Create procedural macro interface library (#1139)

commit-id:32dd0ae0

---

**Stack**:
- #1100
- #1110
- #1093
- #1091
- #1060
- #1139 ⬅


⚠️ *Part of a stack created by [spr](https://github.com/ejoffe/spr). Do
not merge manually using the UI - doing so may have unexpected results.*

Cargo.toml

@@ -6,6 +6,8 @@ members = [
     "extensions/scarb-cairo-run",
     "extensions/scarb-cairo-test",
     "extensions/scarb-snforge-test-collector",
+    "plugins/scarb-macro-attributes",
+    "plugins/scarb-macro-interface",
     "utils/create-output-dir",
     "utils/scarb-build-metadata",
     "utils/scarb-test-support",

plugins/scarb-macro-attributes/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "scarb-macro-attributes"
+version = "0.0.1"
+edition.workspace = true
+
+authors.workspace = true
+categories = ["development-tools"]
+description = "Cairo procedural macro interface primitives."
+homepage.workspace = true
+keywords = ["scarb"]
+license.workspace = true
+readme = "README.md"
+repository.workspace = true
+
+[lib]
+proc-macro = true
+
+[dependencies]
+camino.workspace = true
+quote.workspace = true
+syn = { workspace = true, features = ["full", "extra-traits"] }

plugins/scarb-macro-attributes/README.md

@@ -0,0 +1,3 @@
+# scarb-macro-interface
+
+Shared interface for Scarb procedural macros.

plugins/scarb-macro-attributes/src/lib.rs

@@ -0,0 +1,26 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, ItemFn};
+
+/// Inline macro helper.
+///
+/// This macro hides the conversion to stable ABI structs from the user.
+///
+/// # Safety
+/// Note that token stream deserialization may fail.
+#[proc_macro_attribute]
+pub fn attribute_macro(_args: TokenStream, input: TokenStream) -> TokenStream {
+    let item: ItemFn = parse_macro_input!(input as ItemFn);
+    let item_name = &item.sig.ident;
+    let expanded = quote! {
+        #item
+
+        #[no_mangle]
+        pub unsafe extern "C" fn expand(token_stream: scarb_macro_interface::stable_abi::StableTokenStream) -> scarb_macro_interface::stable_abi::StableProcMacroResult {
+            let token_stream = token_stream.into_token_stream();
+            let result = #item_name(token_stream);
+            scarb_macro_interface::stable_abi::StableProcMacroResult::from_proc_macro_result(result)
+        }
+    };
+    TokenStream::from(expanded)
+}

plugins/scarb-macro-interface/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "scarb-macro-interface"
+version = "0.0.1"
+edition.workspace = true
+
+authors.workspace = true
+categories = ["development-tools"]
+description = "Cairo procedural macro interface primitives."
+homepage.workspace = true
+keywords = ["scarb"]
+license.workspace = true
+readme = "README.md"
+repository.workspace = true
+
+[dependencies]
+anyhow.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+libc.workspace = true

plugins/scarb-macro-interface/README.md

@@ -0,0 +1,3 @@
+# scarb-macro-interface
+
+Shared interface for Scarb procedural macros.

plugins/scarb-macro-interface/src/lib.rs

@@ -0,0 +1,30 @@
+use std::fmt::Display;
+
+#[doc(hidden)]
+pub mod stable_abi;
+
+#[derive(Debug)]
+pub enum ProcMacroResult {
+    /// Plugin has not taken any action.
+    Leave,
+    /// Plugin generated [`TokenStream`] replacement.
+    Replace(TokenStream),
+    /// Plugin ordered item removal.
+    Remove,
+}
+
+#[derive(Debug, Default, Clone)]
+pub struct TokenStream(String);
+
+impl TokenStream {
+    #[doc(hidden)]
+    pub fn new(s: String) -> Self {
+        Self(s)
+    }
+}
+
+impl Display for TokenStream {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}

plugins/scarb-macro-interface/src/stable_abi.rs

@@ -0,0 +1,81 @@
+use crate::{ProcMacroResult, TokenStream};
+use std::ffi::CString;
+use std::os::raw::c_char;
+
+/// Token stream.
+///
+/// This struct implements FFI-safe stable ABI.
+#[repr(C)]
+#[derive(Debug)]
+pub struct StableTokenStream(pub *mut c_char);
+
+/// Procedural macro result.
+///
+/// This struct implements FFI-safe stable ABI.
+#[repr(C)]
+#[derive(Debug)]
+pub enum StableProcMacroResult {
+    /// Plugin has not taken any action.
+    Leave,
+    /// Plugin generated [`TokenStream`] replacement.
+    Replace(StableTokenStream),
+    /// Plugin ordered item removal.
+    Remove,
+}
+
+impl StableTokenStream {
+    /// Convert to String.
+    ///
+    /// # Safety
+    pub unsafe fn to_string(&self) -> String {
+        if self.0.is_null() {
+            String::default()
+        } else {
+            let cstr = CString::from_raw(self.0);
+            cstr.to_string_lossy().to_string()
+        }
+    }
+
+    /// Convert to native Rust representation.
+    ///
+    /// # Safety
+    pub unsafe fn into_token_stream(self) -> TokenStream {
+        TokenStream::new(self.to_string())
+    }
+
+    /// Convert to FFI-safe representation.
+    ///
+    /// # Safety
+    pub unsafe fn from_token_stream(token_stream: TokenStream) -> Self {
+        let cstr = CString::new(token_stream.0).unwrap();
+        StableTokenStream(cstr.into_raw())
+    }
+}
+
+impl StableProcMacroResult {
+    /// Convert to native Rust representation.
+    ///
+    /// # Safety
+    pub unsafe fn into_proc_macro_result(self) -> ProcMacroResult {
+        match self {
+            Self::Leave => ProcMacroResult::Leave,
+            Self::Remove => ProcMacroResult::Remove,
+            Self::Replace(token_stream) => {
+                ProcMacroResult::Replace(token_stream.into_token_stream())
+            }
+        }
+    }
+
+    /// Convert to FFI-safe representation.
+    ///
+    /// # Safety
+    pub unsafe fn from_proc_macro_result(result: ProcMacroResult) -> Self {
+        match result {
+            ProcMacroResult::Leave => StableProcMacroResult::Leave,
+            ProcMacroResult::Remove => StableProcMacroResult::Remove,
+            ProcMacroResult::Replace(token_stream) => {
+                StableProcMacroResult::Replace(StableTokenStream::from_token_stream(token_stream))
+            }
+        }
+    }
+}

scarb/Cargo.toml

@@ -24,8 +24,8 @@ cairo-lang-formatter.workspace = true
 cairo-lang-semantic.workspace = true
 cairo-lang-sierra-to-casm.workspace = true
 cairo-lang-sierra.workspace = true
-cairo-lang-starknet.workspace = true
 cairo-lang-starknet-classes.workspace = true
+cairo-lang-starknet.workspace = true
 cairo-lang-test-plugin.workspace = true
 cairo-lang-utils.workspace = true
 camino.workspace = true
@@ -51,6 +51,7 @@ petgraph.workspace = true
 redb.workspace = true
 reqwest.workspace = true
 scarb-build-metadata = { path = "../utils/scarb-build-metadata" }
+scarb-macro-interface = { path = "../plugins/scarb-macro-interface" }
 scarb-metadata = { path = "../scarb-metadata", default-features = false, features = ["builder"] }
 scarb-ui = { path = "../utils/scarb-ui" }
 semver.workspace = true