Rollup merge of #130598 - gurry:130310-improper-types-stack-overflow, r=compiler-errors

Add recursion limit to FFI safety lint

Fixes #130310

Now we check against `tcx.recursion_limit()` and raise an error if it the limit is reached instead of overflowing the stack.

compiler/rustc_lint/messages.ftl

@@ -395,6 +395,8 @@ lint_improper_ctypes_opaque = opaque types have no C equivalent
 lint_improper_ctypes_pat_help = consider using the base type instead
 
 lint_improper_ctypes_pat_reason = pattern types have no C equivalent
+
+lint_improper_ctypes_recursion_limit_reached = type is infinitely recursive
 lint_improper_ctypes_slice_help = consider using a raw pointer instead
 
 lint_improper_ctypes_slice_reason = slices have no C equivalent

compiler/rustc_lint/src/types.rs

@@ -991,6 +991,8 @@ struct CTypesVisitorState<'tcx> {
     /// The original type being checked, before we recursed
     /// to any other types it contains.
     base_ty: Ty<'tcx>,
+    /// Number of times we recursed while checking the type
+    recursion_depth: usize,
 }
 
 enum FfiResult<'tcx> {
@@ -1296,12 +1298,23 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 
         // Protect against infinite recursion, for example
         // `struct S(*mut S);`.
-        // FIXME: A recursion limit is necessary as well, for irregular
-        // recursive types.
         if !acc.cache.insert(ty) {
             return FfiSafe;
         }
 
+        // Additional recursion check for more complex types like
+        // `struct A<T> { v: *const A<A<T>>, ... }` for which the
+        // cache check above won't be enough (fixes #130310)
+        if !tcx.recursion_limit().value_within_limit(acc.recursion_depth) {
+            return FfiUnsafe {
+                ty: acc.base_ty,
+                reason: fluent::lint_improper_ctypes_recursion_limit_reached,
+                help: None,
+            };
+        }
+
+        acc.recursion_depth += 1;
+
         match *ty.kind() {
             ty::Adt(def, args) => {
                 if let Some(boxed) = ty.boxed_ty()
@@ -1644,7 +1657,8 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
             return;
         }
 
-        let mut acc = CTypesVisitorState { cache: FxHashSet::default(), base_ty: ty };
+        let mut acc =
+            CTypesVisitorState { cache: FxHashSet::default(), base_ty: ty, recursion_depth: 0 };
         match self.check_type_for_ffi(&mut acc, ty) {
             FfiResult::FfiSafe => {}
             FfiResult::FfiPhantom(ty) => {

tests/crashes/130310.rs

@@ -1,15 +0,0 @@
-//@ known-bug: rust-lang/rust#130310
-
-use std::marker::PhantomData;
-
-#[repr(C)]
-struct A<T> {
-    a: *const A<A<T>>,
-    p: PhantomData<T>,
-}
-
-extern "C" {
-    fn f(a: *const A<()>);
-}
-
-fn main() {}

tests/ui/lint/improper-types-stack-overflow-130310.rs

@@ -0,0 +1,20 @@
+// Regression test for #130310
+// Tests that we do not fall into infinite
+// recursion while checking FFI safety of
+// recursive types like `A<T>` below
+
+//@ build-pass
+use std::marker::PhantomData;
+
+#[repr(C)]
+struct A<T> {
+    a: *const A<A<T>>, // Recursive because of this field
+    p: PhantomData<T>,
+}
+
+extern "C" {
+    fn f(a: *const A<()>);
+    //~^ WARN `extern` block uses type `*const A<()>`, which is not FFI-safe
+}
+
+fn main() {}

tests/ui/lint/improper-types-stack-overflow-130310.stderr

@@ -0,0 +1,11 @@
+warning: `extern` block uses type `*const A<()>`, which is not FFI-safe
+  --> $DIR/improper-types-stack-overflow-130310.rs:16:13
+   |
+LL |     fn f(a: *const A<()>);
+   |             ^^^^^^^^^^^^ not FFI-safe
+   |
+   = note: type is infinitely recursive
+   = note: `#[warn(improper_ctypes)]` on by default
+
+warning: 1 warning emitted
+