Minimal reproducible example for rust-lang/rust-analyzer#13360

.gitignore

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+/target

Cargo.toml

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+[package]
+name = "ra-bug"
+version = "0.0.0"
+edition = "2021"
+license = "MIT OR Apache-2.0"
+
+[features]
+default = ["c_api"]
+c_api = []
+
+[dependencies]
+safer-ffi = { version = "0.0.10", features = ["proc_macros"] }

src/lib.rs

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+// This one works
+#[safer_ffi::derive_ReprC]
+#[ReprC::opaque]
+pub struct NotGated {
+    bar: String,
+}
+
+// This one doesn't work
+#[cfg_attr(feature = "c_api", safer_ffi::derive_ReprC, ReprC::opaque)]
+pub struct Gated {
+    bar: String,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_foobar() {
+        let not_gated = NotGated {
+            bar: "yeet".to_string(),
+        };
+        let gated = Gated {
+            bar: "yeet".to_string(),
+        };
+        // Intellisense works for `not_gated` but fails on `gated`, go ahead and try it
+        assert_eq!(gated.bar, "yeet");
+        assert_eq!(not_gated.bar, "yeet");
+    }
+}