feat: allow including a view from an external file (closes #2182) (#2862)

leptos_macro/src/lib.rs

@@ -13,6 +13,7 @@ use component::DummyModel;
 use proc_macro::TokenStream;
 use proc_macro2::{Span, TokenTree};
 use quote::{quote, ToTokens};
+use std::str::FromStr;
 use syn::{parse_macro_input, spanned::Spanned, token::Pub, Visibility};
 
 mod params;
@@ -331,6 +332,31 @@ fn normalized_call_site(site: proc_macro::Span) -> Option<String> {
     }
 }
 
+/// This behaves like the [`view`] macro, but loads the view from an external file instead of
+/// parsing it inline.
+///
+/// This is designed to allow editing views in a separate file, if this improves a user's workflow.
+///
+/// The file is loaded and parsed during proc-macro execution, and its path is resolved relative to
+/// the crate root rather than relative to the file from which it is called.
+#[proc_macro_error::proc_macro_error]
+#[proc_macro]
+pub fn include_view(tokens: TokenStream) -> TokenStream {
+    let file_name = syn::parse::<syn::LitStr>(tokens).unwrap_or_else(|_| {
+        abort!(
+            Span::call_site(),
+            "the only supported argument is a string literal"
+        );
+    });
+    let file =
+        std::fs::read_to_string(file_name.value()).unwrap_or_else(|_| {
+            abort!(Span::call_site(), "could not open file");
+        });
+    let tokens = proc_macro2::TokenStream::from_str(&file)
+        .unwrap_or_else(|e| abort!(Span::call_site(), e));
+    view(tokens.into())
+}
+
 /// Annotates a function so that it can be used with your template as a Leptos `<Component/>`.
 ///
 /// The `#[component]` macro allows you to annotate plain Rust functions as components