Add async-await based lambda.

Author: David Barsky

lambda-attributes/Cargo.lock

@@ -0,0 +1,18 @@
+[package]
+name = "lambda-attributes"
+version = "0.1.0"
+authors = ["David Barsky <[email protected]>"]
+edition = "2018"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = { version = "0.15.33", features = ["full"] }
+proc-macro2 = { version = "0.4.29", features = ["nightly"] }
+quote = "0.6.12"
+runtime = "0.3.0-alpha.5"
+bytes = "0.4.12"
+
+[dev-dependencies]
+runtime = "0.3.0-alpha.5"

lambda-attributes/Cargo.toml

@@ -0,0 +1,104 @@
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+use quote::quote_spanned;
+use syn::{spanned::Spanned, FnArg, ItemFn};
+
+#[cfg(not(test))]
+#[proc_macro_attribute]
+pub fn lambda(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    let input = syn::parse_macro_input!(item as ItemFn);
+
+    let ret = &input.decl.output;
+    let name = &input.ident;
+    let body = &input.block;
+    let attrs = &input.attrs;
+    let asyncness = &input.asyncness;
+    let inputs = &input.decl.inputs;
+
+    if name != "main" {
+        let tokens = quote_spanned! { name.span() =>
+            compile_error!("only the main function can be tagged with #[lambda::main]");
+        };
+        return TokenStream::from(tokens);
+    }
+
+    if asyncness.is_none() {
+        let tokens = quote_spanned! { input.span() =>
+          compile_error!("the async keyword is missing from the function declaration");
+        };
+        return TokenStream::from(tokens);
+    }
+
+    let result = match inputs.len() {
+        1 => {
+            let event = match inputs.first().unwrap().into_value() {
+                FnArg::Captured(arg) => arg,
+                _ => {
+                    let tokens = quote_spanned! { inputs.span() =>
+                        compile_error!("fn main should take a fully formed argument");
+                    };
+                    return TokenStream::from(tokens);
+                }
+            };
+            let arg_name = &event.pat;
+            let arg_type = &event.ty;
+
+            quote_spanned! { input.span() =>
+                #(#attrs)*
+                #asyncness fn main() {
+                    async fn actual(#arg_name: #arg_type, ctx: Option<lambda::LambdaCtx>) #ret {
+                        #body
+                    }
+                    let f = lambda::handler_fn(actual);
+
+                    lambda::run(f).await.unwrap();
+                }
+            }
+        }
+        2 => {
+            let event = match inputs.first().unwrap().into_value() {
+                FnArg::Captured(arg) => arg,
+                _ => {
+                    let tokens = quote_spanned! { inputs.span() =>
+                        compile_error!("fn main should take a fully formed argument");
+                    };
+                    return TokenStream::from(tokens);
+                }
+            };
+            let ctx = match &inputs[1] {
+                FnArg::Captured(arg) => arg,
+                _ => {
+                    let tokens = quote_spanned! { inputs.span() =>
+                        compile_error!("fn main should take a fully formed argument");
+                    };
+                    return TokenStream::from(tokens);
+                }
+            };
+            let arg_name = &event.pat;
+            let arg_type = &event.ty;
+            let ctx_name = &ctx.pat;
+            let ctx_type = &ctx.ty;
+            quote_spanned! { input.span() =>
+                #(#attrs)*
+                #asyncness fn main() {
+                    async fn actual(#arg_name: #arg_type, #ctx_name: Option<#ctx_type>) #ret {
+                        let #ctx_name = #ctx_name.unwrap();
+                        #body
+                    }
+                    let f = lambda::handler_fn(actual);
+
+                    lambda::run(f).await.unwrap();
+                }
+            }
+        }
+        _ => {
+            let tokens = quote_spanned! { inputs.span() =>
+                compile_error!("The #[lambda] macro can accept one or two arguments.");
+            };
+            return TokenStream::from(tokens);
+        }
+    };
+
+    result.into()
+}