feat: add memo! macro (closes #2708) (#2826)

leptos_macro/src/lib.rs

@@ -19,6 +19,7 @@ mod params;
 mod view;
 use crate::component::unmodified_fn_name_from_fn_name;
 mod component;
+mod memo;
 mod slice;
 mod slot;
 
@@ -875,3 +876,35 @@ pub fn params_derive(
 pub fn slice(input: TokenStream) -> TokenStream {
     slice::slice_impl(input)
 }
+
+/// Generates a `memo` into a struct with a default getter.
+///
+/// Can be used to access deeply nested fields within a global state object.
+///
+/// ```rust
+/// # use leptos::prelude::*;
+/// # use leptos_macro::memo;
+///
+/// #[derive(Default)]
+/// pub struct Outer {
+///     count: i32,
+///     inner: Inner,
+/// }
+///
+/// #[derive(Default)]
+/// pub struct Inner {
+///     inner_count: i32,
+///     inner_name: String,
+/// }
+///
+/// let outer_signal = RwSignal::new(Outer::default());
+///
+/// let count = memo!(outer_signal.count);
+///
+/// let inner_count = memo!(outer_signal.inner.inner_count);
+/// let inner_name = memo!(outer_signal.inner.inner_name);
+/// ```
+#[proc_macro]
+pub fn memo(input: TokenStream) -> TokenStream {
+    memo::memo_impl(input)
+}

leptos_macro/src/memo.rs

@@ -0,0 +1,56 @@
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+use quote::{quote, ToTokens};
+use syn::{
+    parse::{Parse, ParseStream},
+    parse_macro_input,
+    punctuated::Punctuated,
+    Token,
+};
+
+struct MemoMacroInput {
+    root: syn::Ident,
+    path: Punctuated<syn::Member, Token![.]>,
+}
+
+impl Parse for MemoMacroInput {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let root: syn::Ident = input.parse()?;
+        input.parse::<Token![.]>()?;
+        // do not accept trailing punctuation
+        let path: Punctuated<syn::Member, Token![.]> =
+            Punctuated::parse_separated_nonempty(input)?;
+
+        if path.is_empty() {
+            return Err(input.error("expected identifier"));
+        }
+
+        if !input.is_empty() {
+            return Err(input.error("unexpected token"));
+        }
+
+        Ok(Self { root, path })
+    }
+}
+
+impl ToTokens for MemoMacroInput {
+    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
+        let root = &self.root;
+        let path = &self.path;
+
+        tokens.extend(quote! {
+            ::leptos::reactive_graph::computed::Memo::new(
+                move |_| {
+                    use ::leptos::reactive_graph::traits::With;
+                    #root.with(|st: _| st.#path.clone())
+                }
+            )
+        })
+    }
+}
+
+pub fn memo_impl(tokens: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(tokens as MemoMacroInput);
+    input.into_token_stream().into()
+}

leptos_macro/tests/memo.rs

@@ -0,0 +1,33 @@
+use leptos::prelude::RwSignal;
+use leptos_macro::memo;
+
+#[derive(Default)]
+pub struct OuterState {
+    count: i32,
+    inner: InnerState,
+}
+
+#[derive(Clone, PartialEq, Default)]
+pub struct InnerState {
+    inner_count: i32,
+    inner_tuple: InnerTuple,
+}
+
+#[derive(Clone, PartialEq, Default)]
+pub struct InnerTuple(String);
+
+#[test]
+fn green() {
+    let outer_signal = RwSignal::new(OuterState::default());
+
+    let _ = memo!(outer_signal.count);
+
+    let _ = memo!(outer_signal.inner.inner_count);
+    let _ = memo!(outer_signal.inner.inner_tuple.0);
+}
+
+#[test]
+fn red() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/memo/red.rs")
+}

leptos_macro/tests/memo/red.rs

@@ -0,0 +1,26 @@
+use leptos::prelude::RwSignal;
+use leptos_macro::memo;
+
+#[derive(Default, PartialEq)]
+pub struct OuterState {
+    count: i32,
+    inner: InnerState,
+}
+
+#[derive(Clone, PartialEq, Default)]
+pub struct InnerState {
+    inner_count: i32,
+    inner_name: String,
+}
+
+fn main() {
+    let outer_signal = RwSignal::new(OuterState::default());
+
+    let _ = memo!();
+
+    let _ = memo!(outer_signal);
+
+    let _ = memo!(outer_signal.);
+
+    let _ = memo!(outer_signal.inner.);
+}

leptos_macro/tests/memo/red.stderr

@@ -0,0 +1,31 @@
+error: unexpected end of input, expected identifier
+  --> tests/memo/red.rs:19:13
+   |
+19 |     let _ = memo!();
+   |             ^^^^^^^
+   |
+   = note: this error originates in the macro `memo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected `.`
+  --> tests/memo/red.rs:21:13
+   |
+21 |     let _ = memo!(outer_signal);
+   |             ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in the macro `memo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: unexpected end of input, expected identifier or integer
+  --> tests/memo/red.rs:23:13
+   |
+23 |     let _ = memo!(outer_signal.);
+   |             ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in the macro `memo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: unexpected end of input, expected identifier or integer
+  --> tests/memo/red.rs:25:13
+   |
+25 |     let _ = memo!(outer_signal.inner.);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in the macro `memo` (in Nightly builds, run with -Z macro-backtrace for more info)