MIR borrowck: implement union-and-array-compatible semantics

Fixes #44831.
Fixes #44834.
Fixes #45537.
Fixes #45696 (by implementing DerefPure semantics, which is what we want
going forward).

src/test/compile-fail/borrowck/borrowck-thread-local-static-borrow-outlives-fn.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// ignore-test will be fixed later
 // revisions: ast mir
 //[mir]compile-flags: -Z borrowck=mir
 

src/test/compile-fail/borrowck/borrowck-union-borrow.rs

@@ -52,12 +52,12 @@ fn main() {
         {
             let ra = &u.a;
             let rmb = &mut u.b; //[ast]~ ERROR cannot borrow `u` (via `u.b`) as mutable because `u` is also borrowed as immutable (via `u.a`)
-                                // FIXME Error for MIR (needs support for union)
+                                //[mir]~^ ERROR cannot borrow `u.b` as mutable because it is also borrowed as immutable
         }
         {
             let ra = &u.a;
             u.b = 1; //[ast]~ ERROR cannot assign to `u.b` because it is borrowed
-                     // FIXME Error for MIR (needs support for union)
+                     //[mir]~^ ERROR cannot assign to `u.b` because it is borrowed
         }
         // Mut borrow, same field
         {
@@ -84,22 +84,23 @@ fn main() {
         {
             let rma = &mut u.a;
             let rb = &u.b; //[ast]~ ERROR cannot borrow `u` (via `u.b`) as immutable because `u` is also borrowed as mutable (via `u.a`)
-                           // FIXME Error for MIR (needs support for union)
+                           //[mir]~^ ERROR cannot borrow `u.b` as immutable because it is also borrowed as mutable
         }
         {
             let ra = &mut u.a;
             let b = u.b; //[ast]~ ERROR cannot use `u.b` because it was mutably borrowed
-                         // FIXME Error for MIR (needs support for union)
+                         //[mir]~^ ERROR cannot use `u.b` because it was mutably borrowed
+
         }
         {
             let rma = &mut u.a;
             let rmb2 = &mut u.b; //[ast]~ ERROR cannot borrow `u` (via `u.b`) as mutable more than once at a time
-                                 // FIXME Error for MIR (needs support for union)
+                                 //[mir]~^ ERROR cannot borrow `u.b` as mutable more than once at a time
         }
         {
             let rma = &mut u.a;
             u.b = 1; //[ast]~ ERROR cannot assign to `u.b` because it is borrowed
-                     // FIXME Error for MIR (needs support for union)
+                     //[mir]~^ ERROR cannot assign to `u.b` because it is borrowed
         }
     }
 }

src/test/compile-fail/borrowck/borrowck-vec-pattern-move-tail.rs

@@ -1,3 +1,4 @@
+
 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
@@ -22,7 +23,7 @@ fn main() {
     println!("t[0]: {}", t[0]);
     a[2] = 0; //[ast]~ ERROR cannot assign to `a[..]` because it is borrowed
               //[cmp]~^ ERROR cannot assign to `a[..]` because it is borrowed (Ast)
-              // FIXME Error for MIR (error missed)
+              //[cmp]~| ERROR cannot assign to `a[..]` because it is borrowed (Mir)
     println!("t[0]: {}", t[0]);
     t[0];
 }

src/test/compile-fail/issue-25579.rs

@@ -24,8 +24,8 @@ fn causes_ice(mut l: &mut Sexpression) {
                                                   //[mir]~| ERROR [E0499]
             l = &mut **expr; //[ast]~ ERROR [E0506]
                              //[mir]~^ ERROR [E0506]
-                             //[mir]~| ERROR [E0506]
                              //[mir]~| ERROR [E0499]
+                             //[mir]~| ERROR [E0506]
                              //[mir]~| ERROR [E0499]
         }
     }}