add placeholders for interface attributes

the interface attributes are only recognized by the redIDL compiler but not the Rust compiler. The Rust compiler will spit out errors if there's no placeholder implementations for them

interface/Makefile

@@ -8,17 +8,33 @@ DOMAIN_CREATE_OUTPUT_PATH = ../kernel/src/generated_domain_create.rs
 .PHONY: all
 all: $(LIB_RS) $(MANIFEST_PATH)
 
-# Copy Cargo.toml and fix dependency path
+# Copy Cargo.toml, and fix dependency path, remove `interface_attribute_placeholder`, and add
+# missing dependencies.
 $(MANIFEST_PATH): Cargo.toml missing_dependencies.toml
 	mkdir -p $(OUTPUT_DIR)
 	sed -E 's/path\s*=\s*"/path = "..\//' $(word 1,$^)  > $@
 	cat $(word 2,$^) >> $@
 
-# Merge all files and inject macro for expansion
+# Add placeholder dependencies and run cargo check.
+# Then restore the Cargo.toml.
+# TODO(issue #49): move the operation to a temp folder to prevent contaminating the source folder.
+.PHONY: compiler_check
+compiler_check:
+	cp Cargo.toml Cargo.toml.backup
+	cat Cargo.toml.backup placeholder_dependencies.toml > Cargo.toml
+	cargo check
+	mv Cargo.toml.backup Cargo.toml
+
+# Merge all files and inject macro for expansion.
+# Since the placeholder removes the interface attributes from the traits, we need to remove
+# them from the file.
 .PHONY: $(OUTPUT_DIR)/merged.rs
-$(OUTPUT_DIR)/merged.rs:
+$(OUTPUT_DIR)/merged.rs: compiler_check
 	mkdir -p $(OUTPUT_DIR)
+	cp src/lib.rs src/lib.rs.backup
+	tac src/lib.rs.backup | sed '/extern crate interface_attribute_placeholder;/I,+1 d' | tac > src/lib.rs
 	cargo expand > $@
+	mv src/lib.rs.backup src/lib.rs
 
 # Inject use statements
 $(LIB_RS): $(OUTPUT_DIR)/merged.rs
@@ -27,6 +43,7 @@ $(LIB_RS): $(OUTPUT_DIR)/merged.rs
 
 .PHONY: clean
 clean:
+	cargo clean
 	-rm -rf $(OUTPUT_DIR)
 	-rm -f $(DOMAIN_CREATE_OUTPUT_PATH)
 

interface/placeholder_dependencies.toml

@@ -0,0 +1,2 @@
+[dependencies.interface_attribute_placeholder]
+path = "../lib/external/interface_attribute_placeholder"

interface/src/lib.rs

@@ -19,6 +19,8 @@ extern crate alloc;
 extern crate num_derive;
 #[macro_use]
 extern crate bitflags;
+#[macro_use]
+extern crate interface_attribute_placeholder;
 
 pub mod bdev;
 pub mod dom_c;

lib/external/interface_attribute_placeholder/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "interface_attribute_placeholder"
+version = "0.1.0"
+authors = ["Redleaf team <[email protected]>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[lib]
+proc-macro = true
+
+[dependencies]
+quote = "1.0.9"
+proc-macro2 = "1.0"

lib/external/interface_attribute_placeholder/src/lib.rs

@@ -0,0 +1,34 @@
+///! Include multiple attributes that 
+use proc_macro::TokenStream;
+
+macro_rules! generate_placeholder_attributes {
+    () => {};
+    ($attr:ident) => {
+        #[doc = "Placeholder attribute; noop besides removing the attribute itself."] 
+        #[proc_macro_attribute]
+        pub fn $attr(_attr: TokenStream, item: TokenStream) -> TokenStream {
+            item
+        }
+    };
+    ($attr:ident, $($attrs:tt)*) => {
+        generate_placeholder_attributes!($attr);
+        generate_placeholder_attributes!($($attrs)*);
+    };
+}
+
+generate_placeholder_attributes! {
+    placeholder,
+    interface,
+    domain_create,
+    domain_create_blob,
+}
+// #[proc_macro_attribute]
+// pub fn a(mut attr: TokenStream, item: TokenStream) -> TokenStream {
+//     let attr = proc_macro2::TokenStream::from(attr);
+//     let item = proc_macro2::TokenStream::from(item);
+//     let output = quote::quote! {
+//         #[$attr(#attr)]
+//         #item
+//     };
+//     output.into()
+// }