From f39ec89ca0d4522e89cbfcf73fee33615dc934bf Mon Sep 17 00:00:00 2001
From: Aaron Hill <aa1ronham@gmail.com>
Date: Wed, 9 Sep 2020 19:38:05 -0400
Subject: [PATCH] Turn block into a closure in test macro

The `doc_test!` macro defines two local variables (`entries` and `doc`),
which are then accessed from the provided `block`.

However, this only compiled due to a bug in rustc: substituted
metavariables cannot refer to names defined within the macro body. For
example, the following ode does not compile:

```rust
macro_rules! foo {
    ($block:expr) => {
        let mut bar = false;
        $block
    }
}

fn main() {
    foo!({bar = true});
}
```

In this case, the `doc_test!` macro was incorrectly allowed to compile
due to the presence of the `#[tokio::test]` macro on the enclosing
function. When the underlying compiler bug is fixed in
https://github.com/rust-lang/rust/pull/75800,
this macro will stop compiling.

I've adjusted the macro to take in a closure instead of a block. This
closure is invoked with the `entries` and `doc` variables, allowing it
to compile with both old and new compilers.

If you have any questions about this change, feel free to ask me.
---
 src/tests.rs | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/tests.rs b/src/tests.rs
index ea9001f7..46fc715e 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -56,15 +56,15 @@ impl DocFileLoader for TestLoader {
 }
 
 macro_rules! doc_test {
-  ( $name:ident, $source:expr; $block:block ) => {
+  ( $name:ident, $source:expr; $block:expr ) => {
     doc_test!($name, $source, false; $block);
   };
 
-  ( $name:ident, $source:expr, private; $block:block ) => {
+  ( $name:ident, $source:expr, private; $block:expr ) => {
     doc_test!($name, $source, true; $block);
   };
 
-  ( $name:ident, $source:expr, $private:expr; $block:block ) => {
+  ( $name:ident, $source:expr, $private:expr; $block:expr ) => {
     #[tokio::test]
     async fn $name() {
       use swc_ecmascript::parser::Syntax;
@@ -83,7 +83,8 @@ macro_rules! doc_test {
       #[allow(unused_variables)]
       let doc = DocPrinter::new(&entries, false, private).to_string();
 
-      $block
+      #[allow(clippy::redundant_closure_call)]
+      ($block)(entries, doc)
     }
   };
 }
@@ -101,7 +102,7 @@ macro_rules! contains_test {
 
   ( $name:ident, $source:expr, $private:expr;
     $( $contains:expr ),* $( ; $( $notcontains:expr ),* )? ) => {
-    doc_test!($name, $source, $private; {
+    doc_test!($name, $source, $private; |_entries, doc: String| {
       $(
         assert!(doc.contains($contains));
       )*
@@ -124,7 +125,7 @@ macro_rules! json_test {
   };
 
   ( $name:ident, $source:expr, $private:expr; $json:tt ) => {
-    doc_test!($name, $source, $private; {
+    doc_test!($name, $source, $private; |entries, _doc| {
       let actual = serde_json::to_value(&entries).unwrap();
       let expected_json = json!($json);
       assert_eq!(actual, expected_json);