Allow relative assets in rust > 1.88 (#4658)

* Allow relative assets in rust > 1.88 and assets outside of the crate in
binary crates

* undo changes to assets outside of the crate

* don't use relative assets in examples

packages/config-macro/Cargo.toml

@@ -13,7 +13,7 @@ keywords = ["web", "desktop", "mobile", "gui", "wasm"]
 proc-macro = true
 
 [dependencies]
-proc-macro2 = { version = "1.0" }
+proc-macro2 = { workspace = true }
 quote = { workspace = true }
 
 [features]

packages/manganis/manganis-macro/Cargo.toml

@@ -15,7 +15,7 @@ proc-macro = true
 # be careful with dependencies you add here - these need to get compiled for the proc macro and therefore
 # prevent the main code from compiling!
 [dependencies]
-proc-macro2 = { workspace = true }
+proc-macro2 = { workspace = true, features = ["span-locations"] }
 quote = { workspace = true }
 syn = { workspace = true, features = ["full", "extra-traits"] }
 manganis-core = { workspace = true }

packages/manganis/manganis-macro/src/asset.rs

@@ -45,7 +45,7 @@ impl Parse for AssetParser {
     fn parse(input: ParseStream) -> syn::Result<Self> {
         // And then parse the options
         let (MacroString(src), path_expr) = input.call(crate::parse_with_tokens)?;
-        let asset = resolve_path(&src);
+        let asset = resolve_path(&src, path_expr.span());
         let _comma = input.parse::<Token![,]>();
         let options = input.parse()?;
 

packages/manganis/manganis-macro/src/css_module.rs

@@ -4,6 +4,7 @@ use proc_macro2::{Span, TokenStream};
 use quote::{format_ident, quote, ToTokens, TokenStreamExt};
 use syn::{
     parse::{Parse, ParseStream},
+    spanned::Spanned,
     token::Comma,
     Ident, Token, Visibility,
 };
@@ -27,7 +28,7 @@ impl Parse for CssModuleParser {
 
         // Asset path "/path.css"
         let (MacroString(src), path_expr) = input.call(crate::parse_with_tokens)?;
-        let asset = resolve_path(&src);
+        let asset = resolve_path(&src, path_expr.span());
 
         let _comma = input.parse::<Comma>();
 

packages/manganis/manganis-macro/src/lib.rs

@@ -9,6 +9,7 @@ use std::{
 
 use css_module::CssModuleParser;
 use proc_macro::TokenStream;
+use proc_macro2::Span;
 use quote::{quote, ToTokens};
 use syn::{
     parse::{Parse, ParseStream},
@@ -169,7 +170,7 @@ pub fn css_module(input: TokenStream) -> TokenStream {
     quote! { #style }.into_token_stream().into()
 }
 
-fn resolve_path(raw: &str) -> Result<PathBuf, AssetParseError> {
+fn resolve_path(raw: &str, span: Span) -> Result<PathBuf, AssetParseError> {
     // Get the location of the root of the crate which is where all assets are relative to
     //
     // IE
@@ -186,8 +187,18 @@ fn resolve_path(raw: &str) -> Result<PathBuf, AssetParseError> {
     // 1. the input file should be a pathbuf
     let input = PathBuf::from(raw);
 
+    let path = if raw.starts_with('.') {
+        if let Some(local_folder) = span.local_file().as_ref().and_then(|f| f.parent()) {
+            local_folder.join(raw)
+        } else {
+            return Err(AssetParseError::RelativeAssetPath);
+        }
+    } else {
+        manifest_dir.join(raw.trim_start_matches('/'))
+    };
+
     // 2. absolute path to the asset
-    let Ok(path) = std::path::absolute(manifest_dir.join(raw.trim_start_matches('/'))) else {
+    let Ok(path) = std::path::absolute(path) else {
         return Err(AssetParseError::InvalidPath {
             path: input.clone(),
         });
@@ -275,6 +286,7 @@ enum AssetParseError {
     IoError { err: std::io::Error, path: PathBuf },
     InvalidPath { path: PathBuf },
     FailedToReadAsset(std::io::Error),
+    RelativeAssetPath,
 }
 
 impl std::fmt::Display for AssetParseError {
@@ -294,6 +306,7 @@ impl std::fmt::Display for AssetParseError {
                 )
             }
             AssetParseError::FailedToReadAsset(err) => write!(f, "Failed to read asset: {}", err),
+            AssetParseError::RelativeAssetPath => write!(f, "Failed to resolve relative asset path. Relative assets are only supported in rust 1.88+."),
         }
     }
 }