lib/scanner: improve tokens! macro error reporting

Cargo.lock

@@ -9,6 +9,12 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "anyhow"
+version = "1.0.40"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "28b2cd92db5cbd74e8e5028f7e27dd7aa3090e89e4f2a197cc7c8dfb69c7063b"
+
 [[package]]
 name = "ctor"
 version = "0.1.20"
@@ -107,5 +113,6 @@ checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 name = "yary"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "pretty_assertions",
 ]

Cargo.toml

@@ -9,4 +9,5 @@ edition = "2018"
 [dependencies]
 
 [dev-dependencies]
+anyhow = "1"
 pretty_assertions = "0.7"

src/scanner/tests/macros.rs

@@ -6,7 +6,15 @@
 ///     <message>   A message to print on failure
 macro_rules! tokens {
     ($scanner:expr => $($id:tt $expected:expr $(=> $msg:tt)?),+ ) => {
-        $( tokens!(@unwrap $id $scanner => $expected $(=> $msg)? ) );+
+        let mut f = || -> std::result::Result<(), ::anyhow::Error> {
+            $( tokens!(@unwrap $id $scanner => $expected $(=> $msg)? ); )+
+
+            Ok(())
+        };
+
+        if let Err(e) = f() {
+            panic!("tokens! error: {}", e)
+        }
     };
 
     // <-- PRIVATE VARIANTS -->
@@ -25,11 +33,21 @@ macro_rules! tokens {
     };
     // Variant for token assert, no message
     (@token $scanner:expr => $expected:expr) => {
-        assert_eq!($scanner.next().expect("Unexpected end of events"), $expected)
+        let event = $scanner
+            .next()
+            .ok_or_else(
+                || anyhow::anyhow!("Unexpected end of tokens, was expecting: {:?} ~{}", $expected, $scanner.buffer)
+            )?;
+
+        assert_eq!(event, $expected)
     };
     // Variant for token assert, no with message
     (@token $scanner:expr => $expected:expr, $msg:tt) => {
-        let event = $scanner.next().expect("Unexpected end of events");
+        let event = $scanner
+            .next()
+            .ok_or_else(
+                || anyhow::anyhow!("Unexpected end of tokens, {}: {:?} ~{}", $msg, $expected, $scanner.buffer)
+            )?;
 
         assert_eq!(event, $expected, $msg)
     };