unsafe_derive_deserialize: do not consider pin!() as unsafe

In Rust 1.88, the `pin!()` macro uses `unsafe` and triggers
`unsafe_derive_deserialize`.

Author: samueltardieu

clippy_lints/src/derive.rs

@@ -432,6 +432,11 @@ impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) -> Self::Result {
         if let ExprKind::Block(block, _) = expr.kind
             && block.rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided)
+            && block
+                .span
+                .source_callee()
+                .and_then(|expr| expr.macro_def_id)
+                .is_none_or(|did| !self.cx.tcx.is_diagnostic_item(sym::pin_macro, did))
         {
             return ControlFlow::Break(());
         }

tests/ui/unsafe_derive_deserialize.rs

@@ -82,3 +82,15 @@ impl H {
 }
 
 fn main() {}
+
+mod issue15120 {
+    #[derive(serde::Deserialize)]
+    struct Foo;
+
+    impl Foo {
+        fn foo(&self) {
+            // Do not lint if `unsafe` comes from the `core::pin::pin!()` macro
+            std::pin::pin!(());
+        }
+    }
+}