1 files changed, 53 insertions, 0 deletions
diff --git a/syn/tests/test_parse_buffer.rs b/syn/tests/test_parse_buffer.rs
new file mode 100644
index 0000000..d3f10c0
--- /dev/null
+++ b/syn/tests/test_parse_buffer.rs
@@ -0,0 +1,53 @@
+use syn::parenthesized;
+use syn::parse::{discouraged::Speculative, Parse, ParseStream, Parser, Result};
+
+#[test]
+#[should_panic(expected = "Fork was not derived from the advancing parse stream")]
+fn smuggled_speculative_cursor_between_sources() {
+    struct BreakRules;
+    impl Parse for BreakRules {
+        fn parse(input1: ParseStream) -> Result<Self> {
+            let nested = |input2: ParseStream| {
+                input1.advance_to(&input2);
+                Ok(Self)
+            };
+            nested.parse_str("")
+        }
+    }
+
+    syn::parse_str::<BreakRules>("").unwrap();
+}
+
+#[test]
+#[should_panic(expected = "Fork was not derived from the advancing parse stream")]
+fn smuggled_speculative_cursor_between_brackets() {
+    struct BreakRules;
+    impl Parse for BreakRules {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let a;
+            let b;
+            parenthesized!(a in input);
+            parenthesized!(b in input);
+            a.advance_to(&b);
+            Ok(Self)
+        }
+    }
+
+    syn::parse_str::<BreakRules>("()()").unwrap();
+}
+
+#[test]
+#[should_panic(expected = "Fork was not derived from the advancing parse stream")]
+fn smuggled_speculative_cursor_into_brackets() {
+    struct BreakRules;
+    impl Parse for BreakRules {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let a;
+            parenthesized!(a in input);
+            input.advance_to(&a);
+            Ok(Self)
+        }
+    }
+
+    syn::parse_str::<BreakRules>("()").unwrap();
+}