Fleshed out the test a lot more.

src/test/compile-fail/borrowck/two-phase-nonrecv-autoref.rs

@@ -13,27 +13,248 @@
 //[nll]compile-flags: -Z borrowck=mir -Z two-phase-borrows -Z nll
 //[g2p]compile-flags: -Z borrowck=mir -Z two-phase-borrows -Z nll -Z two-phase-beyond-autoref
 
-#![feature(rustc_attrs)]
-
 // This is a test checking that when we limit two-phase borrows to
 // method receivers, we do not let other kinds of auto-ref to leak
 // through.
 //
 // The g2p revision illustrates the "undesirable" behavior you would
 // otherwise observe without limiting the phasing to autoref on method
-// receivers (namely, that the test would pass).
+// receivers (namely, in many cases demonstrated below, the error
+// would not arise).
+
+// (If we revise the compiler or this test so that the g2p revision
+// passes, turn the `rustc_attrs` feature back on and tag the `fn
+// main` with `#[rustc_error]` so that this remains a valid
+// compile-fail test.)
+//
+// #![feature(rustc_attrs)]
+
+use std::ops::{Index, IndexMut};
+use std::ops::{AddAssign, SubAssign, MulAssign, DivAssign, RemAssign};
+use std::ops::{BitAndAssign, BitOrAssign, BitXorAssign, ShlAssign, ShrAssign};
 
-fn bar(x: &mut u32) {
+// This is case outlined by Niko that we want to ensure we reject
+// (at least initially).
+
+fn foo(x: &mut u32, y: u32) {
+    *x += y;
+}
+
+fn deref_coercion(x: &mut u32) {
     foo(x, *x);
     //[lxl]~^ ERROR cannot use `*x` because it was mutably borrowed [E0503]
     //[nll]~^^ ERROR cannot use `*x` because it was mutably borrowed [E0503]
 }
 
-fn foo(x: &mut u32, y: u32) {
-    *x += y;
+// While adding a flag to adjustments (indicating whether they
+// should support two-phase borrows, here are the cases I
+// encountered:
+//
+// - [x] Resolving overloaded_call_traits (call, call_mut, call_once)
+// - [x] deref_coercion (shown above)
+// - [x] coerce_unsized e.g. `&[T; n]`, `&mut [T; n] -> &[T]`,
+//                      `&mut [T; n] -> &mut [T]`, `&Concrete -> &Trait`
+// - [x] Method Call Receivers (the case we want to support!)
+// - [x] ExprIndex and ExprUnary Deref; only need to handle coerce_index_op
+// - [x] overloaded_binops
+
+fn overloaded_call_traits() {
+    // Regarding overloaded call traits, note that there is no
+    // scenario where adding two-phase borrows should "fix" these
+    // cases, because either we will resolve both invocations to
+    // `call_mut` (in which case the inner call requires a mutable
+    // borrow which will conflict with the outer reservation), or we
+    // will resolve both to `call` (which will just work, regardless
+    // of two-phase borrow support), or we will resolve both to
+    // `call_once` (in which case the inner call requires moving the
+    // receiver, invalidating the outer call).
+
+    fn twice_ten_sm<F: FnMut(i32) -> i32>(f: &mut F) {
+        f(f(10));
+        //[lxl]~^     ERROR cannot borrow `*f` as mutable more than once at a time
+        //[lxl]~|     ERROR cannot borrow `*f` as mutable more than once at a time
+        //[nll]~^^^   ERROR cannot borrow `*f` as mutable more than once at a time
+        //[nll]~|     ERROR cannot borrow `*f` as mutable more than once at a time
+        //[g2p]~^^^^^ ERROR cannot borrow `*f` as mutable more than once at a time
+    }
+    fn twice_ten_si<F: Fn(i32) -> i32>(f: &mut F) {
+        f(f(10));
+    }
+    fn twice_ten_so<F: FnOnce(i32) -> i32>(f: Box<F>) {
+        f(f(10));
+        //[lxl]~^   ERROR use of moved value: `*f`
+        //[nll]~^^  ERROR use of moved value: `*f`
+        //[g2p]~^^^ ERROR use of moved value: `*f`
+    }
+
+    fn twice_ten_om(f: &mut FnMut(i32) -> i32) {
+        f(f(10));
+        //[lxl]~^     ERROR cannot borrow `*f` as mutable more than once at a time
+        //[lxl]~|     ERROR cannot borrow `*f` as mutable more than once at a time
+        //[nll]~^^^   ERROR cannot borrow `*f` as mutable more than once at a time
+        //[nll]~|     ERROR cannot borrow `*f` as mutable more than once at a time
+        //[g2p]~^^^^^ ERROR cannot borrow `*f` as mutable more than once at a time
+    }
+    fn twice_ten_oi(f: &mut Fn(i32) -> i32) {
+        f(f(10));
+    }
+    fn twice_ten_oo(f: Box<FnOnce(i32) -> i32>) {
+        f(f(10));
+        //[lxl]~^             ERROR cannot move a value of type
+        //[lxl]~^^            ERROR cannot move a value of type
+        //[lxl]~^^^           ERROR use of moved value: `*f`
+        //[nll]~^^^^          ERROR cannot move a value of type
+        //[nll]~^^^^^         ERROR cannot move a value of type
+        //[nll]~^^^^^^        ERROR cannot move a value of type
+        //[nll]~^^^^^^^       ERROR cannot move a value of type
+        //[nll]~^^^^^^^^      ERROR use of moved value: `*f`
+        //[g2p]~^^^^^^^^^     ERROR cannot move a value of type
+        //[g2p]~^^^^^^^^^^    ERROR cannot move a value of type
+        //[g2p]~^^^^^^^^^^^   ERROR cannot move a value of type
+        //[g2p]~^^^^^^^^^^^^  ERROR cannot move a value of type
+        //[g2p]~^^^^^^^^^^^^^ ERROR use of moved value: `*f`
+    }
+
+    twice_ten_sm(&mut |x| x + 1);
+    twice_ten_si(&mut |x| x + 1);
+    twice_ten_so(Box::new(|x| x + 1));
+    twice_ten_om(&mut |x| x + 1);
+    twice_ten_oi(&mut |x| x + 1);
+    twice_ten_oo(Box::new(|x| x + 1));
+}
+
+trait TwoMethods {
+    fn m(&mut self, x: i32) -> i32 { x + 1 }
+    fn i(&self, x: i32) -> i32 { x + 1 }
+}
+
+struct T;
+
+impl TwoMethods for T { }
+
+struct S;
+
+impl S {
+    fn m(&mut self, x: i32) -> i32 { x + 1 }
+    fn i(&self, x: i32) -> i32 { x + 1 }
+}
+
+impl TwoMethods for [i32; 3] { }
+
+fn double_access<X: Copy>(m: &mut [X], s: &[X]) {
+    m[0] = s[1];
 }
 
-#[rustc_error]
-fn main() { //[g2p]~ ERROR compilation successful
-    bar(&mut 5);
+fn coerce_unsized() {
+    let mut a = [1, 2, 3];
+
+    // This is not okay.
+    double_access(&mut a, &a);
+    //[lxl]~^   ERROR cannot borrow `a` as immutable because it is also borrowed as mutable [E0502]
+    //[nll]~^^  ERROR cannot borrow `a` as immutable because it is also borrowed as mutable [E0502]
+    //[g2p]~^^^ ERROR cannot borrow `a` as immutable because it is also borrowed as mutable [E0502]
+
+    // But this is okay.
+    a.m(a.i(10));
+}
+
+struct I(i32);
+
+impl Index<i32> for I {
+    type Output = i32;
+    fn index(&self, _: i32) -> &i32 {
+        &self.0
+    }
+}
+
+impl IndexMut<i32> for I {
+    fn index_mut(&mut self, _: i32) -> &mut i32 {
+        &mut self.0
+    }
+}
+
+fn coerce_index_op() {
+    let mut i = I(10);
+    i[i[3]] = 4;
+    //[lxl]~^  ERROR cannot borrow `i` as immutable because it is also borrowed as mutable [E0502]
+    //[nll]~^^ ERROR cannot borrow `i` as immutable because it is also borrowed as mutable [E0502]
+
+    i[3] = i[4];
+
+    i[i[3]] = i[4];
+    //[lxl]~^  ERROR cannot borrow `i` as immutable because it is also borrowed as mutable [E0502]
+    //[nll]~^^ ERROR cannot borrow `i` as immutable because it is also borrowed as mutable [E0502]
+}
+
+struct A(i32);
+
+macro_rules! trivial_binop {
+    ($Trait:ident, $m:ident) => {
+        impl $Trait<i32> for A { fn $m(&mut self, rhs: i32) { self.0 = rhs; } }
+    }
+}
+
+trivial_binop!(AddAssign, add_assign);
+trivial_binop!(SubAssign, sub_assign);
+trivial_binop!(MulAssign, mul_assign);
+trivial_binop!(DivAssign, div_assign);
+trivial_binop!(RemAssign, rem_assign);
+trivial_binop!(BitAndAssign, bitand_assign);
+trivial_binop!(BitOrAssign, bitor_assign);
+trivial_binop!(BitXorAssign, bitxor_assign);
+trivial_binop!(ShlAssign, shl_assign);
+trivial_binop!(ShrAssign, shr_assign);
+
+fn overloaded_binops() {
+    let mut a = A(10);
+    a += a.0;
+    //[lxl]~^   ERROR cannot use `a.0` because it was mutably borrowed
+    //[nll]~^^  ERROR cannot use `a.0` because it was mutably borrowed
+    a -= a.0;
+    //[lxl]~^   ERROR cannot use `a.0` because it was mutably borrowed
+    //[nll]~^^  ERROR cannot use `a.0` because it was mutably borrowed
+    a *= a.0;
+    //[lxl]~^   ERROR cannot use `a.0` because it was mutably borrowed
+    //[nll]~^^  ERROR cannot use `a.0` because it was mutably borrowed
+    a /= a.0;
+    //[lxl]~^   ERROR cannot use `a.0` because it was mutably borrowed
+    //[nll]~^^  ERROR cannot use `a.0` because it was mutably borrowed
+    a &= a.0;
+    //[lxl]~^   ERROR cannot use `a.0` because it was mutably borrowed
+    //[nll]~^^  ERROR cannot use `a.0` because it was mutably borrowed
+    a |= a.0;
+    //[lxl]~^   ERROR cannot use `a.0` because it was mutably borrowed
+    //[nll]~^^  ERROR cannot use `a.0` because it was mutably borrowed
+    a ^= a.0;
+    //[lxl]~^   ERROR cannot use `a.0` because it was mutably borrowed
+    //[nll]~^^  ERROR cannot use `a.0` because it was mutably borrowed
+    a <<= a.0;
+    //[lxl]~^   ERROR cannot use `a.0` because it was mutably borrowed
+    //[nll]~^^  ERROR cannot use `a.0` because it was mutably borrowed
+    a >>= a.0;
+    //[lxl]~^   ERROR cannot use `a.0` because it was mutably borrowed
+    //[nll]~^^  ERROR cannot use `a.0` because it was mutably borrowed
+}
+
+fn main() {
+
+    // As a reminder, this is the basic case we want to ensure we handle.
+    let mut v = vec![1, 2, 3];
+    v.push(v.len());
+
+    // (as a rule, pnkfelix does not like to write tests with dead code.)
+
+    deref_coercion(&mut 5);
+    overloaded_call_traits();
+
+
+    let mut s = S;
+    s.m(s.i(10));
+
+    let mut t = T;
+    t.m(t.i(10));
+
+    coerce_unsized();
+    coerce_index_op();
+    overloaded_binops();
 }