1 files changed, 167 insertions, 0 deletions
diff --git a/tests/ui/borrowck/two-phase-surprise-no-conflict.rs b/tests/ui/borrowck/two-phase-surprise-no-conflict.rs
new file mode 100644
index 000000000..6d37d1ded
--- /dev/null
+++ b/tests/ui/borrowck/two-phase-surprise-no-conflict.rs
@@ -0,0 +1,167 @@
+// This is a test adapted from a minimization of the code from
+// rust-lang/rust#52934, where an accidental disabling of
+// two-phase-borrows (in the initial 2018 edition integration) broke
+// Clippy, but the scenarios where it was breaking were subtle enough
+// that we decided it warranted its own unit test, and pnkfelix
+// decided to use that test as an opportunity to illustrate the cases.
+
+#[derive(Copy, Clone)]
+struct BodyId;
+enum Expr { Closure(BodyId), Others }
+struct Body { value: Expr }
+
+struct Map { body: Body, }
+impl Map { fn body(&self, _: BodyId) -> &Body { unimplemented!() } }
+
+struct SpanlessHash<'a> { cx: &'a Map, cx_mut: &'a mut Map }
+
+impl <'a> SpanlessHash<'a> {
+    fn demo(&mut self) {
+        let _mut_borrow = &mut *self;
+        let _access = self.cx;
+        //~^ ERROR cannot use `self.cx` because it was mutably borrowed [E0503]
+        _mut_borrow;
+    }
+
+    fn hash_expr(&mut self, e: &Expr) {
+        match *e {
+            Expr::Closure(eid) => {
+                // Accepted by AST-borrowck for erroneous reasons
+                // (rust-lang/rust#38899).
+                //
+                // Not okay without two-phase borrows: the implicit
+                // `&mut self` of the receiver is evaluated first, and
+                // that conflicts with the `self.cx` access during
+                // argument evaluation, as demonstrated in `fn demo`
+                // above.
+                //
+                // Okay if we have two-phase borrows. Note that even
+                // if `self.cx.body(..)` holds onto a reference into
+                // `self.cx`, `self.cx` is an immutable-borrow, so
+                // nothing in the activation for `self.hash_expr(..)`
+                // can interfere with that immutable borrow.
+                self.hash_expr(&self.cx.body(eid).value);
+            },
+            _ => {}
+        }
+    }
+
+    fn hash_expr_mut(&mut self, e: &Expr) {
+        match *e {
+            Expr::Closure(eid) => {
+                // Not okay: the call to `self.cx_mut.body(eid)` might
+                // hold on to some mutably borrowed state in
+                // `self.cx_mut`, which would then interfere with the
+                // eventual activation of the `self` mutable borrow
+                // for `self.hash_expr(..)`
+                self.hash_expr(&self.cx_mut.body(eid).value);
+                //~^ ERROR cannot borrow `*self`
+            },
+            _ => {}
+        }
+    }
+}
+
+struct Session;
+struct Config;
+trait LateLintPass<'a> { }
+
+struct TrivialPass;
+impl TrivialPass {
+    fn new(_: &Session) -> Self { TrivialPass }
+    fn new_mut(_: &mut Session) -> Self { TrivialPass }
+}
+
+struct CapturePass<'a> { s: &'a Session }
+impl<'a> CapturePass<'a> {
+    fn new(s: &'a Session) -> Self { CapturePass { s } }
+    fn new_mut(s: &'a mut Session) -> Self { CapturePass { s } }
+}
+
+impl<'a> LateLintPass<'a> for TrivialPass { }
+impl<'a, 'b> LateLintPass<'a> for CapturePass<'b> { }
+
+struct Registry<'a> { sess_mut: &'a mut Session }
+impl<'a> Registry<'a> {
+    fn register_static(&mut self, _: Box<dyn LateLintPass + 'static>) { }
+
+    // Note: there isn't an interesting distinction between these
+    // different methods explored by any of the cases in the test
+    // below. pnkfelix just happened to write these cases out while
+    // exploring variations on `dyn for <'a> Trait<'a> + 'static`, and
+    // then decided to keep these particular ones in.
+    fn register_bound(&mut self, _: Box<dyn LateLintPass + 'a>) { }
+    fn register_univ(&mut self, _: Box<dyn for <'b> LateLintPass<'b> + 'a>) { }
+    fn register_ref(&mut self, _: &dyn LateLintPass) { }
+}
+
+fn register_plugins<'a>(mk_reg: impl Fn() -> &'a mut Registry<'a>) {
+    // Not okay without two-phase borrows: The implicit `&mut reg` of
+    // the receiver is evaluaated first, and that conflicts with the
+    // `reg.sess_mut` access during argument evaluation.
+    //
+    // Okay if we have two-phase borrows: inner borrows do not survive
+    // to the actual method invocation, because `TrivialPass::new`
+    // cannot (according to its type) keep them alive.
+    let reg = mk_reg();
+    reg.register_static(Box::new(TrivialPass::new(&reg.sess_mut)));
+    let reg = mk_reg();
+    reg.register_bound(Box::new(TrivialPass::new(&reg.sess_mut)));
+    let reg = mk_reg();
+    reg.register_univ(Box::new(TrivialPass::new(&reg.sess_mut)));
+    let reg = mk_reg();
+    reg.register_ref(&TrivialPass::new(&reg.sess_mut));
+
+    // These are not okay: the inner mutable borrows immediately
+    // conflict with the outer borrow/reservation, even with support
+    // for two-phase borrows.
+    let reg = mk_reg();
+    reg.register_static(Box::new(TrivialPass::new(&mut reg.sess_mut)));
+    //~^ ERROR cannot borrow `reg.sess_mut`
+    let reg = mk_reg();
+    reg.register_bound(Box::new(TrivialPass::new_mut(&mut reg.sess_mut)));
+    //~^ ERROR cannot borrow `reg.sess_mut`
+    let reg = mk_reg();
+    reg.register_univ(Box::new(TrivialPass::new_mut(&mut reg.sess_mut)));
+    //~^ ERROR cannot borrow `reg.sess_mut`
+    let reg = mk_reg();
+    reg.register_ref(&TrivialPass::new_mut(&mut reg.sess_mut));
+    //~^ ERROR cannot borrow `reg.sess_mut`
+
+    // These are not okay: the inner borrows may reach the actual
+    // method invocation, because `CapturePass::new` might (according
+    // to its type) keep them alive.
+    //
+    // (Also, we don't test `register_static` on CapturePass because
+    // that will fail to get past lifetime inference.)
+    let reg = mk_reg();
+    reg.register_bound(Box::new(CapturePass::new(&reg.sess_mut)));
+    //~^ ERROR cannot borrow `*reg` as mutable
+    let reg = mk_reg();
+    reg.register_univ(Box::new(CapturePass::new(&reg.sess_mut)));
+    //~^ ERROR cannot borrow `*reg` as mutable
+    let reg = mk_reg();
+    reg.register_ref(&CapturePass::new(&reg.sess_mut));
+    //~^ ERROR cannot borrow `*reg` as mutable
+
+    // These are not okay: the inner mutable borrows immediately
+    // conflict with the outer borrow/reservation, even with support
+    // for two-phase borrows.
+    //
+    // (Again, we don't test `register_static` on CapturePass because
+    // that will fail to get past lifetime inference.)
+    let reg = mk_reg();
+    reg.register_bound(Box::new(CapturePass::new_mut(&mut reg.sess_mut)));
+    //~^ ERROR cannot borrow `reg.sess_mut` as mutable more than once at a time
+    //~^^ ERROR cannot borrow `*reg` as mutable more than once at a time
+    let reg = mk_reg();
+    reg.register_univ(Box::new(CapturePass::new_mut(&mut reg.sess_mut)));
+    //~^ ERROR cannot borrow `reg.sess_mut` as mutable more than once at a time
+    //~^^ ERROR cannot borrow `*reg` as mutable more than once at a time
+    let reg = mk_reg();
+    reg.register_ref(&CapturePass::new_mut(&mut reg.sess_mut));
+    //~^ ERROR cannot borrow `reg.sess_mut` as mutable more than once at a time
+    //~^^ ERROR cannot borrow `*reg` as mutable more than once at a time
+}
+
+fn main() { }