Use typeck_results.node_type to resolve the type in suspicious trait object lint (#349)

plrust/src/tests.rs

@@ -294,6 +294,28 @@ mod tests {
         assert!(res.is_err());
     }
 
+    // Regression for #348
+    #[pg_test]
+    #[cfg(not(feature = "sandboxed"))]
+    #[search_path(@extschema@)]
+    fn plrust_rand_dep() {
+        let definition = r#"
+            CREATE FUNCTION rust_rand() RETURNS INT
+                IMMUTABLE STRICT
+                LANGUAGE PLRUST AS
+            $$
+            [dependencies]
+                rand = "0.8.5"
+            [code]
+                Ok(Some(rand::random()))
+            $$;
+        "#;
+        Spi::run(definition).unwrap();
+
+        let rand = Spi::get_one::<i32>("SELECT rust_rand()").unwrap();
+        assert!(rand.is_some());
+    }
+
     #[pg_test]
     #[search_path(@extschema@)]
     fn plrust_returns_setof() -> spi::Result<()> {
@@ -1405,6 +1427,7 @@ pub mod pg_test {
 owo-colors = "=3.5.0"
 tokio = { version = "=1.19.2", features = ["rt", "net"]}
 plutonium = "*"
+rand = "*"
 "#
                 .as_bytes(),
             )

plrustc/plrustc/src/lints/sus_trait_object.rs

@@ -1,4 +1,3 @@
-use hir::def::{DefKind, Res};
 use rustc_hir as hir;
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::ty;
@@ -29,28 +28,9 @@ impl<'tcx> LateLintPass<'tcx> for PlrustSuspiciousTraitObject {
                 let hir::GenericArg::Type(ty) = arg else {
                     continue;
                 };
-                let is_trait_obj = match &ty.kind {
-                    hir::TyKind::TraitObject(..) => true,
-                    hir::TyKind::Path(qpath) => {
-                        let res = cx.qpath_res(qpath, ty.hir_id);
-                        let did = match res {
-                            Res::Def(DefKind::TyAlias | DefKind::AssocTy, def_id) => def_id,
-                            Res::SelfTyAlias { alias_to, .. } => alias_to,
-                            _ => continue,
-                        };
-                        let binder = cx.tcx.type_of(did);
-                        let ty = binder.subst_identity();
-                        if matches!(ty.kind(), ty::TyKind::Dynamic(..)) {
-                            true
-                        } else {
-                            match cx.tcx.try_normalize_erasing_regions(cx.param_env, ty) {
-                                Ok(t) => matches!(t.kind(), ty::TyKind::Dynamic(..)),
-                                _ => false,
-                            }
-                        }
-                    }
-                    _ => false,
-                };
+                let typeck_results = cx.typeck_results();
+                let is_trait_obj =
+                    matches!(typeck_results.node_type(ty.hir_id).kind(), ty::Dynamic(..));
                 if is_trait_obj {
                     cx.lint(
                         PLRUST_SUSPICIOUS_TRAIT_OBJECT,

plrustc/plrustc/uitests/sus_trait_object_gat.rs

@@ -0,0 +1,30 @@
+#![crate_type = "lib"]
+
+trait Object {
+    type Output;
+}
+
+impl<T: ?Sized> Object for T {
+    type Output = &'static u64;
+}
+
+trait HasGenericAssoc {
+    type Ohno<'a>: ?Sized;
+}
+
+impl HasGenericAssoc for () {
+    type Ohno<'a> = dyn Object<Output = &'a u64>;
+}
+
+fn foo<'a, T: ?Sized>(x: <T as Object>::Output) -> &'a u64 {
+    x
+}
+
+fn transmute_lifetime<'a, 'b>(x: &'a u64) -> &'b u64 {
+    foo::<<() as HasGenericAssoc>::Ohno<'a>>(x)
+}
+
+pub fn get_dangling<'a>() -> &'a u64 {
+    let x = 0;
+    transmute_lifetime(&x)
+}

plrustc/plrustc/uitests/sus_trait_object_gat.stderr

@@ -0,0 +1,10 @@
+error: using trait objects in turbofish position is forbidden by PL/Rust
+  --> $DIR/sus_trait_object_gat.rs:24:5
+   |
+LL |     foo::<<() as HasGenericAssoc>::Ohno<'a>>(x)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-F plrust-suspicious-trait-object` implied by `-F plrust-lints`
+
+error: aborting due to previous error
+