From 85b0944eac901c7bf9922469439579964a066842 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Mon, 27 Apr 2020 15:48:44 -0700
Subject: [PATCH] Reject transparent attr in field attribute position

---
 impl/src/valid.rs              | 6 ++++++
 tests/ui/bad-field-attr.rs     | 7 +++++++
 tests/ui/bad-field-attr.stderr | 5 +++++
 3 files changed, 18 insertions(+)
 create mode 100644 tests/ui/bad-field-attr.rs
 create mode 100644 tests/ui/bad-field-attr.stderr

diff --git a/impl/src/valid.rs b/impl/src/valid.rs
index b5da90d..0d5ba36 100644
--- a/impl/src/valid.rs
+++ b/impl/src/valid.rs
@@ -163,6 +163,12 @@ fn check_field_attrs(fields: &[Field]) -> Result<()> {
             backtrace_field = Some(field);
             has_backtrace = true;
         }
+        if let Some(transparent) = field.attrs.transparent {
+            return Err(Error::new_spanned(
+                transparent,
+                "#[error(transparent)] needs to go outside the enum or struct, not on an individual field",
+            ));
+        }
         has_backtrace |= field.is_backtrace();
     }
     if let (Some(from_field), Some(source_field)) = (from_field, source_field) {
diff --git a/tests/ui/bad-field-attr.rs b/tests/ui/bad-field-attr.rs
new file mode 100644
index 0000000..d5429b2
--- /dev/null
+++ b/tests/ui/bad-field-attr.rs
@@ -0,0 +1,7 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+#[error(transparent)]
+pub struct Error(#[error(transparent)] std::io::Error);
+
+fn main() {}
diff --git a/tests/ui/bad-field-attr.stderr b/tests/ui/bad-field-attr.stderr
new file mode 100644
index 0000000..ecc4702
--- /dev/null
+++ b/tests/ui/bad-field-attr.stderr
@@ -0,0 +1,5 @@
+error: #[error(transparent)] needs to go outside the enum or struct, not on an individual field
+ --> $DIR/bad-field-attr.rs:5:18
+  |
+5 | pub struct Error(#[error(transparent)] std::io::Error);
+  |                  ^^^^^^^^^^^^^^^^^^^^^