fix(ecs-macros): allow for using derive macros via the engine crate

2 files changed, 61 insertions, 6 deletions

diff --git a/ecs-macros/Cargo.toml b/ecs-macros/Cargo.toml
index 792ca34..cf323fc 100644
--- a/ecs-macros/Cargo.toml
+++ b/ecs-macros/Cargo.toml
@@ -10,4 +10,5 @@ proc-macro = true
 quote = "1.0.35"
 syn = { version = "2.0.51", features = ["full"] }
 proc-macro2 = "1.0.78"
+toml = "0.8.12"
 
diff --git a/ecs-macros/src/lib.rs b/ecs-macros/src/lib.rs
index 17a9be6..73709e4 100644
--- a/ecs-macros/src/lib.rs
+++ b/ecs-macros/src/lib.rs
@@ -1,7 +1,34 @@
+use std::path::PathBuf as FsPathBuf;
+
 use proc_macro::TokenStream;
 use quote::{quote, ToTokens};
 use syn::spanned::Spanned;
-use syn::{parse, Attribute, Ident, Item, ItemEnum, ItemStruct, ItemUnion};
+use syn::{parse, Attribute, Ident, Item, ItemEnum, ItemStruct, ItemUnion, Path};
+use toml::value::{Table as TomlTable, Value as TomlValue};
+
+macro_rules! syn_path {
+    ($first_segment: ident $(::$segment: ident)*) => {
+        ::syn::Path {
+            leading_colon: None,
+            segments: ::syn::punctuated::Punctuated::from_iter([
+                syn_path_segment!($first_segment),
+                $(syn_path_segment!($segment),)*
+            ])
+        }
+    };
+}
+
+macro_rules! syn_path_segment {
+    ($segment: ident) => {
+        ::syn::PathSegment {
+            ident: ::proc_macro2::Ident::new(
+                stringify!($segment),
+                ::proc_macro2::Span::call_site(),
+            ),
+            arguments: ::syn::PathArguments::None,
+        }
+    };
+}
 
 #[proc_macro_derive(Component, attributes(component))]
 pub fn component_derive(input: TokenStream) -> TokenStream
@@ -14,8 +41,10 @@ pub fn component_derive(input: TokenStream) -> TokenStream
 
     let drop_last = component_attr.drop_last;
 
+    let ecs_path = find_engine_ecs_crate_path().unwrap_or_else(|| syn_path!(ecs));
+
     quote! {
-        impl ecs::component::Component for #item_ident
+        impl #ecs_path::component::Component for #item_ident
         {
             fn drop_last(&self) -> bool {
                 #drop_last
@@ -32,9 +61,9 @@ pub fn component_derive(input: TokenStream) -> TokenStream
             }
         }
 
-        impl ecs::system::Input for #item_ident {}
+        impl #ecs_path::system::Input for #item_ident {}
 
-        impl ecs::type_name::TypeName for #item_ident
+        impl #ecs_path::type_name::TypeName for #item_ident
         {
             fn type_name(&self) -> &'static str
             {
@@ -52,8 +81,10 @@ pub fn sole_derive(input: TokenStream) -> TokenStream
 
     let item_ident = item.ident();
 
+    let ecs_path = find_engine_ecs_crate_path().unwrap_or_else(|| syn_path!(ecs));
+
     quote! {
-        impl ecs::sole::Sole for #item_ident
+        impl #ecs_path::sole::Sole for #item_ident
         {
             fn as_any_mut(&mut self) -> &mut dyn std::any::Any
             {
@@ -66,7 +97,7 @@ pub fn sole_derive(input: TokenStream) -> TokenStream
             }
         }
 
-        impl ecs::type_name::TypeName for #item_ident
+        impl #ecs_path::type_name::TypeName for #item_ident
         {
             fn type_name(&self) -> &'static str
             {
@@ -178,3 +209,26 @@ impl ComponentAttribute
         Ok(Self { drop_last })
     }
 }
+
+fn find_engine_ecs_crate_path() -> Option<Path>
+{
+    let cargo_manifest_dir = FsPathBuf::from(std::env::var("CARGO_MANIFEST_DIR").ok()?);
+
+    let crate_manifest = std::fs::read_to_string(cargo_manifest_dir.join("Cargo.toml"))
+        .ok()?
+        .parse::<TomlTable>()
+        .expect("Failed to parse crate manifest file");
+
+    let crate_dependencies = match crate_manifest.get("dependencies")? {
+        TomlValue::Table(dependencies) => Some(dependencies),
+        _ => None,
+    }?;
+
+    crate_dependencies.iter().find_map(|(crate_dep_name, _)| {
+        if crate_dep_name == "engine" {
+            return Some(syn_path!(engine::ecs));
+        }
+
+        None
+    })
+}