From fa59c0c0bc9032c5cd0a5941e6d69d8f50792c03 Mon Sep 17 00:00:00 2001
From: Zachary Kohnen <14093962+DusterTheFirst@users.noreply.github.com>
Date: Thu, 1 Apr 2021 17:19:52 -0400
Subject: [PATCH] Prevent the full-file "error[E0601]: `main` function not
 found in crate" error

---
 src/lib.rs | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/lib.rs b/src/lib.rs
index e53c27b..c5bc063 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -44,7 +44,19 @@ use syn::spanned::Spanned;
 #[cfg(not(test))] // NOTE: exporting main breaks tests, we should file an issue.
 #[proc_macro_attribute]
 pub fn main(_attr: TokenStream, item: TokenStream) -> TokenStream {
-    let input = syn::parse_macro_input!(item as syn::ItemFn);
+    let input = match syn::parse::<syn::ItemFn>(item) {
+        Ok(input) => input,
+        Err(err) => {
+            let compile_err = err.to_compile_error();
+
+            return quote_spanned! {err.span()=>
+                #compile_err
+
+                fn main() {}
+            }
+            .into();
+        }
+    };
 
     let ret = &input.sig.output;
     let inputs = &input.sig.inputs;