externally visible test macro

Author: devrandom

Cargo.toml

@@ -12,6 +12,7 @@ members = [
     "lightning-custom-message",
     "lightning-transaction-sync",
     "possiblyrandom",
+    "ext-test-macro",
 ]
 
 exclude = [

ext-test-macro/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "ext-test-macro"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+syn = { version = "1.0", features = ["full"] }
+quote = "1.0"
+proc-macro2 = "1.0"

ext-test-macro/src/lib.rs

@@ -0,0 +1,60 @@
+use proc_macro::TokenStream;
+use proc_macro2::TokenStream as TokenStream2;
+use quote::quote;
+use syn::{ItemFn, ItemMod, parse2};
+
+/// An exposed test.  This is a test that will run locally and also be
+/// made available to other crates that want to run it in their own context.
+///
+/// For example:
+/// ```ignore
+/// #[xtest]
+/// pub fn test_f1() {
+///     f1();
+/// }
+/// ```
+///
+/// May also be applied to modules, like so:
+///
+/// ```ignore
+/// #[xtest(feature = "externalize-the-tests")]
+/// pub mod tests {
+///     ...
+/// }
+/// ```
+///
+/// Which will include the module if we are testing or the `externalize-the-tests` feature
+/// is on.
+#[proc_macro_attribute]
+pub fn xtest(attrs: TokenStream, item: TokenStream) -> TokenStream {
+    let input = syn::parse_macro_input!(item as TokenStream2);
+    let attrs = syn::parse_macro_input!(attrs as TokenStream2);
+
+    let expanded = if is_module_definition(input.clone()) {
+        let cfg = if attrs.is_empty() {
+            quote! { #[cfg(test)] }
+        } else {
+            quote! { #[cfg(any(test, #attrs))] }
+        };
+        quote! {
+            #cfg
+            #input
+        }
+    } else if is_function_definition(input.clone()) {
+        quote! {
+            #[cfg_attr(test, ::core::prelude::v1::test)]
+            #input
+        }
+    } else {
+        panic!("xtest can only be applied to functions or modules");
+    };
+    expanded.into()
+}
+
+fn is_module_definition(input: TokenStream2) -> bool {
+    parse2::<ItemMod>(input).is_ok()
+}
+
+fn is_function_definition(input: TokenStream2) -> bool {
+    parse2::<ItemFn>(input).is_ok()
+}