl_scope! {
     #[impl_default]
     struct Copse {
         tree_type: Tree,
@@ -85,16 +83,17 @@ impl_scope! {
 }
 ```
 
+Note: `#[impl_default]` is matched within an `impl_scope!` regardless of imports.
+
 ### Impl Scope
 
 `impl_scope!` is a function-like macro used to define a type plus its
 implementations. It supports `impl Self` syntax:
 
 ```rust
-use impl_tools::impl_scope;
 use std::fmt::Display;
 
-impl_scope! {
+impl_tools::impl_scope! {
     /// I don't know why this exists
     pub struct NamedThing<T: Display, F> {
         name: T,
@@ -118,7 +117,29 @@ impl_scope! {
 ```
 
 Caveat: `rustfmt` won't currently touch the contents. Hopefully that
-[can be fixed](https://github.com/rust-lang/rustfmt/issues/5254)!
+[can be fixed](https://github.com/rust-lang/rustfmt/pull/5538)!
+
+### Singleton
+
+`singleton!` is a function-like macro to construct a single-use struct with
+custom implementations (similar: [RFC#2604](https://github.com/rust-lang/rfcs/pull/2604)).
+
+Example:
+```rust
+use std::fmt;
+fn main() {
+    let world = "world";
+    let says_hello_world = impl_tools::singleton! {
+        struct(&'static str = world);
+        impl fmt::Display for Self {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                write!(f, "hello {}", self.0)
+            }
+        }
+    };
+    assert_eq!(format!("{}", says_hello_world), "hello world");
+}
+```
 
 
 Extensibility

lib/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "impl-tools-lib"
-version = "0.5.1"
+version = "0.5.2"
 authors = ["Diggory Hardy <git@dhardy.name>"]
 edition = "2021"
 license = "MIT/Apache-2.0"
@@ -19,4 +19,4 @@ proc-macro-error = "1.0"
 version = "1.0.14"
 # We need 'extra-traits' for equality testing
 # We need 'full' for parsing macros within macro arguments
-features = ["extra-traits", "full"]
+features = ["extra-traits", "full", "visit", "visit-mut"]

lib/README.md

@@ -1,11 +1,13 @@
 Impl-tools library
 =======
 
-This is the library behind the [impl-tools](https://crates.io/crates/impl-tools) crate.
+This is the library behind the [impl-tools] crate.
 
-The only reason to use this library directly is to extend the impl-tools macros
-to support custom traits in `#[autoimpl]` or custom attributes evaluated from
-`impl_scope!`.
+This library may be used directly to write custom variants of the [impl-tools]
+macros, for example extending `#[autoimpl]` to support other traits or
+writing new attribute macros to be evaluated within a `impl_scope!`.
+
+[impl-tools]: https://crates.io/crates/impl-tools
 
 
 Copyright and Licence

lib/src/default.rs

@@ -181,3 +181,13 @@ impl Parse for ImplDefault {
         })
     }
 }
+
+/// Helper fn which can be passed to [`Scope::apply_attrs`]
+///
+/// This optionally matches [`AttrImplDefault`].
+pub fn find_attr_impl_default(path: &syn::Path) -> Option<&'static dyn ScopeAttr> {
+    AttrImplDefault
+        .path()
+        .matches(path)
+        .then(|| &AttrImplDefault as &dyn ScopeAttr)
+}

lib/src/fields.rs

@@ -12,6 +12,17 @@ use syn::parse::{Parse, ParseStream, Result};
 use syn::punctuated::Punctuated;
 use syn::{token, Attribute, Expr, Ident, Token, Type, Visibility};
 
+/// Struct style: unit/tuple/regular
+#[derive(Debug)]
+pub enum StructStyle {
+    /// A unit struct (e.g. `struct Foo;`)
+    Unit(Token![;]),
+    /// A tuple struct (e.g. `struct Foo(f32, f32);`)
+    Tuple(token::Paren, Token![;]),
+    /// A regular struct (e.g. `struct Foo { x: f32, y: f32 }`)
+    Regular(token::Brace),
+}
+
 /// Data stored within an enum variant or struct.
 ///
 /// This is a variant of [`syn::Fields`] supporting field initializers.

lib/src/lib.rs

@@ -20,10 +20,12 @@ pub mod fields;
 mod for_deref;
 pub mod generics;
 mod scope;
+mod singleton;
 
-pub use default::{AttrImplDefault, ImplDefault};
+pub use default::{find_attr_impl_default, AttrImplDefault, ImplDefault};
 pub use for_deref::ForDeref;
 pub use scope::{Scope, ScopeAttr, ScopeItem};
+pub use singleton::{Singleton, SingletonField, SingletonScope};
 
 /// Simple, allocation-free path representation
 #[derive(PartialEq, Eq)]