feat(zink): introduce assert for error handling (#290)

* chore(zink-codegen): introduce assert in zink codegen

* feat(zink): introduce proc-macro assert

examples/revert.rs

@@ -9,16 +9,25 @@ fn main() {}
 
 /// check if the passing address is owner
 #[zink::external]
-pub fn run_revert() {
+pub fn revert() {
     zink::revert!("revert works")
 }
 
+/// check if the passing address is owner
+#[zink::external]
+pub fn assert() {
+    zink::assert!(false, "assert works");
+}
+
 #[test]
 fn test_revert() -> anyhow::Result<()> {
     use zint::Contract;
     let mut contract = Contract::search("revert")?.compile()?;
 
     let info = contract.execute(["revert()".as_bytes()])?;
     assert_eq!(info.revert, Some("revert works".into()));
+
+    let info = contract.execute(["assert()".as_bytes()])?;
+    assert_eq!(info.revert, Some("assert works".into()));
     Ok(())
 }

zink/codegen/src/lib.rs

@@ -4,7 +4,9 @@
 extern crate proc_macro;
 
 use proc_macro::TokenStream;
-use syn::{parse_macro_input, Attribute, DeriveInput, ItemFn, ItemStruct, LitStr};
+use proc_macro2::Span;
+use quote::ToTokens;
+use syn::{parse_macro_input, Attribute, DeriveInput, Expr, ItemFn, ItemStruct, LitStr};
 
 mod event;
 mod revert;
@@ -21,6 +23,16 @@ pub fn revert(input: TokenStream) -> TokenStream {
     revert::parse(input)
 }
 
+/// Check and expression and revert with the input message
+///
+/// This is similar with the builtin `assert!` in rust, but the revert
+/// message only support raw string.
+#[proc_macro]
+pub fn assert(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as revert::AssertInput);
+    revert::parse_assert(input)
+}
+
 /// Event logging interface
 ///
 /// ```ignore

zink/codegen/src/revert.rs

@@ -3,7 +3,10 @@
 use proc_macro::TokenStream;
 use proc_macro2::{Literal, Span};
 use quote::{quote, ToTokens};
-use syn::{Ident, LitStr};
+use syn::{
+    parse::{Parse, ParseStream},
+    parse2, Expr, Ident, LitStr, Token,
+};
 
 /// Revert with message
 pub fn parse(input: LitStr) -> TokenStream {
@@ -34,3 +37,41 @@ pub fn parse(input: LitStr) -> TokenStream {
     }
     .into()
 }
+
+/// Parse assert macro
+pub fn parse_assert(input: AssertInput) -> TokenStream {
+    let cond = input.cond;
+    let revert: Expr = syn::parse2(
+        parse(
+            input
+                .message
+                .unwrap_or(LitStr::new("unknown error", Span::call_site())),
+        )
+        .into(),
+    )
+    .expect("Invalid revert message");
+
+    quote! {
+        if !#cond {
+            #revert
+        }
+    }
+    .into()
+}
+
+/// Assert input
+pub struct AssertInput {
+    pub cond: Expr,
+    pub comma: Token![,],
+    pub message: Option<LitStr>,
+}
+
+impl Parse for AssertInput {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        Ok(AssertInput {
+            cond: input.parse()?,
+            comma: input.parse()?,
+            message: input.parse()?,
+        })
+    }
+}

zink/src/lib.rs

@@ -13,7 +13,7 @@ pub mod storage;
 
 pub use self::{asm::Asm, event::Event};
 pub use storage::{DoubleKeyMapping, Mapping, Storage};
-pub use zink_codegen::{external, revert, storage, Event};
+pub use zink_codegen::{assert, external, revert, storage, Event};
 
 /// Generate a keccak hash of the input (sha3)
 #[cfg(not(target_family = "wasm"))]